PSXIV-1 - Impact of slow-release nitrogen or regular protein based supplementation during late gestation on maternal and offspring performance in beef cattle

Abstract: The objective of this study was to determine whether supplementing pregnant beef cows with regular nitrogen or a slow-release nitrogen source at the late gestation could enhance the use of a low protein basal diet and improve the performance of cows and their offspring until weaning. Thirty-five pregnant Brahman cows (556±47 kg and 4.5±1.4 years old) were individually housed in covered pens and randomly divided into three groups. From 180±19 days of gestation until calving, cows were fed either a control (CON, n=12) low crude protein (CP) basal diet (6% of CP, ad libitum) plus mineral mixture (130 g/cow/d), or the CON treatment supplemented with protein concentrate supplements (40% CP, fed 2 g/kg of BW/d in the morning) based either on a regular (REG, n=11) composition (corn, soybean meal, and urea) or on a slow-release N (SRN, n=12) source (Timafeed Boost®, Roullier Group, Saint-Malo, France) which replaced 60% of soybean meal and urea in the supplement composition. The MN, fetal sex (FS), and MN×FS were used as fixed effects in the statistical model, while the number of previous calvings was considered as a random effect. Maternal initial BW was used as a covariate. Statistical differences were declared at P < 0.05. Supplementation with REG and SRN increased total dry matter intake (DMI) and basal diet intake compared to the control treatment (P < 0.01). Protein supplementation allowed the cows to have a higher average daily gain (P < 0.01; 0.177 and 0.193 kg/day, respectively, for REG and SRN) than the CON treatment (-0.255 kg/day). Body condition score (BCS) also increased (P < 0.01) when cows received protein supplementation in late pregnancy, but with no differences between REG and SRN cows (P = 0.31). Interactions between MN and FS were observed for calf birth weight (CBW, P < 0.01) and calves' average daily gain up to 120 days of age (ADG120, P = 0.01), but not at weaning weight (P = 0.69). Male calves born from REG and SRN cows were born heavier and gained more weight up to 120 days after birth than calves born from CON cows (P < 0.05) but did not differ from each other (P = 0.94 and 0.92, respectively, for CBW and ADG120). Female calves had no differences in CBW and ADG120 as a function of maternal dietary treatment during pregnancy. The REG and SRN calves weaned heavier (P < 0.05) than CON calves. In conclusion, supplementing protein to pregnant beef cows during periods of low CP pasture improves maternal and progeny performance. The SRN-based product can replace the major part of soybean and urea in the protein supplement, achieving same level of improvement in forage utilization and animal performance as the regular protein-based supplement.