First calving performance and physiological profiles of 2 yr old beef heifers according to their prebreeding growth

摘要

This experiment was designed to assess the effects of different feeding strategies before first breeding at 15 mo on performance and physiological parameters of beef heifers during their gestation and first lactation. During preweaning (PRE, 0-6 mo) and postweaning periods (POST, 6-15 mo), 25 Parda de Montana heifers were fed to achieve gains of 1.0 kg d(-1) (HI) or 0.7 kg d(-1) (LO) in a 2x2 factorial design (HI-HI, HI-LO, LO-HI, and LO-LO). Although calf birth weights did not differ, heifers from LO-LO treatment had the greatest calving assistance (80%), probably because they were lighter than the rest (436 +/- 39 kg body weight, P 0.01) and had the smallest external pelvic area (19.5 +/- 2.0 dm(2), P 0.01). Milk production and calf gains during lactation were similar among treatments. Cows from POST-HI treatment tended to be cyclic earlier than POST-LO ones (82 +/- 8.4 and 106 +/- 9.4 d post partum, respectively; P = 0.06). Feeding managements did not influence metabolic (glucose, cholesterol, nonesterified fatty acid, beta-hydroxybutyrate, and urea) or endocrine (insulin-like growth factor I and leptin) profiles of heifers. Continued low feeding levels before breeding heifers at 15 mo are not recommended, because they may hinder primiparous calving performance.