Effects of feed processing and frequency of feeding on ruminal fermentation, milk production, and milk composition.

Twenty Holstein cows, averaging 108 d postpartum, were used in five replicated 4 x 4 Latin squares to investigate the effects of feed processing and frequency of feeding on ruminal fermentation, milk production, and milk composition. Four rumen-fistulated cows were used in one of the replicates to monitor ruminal fermentation. Each cow was fed for ad libitum intake a diet of 55% alfalfa and 45% concentrate on a DM basis. Treatments were 1) noncubed diet fed two times daily, 2) noncubed diet fed four times daily, 3) cubed diet fed two times daily, and 4) cubed diet fed four times daily. Alfalfa was fed as long hay in the noncubed diet and chopped and pressed into a cube in the cubed diet. Dry matter intake by cows was not different between treatment comparisons. However, cows fed the noncubed diet consumed 5% more concentrate and 5% less alfalfa than did cows fed the cubed diet. Milk production was greater (1.4 kg/d) when the cubed diet was fed to cows, but the percentage and yield of milk fat were depressed (.43 percentage units and .09 kg/d), causing a decreased production of 4% FCM (.9 kg/d). The depression in milk fat percentage and yield may have been attributed to lowered ruminal fluid pH and a decreased ratio of acetate to propionate in cows consuming the cubed diet. Even though ruminal fluid pH and the ratio of ratio of acetate to propionate tended to be lower when cows were fed four times rather than two times per day, production and composition of milk were not affected by frequency of feeding the diets.