SERIC CONCENTRATION OF REPRODUCTIVE HORMONES AND MINERALS IN PREPUBERTAL AND PUBERTAL POLLED NELLORE BULLS

Resumo

Nellore polled (Bos indicus) bulls are used to introduce characteristics of environmental resistance in meat-producing herds, however, the morphophysiological characteristics related to body structure and reproductive parameters are not well described. The aim of this study was to evaluate the scrotal circumference (SC), body weight (BW) the plasma concentration of LH, testosterone, triiodothyronine (T3), thyroxine (T4), copper and zinc of prepubertal and pubertal Nellore Pulled bulls under field conditions. Records of 2002 and 2003 of fifty-five Nellore pulled bulls between 12 and 24 months old of Boa Vista farm in São Paulo state, Brazil were used. The SC, BW and blood samples for hormonal and microminerals assay were evaluated monthly. The mean values of SC and BW were: 24.91 ± 2.81 cm, 304.35 ± 1.30 kg, respectively. The mean plasma concentrations of LH, testosterone, T3 and T4 were 0.25 ± 0.08 ng/dl-1, 163.5 ± 95.70 ng/ml-1, 1.31 ± 0.12 ng/dl-1 and 2.32 ± 0.1 µg/dl-1, respectively. The average levels of Cu and Zn were 0.29 ± 0.1 mg/l-1 and 0.27 ± 0.03 mg/l-1, respectively. Similarly, to other B. indicus breeds the SC, BW, LH, testosterone, T3 and T4 and the minerals Cu and zinc Zn showed age effect (p<0.01). Body weight and scrotal circumference are important in the estimation of sexual maturity and are dependent on testosterone and LH levels. The results of concentrations of Cu and Zn did not impair the development of Nellore polled bulls. The parameters analyzed in prepubertal and pubertal Nellore polled bulls are influenced by age and are similar to those in Bos indicus bulls in the field condiction.