Efecto de la raza y la edad sobre las concentraciones de hormonas tiroideas T3 y T4 de bovinos en condiciones tropicales

to study the effect of age and breed on blood concentration of thyroid hormones t3 and t4 under the dry tropic conditions, 158 animals from the groups holstein, lucerna, hartón del valle, brahman and crossbred f1 brahman x brown swiss were sampled. the animals were allocated in four age groups from newborns calves until eight month old. the average t3 concentration was of 2.25 mmoll-1 and the t4 was of 57.37 mmoll-1. the correlation between t3 and t4 was of 0.53. a statistical significant difference (p<0.001) was found for the effects of age breed and group, but not difference was found for the interaction between breed and age (p=0.286). the breeds with higher blood concentrations of t3 and t4 were holstein and lucerna. the lowest concentration was found among the crossbred group. the higher concentration of t3 and t4 of thyroid hormones was found in the newborn group. as the calves grow, the concentrations of t3 and t4 decrease progressively. this study found that under dry tropic conditions, in a thermo-neutral borderline zone (according to the thi index) the young bovines show clear differences in the concentration of the thyroid hormones