This study explored how different levels of physically effective neutral detergent fiber from forage (peNDF-F) and the feed additive narasin affect the performance, carcass traits, meat quality, gastrointestinal fermentation, and ruminal papillae development of feedlot lambs consuming high-concentrate diets. Lambs fed higher levels of fiber in the diet (104 g/kg of peNDF-F) consumed more feed, but this did not lead to better weight gain and reduced feed efficiency. In contrast, lambs on a lower level of fiber in the diet (52 g/kg of peNDF-F) were more efficient, gaining weight with less feed. Despite differences in intake, fiber level had little effect on carcass traits, although lambs on the 104 g/kg of peNDF-F diet had slightly more fat in their meat. Adding narasin to the diet did not impact growth performance, but it improved backfat thickness, body wall thickness, and carcass marbling. Adding narasin to the diet of feeder lambs consuming diets with 52 or 104 g/kg of peNDF-F tended to affect ruminal fermentation by increasing the molar proportion of propionate while decreasing acetate and the acetate: propionate ratio. Furthermore, including narasin elevated ruminal total short-chain fatty acid concentrations and pH, while also increasing the cecal proportion of propionate, decreasing isobutyrate, and reducing the acetate: propionate ratio. Increasing peNDF-F levels in the diet increased the number of papillae per cm² and resulted in thinner keratinized layers. Lambs consuming narasin had enhanced ruminal papillae height, surface area, and absorptive capacity while reducing the thickness of the keratinized layer. These findings suggest that lower fiber diets can improve feed efficiency and ruminal fermentation parameters towards propionate, while narasin inclusion enhances gastrointestinal tract fermentation traits, ruminal papillae morphology, and subcutaneous fat thickness and marbling score.

Read the full article in the Journal of Animal Science.