Abstract
Abstract The aim of this study was to evaluate three feed additives for rumen manipulation. Thirty-two rumen-fistulated animals were assigned to a completed randomized block design, according to their initial BW. Steers were fed with 99% of coastcross haylage and 1% of concentrate, used as vehicle for the additives. The forage and concentrate were offered separately, whereas the forage was offered after the entire consumption of the concentrate. The experimental diets consisted in: CON = Control (no feed additive); NAR = 13ppm of Narasin; SAL = 20ppm of Salinomycin; and FLA = 3ppm of Flavomycin. The experimental period lasted 140 d, divided on 5 periods of 28 d each. Rumen fluid was collected on d 0, 28, 56, 84, 112 and 140, at 0, 6 and 12 hours after feeding and combined as a pool for SCFA analysis. Data were analyzed using the MIXED procedure of SAS. Data obtained on d 0 were used as covariate. Tukey test 5% was used for comparisons. There was treatment effect on acetate (CON: 73.5ab; NAR: 73.0a; SAL: 73.9b and FLA: 73.6b mM/100mM, P = 0.01; SEM = 0.16), propionate (CON: 13.7b; NAR: 14.6a; SAL: 13.5b and FLA: 13.4b, P = 0.01; SEM = 0.11), butyrate (CON: 9.06a; NAR: 8.64b; SAL: 8.72ab and FLA: 8.96ab, P = 0.02; SEM = 0.10), isovalerate (CON: 1.51b; NAR: 1.61ab; SAL: 1.55ab and FLA: 1.67b, P = 0.03; SEM = 0.04) and ac:prop ratio (CON: 5.39a; NAR: 4.99b; SAL: 5.49a and FLA: 5.4a, P = 0.01; SEM = 0.05). Therefore, narasin improves energetic efficiency of ruminal fermentation compared to other additives.
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