PSV-21 Effects of supplementation programs for cow-calf operations during the dry grazing period under tropical conditions

Abstract The potential for increasing the productivity in cow-calf operation has gained wide acceptance in the last decade among Brazilian farms. Our objectives were to assess the impacts of providing supplementation to pregnant beef cows during the dry grazing period on cow and calf performance. During a 2-yr period, Tabapuã cows (n = 36) were blocked by parity and body weight (BW), and randomly assigned to pastures at the beginning of the rainy season. Brachiaria pastures were assigned to receive i) no application of N and cows were supplemented with mineral mix (CON), ii) application of 165 kg of Nּ ha-1ּ yr-1 and cows supplemented with a commercial product containing 40% of CP, macro and micro minerals, and vitamins (SUP), or iii) application of 165 kg of Nּ ha-1ּ yr-1 and cows supplemented with grass silage (GS). For SUP system, one-half of the paddocks were deferred in late summer. For GS system, one-half of the paddocks were deferred in early summer and silage was made after 90 d of regrowth. During silage making, 21% of DDGs on a dry matter (DM) basis was mixed into grass. After silage harvesting, the area was differed again. At the beginning of the dry period, deferred areas had free access to animals for SUP and GS treatments. The commercial supplement and silage were fed for 140 d (from 116 ± 27 to 256 ± 27 d of gestation). The mineral mix was offered all year round. The PROC MIXED procedure of SAS was used to analyze all variables. The statistical model included supplementation program as a fixed effect. Block, paddock, and year were included as random variables. Initial BW, initial body condition score (BCS), and gestation period of cows were included as covariates. Initial BW and BCS, and final BW and BCS did not differ among treatments. The GS treatment provided the greatest average daily gain (ADG) during prepartum (0.49 kg/d) than CON and SUP strategies (an average of 0.37 kg/d). Whereas ADG during postpartum was not altered by treatments. Considering the full cycle (prepartum and postpartum), supplementation strategies did not affect ADG and BCS. No differences were obtained for birth weight, weaning weight, and ADG in calves. Overall, the supplementation programs adopted in this study did not influence individual gains in both cow and calf. However, BW gain per area may be altered, since supplementation increases stocking rate.