consistent with growth biology, has been neglected by the other feeding systems here considered. Part of the large variability observed in the comparison of growth requirements (Fig. 6.6) could also be due to the fact that for equal BW, requirements are different depending on the gender considered.
composition in adult goats. A model that predicts the relationship between BW and BCS in various goat breeds was developed. It allows the prediction of cur- rent BW when BCS and breed mature weight at BCS 2.5 are known inputs or the prediction of BW at BCS 2.5 when current BCS and BW are known. The relationship between the proportion of fat in the empty body and BCS is also predicted.
The SRNS computes average daily gain of kids with equations based on the CSIRO (1990) model. Average daily gain depends on the energy available for gain after maintenance costs are covered and on the energy value of the gain.
The latter and the fat and protein composition of the gain are estimated based on the relative maturity of the kids (ratio of current weight to mature weight for a certain gender and breed) and on their feeding level.
The SRNS uses a mechanistic ruminal model that predicts feed biological values based on carbohydrate and protein fractions and their ruminal degrada- tion rates, forage, concentrate and liquid passage rates, microbial growth and physically effective fibre.
The evaluation of the SRNS based on literature data showed that it accu- rately predicted the average daily gain of kids (root of the mean squared error of prediction, RMSEP, 32.5 g/day; r2= 0.85; concordance correlation coefficient, CCC = 0.91; Cannas et al., 2007). In addition, the SRNS was able to predict accurately and precisely the daily MEI (when DM intake inputs were accurate) of adult goats and wethers (RMSEP= 0.24 Mcal/day;r2= 0.99; CCC = 0.99), their milk NE (RMSEP= 0.012 Mcal/day; r2= 0.99; CCC = 0.99) and their energy balance (RMSEP= 0.20 Mcal/day; r2= 0.87; CCC = 0.90), with a
10 12 14 16 18 20 22 24
Body weight (kg)
AFRC (1998) Dairy crossbreed (Resende, 1989) Dairy crossbreed (Ribeiro, 1995) Saanen (Ferreira, 2003) Saanen (Medeiros, 2001) 3/4 Boer 1/4 Saanen (Fernandes et al., 2007) 1/2 Boer 1/2 Saanen (Teixeira, 2004) SRNS – female SRNS – male
NP requirements/100 g BW gain (g/day)
30 40
20 10
0
Fig. 6.7. Comparisons of net protein (NP) requirements for body weight gain (g/day per 100 g BW gain) across studies and feeding systems using different genotypes and ages. For the Small Ruminant Nutrition System (SRNS; see text), a mature weight of 55 kg for females and 85 kg for males was considered to estimate the relative maturity of growing goats.
systematic tendency to under-predict the energy balance slightly as the observed values increased (Cannaset al., 2007).
Conclusions
Estimating energy and protein requirements is a fundamental aspect of goat nutrition. Many feeding systems have been proposed for goats, but many esti- mates are based on research conducted on other species.
For example, the INRA system uses an approach very similar to that devel- oped for dairy sheep and is better suited for confined than grazing goats. The AFRC system uses a simplified approach, based mainly on the ARC (1980), deriving many of its equations from the system developed for sheep and cattle.
The EEZ system, even though not completely developed, is based on exper- imental measurements, often calorimetric ones, conducted on goats by this research group. For some sub-models, such as that for physical activity require- ments, EEZ presented completely new data and equations.
Among the systems compared in this chapter, IGR is the most recent one and is based on the statistical analysis of databases created from the scientific lit- erature on goats. Most of the databases were analysed by linear regressions. This is the only system which proposes specific requirements for breeds with different production aptitudes. In addition, IGR developed a unique procedure to calcu- late requirements for physical activity. Due to the large number of data used and the good information developed, IGR can be considered a modern and com- plete feeding system for goats. However, this system has the major limitation of considering constant growth requirements for animals of different BW, relative maturity and gender.
In general, the systems which predict energy and protein requirements for goats tend to be more empirical and less flexible than the most recent sheep and cattle systems. This depends partly on the scarce number of studies conducted on goats in comparison to those on sheep and cattle. In addition, the distribution of goats throughout very different environments makes the modelling of their requirements more complex. However, more mechanistic feeding systems for goats are currently under development.
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7 Feed Intake
M. A
VONDO,1L. B
IONDI,1R.I. P
AGANO,1A. B
ONANNO2 ANDL. L
UTRI31Dipartimento di Scienze Agronomiche, Agrochimiche e delle Produzioni Animali, Università di Catania, Via Valdisavoia 5, 95123 Catania, Italy;
2Dipartimento di Scienze Entomologiche, Fitopatologiche, Microbiologiche e Zootecniche, Università di Palermo, Viale delle Scienze, 90128 Palermo, Italy;3Istituto Sperimentale Zootecnico per la Sicilia, Via Roccazzo 85, 90136 Palermo, Italy
Introduction
In the classification of herbivores according to their diet (Hofmann, 1989), the goat species is included in an intermediate class between grass and roughage eaters (cattle, sheep) and concentrate selectors, which do not tolerate high fibre levels and are forced to select less fibrous parts of plants. ‘Intermediate feeders’
(or ‘opportunistic feeders’) change their feeding behaviour according to seasonal changes in diet availability (Fedele et al., 1993; Papachristou, 1994) and are much more versatile than the other two categories of animal. ‘Intermediate feed- ers’ are characterized by: (i) high saliva secretion and large absorption surface of the rumen epithelium, which protect the animal from the risk of acidosis; and (ii) considerable enlargement of the digestive apparatus when highly fibrous feed is used (Silanikove, 2000). Because of these characteristics, goats can adapt to a broad range of feeding conditions. Moreover, more than any other species, goats are able to choose, among the available feedstuffs, parts of plants with the high- est protein content and the highest digestibility, selecting feed on the basis of prehension ease, sensorial characteristics and post-ingestive effects learnt from their own experience (Provenzaet al., 2003). It must also be noted that in the presence of certain feeds, such as very young pastures, instead of selecting high-quality parts, goats select more fibrous and dry parts, which can improve rumen functionality. In intensive conditions, goats can tolerate overfeeding. In a free-choice trial Girgentana lactating goats consumed up to 3 kg of dry matter (DM) per day, constantly self-regulating crude protein (CP) and neutral-deter- gent fibre (NDF) levels at 16.5 and 34%, respectively, with minimal daily varia- tions. In no cases did the goats display noteworthy differences in the main blood parameter levels compared with normal reference values (Avondo et al., per- sonal communication). It has been demonstrated that even in diets with concen- trate levels above 60–70%, goats do not greatly alter their productive capacity or
CAB International 2008.Dairy Goats Feeding and Nutrition
(eds A. Cannas and G. Pulina) 147
their metabolic well-being (Bailoni and Andrighetto, 1995; Economides, 1998;
Goetschet al., 2001; Fedeleet al., 2002).
Indeed, once goats perceive the metabolic effects of a diet very rich in con- centrates, they change their feeding behaviour to have small and numerous daily meals (Abijaoudéet al., 2000), thereby avoiding the dangerous effects of exces- sive starch in the rumen. Several experimental trials have been carried out on