Rate and Extent of Neutral Detergent Fiber Degradation of Feedstuffs in Situ

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Abstract
Rate and extent of neutral detergent fiber degradation were determined for 22 feedstuffs in situ. Polyester bags containing 8 g of a forage or 5 g of a grain were suspended in the rumen of cannulated dairy animals 0.5 h after feeding and were removed at intervals up to 48 h. Major differences among feeds were in both extent and rate of neutral detergent fiber degradation, but the correlation between these 2 measures of digestion was not close. Lag times were associated with variability of digestion of the neutral detergent fiber fraction of forages as well as of some grains. Neutral detergent fiber fill, representing the ratio of ruminal neutral detergent fiber to neutral detergent fiber turnover rate, was calculated for each feed from its turnover rate constant, lag time, potential digestibility in situ, and rate of passage. Two diets then were formulated to be similar in chemical composition but to differ in fill. When these diets were tested in situ, the rate and extent of neutral detergent fiber degraded at 24 h was 0. 024 h-1 and 43% vs. 0.074 h-1 and 58% for the high and low fill diets, respectively. Variability in the rate and extent of neutral detergent fiber degradation among feeds can be used to formulate diets that may promote greater intake.