The Age and Climate Related Changes in Stress and Metabolic Hormones of Goat Bucks Raised Under Tropical Conditions

Abstract

This study determined the stress and metabolic potentials of 63 goat bucks of different breeds - Kalahari Red (KR), West African dwarf (WAD) and Kalawad (KW) with 21 animals each. They were assigned to three age groups – 11 - 24, 25 - 36 and 37 - 48 months and evaluated across four seasons (early/late rainy and early/late dry) in a 3 × 3 × 4 factorial design. Animals were managed under same conditions for one year. Bimonthly blood samples were collected to analyze hormonal profile on stress and metabolic indices. Three-way ANOVA was used for data analysis using SAS (1999). All determined hormones were significantly (p <0.05) influenced by breed, age and season. The cortisol level was highest (13.91±0.04 ng/mL) in the animals at age 37 – 48 months (p <0.05) and during early dry season (14.43±0.03 ng/mL) while thyroxine and triiodothyronine concentrations had least values (5.79±0.05 ng/dL and 1.75±0.04 ng/mL) but peaked (7.45±0.04 ng/dL and 1.76±0.04 ng/mL) respectively during early rainy season. The least cortisol value (9.42±0.03 ng/mL) was recorded in WAD. Breed, age and season exert influences on hormones considered in goats bucks. This information provides reference values for selection of these breeds in heat-stressed environments.