MAXIMUM LOSS OF FEED FROM NYLON BAGS IN THE RUMENS OF STEERS AS RELATED TO APPARENT DIGESTIBILITY

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Abstract
Nylon bags containing rolled barley or mixtures of rolled barley and finely chopped alfalfa hay in ratios of 1:1, 2:1, and 3:1 were removed from two fistulated steers 1, 2, 4, 8, 14, 24, 48, and 72 hours after placement in the rumen. The cumulative loss of dry matter and protein from the bags was described for each ration by an equation of the form X/Y = k1 + k2X. The asymptotes of the curves so calculated were taken as estimates of the theoretical maximum loss of dry matter and protein. Maximum dry matter losses were 77.4, 80.7, 82.4, and 90.5% and apparent dry matter digestibilities were 73.0, 78.3, 79.1, and 80.7% for the 1:1, 2:1, 3:1, and all-barley rations, respectively. The corresponding values for maximum protein loss were 95.3, 94.2, 94.6, and 98.8% while those for apparent protein digestibility were 76.8, 83.2, 83.7, and 82.0%. From estimates of endogenous fecal protein loss, it was calculated that fecal loss of potentially available feed dry matter accounted for 60% of the difference between the apparent and maximum digestible dry matter content of the three rations containing hay, and 89% of that of the all-barley ration. Endogenous fecal protein loss accounted for about half of the difference between maximum and apparent protein digestibility.