PSIV-3 Effect of winter-feeding system and roughage level in feedlot ration on subsequent spring grazing behavior and dry matter intake of beef growing heifers

Abstract

Abstract This study aimed to evaluate the effect of winter-feeding system (grazing, GFS vs. feedlot, FFS) and ration roughage level (RL), on subsequent spring grazing behavior and forage dry matter intake (DMI). Thirty-two Hereford female calves (149 ± 13 kg) were assigned to four winter dietary treatments (110 days) in a randomized block design (n = 2/treatment): three feedlot rations differing RL (Setaria italica) (0%, 35% or 70% DM) or oats grazing (5 kg DM/100 kg LW). In spring (84 days) all treatments grazed a mixed grass-legume pastures (4317 ± 1009 kg DM/ha; 6 kg DM/100 kg LW). During weeks 1, 3 and 5 after changing diets, diurnal behavior activity (effective/search grazing, rumination, idling or water intake) was visually recorded and DMI estimated from the in vivo DM digestibility (DMD) and fecal production. Data were analyzed according to a block design with repeated measures, with general model including block, treatment (T), week (W) and T×W effects. Means were compared through orthogonal contrasts (Table 1). Spring DMI varied with T (P = 0.0084) regardless of W effect (P = 0.1619), with higher values for GFS compared to FFS (1.55 vs. 1.16 kg/100 kg LW, P = 0.0034) and for 70RL compared to 35RL (P = 0.0286). DMD did not differ between treatments (P = 0.2488) but was lower on W1 than W5 (55 vs. 64 %, P = 0.0150). T×W was significant (P < 0.0001) for effective grazing, rumination and idling. On W1, heifers from GFS grazed less (0.40 vs. 0.49, P = 0.0268) but tended to ruminate more (0.26 vs. 0.18, P = 0.0591) than FFS. As pasture DMD improved (W5) GFS grazed more (0.64 vs. 0.51, P = 0.0020) but ruminated less (0.14 vs. 0.21, P = 0.0450) than FFS. Transition from FFS to spring grazing might reduce pasture DMI modifying animal ingestive behavior compare to animals from GFS. Impact could be higher when ration RL is below 70%.