Fresh brewer's yeast slurry as a supplementary nitrogen source for cattle given native pasture hay or grain-based diets

Two experiments evaluated brewer's yeast slurry [mean (¦ s.d.) dry matter (DM) 9.7 ¦ 3.8% and nitrogen (N) content 45.6 ¦ 19.5 gkg DM] as a source of dietary protein for steers on a low N hay diet (experiment 1) and as a low cost supply of protein in a feedlot diet (experiment 2). Experiment 1 was an attempt to improve the N supply to rumen microflora, and total protein to the intestine. There was no improvement in liveweight gain of steers, or in their feed conversion efficiency (FCE), when up to 4.4 kg of yeast slurry (i.e. 423 g DM) was added to the basal diet. Mean (¦ s.e.) liveweight gain of non-supplemented steers was 402 f 13 1 g/day, with a mean (¦ s.e.m.) FCE of 12.2 ¦ 1.9 kg DM intake/kg liveweight gain. There was a significant (P<0.05) improvement in liveweight gain (714 g/day) and FCE (7.8 kg DM intake/kg liveweight gain) when cottonseed meal, included as a positive control treatment, was added to the hay diet; however, N intake was higher in this diet (97.7 g/day) than in those based on yeast slurry (range 43.6-62.3 g/day). Experiment 2 was designed to assess the suitability of yeast slurry for replacing cottonseed meal and lucerne chaff as a protein source in grain-based feedlot diets. Yeast slurry did not significantly increase liveweight gain of steers, but when 1 diet with 61% yeast slurry (percentage fed, range 0-71.4%) was excluded from the evaluation, increased dietary proportions of yeast were associated with increased liveweight gains (r = 0.99) and carcass yield (r = 0.89). The range in slurry DM contents (4.8-15.6%) required close monitoring, with daily changes made to the amounts of slurry offered to maintain dietary N and protein levels in the experiments. This range would make it difficult for commercial feed compounders to produce a diet of consistent quality.

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