Effects of nutrition level during lactation and rearing periods on growth patterns, puberty onset and fertility rate in beef heifers

Abstract

This study analysed the effects of different nutrition levels from heifer birth to first Timed Artificial Insemination (TAI) at 15 months, on their growth patterns, puberty onset and fertility rate. Twenty-nine Parda de Montaña heifers, born in autumn, were assigned to two growth rates in the lactation period (0-6 months: 700 vs. 1000 g/d, to Low (L) and High (H), respectively) and in the rearing period (6-15 months: 700 vs. 1000 g/d, to Low (L) and High (H), respectively), resulting in 4 treatments: LL, LH, HL, HH. At 15 months of age an Ovsynch protocol with an intravaginal progesterone device was used to synchronize and breed the heifers. Weight was taken weekly from birth until breeding season was finished to study the evolution of weight and average daily gain (ADG) along the experiment. Heifers were bled weekly throughout the rearing period to determinate the onset at puberty through plasma progesterone concentration. Heifers’ average daily gains were influenced by the lactation and the rearing nutrition levels, animals compensating the growth rates in the different phases. The age at onset of puberty was higher in the animals receiving the Lactation low nutrition level (P<0.01) and the Rearing low nutrition level (P<0.001). Heifers of all lots showed similar weights at onset of puberty (55% adult weight), conception age (16.4 months) and fertility rate (89%). It can be concluded that the advance of the first service from 21 to 15 months of age is possible in extensive systems of beef cattle, if growth rates of 1 kg/d during lactation or/and rearing are guaranteed. Additional research is needed to determinate the impacts on adult size and frequency of dystocia at first and subsequent calvings of early-bred heifers