Little research has been done on within breed differences in seasonality of reproduction in rams. We took 16 Dorset x Romney rams (8 BV+ and 8 BV-, selected on the basis of their breeding value for date of lambing derived for the lambing performance of their female relatives). These rams were housed indoors under natural light conditions and fed a ration of pellets and hay. Semen samples, testis diameter and body weight measurements were taken weekly. Blood samples were taken monthly (every 20mins for 26hrs, and then every 10mins for a further 4hrs following a 1 ml IV injection of 0.001 mg GnRH). Samples were assayed for oLH and oFSH. The trial ran from September 1993 to August 1994. More BV- (early lambing group) rams (70% vs 25%) produced ejaculates in the first 3 months of the trial. The BV- rams had significantly (P<0.001) lower ejaculate volumes than the BV+ rams with both showing significant (P<0.001) seasonal changes. There were significant (P<0.01) seasonal effects on semen concentration with a January maximum of 6300 x 10 6 sperm/ml and a minimum in July of 3350 x 10 6 sperm/ml. There was a seasonal effect on testis diameter (55mm in Dec-Feb and 38mm in July). There was a significant (P<0.05) seasonal shift in live weight between Feb-Apr (70kg) and July 58kg). There was significant (P<0.01) seasonal effect on basal LH levels and LH pulse frequency, but there were no detectable BV effects. The BV- rams had greater pulse amplitude and longer durations of peaks than did the BV+ animals. LH response to GnRH was significantly different only in Nov (BV- rams showed greater area under the curve 162

DB, Pownall, AS Familton, RJ Field, LR Fletcher, and GA Lane

Proceedings of the New Zealand Society of Animal Production, Volume 55, , 186, 1995
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