Alternative management strategies for maximising productivity in beef cattle in the subtropics

Abstract

Two concurrent factorial experiments investigated the relative merits of the following management options to maximise liveweight gains in finishing cattle: breed [Hereford (Bos taurus) v. Belmont Red (B. taurus x B. indicus)]; implantation with zeranol; feed energy source (sorghum grain, molasses + urea, tropical grass pastures); feed protein source (sunflower meal, Leucaena leucocephala, tropical pasture legumes). These combinations of treatments were delivered by using nil, intermittent, or continuous grazing systems. Sixty steers of initial liveweight (¦ s.e) 321 ¦ 3.6 kg were held on their respective treatments for 77 or 98 days, by which time all except those on pasture without supplement had attained at least 400 kg liveweight. Steers were slaughtered in a commercial abattoir and carcass characteristics recorded. Zeranol-implanted cattle grew faster than untreated (0.84 v. 0.66 kg/day), and there was a trend (P = 0.14) for Belmont Red cattle to grow faster than Herefords (0.83 v. 0.67 kg/day). In all systems, cattle given ad libitum sorghum grain grew significantly (P<0.05) better than those given molasses + urea (1.54-0.65 v. 0.72-0.45 kg/day). The poor performance of molasses-fed cattle was associated with low voluntary feed consumptions. The highest rates of gain (1.54 kg/day) were for penned cattle on a sorghum grain + sunflower ration. The provision of either supplement promoted better gains than that found for unsupplemented steers grazing tropical grass-legume pastures (-0.29 to +0.26 kg/day). However, cattle continuously grazing (10 steers/ha) leucaena-grass pastures and those given sunflower meal had significantly (P<0.05) higher rates of gain (0.82 and 0.91 kg/day, respectively) than cattle given molasses supplements or grazing alone. Cattle given sorghum had higher carcass weights and fat contents than those fed molasses or with grazing alone, although only those in the feedlot had acceptable fat cover at slaughter. There was no significant effect of treatments on the fatty acid composition of subcutaneous fat.