Forestomach and Whole Tract Digestibility for Lactating Dairy Cows as Influenced by Feeding Frequency

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Abstract
Three lactating Holstein cows, averaging 510 kg and fitted with T-type duodenal cannulae in the proximal duodenum, were in a 3 .times. 3 Latin-square experiment to measure digestion in forestomachs and whole tract of feed N and neutral detergent fiber components as influenced by frequency of feeding. Cows were fed 1 diet containing 65% chopped grass-legume hay, 26% cracked corn and 8% soybean meal. Mixed ration was fed either once daily, 4 times daily or the concentrate portion of the diet was fed once daily and the forage portion 4 times. Yb, as YbCl3, was included with diets to allow calculation of flow rates of duodenal and fecal dry matter. Assayed ratios of N to diaminopimelic acid in ruminal bacteria and duodenal digesta or fecal bacteria and feces were used to calculate duodenal and fecal bacterial N flows, respectively. Ratios of N to diaminopimelic acid in ruminal and fecal bacteria average 4.15 and 2.38 g/mmol, respectively. Apparent digestibility of organic matter in the forestomachs and whole tract averaged 43.7 and 66.4%, respectively. Forestomach and whole tract digestibility of cellulose, hemicellulose and lignin averaged 56.1, 52.0, 14.7 and 58.7, 58.5, and 16.8, respectively. Bacterial N flows averaged 255 and 91 g/day at the duodenum and in the feces, respectively. Bacterial N yield in the rumen averaged 36.6 g/kg organic matter apparently digested in the forestomachs. Frequency of feeding had no effect on most measures and components of rumen and whole tract metabolism and digestion. For these intakes, frequency of feeding had little effect on feed intake and nutrient utilization.