PSXIV-8 Effects of narasin on rumen parameters of steers fed a high-forage diet.

Abstract

The objective of this study was to determine the effects of narasin on rumen fermentation of steers fed a high-forage diet. Thirty rumen-fistulated Nellore steers were assigned to a randomized completed block design, defined by initial BW. Steers were fed daily and diets were composed of 99% of coastcross haylage and 1% of concentrate, used as delivery vehicle for the narasin. The concentrate was offered separately, and the forage was offered after the total consumption of concentrate. The experimental diets were: N0 = concentrate without narasin; N13: inclusion of 13 ppm of narasin; and N20 = inclusion of 20 ppm of narasin. The trial lasted 140 days, divided on 5 periods of 28 days each. Rumen fluid was collected on days 0, 28, 56, 84, 112 and 140, starting 6 hours after feeding, in order to evaluate rumen pH and SCFA. Data were analyzed as repeated measures over time using the MIXED procedure of SAS and the LSMEANS option was used to generate individual means. Data obtained on d 0 were used as covariate. Orthogonal polynomials were determined by linear and quadratic effect. There was no treatment and day interaction for any of the parameters evaluated (P > 0.05). There was a quadratic effect on acetate (73.9, 72.6, and 72.6 mM/100mM; P < 0.01), propionate (13.9, 15.9, and 15.3 mM/100mM; P < 0.01), butyrate (9.1, 8.7, and 9.0 mM/100mM; P < 0.01), valerate (1.0, 0.9, and 1.0 mM/100mM; P = 0.01), and Ac:Pr ratio (5.3, 4.6, and 4.8; P < 0.01). The narasin inclusion linearly increased total SCFA (93.1, 98.9, and 104.4 mM; P < 0.01), whereas no effects were noted on rumen pH (6.69 ± 0.05; P = 0.23). Hence, the inclusion of 13 ppm of narasin increased propionate and decreased the Ac:Pr ratio. Key Words: