PSIV-4 Effect of winter nutrition (pasture vs. feedlot) of beef calves on further spring grazing performance and feed conversion efficiency for the winter-spring period

Abstract

Abstract Feeding high grain rations during winter allows for calves′ higher liveweight gains (LWG) compared to grazing improved pasture, however, it may impair further spring-grazing performance, affecting the feed to gain ratio (F:G) for the whole winter-spring period. This work aimed to evaluate the effect of winter lot-feeding and roughage level (RL) in the feedlot ration, on performance and F:G during spring grazing and the whole winter-spring period. Thirty-two Hereford calves (143 ± 12.2 kg) were assigned in a randomized block design to four winter treatments (WT, 110 d): oat grazing (5 kg DM/100 kg LW), and three feedlot rations supplied ad libitum, differing in RL (Setaria italica hay): 0%, 35%, 70% DM (n = 2/treatment). During spring (80 d), all treatments strip-grazed a mixed grass-legume pasture (6 kg DM/100 kg LW; 4317 ± 1009 kg DM/ha), independent paddocks per replication, 7-day strips. Liveweight was recorded every 14 days. DMI was measured daily at feedlot, while during grazing it was estimated on even weeks as the difference between pre and post-grazing pasture DM biomass. Data were analyzed according to the following general model: yijk=μ+Blocki+WTj+b1LWinitial+eijk and adjusted means were compared through orthogonal contrasts using the Tukey test (Table 1). Winter F:G was lower for feedlot than grazing calves (6.37 vs. 12.30; SE: 0.39, P = 0.0006), and for RL0 compared to higher roughage rations (4.94 vs. 7.08; SE:0.42, P = 0.0141). This last response was reversed during spring, when higher F:G value was observed for RL0 (27.5 vs. 12.12, SE: 2.50, P = 0.0087), due to a lower LWG (0.09 vs. 0.26, SE: 0.08, P = 0.0320). However, considering the winter-spring period, feedlot calves, and within these, the RL0 calves, showed the highest LWG (0.78 vs. 0.57, SE: 0.05, P < 0.0001), the lowest F:G (6.52 vs 8.45, SE: 0.16, P = 0.0012), and were the heaviest by the end of spring.