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Abstract. To test the hypothesis that seasonal variations in testicular morphology and function differ in Corriedale rams subject to different feeding levels, 24 spring-born Corriedale rams, aged 14-15 months at the beginning of the trial and raised under extensive grazing conditions in Uruguay, were allotted at random to two groups: Group H, that grazed on improved (sown) pastures, and Group L, the control, that grazed on natural pastures (range). Clinical data (live weight, scrotal circumference), semen, blood and tissue samples (testis, epididymis and seminal vesicle) were collected during each of four seasons (for one month/season) of the year. According to data measured, testicular form and function had its peak in autumn followed by a decline in winter and a subsequent recovery in spring and summer. Live weight loss during winter was significantly decreased in Group L but not in Group H. Scrotal circumference, seminiferous tubules diameter and seminal vesicle epithelial height decreased significantly during winter in both groups. Group H scrotal circumference returned earlier (spring) than Group L (summer) to autumn values. By summer, seminiferous tubules and seminal vesicle epithelial height had returned to autumn values in Group H, but not in Group L. Decrements of scrotal circumference in winter and spring were milder in Group H than in Group L animals. Group H testosterone values in autumn were higher than those from Group L in spring. In summary: 1) differences existed in seasonal variations in testicular morphology and function between Corriedale rams subjected to different feeding levels and, 2) the findings suggest that nutritional factors contributed, at least partly, to the differences in variations observed throughout the experiment. Key words: Rams, Testis, Seasonality, Nutrition, Morphology.(J. Reprod. Dev. 43: [171][172][173][174][175][176][177][178][179][180] 1997) ale sheep reproduction is seasonal. However, the degree of seasonality in male sheep factors. The most important cue for rams reproductive seasonal variations in cold-temperate regions is the annual cycle of increasing and decreasing photoperiod. The magnitude of the change in daylength among seasons varies widely depending on the latitude. Nutrition is another M reproduction varies, depending on a number of

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The research has shown the interesting contributions of shearing in mid-gestation on the performance of lambs from birth to weaning. Other studies have reported that shearing at early pregnancy influences the development of the placenta and lamb live weight at birth. However, there was a lack of information on the effect of early-prepartum shearing on the behavior of the offspring from weaning onward. This study evaluated the effect of shearing ewes at 50 days of gestation on the growth, reproductive behavior and response to a gastrointestinal parasite challenge in the female offspring from weaning to 18 months old. Fifty-seven Polwarth female lambs were used, 22 being singles and 35 twins born to ewes either shorn at 50 days of pregnancy (PS, n = 23) or shorn at 62 days postpartum (U, control, n = 34) resulting in four subgroups: single lambs born to PS ewes (n = 8), born to U ewes (n = 14), twin lambs born to PS ewes (n = 15) or born to U ewes (n = 20). All progeny were managed together under improved pasture with a minimum forage allowance of 6% live weight on dry basis. Body weight, body condition score and fecal eggs count were recorded every 14 days from weaning to 18 months of age. Concentrations of progesterone were measured weekly (from 4 to 10 months of age and from 14 to 18 months of age) to establish the onset of puberty. Ovulation rate at an induced and a natural heat (545 ± 1.0 and 562 ± 1.0 day old) was recorded. Prepartum shearing did not affect the age at puberty or the ovulation rate of female offspring, but those born as singles were more precocious ( P = 0.03) and heavier ( P = 0.02) at puberty than twin born lambs. Both the average value of parasite egg count ( P = 0.0 7) and the Famacha index ( P = 0.02) for the entire study period were lower in lambs born to prepartum shorn ewes than those born to postpartum shorn ewes. In conclusion, shearing at 50 days of gestation did not affect the growth or the reproductive behavior of female offspring. However, female lambs born from ewe shorn during gestation showed a better response to the parasitic challenge, and further research is required to confirm this.

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