Evaluation of male reproductive hormones of Kalahari Red and Kalawad goat bucks as affected by age and season under tropical conditions.

Comprehensive understanding of reproductive hormones and environmental cues with their relationship is essential for efficient production in livestock sectors involving either assisted or natural reproductive methods. This study evaluated the effects of age and seasonal-associated changes in the blood concentrations of testosterone and follicle stimulating hormone (FSH) of male Kalahari Red (KR) and Kalawad (KW)-crossbred goats. Based on a 2 × 3 × 4 factorial arrangement, a total of 42 bucks (KR n = 21 and KW n = 21) were allotted into three age groups (> 1 ≤ 2 years, > 2 ≤ 3 years and > 3 ≤ 4 years) with seven KR bucks and seven KW bucks each per age group; reared under different seasons (early rainy, late rainy, early dry and late dry). The animals were managed semi-intensively, kept in an open-ventilated pen and subjected to same nutritional regime throughout the one-year experimental period. Follicle stimulating hormone and testosterone concentrations were analyzed in serum samples. Data obtained reproductive hormones were subjected to three-way Analysis of Variance using SAS 1999. Results show that breed had a significant effect (p < 0.05) on both serum FSH and testosterone concentrations. The highest FSH (0.49 ± 0.02 ng/mL, 0.45 ± 0.01 ng/mL, 0.41 ± 0.1 ng/mL and 0.47 ± 0.07 ng/mL) mean values (P > 0.05) were observed in KR in September, October, November and May, respectively while the highest (2.6 ± 0.02 ng/mL) testosterone concentration in KW (p < 0.05) was obtained in December. Testosterone had irregular patterns between breeds and months of sampling. FSH was at peak (p > 0.05) in KR during the late rainy season at all ages while the values of FSH concentration in KW were not significantly different at all ages and seasons. The highest (2.05 ± 0.11 ng/mL) serum testosterone mean value in KW peaked (p < 0.05) age > 3 ≤ 4 years during the late rainy season. Testosterone concentration was lower and steady at all ages during rainy seasons in KR but started fluctuating during the early dry season. The least mean (0.62 ± 0.07 ng/mL and 0.68 ± 0.05 ng/mL) were recorded (p > 0.05) in KW during the late dry season at age > 2 ≤ 3 and > 3 ≤ 4 years respectively. In KR and KW goat breeds raised under tropical condition, the high seasonal variations were responsible for the fluctuations in the reproductive hormones which resultantly altered or lowered the sexual activity of the animals at certain season(s).