SAMANTHA E. C. ENGELDAL
GRADUATE SCHOOL
BOGOR AGRICULTURAL UNIVERSITY
BOGOR
document entitled:
‘STRESS-INDUCED BEHAVIOUR IN RAMS OF THREE DIFFERENT SHEEP (Ovis aries) BREEDS: INDICATOR OF WELFARE?’
has been obtained and presented in accordance with academic rules and ethical conduct. I also solemnly declare that this thesis was composed by myself through guidance of my supervisory committee. This work has not been submitted for the awards of any other academic degree, diploma, certificate or other professional qualification except as specified. As required by academic rules, all material and results that are not original to this work have been clearly and fully cited and referenced.
Bogor, December 2012
Samantha E.C. Engeldal
RONNY RACHMAN NOOR and SUBANDRIYO.
Growing importance of and concern for the welfare of farm animals within production systems has been the basis for an enormous amount of scientific studies. The goal of the present study was to investigate whether both vocal and social behaviour of sheep, under specific stress-inducing situations, could be used as an indicator of the animals’ welfare status. Two separate experiments were carried out with 2-3 year old adult rams. The animals were of three breeds, namely Barbados Blackbelly Cross, Local Garut and Composite Garut. In the first experiment twelve clinically healthy animals, four from each breed, were subjected to three different levels of social isolation. The animals were held completely alone, in the presence of a human and alone in a group pen adjacent to a pen with conspecifics. During the isolation sessions both vocal and locomotive behaviour of each animal were recorded. The recorded calls were acoustically analyzed using specialized acoustic software. The results showed that the levels of isolation were characterized by very specific behavioural responses with an increased amount of locomotor activity and vocalization in partially isolated animals. The animals that were completely isolated showed a higher amount of inactive behaviour. No specific differences were found in the behaviour of animals that were held completely alone and the ones which were in the presence of a human observer. Acoustic analysis of the recorded calls showed significant differences in a number of temporal and structural features. Spectral analysis revealed the most notable differences in the amount of sound energy integrated in the calls. Differences were found in both locomotive and vocal behaviour based on isolation level and breed. The second experiment focused on the effect of stocking density on the social behaviour of newly regrouped rams. Thirty-six animals were subjected to three different stocking density levels, namely low (3.2 m2/ram), medium (1.6 m2/ram) and high (0.8 m2/ram). Recorded data consisted of frequencies of agonistic-, exploratory, locomotive-, aberrant-, inactive-, self-care-, mating- and vocal behaviour. The results of this experiment showed that the animals responded differently to the different stocking density levels. The highest stocking density level was characterized by the highest number of inactive behaviour and the lowest number of locomotor activity. There were also significant differences found in the frequency of displayed behaviours based on the amount of time the animals had spent within the new group settings. The amount of agonistic-, mating- and exploratory behaviour was found to be significantly higher on the day of regrouping as compared to the level of these behaviours on the day after regrouping. Significant differences were also found in the behavioural response of animals from different breeds. The results from both experiments thus lead us to conclude that both vocal- and social behaviour of rams are able to provide humans with important information on their affective state which may be helpful in the design of production systems that are beneficial to the animals their welfare.
of RONNY RACHMAN NOOR and SUBANDRIYO.
Animal domestication has played a central role in the development of human civilization. Modern animal production systems are principally characterized by a larger number of farm animals which are kept together in reduced space. A great number of the management practices which are currently applied in intensive systems along with the conditions under which the animals are kept, are thought to have a negative influence on both physiological and production traits of the animals. The perception that humans have a moral obligation to ensure that the animals their welfare, which is thought to be the extent to which the animals are able to successfully adapt to their environment, is never excessively poor has become widespread. The attempts of an animal to cope to its environment and the results of failure to cope can be measured. This meaning that the welfare of an individual animal can be assessed in scientific ways using different types of indicators. An appreciation of how to handle animals appropriately necessitates knowledge of their behaviour.
The purpose of this study was to evaluate both vocal- and social behavioural response of different breeds of sheep to situations which have been found to be very stressful for this gregarious species, in an attempt to discover non-invasive ways that might reveal information on the animals’ affective state. It was also intended to discover whether the animals would differ in their behavioural response based on their breed.
The research consisted of two separate experiments. A total of forty-eight rams from three different sheep breeds were used throughout the entire study. The following breeds were included: Barbados Blackbelly Cross (BC) (50% Local Sumatera, 50% Barbados Blackbelly), Local Garut (LG) and Composite Garut (KG) (50% Local Garut, 25% St. Croix, 25% Moulton Charollais). In the first experiment twelve clinically healthy, 2-3 year old adult sheep were subjected to different levels of social isolation. Each individual animal was kept alone without visual- and tactile contact with conspecifics, kept in the presence of an observer without visual – and tactile contact with conspecifics, and kept alone in a group pen at a specific distance from conspecifics with whom visual-, acoustic- and olfactory contact was possible. During a maximum of 15 minutes both vocal and locomotive behaviour were recorded. High-pitched bleats were recorded using a Digital Voice Recorder after which the calls were acoustically analyzed using the acoustic software program Raven Pro 1.4. Thirty-six acoustic parameters were calculated after which their values were subjected to statistical analysis. Frequencies of locomotive behaviours were observed and recorded during 5 minutes per isolation session using a predefined ethogram.
09.30 am, 12.00 pm and 14.30 pm.
The results from the first experiment showed that the animals were more active during partial isolation compared to complete isolation. The frequency of locomotive behaviours and vocalizations during partial isolation was also found to be higher compared to that during complete isolation. Significant effects of isolation level and breed on both temporal and structural acoustic properties were found. Amplitude, power and time acoustic properties were found to affect acoustic quality of vocal responses to isolation, whereas frequency related properties were also found to differ significantly (P < 0.05) between breeds. From spectrogram analysis, the patterns of energy distribution within the calls proved to offer the most distinctive difference between isolation levels and breeds. Calls uttered during complete isolation were all identified by a higher level of noise-energy compared to calls uttered during partial isolation. It was concluded that the acoustic analysis of calls uttered during social isolation of adult rams revealed information on the affective state of the animals. This was found to be predominantly expressed by both temporal and structural variations in acoustic cues within distress calls and to differ per breed.
The results of experiment 2 showed that agonistic behaviour was observed at the highest frequency throughout the entire study. Stocking density was found to have a significant effect on exploratory-, locomotive- and standing behaviour. The effect of breed caused significant differences in agonistic-, self-care-, aberrant- and mating behaviour. Significant differences were also found between day 1 and day 2 of regrouping for agonistic-, exploratory, self-care- and mating behaviour. These results led to the conclusion that the animals’ behavioural response to regrouping and space allowance was characterized by specific patterns and that the three breeds do differ in their reactions to novel situations. It is believed that the animals their welfare might be compromised by housing them at high stocking densities.
Keywords: vocalization, behaviour, stress, sheep, animal welfare
Copyright © IPB 2012
All Rights Reserved
This work is deposited at the university library to be made available to borrowers under rules of the library. Brief quotations from this thesis are allowable provided that accurate acknowledgment of the source is made. Request for this manuscript in whole or in part may be granted by Bogor Agricultural University when in its judgment the proposed use of the material will be beneficial for educational purposes. In all other instances, however, no part or all of this thesis may be reproduced or transmitted in any form or by any means.
SAMANTHA E.C. ENGELDAL
A thesis sumbitted to the Graduate School of Bogor Agricultural University
in partial fullfillment of the requirements for the degree Master of Science
in the Department of
Animal Science and Production Technology
GRADUATE SCHOOL
BOGOR AGRICULTURAL UNIVERSITY
BOGOR
External examiner: Prof. Dr. Ir. Cece Sumantri, M. Agr. Sc.
motivation for investigating the way in which farm animals behave in stressful situations. By using animal behaviour as an indicator of the animals’ affective state, an attempt can be made to create such farming environments which support their overall welfare.
My journey in pursuit of a Master of Science degree has been very insightful, energized by numerous special moments. Each and every experience which I have had throughout these past two years has led me to view life in an entirely new light, of which an increased amount of respect for nature and its perfect natural order is just one result. In short, my time spent in Indonesia can be summed up by the words: ‘Without GOD, I am not’. Through HIS mercy I have been blessed with Spiritual Guides and Ancestors who provide me with divine insight, guidance and protection at all times. For this I am so grateful. THEY are the sole reason for this achievement.
My parents have always encouraged me to pursue my dreams. I have been blessed with a Mother who has always motivated and supported me throughout my educational journey. The example she has set for me through her own life fostered my enthusiasm and has also been the basis for all of the success I have been fortunate to experience so far. My father instilled in me two traits: a strong work ethic and to always strive for the best results. They have both taught me that final victory ALWAYS comes to the one who stays connected and perseveres. For this I am so grateful. I would not have reached this level had it not been for their uninterruptible love, care, encouragement and prayer.
Words of gratitude are due to my family and friends for always taking an interest in what I have been doing and offering me their much-valued support. I would thank you from the bottom of my heart, but for you my heart has no bottom.
I would also like to thank my head supervisor, Prof. Ronny Rachman Noor. Without his willingness to take me under his supervision I might not have had some of the wonderful experiences that I have had. He has provided me with supreme counseling while exploring a topic that I am very passionate about. I am thankful to him for his guidance, advice and encouragements throughout my study. I have learned a lot from him during my research, which greatly increased my skills in the field. His supervision challenged me intellectually and has helped enrich my knowledge.
I would also like to acknowledge, Prof. Subandriyo for his support and constructive criticism throughout this project.
Indonesia will always be greatly valued.
I am very grateful to everyone I have met at the Indonesian Research Institute for Animal Production, especially the technicians who assisted me during the collection of my data. The support and assistance received from Bapak Sumantri, Pak. Koesma, Pak. Tohir, Pak. Njurjaja and Pak. Maplani in carrying out my research will always be greatly appreciated.
I would like to convey my gratitude to all the staff at IPB for their enormous and continuous support, patience and help throughout my study.
After having finished all of the basic education levels, the author was admitted to
the Anton de Kom University of Suriname (ADEK). In the year 2009 the author
graduated with a Bachelor’s Degree in Animal Science.
In 2010 the author attained her teaching certificate for becoming a licensed
teacher. In that same year she was awarded a scholarship under the Developing
Countries Partnership Program to further her studies in Indonesia at Bogor
Agricultural University. The author successfully completed the Master’s program
LIST OF TABLES ... xiii
LIST OF FIGURES ... xiv
LIST OF APPENDICES ... xv
GENERAL INTRODUCTION ... 1
Background to the Study ... 1
Purpose of the Study ... 4
Significance of the Study ... 5
Hypothesis ... 5
LITERATURE REVIEW ... 7
Systematics and Distribution of Sheep ... 7
Barbados Blackbelly Cross ... 7
Local Garut ... 8
Composite Garut ... 8
Importance of Animal Behaviour ... 9
Behaviour, Welfare and Environmental Design . ... 11
Motivation and Stress in Farm Animals ... 15
Relations of Vocalization to Animal Welfare ... 17
Vocalization Analysis ... 21
EFFECT OF DIFFERENT LEVELS OF SOCIAL ISOLATION ON THE ACOUSTICAL CHARACTERISTICS OF SHEEP VOCALIZATION ... 23
Abstract ... 23
INTRODUCTION ... 24
MATERIAL AND METHODS ... 27
Location and Time of the Study ... 27
Study Subjects and Housing ... 27
Isolation Procedures ... 27
Recorded Behaviour ... 28
Bleat Recordings ... 29
Bleat Analysis ... 29
Data Analysis and Statistics ... 34
RESULTS AND DISCUSSION ... 35
Behavioural Parameters... 35
Vocalization and Call Measures ... 41
Breed Differences of Acoustic Structure of High Bleats ... 45
CONCLUSIONS ... 53
Abstract ... 61
INTRODUCTION ... 62
MATERIAL AND METHODS ... 65
Location and Time of the Study ... 65
Study Subjects and Housing ... 65
Experimental Setup and Procedure ... 65
Behavioural Parameters ... 66
Data Analysis ... 68
RESULTS AND DISCUSSION ... 69
Behavioural Budget ... 69
Effect of Space Allowance on Behaviour of Rams ... 70
Breed Effect ... 72
Impact of Day of Regrouping on Ram Behaviour ... 75
Vocal Behaviour ... 78
CONCLUSIONS ... 81
REFERENCES ... 83
GENERAL DISCUSSION ... 87
RECOMMENDATIONS ... 91
REFERENCES ... 93
1 Values of acoustic parameters based on isolation level ... 105
2 Values of acoustic parameters based on breed ... 106
3 ANOVA test results from the GLM procedure for comparison of acoustic parameters for isolation level and breed ... 107
4 Output of Duncan’s multiple range test for isolation level ... 117
5 Output of Duncan’s multiple range test for breed ... 122
6 Output of Kruskall-Wallis test ... 126
7 Output of Mann-Whitney U test ... 129
1 An operational defination of animal welfare developed
in the Welfare Quality Project (Welfare Quality 2009) ... 12
2 Scheme for judging welfare indicators in animal management
and housing systems ... 13
3 Experimental design of isolation procedures ... 28
4 Frequencies of observed behaviours at different levels of isolation ... 35
5 Breed differences in frequencies of observed behaviours
at different levels of isolation ... 37
6 Comparison of acoustic parameters of high-pitched bleats
at different levels of isolation ... 42
7 Comparison of acoustic parameters of high-pitched bleats
from different breeds ... 46
8 Experimental design. Number of animals per breed group
and per stocking density ... 66
9 Ethogram used for studying behaviour of rams at various
stocking densities ... 67
10 Pooled behavioural categories ... 68
11 Frequencies of displayed behaviour at different
stocking densities ... 70
12 Influence of breed on ram behaviour ... 72
1 Adult rams of the breeds Barbados Blackbelly Cross
and Local Garut ... 8
2 Adult rams of the breed Composite Garut ... 9
3 Assessment of welfare and consequences of lack of welfare ... 16
4 Neuronal, anatomical and functional elements of call
production in animals ... 19
5 Frequency of locomotor activity by animals from different
breeds at different levels of social isolation ... 39
6 Frequency of standing by animals from different breeds at
different levels of social isolation ... 40
7 Frequency of vocalizations per breed group at different levels
of social isolation ... 41
8 Representative spectrographs of high-pitched bleats from the same Barbados Blackbelly Cross ram while (A) completely alone,
(B) with observer and (C) partially isolated ... 48
9 Representative spectrographs of high-pitched bleats from the same Local Garut ram while (A) completely alone, (B) with observer
and (C) partially isolated ... 49
10 Representative spectrographs of high-pitched bleats from the same Composite Garut ram while (A) completely alone, (B) with observer and (C) partially isolated ... 50
11 Frequency of observed behaviours throughout the experiment ... 66
12 Frequency of vocalizations at different stocking densities
on day 1 and day 2 of regrouping ... 78
13 Frequency of vocalizations per breed group at different
1 Values of acoustic parameters based on isolation level ... 105
2 Values of acoustic parameters based on breed ... 106
3 ANOVA test results from the GLM procedure for comparison
of acoustic parameters for isolation level and breed ... 107
4 Output of Duncan’s multiple range test for isolation level ... 117
5 Output of Duncan’s multiple range test for breed ... 122
6 Output of Kruskall-Wallis test ... 126
7 Output of Mann-Whitney U test ... 129
Background to the Study
There is no better way of generating progress and development than by
looking beyond the boundaries of one’s current knowledge. For centuries
mankind has attempted to subject nature to obeying its rules in order to fulfill its
boundless needs. We are now, however, approaching an era in which change is
essential. Humans are becoming increasingly aware of the importance of
understanding and respecting both the animal and plant kingdom in order for us to
survive. In the development of human civilization the farming of animals has
played an important part. Animals have been used by humans for many purposes
including the production of food, clothing, draught power, companionship,
recreation, scientific research and education. In all cases some degree of
modification of genetics and/or environment of the species concerned has taken
place. According to Leaver (1999) those responsible for the animals and society as
a whole, have a duty to ensure that the welfare of animals is not unacceptably
compromised in these processes.
The feeling that man has a moral obligation to ensure that the welfare of
animals which are kept on farm is never poor has become widespread. At present
animals can no longer be considered machines that can be manipulated at will for
human purposes. It is believed by an increasing number of researchers (Duncan
1993; Whittaker et al. 2012) that because animals are sentient, their welfare matters. The welfare of an animal depends on how it perceives the situation with
which it is confronted and on how it perceives itself in that situation (de Jong et al. 2012). According to Fraser and Broom (1997) the attempts of an animal to cope and the result of failure to cope to its surroundings can be measured. Hence
welfare can be assessed in a precise scientific way using a variety of indicators.
Knowledge of animal behaviour may be more important today as intensive
husbandry systems place animals in environments far removed from those they
were originally selected for, and even more distantly removed from those their
wild ancestors were adapted to (Lawrence & Rushen 1993). It is believed by
not soluble by investigating nutrition, body physiology, or disease control but
require investigations of the behaviour of the animals before progress can be made
towards a solution. Behaviour can be defined as that which animals do to interact
with, respond to, and control their environment. An appreciation of how to handle
animals thus necessitates knowledge of behaviour, which is generally the animal's
"first line of defense" in response to environmental change. As such, careful
observations of behaviour can provide us with a great deal of information about
animals' requirements, preferences, dislikes, and internal states (Mench & Mason
1997).
Over the last few decades, scientists have made huge progress in
understanding how animals perceive their environment and the feelings prompted
by this perception. Investigating the modern farming environments and
management strategies which livestock are subjected to might help determine
where mismatches exist (Leone & Estevez 2008). Substantial new knowledge of
the behaviour of livestock under intensive husbandry systems is therefore needed
to assess these systems of management. This knowledge can be applied in the
animal production industry in order to improve production and welfare. Whittaker
et al. (2012) stated that space provided to animals is one easily recognizable aspect of husbandry systems that is perceived by the public to imply that welfare
is poor. According to them features such as the structural characteristics of the
environment or social aspects of the group (such as group size or density) must be
considered to establish meaningful recommendations on how to create the most
beneficial environment for animals. Craig (1981) suggested that in many instances
it may be easier to modify an animal’s environment to provide or eliminate some
key stimulus than to use artificial selection to exploit a favorable behaviour or
eliminate an unfavorable one. When decisions are taken about methods in animal
husbandry, animals should be considered as individuals and their responses to
their environment should be evaluated and understood.
The vast majority of farmed animals is gregarious and reacts heavily to
being separated from group-mates. Much research has focused on the potential
role played by conspecifics in the elicitation of emotions. This is valid both for
given a great deal of consideration in the design of housing systems and
equipment, even though behaviourally inappropriate design can lead to injury and
other welfare problems (NRAES 1995). A careful description of the behaviour
patterns or a sequence of behaviours of animals offers the possibility to identify
all of the relevant components and to link their performance to the wider context
of the physical and biological environment of the animal (Scott 2005).
Particular states of mood or emotion may be accompanied by specific
behaviours, vocalization being one of them. Hence, in farm animals vocalizations
may supply us with hints on their well-being in an easy way, given that the
meanings of the respective calls are well-established. Then, it is possible to judge
acoustically uttered current needs and impaired welfare by non-invasive, possibly
even automatized continuous monitoring in farm-housing. Vocalizations may also
modulate emotions of the receivers such that welfare may also be affected in
conspecifics hearing distress utterances. For these reasons, the analysis of farm
animal vocalization has gained increasing interest in the last years and a variety of
attempts to decode the meaning have been made. According to Manteuffel et al.
(2004) future bioacoustical research for welfare assessment should focus on
comprehensive studies of a broad spectrum of species specific distress
vocalizations.
Sheep (Ovis aries) are a highly adaptable and versatile domestic species, which has made them a critically important resource in human societies around
the world (Meadows et al. 2005). According to statistical data on the Indonesian livestock sector, the amount of sheep raised for production purposes has increased
significantly in the past five to six years. The size of the national sheep population
was estimated at 8,979,849 animals in 2006. In 2010 this amount had increased to
10,915,000 (Direktorat Jenderal Peternakan 2010). It was reported by Johannes
and Budisatria (2011) that, in South East Asia, Indonesia has the largest small
ruminant population. According to them the rapid growth of the local population
serves as a major impulse for further increasing the number of small ruminants.
Although the welfare of farm animals has been of concern, and a focus for
research for decades, this has concentrated on those species generally farmed
managed extensively, sheep have received relatively little attention from a welfare
perspective (Dwyer 2009). Recently, Veissier et al. (2012) found that the emotional responses of sheep to a threatening event are influenced by the animal’s
social environment. Therefore, sheep are likely to form social standards of
emotional responses according to their rank in hierarchy which makes them a
perfect candidate species for behavioural studies.
The general breeding strategy for any production environment is to match
genetic potential to the feeding and management system (Bradford 1993). In order
for farmers to increase the productivity of their livestock with the use of limited
resources, it is important for them to facilitate the needs of their animals as much
as possible. More precise welfare assessments need to consider specific
behavioural response of genetic lines, as different lines react differently when
facing environmental challenges (McGary et al. 2003). Behaviour, like physiology and anatomy, is part of the general functioning an make-up of an
animal. An interesting question in the context of animals’ genetical background
concerns how differences in genotype and in the environment result in differences
in behaviour (Broom 1981).
Farmers and the food industry have the responsibility of meeting the
demands of the consumers for high welfare products and quality products by
adjusting their farming systems. Research in the area of animal behaviour will
therefore be able to provide farmers with important information for developing
better livestock management systems and designing captive environments catering
to the specific needs of each breed, which will automatically result in an
improvement of the production level of the local animals.
Purpose of the Study
The purpose of this study was formulated as follows:
1. To discover whether, and if so, to what extend the vocal output of sheep is
influenced by the stressfulness of different levels of social isolation
2. To determine whether there are differences in the vocal behaviour of different
3. To analyze the impact of farming practices i.e. regrouping and housing (space
allowance) on sheep behaviour
4. To assess the degree of variability in behaviour between sheep breeds
5. To discover amount of time needed for newly regrouped animals to establish
affinity and affiliative relationships
Significance of the Study
The output of this research is aimed at providing livestock farmers with a
valuable, less invasive and convenient method for assessing overall welfare of
sheep, in which behaviour can serve as a key indicator for the animals’
motivational state and welfare status. It is also hoped that the results of the study
will be able to provide valuable information about the optimum stocking density
and regrouping method for different breeds of sheep.
Hypothesis
The hypothesis that was tested during this study is that the acoustic output
of sheep is affected by their motivational state and that the quality of the vocal
repertoire differs per breed. The prediction was that the vocalizations of the sheep
would reflect the stress response induced by different levels of social isolation. It
was therefore thought that the quality of the vocal output would differ depending
on the intensity of the stressor and on the breed. It was also hypothesized that the
animals’ behaviour would be affected by the novelty of the new housing
conditions and amount of space available per animal. It was predicted that the
frequency of agonistic behaviour would be higher on the first day right after
regrouping and that the amount of agonistic behaviour displayed would differ per
LITERATURE REVIEW
Systematics and Distribution of Sheep
Domesticated sheep (Ovis aries) belong to the tribe Caprini (Shackleton & Shank 1984). Following Mesolithic mans’ domestication of the sheep
approximately 8000–9000 years ago (Ryder 1984), selection has proceeded on
traits such as coat color, environmental tolerance, wool characteristics, and meat
and milk production. The result is a spectrum of phenotypic differences between
breeds (Meadows et al. 2005).
According to Sodiq and Tawfik (2004) Indonesia has various indigenous
sheep breeds distributed throughout its different tropical environments which are
well suited for intensive and extensive exploitation. Throughout the years
different crossbreeding programs have been used in the hope of creating the ideal
animal, one which is well adapted to the various environmental conditions and
thus able to produce optimally. It is believed that there are two distinct types of
sheep in Indonesia: thin-tailed - and fat-tailed sheep (Edey 1983). In the hope of
improving the production of local animals, certain temperate breeds such as
Merino, Suffolk, Suffas, Dorset and, more recently, Barbados Blackbelly and
St.Croix were introduced to Indonesia (BPPT 2007).
Barbados Blackbelly Cross
Barbados Blackbelly sheep are a breed of hair sheep. Although there can
be little doubt that the Barbados Blackbelly has African ancestry, there is
compelling evidence that the breed originated and evolved on the Island of
Barbados. The fleece color of these animals ranges from light tan to a dark mahogany red, with black breed markings on the face, legs, belly, inguinal region,
chin, and chest (BBAI 2011). The animals of this breed are believed to be more
tolerant than other sheep breeds to internal parasites (CARDI 2006). A composite
breed, named Barbados Blackbelly Cross was created by crossing Barbados
Blackbelly sheep with animals from the breed Local Sumatera. This composite
breed is believed to possess the combined attributes of adaptation to widespread
Local Garut
Local Garut, a breed indigenous to Indonesia, is believed to have
originated from a crossing between Merino sheep, Kaapstad sheep and animals
from a breed local to Indonesia (Merkens & Soemirat 1926). Garut sheep possess
certain characteristics which make them very suitable for use in livestock
production systems, one of which is their adaptability to novel environments
(BPPT 2007). Under rural conditions, Garut sheep are generally raised on a small
scale as an additional source of income (Bradford & Inounu 1996). Due to its
rather dominant temperament, animals of this breed have been known to be used
for fighting purposes (Edey 1983).
Figure 1 Adult rams of the breeds Barbados Blackbelly Cross (left) and Local Garut (right). Source: private collection of the author
Composite Garut
St. Croix, a species of sheep known for its rather large size, high
adaptability to hot climates and ability to sustain a good production level under
poor feeding conditions together with Moulton Charollais, famous for its high
milk production, large body size and rapid growth rate, were used to create a
composite breed (Sodiq & Tawfik 2004). The before mentioned two breeds were
crossed with the previously described breed Local Garut to create the breed
Composite Garut. The animals of this composite breed are believed to have a very
Figure 2 Adult rams of the breed Composite Garut Source: private collection of the author
Importance of Animal Behaviour
Farm animals are kept to produce food an other essentials for humans, and
the farmers need to make profit from their enterprises. It is therefore necessary
that the difference between the value of what animals produce and the costs that
the farmer incurs for this production is sufficiently high. By taking animal
behaviour into account, such optimization may be easier to achieve (Jensen 2009).
Initially, before animal domestication, man used his knowledge of wild animal
behaviour to hunt them successfully. Later, whether by design or accident, he used
behaviour traits, particularly social ones, as key criteria in his selection of and
success with domestic animals (Tennessen & Hudson 1981).
Broom (1981) believes that behaviour, like physiology and anatomy, is
part of the general functioning of an animal. The term ethology is often used for
the observation and description of behaviour with the objective of finding out how
biological mechanisms function (Fraser & Broom 1997). Behaviour is the aspect
of an animal’s phenotype that involves the presence or absence of definable motor
activities, vocalizations and odor production by means of which it conducts its
daily affairs of self-maintenance and social interaction. Like other phenotypic
traits, behaviour is the outcome of environmental and genetic causal agents
(Banks 1982). Fletcher (1992) explained that research on animal behaviour has an
inherently integrative nature, for it gathers together questions and methodologies
across levels of analysis, across levels of explanation and across diverse taxa.
appreciation of animals. In addition to providing knowledge about the diversity
and complexity of behaviour in nature, such studies also provide information
crucial to improvements in the welfare of animals maintained in laboratories,
agricultural settings and zoos, and as companion animals (The Association for the
Study of Animal Behaviour 2003).
According to Fraser and Broom (1997) there are two types of questions
which can be asked when trying to understand a particular kind of behaviour.
These are: “How does it work?” and “Why does it happen?” The answers to the
first question refer to the mechanisms underlying the behaviour which cause it to
occur at the time of observation and with the form which is seen. The answers to
the second question refer to the way in which this behaviour has arisen in the
species under observation. The authors have suggested that since all behaviour
depends on the genetic information in an animal and environmental factors will
always affect the expression of genes, it is not useful to try to distinguish between
instinctive and innate behaviour and which is environmentally determined. The
questions of interest here, concern how differences in genotype and in the
environment result in differences in behaviour.
It was mentioned by Arney (2009) that sheep are an attractive animal for
scientific research on behaviour due to the facts that they are docile, have a
(relatively) short flight distance and are gregarious. In sheep, several studies have
been carried out concerning the behavioural reactivity of animals to a novel
environment. Breed differences are known to exist in several behaviours, such as
selection of lambing sites (Alexander et al. 1983; Poindron et al. 1984), open-field behaviour and reaction to the presence of a dog (Torres-Hernandez &
Hohenboken 1997). It is possible that the breed differences found in open-field
tests reflect genotypic variations in reactivity of animals to various stressful
situations according to Le Neindre et al. (1993).
Abnormal behaviour may be the first indicator that there is a problem with
an individual sheep, or the whole flock. Such abnormal behaviours observed in
sheep include: lethargy, becoming uninterested in feeding, increased vocalization,
isolation of individuals from the flock, restlessness and an increased respiration
irrespective of professional expertise, observers' interpretation of animals'
behavioural expressions, including their emotional state, are in close agreement.
This includes assessments of sheep.
In an attempt to emphasize the importance of behavioural studies Fraser
and Broom (1997) even stated that every farmer, every veterinary surgeon and
indeed all those who have an interest in livestock production need to know about
farm animal behaviour in order for them to carry out their job properly. Research
on the behaviour of farm animals is thus relevant and needed for animal
production enterprises to be carried out effectively and economically.
Behaviour, Welfare and Environmental Design
It has been stated by Rollin (1995) that society is currently demanding that
agriculture be modified to reduce suffering and to accommodate the physical and
psychological needs of animals, as determined by their biological natures.
According to the author the aim of research into animal welfare that will be
undertaken in the future therefore, must be primarily to improve the well-being of
animals, presumably within the constraints of economic reality. This, in turn,
means that research should be directed toward making production systems
“animal-friendly”, so as to alleviate suffering and increase animal happiness. To
date there is no consensus on the definition of welfare, however definitions have
been proposed based on the ability of the animals to perform natural behaviour,
the animals’ subjective experiences, or the biological functioning of the animals
(Dwyer 2008).
Table 1 gives an operational definition of animal welfare developed in the
Welfare Quality Project (2009). At present the innovations in management are
principally characterised by larger livestock numbers kept together in markedly
reduced space. Such conditions have effects on disease transmission and they
require considerable physological and behavioural adaptation. It has been
assumed that farm animals are, in certain cases, able to adapt to the environmental
restrictions, but that both adaptation and failure to adjust are recognisable in the
Table 1 An operational definition of animal welfare developed in the Welfare Quality Project (Welfare Quality 2009)
Principle No. Welfare criterion Example of potential measures
Good feeding 1 Absence of prolonged hunger Body Condition Score
2 Absence of prolonged thirst Access to water
Good housing 3 Comfort aroused resting Frequency of different lying
positions, standing up and lying down behaviour
4 Thermal comfort Panting, shivering
5 Ease of movement Slipping or falling, possibility
of exercise
Good health 6 Absence of injuries Clinical scoring of integument,
carcass damage, lameness
7 Absence of disease Enteric problems, downgrades
at slaughter
Evidence of routine mutilations such as tail docking and
dehorning, stunning effectiveness at slaughter
Appropriate behaviour
8 Expression of social behaviours Social licking, aggression
Expression of other behaviours Play, abnormal behaviour
Good human-animal relationship Approach or avoidance tests
Positive emotional state Novel object test
Adapted from Rushen et al. (2011)
The welfare of different farm animal species has been a scientific issue for
a relatively long time, generating a significant quantity of information related to
welfare of different farm animal species in the scientific literature (Fregonesi
1999). Behaviour has been of great importance as an indicator of animal welfare.
It can be recorded without complicated equipment under field conditions and it
does not have the same difficulties and limitations associated with all other
indicators (Duncan & Poole 1990). The welfare of managed animals relates to the
degree to which they can adapt without suffering to the environments designated
by man. So long as a species remains within the limits of the environmental range
to which it can adapt its well-being is assured (Carpenter 1980).
In addressing the issue of how we can use behaviour in the assessement of
animal welfare, we next need to ask what behaviour can tell us about animal
health and also what it can tell us about what animals want. Behaviour has a
number of major advantages in welfare studies. Not only is it non-invasive (does
not include breaking the animal’s skin), but it is also in many cases
Table 2 gives an overview of commonly used indicators for judging the
suitability of management and housing systems for animals based on their
[image:41.595.113.517.190.315.2]welfare.
Table 2 Scheme for judging welfare indicators in animal management and housing systems
Behavioural indicators Non-behavioural indicators Meeting requirement Behaviour Fitness of facility
quality form measurements clinical
quantity frequency space allowance pathological
duration social integration physiological
intensity type of material biophysical
modification hygienic and reproduction
climatic
characteristics
production
Adapted from Zeeb (1983)
Farm animals are social species with a strong tendency to form groups.
Living in groups has associated costs and benefits. Variation in the size of a group
in natural populations is self-regulated through cost–benefits balance and can be
considered a byproduct of the environmental conditions, as animals will join or
leave the group depending on the overall benefits. This possibility does, however,
not exist in the farm environment, as animals will have no opportunities to leave a
“costly” group setting, creating a situation of increased aggressive interactions
that may favor despotic behaviour, with negative consequences for some
individuals in the group (Estevez et al. 2007). Group size in sheep varies widely within species in response to local environmental conditions and to population
characteristics according to Shackleton and Shank (1984).
In confinement, animals are constrained by the space and conditions
provided for them; they cannot disperse or abandon the group when conditions
become adverse, as they are restrained within the limits of the enclosure.
Inadequate physical and social features of the captive environment can therefore
be considered a source of discomfort and stress that can lead to serious
physiological, behavioural and welfare problems (Estevez & Andersen 2007;
Würbel 2001; Morgan & Tromborg 2007). Enclosure size is a feature of critical
importance for captive animals, because they are willing to work actively to gain
size, animal movement in captive environments may be limited by specific
features such as environmental complexity.
The European Commission (2005) believes that group size has to be
manipulated when testing for density effects in enclosures of equal size, leading to
confounding between density and group size. Yet a clear understanding of the
effects of each factor is critical to improve the quality of the environment for
captive animals. It is believed that this is particularly relevant in production
systems in which space is a precious commodity. Scott (2005) mentioned that
recommendations on minimum space requirements cannot be based on the
simplistic view of mere units of space per animal. According to the author
features such as the structural characteristics of the environment or social aspects
of the group must also be considered to establish meaningful recommendations. A
careful description of the behaviour patterns or a sequence of behaviours of
animals offers the possibility to identify all of the relevant components and to link
their performance to the wider context of the physical and biological environment.
In designing an environment for domestic or captive animals, it is common
to consider one feature at a time: a feature such as space allowance. According to
Jensen (2009) the essence of keeping animals in captivity is to control their
behaviour by preventing their escape, controlling their breeding and making them
adapt to the housing environment. The way in which animals behave in different
environments has been used informally in modifying those environments or in
designing new ones ever since animals have been kept in captivity. With the
development of behavioural science, however, particularly in the second half of
this century, this process has been made more formal (Appleby 1997). Dethier and
Stellar (1964) mentioned that the assertion that an organism maintains relations
with its evironment, whether nonliving or living, implies that an organism
changes in response to changes in the environment.
Whenever animals have to be grouped or decisions have to be taken about
the housing and density of animals, information about social behaviour is
important (Fraser & Broom 1997). Social behaviour, by definition, implies the
interaction of two or more individuals, the influence of one individual on another
various behavioural disorders. Aggression levels may become excessively high
and dramatic behaviour such as cannibalism and several other types of abnormal
behaviour may develop (Lawrence & Rushen 1993).
By using ethological knowledge environmental conditions can be created
that best suit the needs of the animals. This thus leading them to produce
optimally (Jensen 2009). Ethological indicators are believed to permit statements
about whether housing and management conditions of the animals fit their needs
and therefore also their welfare (Duncan 1993).
Motivation and Stress in Farm Animals
It is recognized that a reliable assessment of stress cannot be made solely
with the aid of hormonal variables (Toates 1995). Even if there is no consensus
about the precise meaning of the word ‘stress’, its frequent usage suggests that it
captures some essential features of the reactions of animals to harmful stimuli.
Stress, as described by Burchfield (1979), is an environmental effect on an
individual which overtaxes its control systems and reduces its fitness or seems
likely to do so. The relationship between stress and welfare is very clear using this
definition of stress. Since welfare refers to a range of states of the animal from
very good to very poor, whenever there is stress, welfare is poor.
The physiological responses of animals to aversive situations are complex
and often inconsistent according to (Mason 1975). In addition, different
individuals may react consistently differently to the same challenge and in
situations of unambiguous stress there can either be a sympathetic or
parasympathetic/HPA dominance, due to constitutional differences between
individuals of the same species (van Holst 1985; Benus et al. 1991). Broom (1996) believes that stress concerns situations when there is failure to cope, but
poor welfare includes the state of an animal both when there is failure to cope and
when the individual is having difficulty in coping.
When the assessment of welfare is related with the coping definition there
are a considerable number of scientifically acceptable indicators. The following
groups of indicators are commonly used in research according to Smidt (1983):
Veissier et al. (2000) have created a model which shows the relationship between an animal, its surroundings and its welfare status.
Figure 3 Assessement of welfare and consequences of lack of welfare Adapted from Veissier et al. (2000)
Kilgour (1983) suggested behaviour, stress and production as means to
assess welfare of housed animals. Behavioural responses are first used to cope
with an arousal. If with behavioural changes the individual is unsuccessful in
coping with the problem, physiological mechanisms of coping might then be used.
stressed and with this its welfare becomes an issue. Production may also be
adversely influenced. The primary experimental research linking the social
environment with disease has tied ‘stress’ to biological intermediaries of disease
(e.g. reduced immunity and resistance to infection) and consequent disease risk.
The concept of ‘stress’ in mammals has been reviewed extensively (Proudfoot et al. 2012). Consequently, stress can induce a malfunction of the immune system having negative repercussions on animal health and welfare. The effect of
stressors on the immune response to foreign antigens like ovalbumin has been
tested in several species by measuring the level of antibody in the serum in sheep
(Cockram et al. 1993).
Relations of Vocalization to Animal Welfare
Communication can broadly be defined as “the sharing of information
between A and B”. In the context of animal behaviour, communication is the
sharing of information between two or more individual animals (Scott 2005). One
question that arises from this statement is: ‘What information is shared when
animals communicate’? Vocal communication is believed to play a central role in
animal societies. Animals rely upon their acoustic and vibrational senses and
abilities to detect the presence of both predators and prey and to communicate
with members of the same species (Fletcher 1992). It is accepted that calls provide
various types and amounts of information (Setchell & Curtis2011).
Mammalian vocalization consists of a varied number of different call types
and contexts in which these calls typically occur. While it is now well established
that vocalizations carry information about the emitter such as its species, its sex or
its identity, few studies have thus far focused on how vocalizations could hold
information about the emotional state of the sender. Nevertheless, some recent
studies in mammals revealed that physiological stress is often associated with
modified vocalizations, implying that an emotion of stress could be expressed
It has been demonstrated that isolation is a strong stressor in many species,
which is assumed to provoke a raise of stress hormones and/or a change in
behaviour such as emission of stress-induced vocalization (Perez et al. 2011). It is therefore of great importance to gain understanding in the process of vocal
production. According to Brandbury and Vehrencamp (1998) the starting point of
an approach to understanding the vocal repertoires of non-human mammals is a
thorough evaluation of the physics and physiology of their vocal production
system. This is essential to the study of animal behaviour and ecology, as the
progression of interactions between individuals is mediated by visual, olfactory
and vocal signals
The ability to produce calls depends on the existence of a vocal tract which
is constituted by specialized elements of the tracheal tract and, in mammals, the
pharyngeal cavities. The anatomy and function of the acoustical elements
determine the range, the acoustic characteristics and the limits of sound
production in a species. Regarding aspects of animal welfare, however, they may
be of less importance than the trigger and vocalization control systems within the
central nervous system which determine the onset, the character, and the intensity
of vocalization (Manteuffel et al. 2004).
The function of animal utterances is probably in most cases directed to
conspecifics and signals attraction or warning (in a double sense: warning against
a predatory threat or of the warner himself as a habitat resident). In domestic
animals, where some original ultimate causes of vocalizations may have vanished,
it can be hypothesized that the respective repertoire has survived in other contexts.
In farm animals, vocalization characteristics and releasers have not changed much
during the process of domestication (Andersson et al. 2001).
Results from research (Fraser 1974; Von Borell & Ladewig 1992; De
Passillé et al. 1995) have shown that an increased vocalization rate is indicative of the excitement of pigs and calves and their degree of fearfulness to novelty and
social separation. It has also been discovered that vocalizations can be elicited by
the injection of drugs that stimulate neuronal circuitries involved in mood and
homeostatic factors influencing mood, are perceived by limbic centres of the
forebrain. Signals are then transferred via centres of the midbrain (periaqueductal
grey) and the lower brainstem to effector muscles of the vocal system (Figure 4).
Figure 4 Neuronal, anatomical and functional elements of call production in animals. Adapted from Manteuffel et al. (2004)
Sheep is a mammalian species which produces a number of different
vocals. Some of the specific vocalizations that may be discriminated within this
species are, a low-pitched bleat usually produced by lambs, and high-pitched
bleats usually produced by ewes, considered to be “protest” or distress bleats. The
fact that sheep are a prey species causes these animals to use less vocal
communication in comparison with other social animals. As a result, there is
likely to be little vocal "redundancy" (Krause & Ruxton 2002). Dwyer et al.
(1998) believe that this offers the advantage that a functional and
situation-specific analysis of bleating behavior in this species, has an increased chance of
being fruitful.
Social isolation is known to be particularly stressful for gregarious species.
Among farm animals, sheep are known to be very sensitive to social isolation
(Price & Thos 1980). Sheep, being gregarious animals, are very sensitive to the
stress of becoming separated from the flock. Minton and Blecha (1990) and
Coppinger et al. (1991) have shown that subjecting sheep to restraint and isolation stress (RIS) caused robust increases in plasma concentrations of ACTH and
cortisol. The strong stressful effects induced by social isolation in sheep have also Amygdala
Cingulate Cortex
Periaqueductal Grey
Brainstem and Cervical Cord
been characterized by behavioral (Poindron et al. 1997) or endocrine responses (Apple et al. 1993) but rarely by concomitant behavioral and endocrine responses (Cockram 2004). The results found by Viérin and Bouissou (2003), however,
concluded that distress in sheep, is also characterized by increased number of
vocalizations, pawing the ground, decreased time of lying down, feeding,
locomotion and increases in plasma cortisol or heart rate.
Understanding negative animal responses and observing and recognizing
animals in distress is a key skill to implement appropriate practices in order to
reduce the stress effects. A possibility toward this goal is applying sound analysis,
in livestock farming compartments, as a tool for early detection of disease and
distress from continuous recording and automatic processing of animal sounds
(Ferrari et al. 2011). Grandin (1998) defines vocalization as being the active generation of sounds with specific organs as an expression of a distinctive inner
state of an animal that may occur spontaneously or may be the result of an
external event. Recent studies in mammals revealed that physiological stress is
often associated with modified vocalizations, implying that an emotion of stress
could be expressed through vocalizations (Briefer 2012). According to Dawkins
(1998) animal calls have partly evolved as communication signals to indicate
some types of “need” and they are relatively easy to record. It therefore seems to
be reasonable to regard vocalizations as easy indicators of an animal’s state of
welfare.
In the ideal case, a given animal’s vocalization can be clearly attributed to a
distinct inner state (or a class of inner states) which - sometimes context
specifically - defines the subjective meaning of the utterance. Weary and Fraser
(1995) reported that alterations of the inner state of an animal may result in
physiological and/or behavioural reactions which can be measured and used to
draw conclusions on the intra-individual and intra-specific meaning of the
vocalization (its semantic content). The dependence of animal vocalizations on
inner states thus makes them useful tools for judgments on the state of well-being
or stress in an individual. According to these authors vocal signals are particularly
useful in the assessment of animal welfare when they reflect aspects of the
occur (“honest signaling”). Judgments on welfare require that, in a given
environment, the physical and physiological conditions of the vocalizing animal
can be clearly attributed to its state of welfare. The vocalization by itself is not an
indicator because forms of utterances are arbitrarily attributed to the carried
message (Guilford & Dawkins 1995).
According to the Motivation Structural Rules (Morton 1977) almost all
sounds used for close-range communication follow a certain pattern reflecting the
motivational state of the caller. Whereas high-pitched, tonal sounds are thought to
signal appeasement in fear-associated contexts, low-pitched, harsh sounds are
attributed to more aggressive emotions. Although there is some evidence
supporting this concept (Seyfarth & Cheney 2003), clearly designed systematic
studies to test this concept in farm animal species are lacking up to now.
Vocalization Analysis
Animal acoustic behaviour can be termed as being rather complex due to
its variability. The distinction and scientific communication of various types of
farm animal vocalizations requires formal description based on physical
parameters. Frequently the majority of vocalizations is initially recorded in
common environments (e.g. in a husbandry system) and / or behavioural contexts.
The recorded calls are subsequently open to any kind of analysis to find and
describe specific acoustic parameters. Digital signal processing now allows more
diverse numerical descriptions and statistical examinations (Hopp et al. 1997) that can be applied for the analysis of vocal utterances of farm animals. It is of utmost
importance to find an approach to the causal links between welfare-relevant
stressors and respective vocalizations.
Manteuffel et al. (2004) have listed the following procedures which have
been applied in distinguishing various types or individual characteristics of
vocalizations:
¾ Standard statistical methods (e.g. ANOVA, t-test, Wilcoxon test) if few
selected features (e.g. fundamental frequency, duration, rate) are sufficient
for discrimination
¾ Complex statistical methods to compare groups of features (e.g.
quality of a call, described by a set of features is important (Schrader &
Hammerschmidt 1997)
¾ Neural networks (NN) allow applications in noisy environments because
they tolerate variations of a trained feature set (Schön et al. 2001)
¾ Hidden Markov Models (HMM) allow an arbitrary number of different
vocalizations to be classified, but this demands a specific HMM for each
type of vocalization. A given utterance is then attributed to the best fitting
HMM (Jahns 2002).
One of the latest methods in analyzing animal vocalizations is the
interpretation of non-linear phenomena. The vocalizations of animals range from
periodic vocal-fold vibration to completely atonal turbulent noise. Between these
states non-linear dynamics appear in the sounds. It has been hypothesized that an
increased appearance of non-linear phenomena is correlated with a worsened
condition of an animal (Riede et al. 2001; Tukoda et al. 2002) or with the effort that was put in the vocalization production. If that can be proven, the search for
non-linearities in an utterance will be a suitable additional indicator of welfare
EFFECT OF DIFFERENT LEVELS OF SOCIAL ISOLATION
ON THE ACOUSTICAL CHARACTERISTICS OF SHEEP
VOCALIZATION
ABSTRACTIt is commonly accepted that social isolation represents a stressful challenge to gregarious species and is able to impair welfare. Vocalization is believed to be a form of commentary by an animal on its own internal state. Animal vocalizations are therefore thought to be useful for determining the emotional state of an animal. In farm animals, vocal analysis is accepted as a non-invasive method forassessing animal welfare in comparison to most physiological measurements. The aim of this study was to investigate the influence of different degrees of social isolation on the acoustic characteristics of stress-induced bleats from three different breeds of sheep. A total of twelve adult male sheep, 2–3 years old, divided in three equal groups based on breed, were used. The animals were subjected to three different degrees of social isolation. At the first isolation level each animal was kept completely alone. At the second level each animal was kept in a room in the presence of a human. At the third level the animal was only partially isolated from conspecifics. Both locomotive and vocal behaviour were recorded during 15-minute sessions on three consecutive days. The locomotive behaviour was subjected to descriptive analysis while the vocal data were first visualized using the acoustic software Raven Pro 1.4, after which a total of thirty-six acoustic parameters were measured. Statistical analysis of the measured parameters was done using the software program SAS 9.2. The descriptive analysis of the observed behaviour showed that the animals were more active during partial isolation compared to complete isolation. The number of bleats during partial isolation was also found to be higher compared to the number of bleats during complete isolation. The application of two-way analysis of variance showed a significant effect of isolation level and breed type on both temporal and structural acoustic properties. Amplitude, power and time acoustic properties were found to affect acoustic quality of vocal responses to isolation, whereas frequency related properties were also found to differ significantly (P < 0.05) between breeds. From spectrogram analysis, the patterns of energy distribution within the calls proved to offer the most evident difference between isolation level and breed. Calls uttered during complete isolation were all identified by a higher level of noise-energy compared to calls uttered during partial isolation.
In conclusion the acoustic analysis revealed that the affective state of the animals was expressed by both temporal and structural variations in acoustic cues within distress calls and that this differs per breed.
INTRODUCTION
Communication, as reported by Hauser (1996), can occur through a range
of modalities- by sound, smell, sight and touch. Acoustic communication has been
found to play an important role in the social life of many animals. Communicative
behaviour occurs in any form of social interaction and implies an exchange of
information between at least two individuals: a signaler and a receiver. The
acquisition and the use of information helps animals to anticipate and respond
appropriately to events, and therefore to increase their survival (Owings et al.
1997). Through communication, for example, social dominance hierarchies are
established without dangerous fights occurring, members of groups warn each
other about potential danger, and recognition occurs between mothers and their
young (Halpin 1991; Huntingford et al. 2000).
Vocalizations are essential in communication and social interactions,
conveying the speaker’s identity, gender, intentions, and emotional state (De
Lucia et al. 2010). Dawkins (2004) suggested that vocalizations may perhaps be a rather special case of an indicator of what an animal wants because they are
signals, that is, behaviours that have specially evolved to alter the behaviour of
another animal, and which can therefore be “listened in on” by humans. In
communication, information is made available by signals that vary in relation to
the type of information delivered and to the surrounding environment (Vannoni et al. 2005).
The passing of more restrictive animal welfare laws has caused the
detection of stress, especially in domesticated animals, to become an important
issue. One suggested method of detecting stress has been through monitoring the
vocalizations of the animals (Clemins et al. 2005). The vocalizations produced by an animal species can be categorized from both structural and functional
standpoints, and the relationship between the two may take many forms (Soltis et al. 2005).
It is possible to assess welfare using some animal signals shown when they
need certain resources. Weary and Fraser (1995) have reported that vocal and
other natural signals provide reliable indicators of the signaller’s needs. However,
of a signal before invoking this as a measure of welfare. Acoustic signals can vary
in their duration, pitch (vibration frequency), or amplitude. These features can be
described and studied with the aid of spectrograms which give a visual
representation of a sound (Hauser 1996).
Regardless of how the communication occurs, it is important to understand
how animals can benefit from producing signals, and how others can benefit from
responding. It has been found,for example, that some animals vocalize in response
to pain while other animals are stoic. This difference in behaviour probably
reflects differences in potential audience (Briefer 2012).
Bioacoustics is the study of sound in animals and includes, but is not
limited to, animal communication with associated behaviour (Waring 1975;
Bradbury & Verencamp 1998; Mulligan et al. 1994), sound production anatomy and neurophysiology, auditory capacities and auditory mechanisms, and animal
welfare (Manteuffel et al. 2004). Bioacoustics is extremely important to animal welfare and