Induced or Synchronized Puberty in Heifers

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Abstract
Three experiments were conducted to examine different hormone treatments for their effectiveness in inducing or synchronizing a fertile estrus in prepuberal heifers. In experiments I and II, heifers which averaged 8.5 months of age and 249 kg in weight were given treatment E (5 mg E2β, experiment I), treatment PE (silastic rubber implant containing 2.1 g progesterone for 6 days and an injection of 5 mg E2β 24 hr after implant removal, experiments I and II) or treatment S-6 (6 mg SC-21009 progestogen implant for 6 days with an injection of 3 mg SC-21009 and 5 mg estradiol valerate at the time of implanting, experiment II). In experiment I, treatment PE increased the number of heifers showing estrus within 4 days (P<.01) and ovulating (P<.05). However, no significant differences in pregnancy rate were found after 4 or 45 days of breeding. In experiment II, more PE treated heifers than S-6 treated heifers were in estrus after 4 days (P<.01) but pregnancy rates were low and differences were small after 4 (P>.25) or 45 (P.5) in all groups. Pregnancy rates were lower in SE heifers at the first estrus (P<.01) and after 45 days of breeding (P<.05). These data indicate that a fertile estrus can be hormonally induced or synchronized in prepuberal heifers of normal age (13 to 15 months) and to a lesser degree in very young heifers (<9 months). Copyright © 1976. American Society of Animal Science . Copyright 1976 by American Society of Animal Science

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