Interrelationships of Rumen Ingesta Composition, Removal Rate from the Rumen, and Digestibility in Identical Twin Cows Fed Alfalfa Hay

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Abstract
Four sets of fistulated, identical-twin cows were used to determine the relationship between the rate of removal of nutrients from the rumen and nutrient digestibility. The cows were fed alfalfa hay at 12-hr intervals. The day after each digestion trial the rumen was emptied and the contents weighed, sampled, and returned to the rumen 3 times: before the cows were fed and 6 and 12 hr. after they were fed. Except for rumen dry matter, which increased in amount 6 hr. after feeding, there was little change in the composition of rumen ingesta from sample to sample when sampled 3 times in 12 hr. The percentages of crude fiber and ash in rumen ingesta were greater than, and the percentages of protein and nitrogen-free extract were less than, the percentages of these constituents in the hay fed. The ratio of nutrients fed to those present in the rumen before the cows were fed is an indication of rate nutrients are removed from the rumen. On the average, an amount of dry matter (13.2 lb) equivalent to approximately twice the intake (7.75 lb) was present in the rumen before hay was fed. A small variation was observed within twin pairs and between twin pairs in digestibility; a. large variation within and between twin pairs in nutrient removal rate from the rumen. Consequently, no correlation was shown among individual animals between rate of removal and digestibility. Within individual animals, the most digestible nutrient was removed from the rumen fastest.