Rate of Passage of Feeds through the Digestive Tract of Holstein Cows

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Abstract
Twelve Holstein cows were used to study rate of passage of feedstuffs through the digestive system. Four of the twelve were used twice in a crossover design, each being tested when milking at relatively high and low levels. Eight additional animals, four each of high and of low production, were used once in a group comparison. All cows were fed normal herd rations according to size and production. Rate of passage was determined by feeding a meal of stained hay and observing appearance of stained particles in the feces. Total fecal collections were made and feed intake was held constant during the experiment. Rate of passage was faster in those cows producing milk at the higher levels, and consuming greater quantities of feed and water, although the magnitude of the differences was not great. Level of dry matter intake was significantly correlated with rate of passage. Several previously suggested methods of calculating passage rate were employed; all appeared satisfactory, but those measuring the mean time spent by each stained particle in the digestive tract appeared to be slightly more reliable. Dry matter digestibility averaged 65.7% and was not different between cows of high and low production.

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