Strategic supplementation of growing cattle on tropical pastures improves nutrient use and animal performance, with fewer days required on the finishing phase.

Context: Cattle grazing tropical forages usually perform below genetic potential due to limited nutrient intake. Aims: Four experiments were conducted to evaluate supplementation strategies on performance and metabolism of cattle grazing intensively managed marandu palisade grass (Urochloa brizantha). Methods: Experiment 1 evaluated the average daily gain (ADG) of 72 young bulls (222 ± 25 kg bodyweight, BW) grazing palisade grass and supplemented (22% crude protein, CP) at 0.0%, 0.3%, 0.6% and 0.9% BW, and their ADG during the feedlot finishing phase. Experiment 2 evaluated the ADG of 80 bulls (240 ± 18 kg BW) grazing palisade grass and supplemented with energy (11.3% CP) or three protein sources (≈20.5% CP) at 0.6% BW. Experiment 3 investigated intake, rumen parameters and digestibility of nutrients in fistulated steers (410 ± 8.6 kg BW) fed an energy supplement, that is, ground corn, at 0.0%, 0.3%, 0.6% and 0.9% BW, with a parallel in vitro study of fermentation kinetics (Experiment 4). Key results: Increased levels of supplementation resulted in linear increases (P < 0.05) in ADG, stocking rate (SR) and in BW gain per area. There were no differences (P > 0.05) in ADG, SR and BW gain per area among supplemental sources of protein or the energy supplement. Increasing energy levels caused a linear decrease (P < 0.05) in forage intake and grazing time and a linear increase (P < 0.05) in total dry matter and digestible-nutrient intakes, but did not affect (P > 0.05) fibre degradability. Corn supplementation also caused a linear decrease (P < 0.05) in acetate : propionate ratio, in ruminal ammonia-N and in N excretion, and a linear increase (P < 0.05) in rumen propionate concentration, in microbial synthesis and in N retention. The supplementation increased BW at the start of the feedlot phase, resulting in similar hot carcass weights with fewer days on feed and no effects on meat quality. Conclusions: Overall, despite the source utilised, supplementation increased ADG, SR and BW gain per area, with fewer days being required on the finishing period. Implications: Having adequate supplementation strategies in place will help producers increase the efficiency of their systems. Average daily gain of cattle grazing tropical grasses is usually low due to restricted nutrient intake. Aiming to increase the efficiency of these systems, sources and levels of supplements was studied to evaluate the effects on animal performance, metabolism and nutrient utilisation. Energy supplementation increased animal performance and beef productivity, enhanced rumen fermentation and improved nitrogen metabolism. These results could help farmers improve the efficiency of their systems and reduce the detrimental effects of excess nitrogen released in the environment. [ABSTRACT FROM AUTHOR]
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