EFFECT OF SUPPLEMENTATION WITH PROTEIN MEAL ON THE GROWTH OF CATTLE GIVEN A BASAL DIET OF UNTREATED OR AMMONIATED RICE STRAW

A 98 d feeding trial carried out to study liveweight change and rumen metabolites in heifers weighing initially 275 kg and given either untreated or ammoniated rice straw supplemented with 0, 0.4, 0.8 or 1.2 kg protein meal consisting of cottonseed meal (60). All 32 animals received 0.6 kg rice polishings/hd/d and had continuous access to molasses/urea block-licks containing 15% urea. The effects on growth rates of treatment of the straw with ammonia and of supplementation with bypass protein were additive. The heifers fed ammoniated straw grew 267 g/hd/d (p<0.001) faster and consumed 11% (p<0.05) more straw than the heifers on untreated straw. The mean growth response to bypass protein was 0.37 kg gain/kg protein meal supplied. Supplementation with protein meal tended (p=0.06) to depress intake of straw, but straw intakes of the unsupplemented groups were high. Small changes in the composition of the block-licks that were fed throughout the feeding trial led to changes in block intake and in intake of untreated straw. Increasing quantities of protein meal fed were associated with linear increase in concentrations of ammonia (p<0.05) and in molar percentages of iso-butyrate (p<0.01), iso-valerate (p<0.01) and valerate (p<0.01) in the rumen fluid of the heifers on a basal diet of untreated straw. However, in the rumen fluid of the heifers given ammoniated straw, the levels of these metabolities were not affected by the quantity of protein meal given.