SEASONAL-VARIATIONS IN CIRCULATING TESTOSTERONE AND LUTEINIZING-HORMONE IN PELIBUEY LAMBS

Abstract

This study was carried out to determine seasonal variations in circulating testosterone and luteinizing hormone levels in ram and castrate male Pelibuey lambs. Body weights at the end of the study were 36.9 +/- 1.2 kg for the intact and 38.8 +/- 1.6 kg for the castrate lambs. Ram lambs showed greater (P<0.01) daily gains than the castrates (50 g/d vs. 28 g/d). Body weights, average daily gains or scrotal measurements were not different among individual ram lambs. Mean testosterone levels were different for months (P<0.001) and seasons (P<0.001), but not among individual ram lambs. Testosterone was higher (P<0.05) from March through August. Season only affected magnitude (P<0.01) of LH peaks in ram lambs, whereas, in the castrate lambs it affected both the frequency (P<0.001) and magnitude (P<0.001) of LH peaks. In conclusion, season affects circulating levels of testosterone and LH, and LH in the ram and castrate lambs, respectively. However, it remains to be determined if such changes in testosterone and LH in ram lambs are sufficient to completely suppress reproduction and induce seasonal anestrus.