Effects of Lasalocid and Monensin on Nutrient Digestion, Metabolism and Rumen Characteristics of Sheep

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Abstract
Two experiments were conducted to evaluate metabolism and rumen fermentation responses of lambs fed either monensin or lasalocid (33 mg/kg level) in an alfalfa-corn diet. Experiment 1 was a lamb metabolism trial where rumen samples were taken at the end of each excreta collection period. In Exp. 2, ruminally cannulated sheep were used and cotton thread cellulose and soybean nitrogen (N) disappearance were measured by the in situ dacron bag technique. Rumen turnover rates and volatile fatty acid (VFA) and ammonia pool sizes were determined. In Exp. 1, dry matter and fiber (neutral detergent fiber, NDF; acid detergent fiber, ADF and hemicellulose) digestibilities were not influenced by treatment. Absorbed N was increased (P<.05) with lasalocid, but not with monensin. No direct or adaptive rumen effects on in situ cellulose or N disappearance were noted in Exp. 2 for either additive. In Exp. 1, at 6 h postfeeding, both additives increased (P<.05) propionate concentration and lowered (P<.05) the acetate:propionate (A:P) ratio, while only monensin decreased (P<.05) rumen ammonia levels. However, no differences in ammonia or VFA concentrations were noted at 2 and 4 h post-feeding. In Exp. 2, where pool size was considered, monensin-fed sheep had lower (P<.05) total quantities of rumen ammonia at 8 and 12 h postfeeding. Both additives decreased A:P ratios at 6 and 12 h. Lasalocid increased (P<.05) acetate, propionate and total VFA pool size at 12 h. Copyright © 1984. American Society of Animal Science . Copyright 1984 by American Society of Animal Science.