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The Impact of Non-Forage Fiber Sources on Fiber Digestibility
Non-forage fiber sources (NFFS) have been used in ruminant diets for many years. However, some dairy operations are now reaching inclusion rates of these feedstuffs that substantially greater than the traditional target of 10-15% of dry matter. Heavy reliance on feedstuffs with high NDF content, but small particle size, could potentially have major impacts on kinetics of both fiber digestion and passage. Furthermore, when such ingredients are used to partially replace starch sources, there is potential for positive associative effects on forage fiber digestion. Critical impediments to a clearer understanding of NFFS-reliant diets include the lack of relevant data on digestion kinetics, and more importantly, the great diversity in composition and characteristics of different NFFS. Nevertheless, several studies have investigated the effects of common NFFS on ruminal fermentation characteristics, microbial populations, and total-tract nutrient digestion. In general, NFFS-reliant diets that are formulated to support high levels of milk production do not appear to provide an associative benefit for forage fiber digestibility, nor have consistent increases in ruminal pH or shifts in rumen microbial populations been observed. Although empirical data are limited, sufficient physically-effective forage NDF is likely critical for efficient ruminal digestion of NDF from NFFS, both by maintaining ruminal pH and by providing a fiber mat to slow passage of the small particles. Determining the ideal forage NDF level in low-starch, high NFFS diets is key to allowing increased dry matter intake while maintaining high digestive efficiency.
Keywords: ruminal kinetics, byproducts, digestion, fiber