Effects of sulfur and different sources and levels of nitrogen and energy on the intake and liveweight change of steers fed tropical native pasture hay

Abstract

Weaner steers were fed low quality native pasture hay in pens for 84 days to determine the differences in response to supplements of molasses (280 g/steer.day) and grain sorghum (265 g/steer.day), fed with urea (45 g/steer.day), and to determine the role of sulfur in these differences. The control group consumed 1.63 kg/steer.day organic matter (OM) and lost 277 g/steer.day over the feeding period. Supplements of urea alone or urea + grain did not affect hay intake or liveweight performance but both parameters were markedly improved by supplements of urea + molasses and urea + sodium sulfate. It was concluded that sulfur, in addition to urea, was necessary to increase feed intake and reduce liveweight loss in steers fed the low-protein pasture hay. With an increase in molasses intake from 280 to 1120 g/ steer.day, total OM intake remained constant while roughage OM intake declined (P> 0.05). At the higher molasses intake both roughage and total OM intakes were greater when 37 g/steer.day of supplemental nitroin-was fed (P>0.05), suggesting that energy substitution could be countered by ensuring a non-limiting nitrogen supply. Urea, meat and bone meal or the combination of the 2 were equally effective as the nitrogen source. In a second experiment weaner steers were fed a similar hay in pens for 56 days to compare the effects of either urea or protein meal as the nitrogen source in molasses. Molasses was fed at 1120 g/steer.day. The protein meal was a formaldehyde-treated mix of cottonseed meal, meat and bone meal and fish meal (8:1:1). Unsupplemented animals consumed 2.86 kg/ steer.day OM and lost 210 g/steer.day liveweight. Total OM intake was increased similarly by both nitrogen sources (P<0.05) but, whereas steers fed urea-molasses maintained weight, those given urea molasses plus the formaldehyde-treated protein meal gained weight at 163 g/steer.day (P<0.05). The advantage of providing a protein source protected from rumen degradation was demonstrated.