1684 Effect of Narasin on nutrient intake and digestibility in wethers fed high-forage diets.

The objectives in this trial were to determine the effects of adding increased levels of narasin on nutrient intake and digestibility in wethers fed low quality forage. Five White Dorper × Santa Inês wethers (BW 68.7 ± 2.1 kg), cannulated in the rumen, were used in a 5 × 5 Latin square design. Animal were fed daily and diet was composed of coastcross bermudagrass hay (91.0% DM; 67.2% NDF; 32.1% ADF; 6.8% CP; 3.2% EE; 17.3% NFC; 5.5% ash). Narasin was offered twice a day and levels were 0 (control, N0), 8 (N8), 16 (N16), 24 (N24), or 32 (N32) mg/kg DM, corresponding to 0, 80, 160, 240, and 320 mg of Zimprova 100®. The delivery vehicle of narasin was 20 g of ground corn containing the set dosage of narasin in 1 kg of DM. Every experimental period lasted 20 d. The first 15 d were used to adapt the wethers with the experimental diets. Daily feed intake and fecal output were determined on Days 16, 17, 18, and 19 of each period. For total collection of feces, harnesses with collection bags were used to avoid contamination of feces by urine. Data were analyzed using the MIXED procedure (SAS Inst. Inc.) and the LSMEANS option was used to generate individual means. The effect of narasin levels were evaluated using linear and quadratic orthogonal contrasts. The effects were considered significant when P < 0.10. Increasing levels of narasin did not affect dry matter (1.1 ± 0.2 kg; P = 0.70), organic matter (1.0 ± 0.2 kg; P = 0.69), NDF (0.7 ± 0.1 kg; P = 0.69), and ADF (0.3 ± 0.01 kg; P = 0.68) intakes. Experimental diets did not affect DM (50.5 ± 2.6%; P = 0.57) and OM (50.9 ± 2.6%; P = 0.63) digestibilities. However, narasin increased linearly NDF digestibility (N0: 50.4%; N8: 53.7%; N16: 51.8%; N24: 55.0%; N32: 55.2%; P = 0.06). ADF digestibility tended to differ with increased levels of narasin (N0: 49.1; N8: 51.1; N16: 49.2; N24: 53.4; N32: 53.0%; P = 0.15). Levels of narasin improve NDF digestibility in wethers fed a low quality forage diet without affecting nutrient intake.