Effect of forage-to-concentrate ratio in complete feeds and feed intake on digestion of starch by dairy cows.

In digestion trials, 16 Holstein cows were fed complete mixed feeds of (a) 75:25, (b) 60:40, (c) 45:55, and (d) 30:70 ratios of forage to concentrate on a dry basis. At an intake of feed for maintenance, digestibility of starch ranged from 96.2 to 96.8%. During the lactation phase when intakes of feed were 2.5 to 3.2 times maintenance, digestibility of starch ranged from 84.7 to 88.1%. Starch in feces represented 2.9, 3.7, 5.5, and 5.9% of the intake of dry matter during the lactation phase, and .6, 1.0, 1.3, and 1.6% of intake at maintenance for the respective rations. At high intakes of concentrate, substantial amounts of dietary starch escaped degradation in the rumen and small intestine and were lost in the feces.