Influence of Ovariectomy on Body Weight Gain and Plasma Insulin-like Growth Factor-I Concentration in Beef Heifers

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Fattening heifers were ovariectomized at two different ages and changes in body weight gain were examined for 16 months. Plasma insulin-like growth factor-I (IGF-I) concentration was also determined during the experiment. Heifers at 7 months of age or at 10 months of age were randomly divided into 2 herds. Eight heifers comprised a younger herd and 9 heifers comprised an older herd were ovariectomized. The heifers in the other herds were intact. Body weight gain was significantly stimulated during 2 months after ovariectomy, irrespective of age at the surgery. However, this stimulative effect of ovariectomy disappeared in the following periods and ovariectomy did not significantly affect body weight gain during the overall experimental-period. The body weight gain was decreased as the heifers aged. Ovariectomy did not affect plasma IGF-I concentration from 2 months after the surgery to the end of the experiment. Plasma IGF-I concentration was decreased during the experimental period and plasma IGF-I concentration was positively correlated with average daily gain following 2 months. These results suggested that the stimulative effect of ovariectomy on body weight gain was temporal. Thus, ovariectomy is possibly favorable for body weight gain in heifers if performed in a latter fattening period.
公益社団法人日本畜産学会の論文