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IGF-I and leptin effect on the female bovine (Bos indicus) Nellore puberty


From researches conducted in our laboratory with prepubertal heifers, it were found greater weight but no increase in leptin concentrations around 60 days before the first ovulation between heifers that ovulated and the ones that did not ovulated until 16 months of age. On the other way IGF-I concentration was higher in heifers that became pregnant before 16 months, suggesting that weight gain and IGF-I are important for the first ovulation but there was no evidence that leptin increase is related to sexual precocity in Nellore heifers. This research will evaluate whether rbST administration will increase IGF-I at the same time decreases the percentage of fat (which results in lower concentrations of leptin) and interferes with the age at first ovulation in Nellore heifers; IGF-I, leptin, insulin, glucose and progesterone concentrations will be measured as well as number and diameter of ovarian follicle and body development. Sixty Nellore heifers will be sorted in two different groups, one will be injected every 14 days with 250 mg (S.C.) rbST from the seven, until the 19-month of age. The second group will be injected with saline solution (2.5 ml SC). All animals will be at pasture and receive mineral supplement and water ad libitum. At rbST injection day venous blood sample will be collected for IGF-I, leptin, glucose, insulin and progesterone quantification, also follicular diameter will be evaluated. After the 12th month a teaser with a chin ball is will be inserted whit the heifers, and every week the heifers will be inspected for ink marks. Every other month fat thickness at the 12th rib and body weight will be measured by ultrasound. The results will be analyzed by repeated measures ANOVA, PROC GLM in SAS. (AU)

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