Effect of nutrition and endoparasitic treatment on growth, onset of puberty and reproductive activity in Menz ewe lambs

Ewe lambs of the Ethiopian Menz breed were assigned at weaning (90+/-3 days) to four levels of nutrition (poor, low, medium and high) to achieve different premating growth rates with or without treatment for endoparasites. A concentrate mixture providing 2.5 Mcal/kg dry matter (DM) metabolizable energy and 15.2 g/kg DM digestible protein was used. Improved nutrition increased lamb postweaning average daily weight gain up to puberty by 6 to 26 g/day and the conception rate to first estrus by 9 to 16% while it reduced the mortality rate by 24 to 31% and age at first lambing by 2 to 5 months. Lambs reached puberty (age at first estrus) at 16.9+/-0.1 kg (+/-SEM) or 60% of mature body weight and 350+/-12 days of age. The onset of puberty was advanced by weaning weight (P<0.05), itself being well correlated with birth weight (r = 0.51, P<0.001), and by level of nutrition (high=299+/-19, medium=301+/-18, low=383+/-23 and poor=454+/-31 days, P<0.001) through enhanced growth rate (r = -0.82, P<0.001). No independent effect of drenching for endoparasites on pubertal development was observed (P>0.05), but its interaction with season-of-birth improved the growth of lambs born during the period of short rains (P<0.05). Overall mean litter size at first lambing was 1.07; the twinning rate was 6.5% and the birth weight was 1.9+/-0.1 kg. Up to 13.4% of newborn lambs, averaging 1.3+/-0.6 kg, died on the day of parturition. The results indicate that improved growth rate and body weight, resulting from better postweaning nutrition, affects the attainment of puberty in Menz ewe lambs. Mitigation of nutrition stress and endoparasitic infection depending on season-of-birth would thus increase the annual reproductive rate of breeding ewes and flock productivity.     

Relationship of scrotal circumference to age, body weight and onset of spermatogenesis in goats

Scrotal circumference (SC) and body weight (BW) measurements were obtained from 122 crossbred (Saanen x Loca; Jumnapari x Local) bucks, ranging in age from 3 to 28 months. Spermatogenesis and semeniferous tubule diameters were studied from testicular biopsies in 24 bucks. The results showed that SC increased curvilinearly and was significantly correlated with age (P < 0.05). Scrotal circumference correlated more significantly with BW (P < 0.001). Spermatogenesis was completed at 6-7 months with a sudden increase in tubular diameter at the same time. Since SC is an indirect measurement of testicular size, a marked increase in testicular size indicated the onset of active spermatogenesis and, hence, the possibility of using bucks for breeding at an earlier age than normally recommended. Further, SC norms obtained in this study may become useful in the evaluation of bucks for breeding soundness.     

Evaluation of mathematical models to describe testicular growth in Blackbelly ram lambs

The primary objective was to compare various mathematical models to describe scrotal circumference (SC) and paired testis volume development in Blackbelly ram lambs. The study was conducted in the state of Querétaro, México (20° 43' N, 100° 15' W). Spring-born Blackbelly ram lambs (n = 41) were housed outdoors and fed alfalfa hay and concentrate. Body weight, SC, and testis length, diameter, and volume were recorded every 2 wk from 24 to 172 d of age (June 18 to November 3). The following mathematical functions were used to model SC-age and testis volume-age relationship: Von Bertalanffy, Brody, Gompertz, Logistic, and Richards. The suitability of the models was evaluated based on parameter values and standard errors, residual mean square, the coefficient of determination (R²), and the average prediction error (APE). All models, except for Brody's, had good fit to SC (R² > 0.98) and testis volume (R² > 0.95), and produced similar growth curves in the range of ages studied. The logistic model predicted SC at maturity quite well, 33.6 ± 0.6 cm as compared with 33.9 ± 0.5 cm observed in adult animals; all models had APE's smaller than ±7% between 56 and 168 d of age. The Bertalanffy model predicted testis volume at maturity quite well, 513 ± 22 cm³ as compared with 488 ± 20 cm³ calculated for adult animals. The logistic model had a good fit to testis volume during the period of study, but underestimated the volume at maturity by 28%. All models, except for Brody's, had APE's smaller than ±14% between 98 and 168 d of age. The logistic and Bertalanffy models predicted the inflection point for SC at 83 and 59 d of age, and testis volume at 116 and 109 d of age, respectively. In conclusion, all models, except for Brody's, had good fit to actual SC and testis volume data in the range of age evaluated, whereas the logistic and Bertalanffy's models made the best predictions for adult SC and testis volume, respectively.     

Delayed puberty caused by hyperthyroidism in ram lambs is not a result of suppression in body growth

Over a period of 8 weeks ram lambs (16 weeks old) were made hyperthyroidal (serum thyroxine approximately equal to 150 ng/ml, compared with control approximately equal to 48 ng/ml) by daily subcutaneous injections of thyroxine or maintained at a constant body weight by restriction of the feed intake. Hyperthyroidal and restricted-intake lambs remained at a constant body weight during the period of treatment whilst control rams gained body weight. Testicular growth was normal in restricted-intake lambs but was suppressed in hyperthyroidal animals. Hyperthyroidism, but not feed restriction, was also associated with decrease in LH pulse frequency (1.3 +/- 0.3/12 h compared with controls 4.8 +/- 0.9/12 h. Hyperthyroidal lambs showed normal LH responses to exogenous LHRH. After cessation of treatment testicular growth continued to be suppressed for up to 16 weeks in previously hyperthyroidic rams; thereafter testes began to increase in size but at 30 weeks after treatment were still smaller than those of control rams. It is concluded that elevated thyroxine concentrations directly influence sexual maturation in ram lambs through actions at hypothalamic and/or higher brain centres which control LH secretion. Transient hyperthyroidism during sexual maturation may cause permanent impairment of sexual development.     

Breed differences in testicular growth and gonadotropin secretion in prepubertal ram lambs

Scrotal circumference (SC) and plasma concentrations of luteinizing hormone (LH) and follicle stimulating hormone (FSH) were measured in 19 Finnish Landrace (Finn) and 29 Rambouillet crossbred ram lambs raised in confinement and in 21 Finn and 19 Dorset crossbred ram lambs raised on pasture. SC was larger (P<0.05) for Finn crossbreds than for Rambouillet crossbreds only at 70 and 100 days of age. Finn crossbreds had more (P<0.05) plasma LH and FSH than did Rambouillet crossbreds at 20 and 44 days but not at 70 days. SC was larger for Dorset crossbreds than for Finn crossbreds at the same age, but SC was larger (P<0.05) for Finn crossbreds than for Dorset crossbreds at the same weight. Finn and Dorset crossbreds differed (P<0.10) in plasma LH and FSH concentration at 77 days only (Finn>Dorset).     

Relation between body weight, growth rate, chronological age and puberty in male and female rats

Body weight, growth rate, chronological age and puberty in female and male rats from litters of 8 and 12 offsprings/mother have been studied. Age and body weight at the moment of vaginal opening (VO) and balanopreputial separation (BPS) were analyzed. Results show that animals reared in smaller groups grew faster than others. After weaning there was an increase in growth rate. VO and BPS occurred at the same age in groups with different growth rates and different body weights. In conclusion this work evidences that external signs of sexual maturation are not linked to a "critical weight" or to a "growth rate".     

Plasma LH,FSH, testosterone,and age at puberty in ram lambs actively immunized against an inhibin alpha-subunit peptide

Active immunization against inhibin has been shown to advance puberty and increase ovulation rate in ewe lambs; but in ram lambs, effects on puberty and sperm production are equivocal. The objective of the present study was to determine whether active immunization against an inhibin alpha-subunit peptide advances the onset of puberty in ram lambs. St. Croix hair sheep ram lambs were assigned to inhibin-immunized (n = 7) and control (n = 8) treatment groups. Lambs in the inhibin-immunized group were immunized against a synthetic peptide-carrier protein conjugate, alpha-(1-25)-human alpha-globulin (halpha-G), and control lambs were immunized against halpha-G. Lambs were immunized at 3, 7, 13, 19, 25, 31, and 37 weeks of age. On the day of immunization a blood sample was collected and lambs were weighed. Another blood sample was collected 1 week following each immunization. At 20 weeks of age additional blood samples were collected at 20 min intervals for 8h. Beginning at 20 weeks of age and at weekly intervals thereafter, scrotal circumference (SC) was measured and semen was collected using electroejaculation. A subsequent ejaculate was collected 1 week following onset of puberty, which was defined as the week of age when an ejaculate first contained > or =50 x 10(6) sperm cells. In control lambs, plasma alpha-(1-25)-antibody (Ab) was nondetectable. In inhibin-immunized lambs, alpha-(1-25)-Ab titer increased from 7 to 25 weeks of age and then plateaued at a level that varied (P<0.001) among animals. Body weight and SC of control and inhibin-immunized lambs were similar at the onset of puberty. At pubertal onset inhibin-immunized lambs were older than control lambs (31.9+/-0.5 vs. 29.5+/-0.7 weeks of age, P<0.05). Plasma FSH concentrations were similar in control and inhibin-immunized lambs from 3 to 38 weeks of age. Plasma LH levels were lower (P<0.01) in inhibin-immunized than control lambs. During the 8-h blood sampling period at 20 weeks of age, LH and testosterone concentrations were lower (P<0.05) in inhibin-immunized than control ram lambs, and the LH pulse frequency was similar in the two groups of animals. The decreased LH secretion is consistent with the immunoneutralization of a putative inhibin alpha-subunit-related peptide that stimulates LH secretion in ram lambs. Present findings show that active immunization against an inhibin alpha-peptide delays rather than advances puberty in ram lambs.     

Dietary protein or energy restriction influences age and weight at puberty in ewe lambs

The working hypothesis was that restricted protein content in diets of prepubertal ewe lambs would delay time of onset of puberty to a greater extent than restricted energy content. Restriction of dietary protein (metabolizable protein, MP) or energy (ME) intake on age and weight at puberty was studied in ewe lambs in two experiments. In Experiment 1, 85 crossbred ewe lambs were assigned by weight to one of five dietary treatment groups: control (CTL; 18 mg ME day⁻¹ and 173 g MP day⁻¹); energy restricted (ER; 10.2 mg ME day⁻¹ and 96 g MP day⁻¹); protein restricted (PR; 11 mg ME day⁻¹ and 66 g MP day⁻¹); ER for 9 weeks then switched to CTL (ER/CTL); PR for 9 weeks then switched to CTL (PR/CTL). Ewe lambs were weighed biweekly, bled weekly, and serum was assayed for progesterone to determine time of puberty. Average age at puberty differed among lambs fed the various diets (P < 0.01). Ewe lambs in the CTL group were younger and weighed more at puberty. Lambs fed diets restricted in protein or energy content were similar in age at puberty. Dietary switching, ER/CTL and PR/CTL, affected body weight and gain (P < 0.05), but did not result in changed age at puberty compared with lambs fed ER or PR diets. In Experiment 2, two breed types (maternal type and meat type) were used to compare responses of dietary protein restriction to dietary energy restriction. In Experiment 2, lambs (n = 60) were assigned to either the CTL, PR or ER diets. Lambs in the CTL group gained more weight than lambs fed the PR diet and lambs fed the PR diet gained more weight than lambs fed the ER diet (P < 0.05). Diet affected age (P < 0.001), but not weight at puberty (P = 0.13). Dietary energy and protein restriction influenced age at puberty in ewe lambs with energy restriction having a greater influence on delaying onset of puberty than protein restriction. Realimentation did not overcome effects of previous feed restriction by inducing an earlier age at puberty than ewe lambs fed the ER or PR diet throughout the experimental period. Body weight gain prepuberty is more important than type of dietary restriction (protein or energy) with regard to impacting age at puberty. We, therefore, reject the working hypothesis that dietary protein restriction prepuberty would have a greater impact in delaying onset of puberty than dietary energy restriction.     

Relationship of scrotal circumference and testicular volume to age and body weight in the swamp buffalo (Bubalus bubalis)

Scrotal circumference (SC) and testicular volume (TV) were measured in 65 swamp buffalo bulls ranging in age from 7 to 60 months and weighing 130 kg to 560 kg. Ages and body weight (BW) were recorded for each male at the time of measurement to find out if they correlated with SC and TV. SC and TV increased linearly and correlated significantly with age and BW (SC vs age: r = 0.74, p<0.01; SC vs BW: r = 0.88, p<0.01; TV vs BW: r = 0.82, p<0.01). SC measurements ranged from 15.1 +/- 1.1 cm to 24.0 +/- 0.4 cm for ages ranging from 10.0 +/- 0.6 to 48.5 +/- 6.3 months, revealing that testicular size in swamp buffaloes was very much smaller than domestic cattle. The SC norms distributed with age would be useful in the evaluation of swamp buffalo males for breeding soundness.     

Direct responses in males and correlated responses for reproduction in females to selection for testicular size adjusted for body weight in young male lambs

Selection based upon testicular diameter adjusted for body weight at 6, 10 and 14 weeks of age was used to produce two lines of sheep, with either high or low testicular size. Ten generations of selection were carried out and the estimate of the realized heritability of the selection criterion was 0.53 +/- 0.01. There were significant positive correlated responses to selection for testicular diameter at 6, 10 and 14 weeks of age, but the correlated responses in body weight at these ages were negative. In mature females, there were significant negative correlated responses to selection in premating body weight in the 1st, 2nd and 3rd breeding season and in the day of the first oestrus in the 2nd breeding season. Litter size per ewe mated had a small positive correlated response to selection in the second breeding season. This latter response appeared to be due to a positive correlated response in fertility, ewes from the High-line having a significantly higher probability of conceiving to a single mating than those from the Low-line. There was no significant correlated response in ovulation rate or litter size per ewe lambing and the genetic correlation between these traits and the selection criterion is likely to be close to zero. This may be due to the adjustment for body weight used, but it is possible that, in any event, body weight in young rams may be a better predictor of female ovulation rate than testicular diameter. These results do not rule out the possibility that testicular size in rams older than those selected would provide a good predictor of genetic merit for female ovulation rate.     

Selection for superior growth advances the onset of puberty and increases reproductive performance in ewe lambs

The reproductive efficiency of the entire sheep flock could be improved if ewe lambs go through puberty early and produce their first lamb at 1 year of age. The onset of puberty is linked to the attainment of critical body mass, and therefore we tested whether it would be influenced by genetic selection for growth rate or for rate of accumulation of muscle or fat. We studied 136 Merino ewe lambs with phenotypic values for depth of eye muscle (EMD) and fat (FAT) and Australian Sheep Breeding Values at post-weaning age (200 days) for live weight (PWT), eye muscle depth (PEMD) and fat depth (PFAT). First oestrus was detected with testosterone-treated wethers and then entire rams as the ewes progressed from 6 to 10 months of age. Blood concentrations of leptin and IGF-I were measured to test whether they were related to production traits and reproductive performance (puberty, fertility and reproductive rate). In total, 97% of the lambs reached first oestrus at average weight 39.4 ± 0.4 kg (mean ± s.e.m.) and age 219 days (range 163 to 301). Age at first oestrus decreased with increases in values for PWT (P < 0.001), and concentrations of IGF-I (P < 0.05) and leptin (P < 0.01). The proportion of ewe lambs that achieved puberty was positively related with increases in values for EMD (P < 0.01), FAT (P < 0.05) or PWT (P < 0.01), and 75% of the ewe lambs were pregnant at average weight 44.7 ± 0.5 kg and age 263 days (range 219 to 307). Ewe lambs that were heavier at the start of mating were more fertile (P < 0.001) and had a higher reproductive rate (P < 0.001). Fertility and reproductive rate were positively correlated with increases in values for EMD (P < 0.01), FAT (P < 0.05), PWT (P < 0.01) and leptin concentration (P < 0.01). Fertility, but not reproductive rate, increased as values for PFAT increased (P < 0.05). Leptin concentration increased with increases in values for EMD (P < 0.001), FAT (P < 0.001), PWT (P < 0.001), PEMD (P < 0.05) and PFAT (P < 0.05). Many of these relationships became non-significant when PWT or live weight was added to the statistical model. We conclude that selection for genetic potential for growth can accelerate the onset of puberty and increase fertility and reproductive rate of Merino ewe lambs. The metabolic hormones, IGF-I and leptin, might act as a physiological link between the growing tissues and the reproductive axis.     

Postnatal changes in testicular development and androgen receptors immunolocalization in D'Man ram lambs

The purpose of this study was to characterize testicular development in D'Man ram lambs, focusing primarily on androgen receptors (ARs) immunolocalization in the adenohypophysis and testis that is not still known in the D'Man ram lamb. Lambs (n = 12) were divided into four groups (three lambs per group). Adenohypophysis and testis were fixed and paraffin embedded; cross-section (3 μm) were stained and evaluated with immunohistochemistry. Testis weight increased at a greater rate between two and five months after birth, which was associated with remarkable changes in testicular histology, including significant increases in the diameter of seminiferous tubules. Spermatogenesis started between three and five months after birth; lumen and elongated spermatids were observed for the first time in three and four months-old animals respectively. ARs detected with immunohistochemistry were located in the nuclei and cytoplasm of adenohypophysis cells, and only in nuclei of testis cells (Leydig, Sertoli, peritubular myoid and germ cells).     

Effect of pre-pubertal growth rate of Sohagi ram lambs on some physiological parameters and sexual behavioral patterns at puberty

Thirty healthy Sohagi ram lambs with an average age of 188.6±7.3 days were used to study the effect of pre-pubertal growth rate on some physiological parameters and sexual behavioral patterns at puberty. Ram lambs were divided into three groups (10 animals per each group) according to the previous growth rate until 6 months of age. Groups were marked as fast, medium and slow growing. Animal groups were housed in closed barns with access to an open area. Results showed that age and weight of ram lambs at puberty were significantly affected (P<0.05) by the pre-pubertal growth rate. Ram lambs in the fast growing group were reached to onset puberty firstly at 272.6 days with body weight (BW) 37.1 kg on average then ram lambs in medium group (284.8 days with BW 32.7 kg), while ram lambs in slow growing group were the last (314.1 days with BW 32.5 kg). Blood‎ testosterone‎ concentration at puberty was not significantly different among growing groups (1.494± 0.03 ng/ml on average, ranged from 1.287 to 1.902 ng/ml). Testes measurements from 6 months of age until puberty show that ram lambs in fast growing group had the highest values of testes length, circumference and volume followed by those in medium and slow growing group. Sexual behavioral observation showed that flehmen and mounting behavior were significantly higher for ram lambs in fast growing group (5.63 and 6.75 number/12h) than slow growing group (4.25 and 5.38 number/12h) while in medium growing group were intermediate (4.88 and 5.88 number/12h). From these findings, could be concluded that age, weight and sexual behavioral patterns of Sohagi ram lambs at puberty were affected by pre-pubertal growth rate, and the breeders should strive to achieve good growth rates for their lambs before puberty which led to improving reproductive performance.     

Effects of sexual stimulation on testicular size in the ram

Experiments were conducted to determine the influence of sexual stimulation on testicular size and morphology.Scrotal volume decreased by 18–26% in rams mated for 4–6 weeks on two commercial farms, with only part of the decrease being accounted for by the 4–12% decrease in live weight. Similar observations were made over 7–8 weeks on rams exposed to increasing intensity of sexual stimulation by having rams either isolated, non-mated with or without non-oestrous ewes or mated with oestrous ewes. Again live weight change could not account entirely for the decrease in scrotal volume. The decrease in testicular size was confirmed on castration of the rams at the end of the experimental period. In addition to the 15–42% reduction in testicular weight with increased sexual stimulation, there was a reduction in the number of spermatozoa in the testes (21–36%) and an increase in the volumetric proportion of intertubular tissue (16–58%). A decrease in the volumetric proportion of spermatocytes (18–47%) and of round spermatids (13–57%) in the testicular tissue indicated that sexual stimulation was affecting spermatogenesis and decreasing daily production of spermatozoa.A decrease in the number of spermatozoa in the epididymides (24–26%) with increased sexual stimulation reflected an increased outflow of spermatozoa and/or reduced production of spermatozoa.     

Effects of rapid weight gain to puberty on reproduction, mammary development and lactation in ewe lambs

The effects of rapid weight gain to puberty on reproduction, mammary development and milk production in ewes lambing at 13 mo of age were investigated on three trials. A total of 64 Dorset and 93 Suffolk ewe lambs were weaned at 42 d of age and their mean weight was 16 kg. These ewes were assigned, within breed groups, to either a finishing diet or a growing diet. Onset of puberty was determined by daily checks for estrus and ewes were bred beginning at 7 mo of age. In Trial 2, mammary gland development was determined in eight Suffolk ewes from each diet. Ewes on the finishing diet were younger at puberty than those on the growing diet (199 vs 206 d, P<0.05) but required more services per conception (1.3 vs 1.1, P<0.05). Dietary conception rate and lambing rate means were similar. Mean 4-h milk yield was lower (P<0.10) for ewes on the finishing diet (283 g) than for those on the growing diet (310 g). Mammary gland fat pad area was higher (P<0.05) for ewes on the finishing diet compared with those fed for growth. Gross and adjusted duct areas were higher in ewes on the growing diet, but differences were not significant. At puberty, negative correlation coefficients for milk yield with performance traits were as follows: daily weight gain, -0.184 (P<0.08); weight-to-height ratio -0.262 (P<0.01); body condition score, -0.189 (P<0.07); and body weight, -0.212 (P<0.05). Results of this study indicate that rapid weight gain to puberty impairs mammary gland development and milk production in ewe lambs.     

Photoperiodic control of testicular growth in the ram lamb

Two groups (A and B) of Ile-de-France (IF) (n=6) ram lambs born in mid-October and 3 groups (C, D, E) of Dairy Lacaune (Lac) (n=15) ram lambs born in November were used in this study. Experimental ram lambs were exposed at 10 (IF) or at about 9 (Lac) weeks of age to long days (LD) for 11 weeks (group B) or 8 weeks (groups D, E) then to short days (SD) for respectively 14 and 16 weeks. Following exposure to artificial light, all experimental animals were returned to the control animals' (A,C) barn. LD treatment consisted of either 8 h of light split into two periods, one of 7 h and one of 1 h given 16 h after the beginning of the 7-h light period (“LD flash”, groups B and D) or by progressively increasing the light duration from 10 h (14 h of darkness) to 16 h (8 h D) (“LD 16”, group E). SD treatments consisted of progressively decreasing daylength from 16 h (8 D) to 8 h (16 D) (groups B, D, E).Scrotal diameter, TD (IF, Lac) and testis volume, TV (IF) were recorded regularly from January to the end of June (IF) or mid-July (Lac) and from mid-September to mid-November (IF).As expected, average body weight of treated and control animals was never significantly different in either breed.In IF from January to March, TD and TV increased in both groups but more rapidly in animals of group B. Afterwards, testes size continued to increase in experimental lambs whilst it remained almost constant in control animals. At the end of the photoperiodic treatment (31 May), TD and TV were much higher in treated than in control animals. From mid-September to mid-November, TD and TV increased rapidly in Group A and became significantly higher again than in the control lambs.In Lac TD was significantly higher in the light-treated lambs only from the 14th week onwards (just prior to the elimination of certain animals in each group). It was also similar throughout the experiment in groups D and E.These results show that exposure of ram lambs (born in autumn) to long days and then to short days accelerates their sexual development but this effect varies according to the breed.     

The effect of repeated follicular aspiration on the onset of puberty and growth rate of winter- or autumn-born lambs

The effects of follicular aspiration for oocyte retrieval on the attainment of puberty and growth rate were studied in winter-born (9 treated and 6 control) and autumn-born (5 treated and 5 control) ewe lambs. In the treated animals (i.e. in which follicular aspiration was performed after ovarian stimulation), laparoscopic oocyte pick-up (OPU) was performed at the age of 12–13, 16–17 and 20–21 weeks. From the 8th until the 57th week of age, serum progesterone concentration was determined in blood samples collected at weekly or bi-weekly intervals. Serum oestradiol concentration was measured in blood samples collected prior to each FSH administration at OPU, and 2 and 24 h thereafter. All lambs were weighed at birth, the 6th and 8th week of age and thereafter at monthly intervals until the 34th (winter-born) or 52nd (autumn-born) week of age. Radiographic images of the right antebrachium and completion of skeletal maturation (radius) were used to assess the growth rate. Serum oestradiol concentration increased in response to FSH administration, but decreased to normal basal values 24 h after OPU. Autumn-born ewe lambs attained puberty at a later stage, compared to the winter-born animals. In most OPU-treated winter-born lambs, the first luteal phase was of short duration. This was not observed in winter-born controls, nor in any of the autumn-born lambs. No differences were detected regarding the age at the onset of puberty between treated and control animals. From the 13th to the 26th week of age, winter-born treated lambs were lighter than the controls (27.3 ± 1.6 vs 34.3 ± 1.9 kg at 26 weeks of age, respectively). From the 16th to 34th week of age, radius length differed between the treated and control winter-born lambs, but not between autumn-born lambs. Ossification of the radial growth plate was not complete until the 34th (winter-born labs) or the 52nd (autumn-born lambs) week of age. It is postulated that repeated OPU can be safely applied to prepubertal lambs, with no consequences on the time to onset of puberty, whilst the growth rate of donor animals is also not affected.     

Age at puberty, fertility and litter size of ewe lambs reared under different photoregimens

Age at puberty, fertility and litter size of ewe lambs of synthetic sire and dam strains raised under different photoregimens were determined. The lambs were bred during January, May or September at 30 to 32 weeks of age. Irrespective of birth date, the lambs were reared under continuous light from birth to 5 weeks of age. From 5 to 20 weeks of age, they were kept under 16 hours of light dairy (16L:8D; Treatment A), 8 hours of light daily (8L:16D; Treatment B), or a split photoperiod of 8 hours total light daily (7L:9D:1L:7D; Treatment C). Subsequently, all lambs were exposed to 9 hours of light daily until after breeding. Lambs were exposed to rams for two estrous periods after treatment with fluorogestone acetate-impregnated intravaginal sponges and pregnant mares' serum gonadotropin (PMSG) to induce synchronized estrus. Although the age at puberty (174 days) was similar among treatments, the incidence of puberty prior to progestagen sponge treatment was higher ( approximately 50%) for lambs reared under Treatments A and C than under Treatment B. Fertility and litter size of lambs were not influenced by the previous photoperiod history or by sexual maturity, i.e., puberal or prepuberal, at the start of the sponge treatment. However, strain, age and weight of lambs at breeding influenced significantly the reproductive outcome.     

Accuracy of estimation of testis weight from in situ testis measures in ram lambs

At a mean age of 93 +/- 5 days and a mean weight of 29 +/- 5 kg, 44 crossbred ram lambs were castrated to evaluate the accuracy of the estimation of testis weight from in situ testis measures (scrotal circumference and testis diameter). Means and standard deviations for testis weight (both testes), scrotal circumference and average in situ testis diameter were 134 +/- 57 g, 20.2 +/- 3.1 cm and 3.7 +/- .7 cm, respectively. Testis weight (W) was predicted from scrotal circumference (C) and average in situ diameter (D(o)) as W=.131C(1.90) D(o)(.88) (R(2)=.949). When adjusted to the same scrotal circumference and in situ diameter, testes of 3/4-Finnish Landrace rams were heavier (P<.05) than testes of 7/8-Dorset rams. However, the additional accuracy obtained by using equations specific to each crossbred group was small.