Plasma cortisol in Bos taurus and Bos indicus heifers in seasonal tropical climate.
Cortisol concentration in blood plasma was measured in Brown Swiss, Holstein-Friesian, and White Fulani heifers over two consecutive estrous cycles during each of the four quarters of the hot humid seasonal tropical climate of Ibadan, Southern Nigeria. Basal cortisol in plasma was low (between 1 and 10 ng/ml). Differences between breeds were not significant. Averages and increases with proestrus and estrus were higher in the wet season (March to August) than in the dry season (November to January). Packed cells volume was higher in the dry season than in the wet season. Seasonal changes in rhythmicity of the estrous cycle were not significant. The low cortisol in plasma probably reflects adaptation to the hot climate and a mechanism to prevent high metabolic heat.
D000302:Adrenal Cortex / Q000502:physiology; D000818:Animals; D002417:Cattle / Q000097:blood*; D002980:Climate; D005260:Female; D006854:Hydrocortisone / Q000097:blood*; D013696:Temperature
D006854:Hydrocortisone