Sexual activity and body and testis growth in prepubertal ram lambs of
Friesland, Chios, Karagouniki and Serres dairy sheep in Greece
S. Belibasaki
*, S. Kouimtzis
NAGREF, Veterinary Research Institute, GR-570 08 Ionia, Thessaloniki, Greece
Accepted 14 October 1999
Abstract
Sexual activity, body size and testis growth in the prepubertal period (120±210 days of age) were studied in ®ve male lambs of each of four dairy sheep breeds. Sexual responses developed earlier in Friesland than in Chios and Karagouniki and latest in Serres ram lambs. Friesland lambs expressed interest in females at 127 days of age and 34 kg live weight 18±36 days younger and 3.4±6.3 kg lighter than the three Greek breeds. Puberty (®rst mounting with ejaculation occurred) of ram lambs appeared to be more closely associated with body weight than with chronological age. Age at puberty averaged 179 days in Friesland, 8, 10 and 30 days younger (P< 0.05) than in Karagouniki, Chios and Serres, respectively. On the other hand, weight at puberty averaged 50 kg for Friesland and Chios compared to about 44 kg for the two other breeds (P< 0.05). In the four breeds studied there was a 41±52 days interval between the time when lambs ®rst expressed interest in females and the time puberty occurred, the longest was that of Friesland lambs. There was a signi®cant breed difference in scrotal circumference. At puberty the scrotal circumference was 33.9 cm in Friesland lambs, 4±6 cm greater than in the three Greek breeds. Friesland ram lambs had a greater scrotal circumference throughout the entire period studied.#2000 Elsevier Science B.V. All rights reserved.
Keywords:Ram lambs; Puberty; Body weight; Scrotal circumference
1. Introduction
The study of reproduction in male sheep from breeds or strains of differing female reproductive characteristics has indicated that differences may be recognized in the reproductive characteristics of both young and adult males. Rate of testis growth was found to be more rapid in ram lambs of a breed with high proli®cacy such as the Finnish Landrace than in a
non-proli®c breed such as the Scottish Blackface (Land and Carr, 1975). Also, Louda et al. (1981), after observing testis growth, and small but consistent differences in the development of sexual activity and of sperm production, suggested that young rams of proli®c breeds (Romanov and Finnish Landrace) may differ in their potential reproductive performance, though slightly.
In general, sexual development of ram lamb appears to be more closely associated with body growth than with chronological age (Dyrmundsson and Lees, 1972). Dyrmundsson (1973), concluded that body weight is a better criterion for the attainment of puberty than chronological age alone.
*Corresponding author. Tel.:30-31-781701;
fax:30-31-781161.
E-mail address: [email protected] (S. Belibasaki)
The only study reporting on puberty in ram lambs of Greek breeds is that of Alexopoulos et al. (1991). There is a lack of detailed information on the onset of puberty in male lambs from dairy sheep.
The purpose of this investigation was to determine the onset of puberty and associate that with body and testis growth in three breeds of Greek dairy sheep (Chios, Serres and Karagouniki) and Friesland, a proli®c breed imported to improve dairy potential of these Greek breeds
2. Materials and methods
A total of 20 male lambs, ®ve each of Chios, Serres, Karagouniki and Friesland were used. These animals were born between the 10 and 25 of December to selected ewes, inseminated after they had been syn-chronized for oestrus during the normal breeding season.
The lambs were weaned at 60 days of age and were housed together in a shed at the Veterinary Research Institute, Thessaloniki, Greece, (latitude 408 410
N longitude 228480
E). They were raised under the same management and nutrition conditions.
Body weight was recorded at regular fortnightly intervals from birth to 210 days of age. Scrotal cir-cumference (SC) was measured every 2 weeks from 120 to 210 days of age using a circular plastic tape at the point of maximum circumference of the paired testes (Notter et al., 1981). Ram lambs from each breed were introduced into pens containing ®ve adult females of their own breed for a period of 20 min. Oestrus was arti®cially induced in three of these ®ve ewes and the manifestations of sexual behaviour were observed and recorded. This proce-dure was repeated twice a week from week 12 to puberty which in the present study was de®ned as the ®rst observed mounting with ejaculation. Semen was collected from each ram lamb 3 days after the ®rst mating by electro-ejaculation to ensure the presence of viable spermatozoa in the ejaculate. Although using arti®cial vagina for collecting semen gives more con-sistent results, it requires training the rams, no such training is required when using electro-ejaculation collections.
Body weight and SC were also recorded at two special occasions: when the ram lambs expressed
`interest' in females in oestrus and when they attained puberty.
A two-way analysis of variance was applied, the two factors were breed and age. Signi®cant differ-ences among means were detected using Duncan's multiple range test (Duncan, 1955).
3. Results
3.1. Sexual activity
On the ®rst day the ram lambs were mixed with the ewes they all tried to suck them. The second time (3 days later), the Friesland rams, whilst still attempting to suck the ewes, alternated this activity with a sexual approach by nosing around the external genitalia of the ewes. The following week, two Friesland rams showed a marked interest in ewes and attempted to mount those in oestrus. Three days later all the Fries-land lambs showed interest but only for ewes in oestrus and they attempted to mount them. The mean age of these rams was 126.69.3 days (Table 1). The Friesland lambs succeeded in mounting with ejacula-tion nearly 2 months later at the average age of 178.610.8 days (Table 1).
Chios and Karagouniki ram lambs continued to show only the suckling re¯ex during the ®rst 10 days. During the second week one Chios ram lamb showed `interest' in a ewe in oestrus. On the third week all rams began to approach the ewes and make attempts to mount. Chios and Karagouniki lambs tried to mount ewes and showed the beginning of an erec-tion re¯ex at the average age of 146.65.1 days and 144.67.9 days, respectively (Table 1), about 20 days later than Friesland rams.
The corresponding behaviour for Serres lambs was much later than the other local breeds, and there was a great variation in age. The ®rst Serres ram lamb showed interest and tried to mount ewes in oestrus at the age of 158 days and the last one at the age of 176 days. Average age at which Serres ram lambs expressed interest for ewes in oestrus and attempted to mount them was 163.413.8 days (Table 1).
Whilst the full range of sexual re¯exes were attained by all rams at nearly 22 weeks of age, it was not until 50±60 days later that all rams succeeded in mounting and ejaculating (Table 1).
Breed differences for age at puberty were similar to those found for age at which the rams expressed `interest' in females in oestrus (Table 1).
3.2. Testis growth
Scrotal circumference was greater (P< 0.05) in Friesland rams than in the other three breeds at each age from 120 to 210 days. It remained almost constant from 180 to 210 days of age (Fig. 1). Scrotum cir-cumference was similar in the three Greek breeds between 120 and 135 days of age. From 150 to 210 days of age, Chios rams had greater SC than
Serres rams (P< 0.05). Signi®cant differences were also observed between Chios and Karagouniki at the ages180and195 days,theformersbeinggreater (Fig.1).
3.3. Live weight
Live weight rose steadily from birth to 210 days of age in the four breeds (Fig. 2). The growth rate was 245 g/day for Friesland lambs, 240 g/day for Chios, 215 g/day for Karagouniki and 191.3 g/day for Serres. The Friesland rams showed `interest' in females in oestrous at lighter body weight than the three Greek breeds. Serres ram lambs had smaller body weight at the same sexual stage compared to Chios and Kar-agouniki ram lambs. At puberty, Friesland and Chios ram lambs were heavier than Karagouniki and Serres (Table 1).
Table 1
Average age, body weight and scrotal circumference of ram lambs when ®rst expressed `interest' in females in oestrous and when attained pubertya
Breed Age (days) Body weight (kg) Scrotal circumference (cm) When first expressed `interest' in females
Friesland 126.6a9.3 34.1a2.6 27.5a1.6 Chios 146.6b5.1 40.4b2.1 23.0b3.9 Karagouniki 144.6b7.9 39.7b3.4 28.0b1.0 Serres 163.4c13.8 37.5c3.3 23.5b1.4
When attained puberty
Friesland 178.6a10.8 49.8a3.7 33.9a1.0
Chios 189.6b12.7 50.2a2.6 28.9b2.9
Karagouniki 186.7b10.2 44.9b3.2 27.5b2.0
Serres 209.4c4.6 44.5b3.9 27.0b1.1b
aNumber of observations per breed is 5 and means followed by different letters in superscripts are signi®cantly different (P< 0.05).
4. Discussion
The lambs used in this study were already display-ing male behaviour by attemptdisplay-ing to mount their pen mates at 30 days of age and they showed interest in females in oestrous at ages ranging from 126 to 160 days depending on breed. Puberty, de®ned by successive mounting with ejaculation, occurred at different ages and at different body weights in the breeds studied.
The signi®cant differences in the live weight observed between the two proli®c breeds, Friesland and Chios (litter size of the adult females 2.0 and 1.75, respectively), and the less proli®c Karagouniki and Serres (litter size 1.12 and 1.25, respectively) (Kat-saounis, 1980; Pappa-Michailidou et al., 1997), sug-gest that the live weight of the ram lambs at puberty is probably related to genotype. Similar results were observed in ram lambs of different proli®c breeds by Skinner and Rowson (1968); Louda et al. (1981); Jimenez Severiano and Pijoan (1984).
In the present study, there was a marked variation in age and body weight of rams when they ®rst showed `interest' in females in oestrous and the age at which they attained physiological puberty. Ram lambs of the proli®c breeds Friesland and Chios attained puberty when they had reached approximately 50 and 55% of their adult body weight, respectively. While the ram lambs of the less proli®c breeds Karagouniki and Serres attained puberty when they had reached 65 and 67% of their adult body weight, respectively.
Dyrmundsson and Lees (1972) reported that Clun Forest ram lambs attained puberty when they reached 35±45% of their adult body weight. The correspond-ing ®gures for RambouilletBritish Down rams was 46.5% (Jimenez Severiano and Pijoan, 1984) and 65% for Suffolk and 50% for crossbred Suffolk ram lambs (Skinner and Rowson, 1968).
In the present study there was an interval between the age at which ram lambs showed `interest' in females in oestrous and the age at which physiological puberty actually occurred (varied between 43 and 53 days depending on the breed). Since spermatogen-esis in ram lasts approximately 50 days (Ortavant, 1958; Alexopoulos et al., 1991), it could be hypothe-sized that spermatogenesis must have started at the age when ram lambs expressed `interest' in females in oestrus and probably the onset of puberty coincided with this stage. Skinner and Rowson (1968), also reported that spermatozoa appear some time after the onset of male puberty. Our hypothesis is in agree-ment with the ®ndings of Alexopoulos et al. (1991) in which the ®rst spermatozoa appeared in the ejaculate of Chios, Karagouniki and Serres ram lambs at the age of 5 months and when live weight ranged from 35 to 37 kg. In a number of cases ram lambs which grew at a fast rate had no spermatozoa in their epididymides when castrated at early ages and heavy body weights. Testis of these lambs were equal or even better developed in terms of weight and volume than those of slower growing lambs which attained puberty at older ages and lower body weights. Thus, there appeared to be an
interaction between chronological age and body weight in relation to the appearance of spermatozoa in epididymides. Furthermore, it seems that not only was there a certain degree of body growth and testi-cular size required before sperm could be released, but also a limit of chronological age below which puberty is not attained irrespective of both body and testis weight (Dyrmundsson and Lees, 1972).
Differences were observed between the proli®c (Friesland and Chios) and the less proli®c (Karagouniki and Serres) breeds in body weight at which ram lambs showed `interest' in female in oestrus and when puberty occurred but whereas SC was greater in the Friesland in both stages, no difference was observed in SC between the Greek breeds. It must be recalled that Friesland lambs grew faster from birth to puberty (254 g/day) than the three Greek breeds. Echternkamp and Lunstra (1984), reported that ram lambs of proli®c Finnsheep had greater SC than the less proli®c Rambouillet, but not greater than Suffolk rams. The lack of advantage for Finnsheep rams over the less proli®c Suffolks contra-dicts previous reports on preburtal testis size and breed fecundity by Carr and Land, (1975); Land (1978).
In conclusion, the present study indicated that onset of puberty coincides with the time when rams show `interest' in females in oestrous, there is a signi®cant difference in body weight at which puberty is attained between proli®c and less proli®c breeds, and the variation among various breeds observed supports the concept that differences in the reproductive per-formance of females may be associated with that of males of the same genotype.
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