The effect was assessed of pre-mating supplementary feeding on the reproductive performance of 13-15 month old beef heifers. Eighty-nine heifers were used with a mean age of 12 months and mean body weight (BW) of 242 kg from three herds Aberdeen Angus heifers from the Santa Cecilia and Capitao Rodrigo ranches and crossbred Aberdeen Angus heifers) in a feeding system of only grazing pasture or supplemented heifers on pasture with milled corn grain. The supplement was offered daily at the proportion of 0.7% of the BW for 29 days on Oats (Avena strigosa Schreb) and annual Ryegrass (Lolium multiflorum Lam) cultivated pastures and 19 days on natural pasture. The grazing was continuous with variable stocking rate. The variables analyzed were: body weight, body condition, average daily live weight gain, body condition gain, percentage of pubescent heifers, pregnancy rate and conception order. There was no feeding systems ×herd interaction. During the pre-mating, the supplemented heifers had greater ADG, 0.800 kg, compared to those without supplementation, 0.658 kg. During the mating period, the heifers lost weight, mean of -0.104 kg/day. The variables body weight and body condition did not differ at the beginning of the mating period mean of 277 kg and 3.6 points, respectively. The supplemented heifers showed higher percentage of pubescent heifers (78%) and higher pregnancy rate (47%). There was herd ×period interaction for body weight. The body weight variation was quadratic for the three herds. Crossbred heifers always had greater body weight compared to the Santa Cecília Angus heifers. Capitão Rodrigo Angus heifers had higher higher percentage of pubescent heifers (80%) and PR (48%). Energy supplementation during 48 days pre-mating promoted higher pregnancy rate in 13 to 15 month old beef heifers.
body condition; cultivated pasture; native pasture; performance; pregnancy
