PSIV-8 - Effect of pre-grazing herbage mass, post-grazing sward height and finishing diet on performance of late-maturing beef steers

Grazing sward structure can influence animal performance in forage-only and forage plus concentrate-based production systems. The objective was to determine the effects of pre-grazing herbage mass (PGHM), post-grazing sward height (PGSH) and indoor finishing diet on performance of weaned, spring-born beef steers. Steers (n = 96, ca. 12 months of age, 396 ± 20.1 kg) previously fed grass silage only over the first winter, were assigned to one of twelve grazing groups, balanced for live weight. Grazing groups were randomly assigned to a two PGHM (1500 or 2500 kg DM/ha) × two PGSH (4 or 6 cm) factorial arrangement of treatments (n = 3 groups/treatment). Steers rotationally grazed Lolium perenne-dominant swards (not mechanically topped) for 222 days. Steers were then accommodated indoors and offered grass silage only (SO) or grass silage + 3.8 kg concentrate DM/head daily (SC) for a 146 day finishing period. Data were analysed using the mixed procedure of SAS with terms for PGHM, PGSH, finishing diet and their interactions in the model. Grazed herbage intake was unaffected by PGHM but was greater for PGSH-6 than PGSH-4 (6.94 vs. 6.18 kg DM/day; P < 0.001). Steer average daily gain at pasture was greater for PGHM-1500 than PGHM-2500 (0.65 vs. 0.60 kg; P < 0.05) and for PGSH-6 than PGSH-4 (0.70 vs. 0.55 kg; P < 0.001). After indoor finishing, carcass weight was unaffected by PGHM, but was heavier for PGSH-6 than PGSH-4 (386 vs. 367 kg; P < 0.01); carcass traits were unaffected by PGHM or PGSH. Carcasses were heavier (+43 kg), fatter (P < 0.001) and more conformed (P < 0.01) for SC than SO. In conclusion, both PGHM-2500 and PGSH-4 restricted animal growth at pasture; however, following an indoor finishing period, carcass weight did not differ between PGHM, but was heavier for PGSH-6 than PGSH-4.