Forestomach and whole tract digestibility for lactating dairy cows as influenced by feeding frequency.

Three lactating Holstein cows, averaging 510 kg and fitted with T-type duodenal cannulae in the proximal duodenum, were in a 3 X 3 Latin-square experiment to measure digestion in forestomachs and whole tract of feed nitrogen and neutral detergent fiber components as influenced by frequency of feeding. Cows were fed one diet containing 65% chopped grass legume hay, 26% cracked corn, and 8% soybean meal. Mixed ration was fed either once daily, four times daily, or the concentrate portion of the diet was fed once daily and the forage portion four times. Ytterbium, as ytterbium chloride, was included with diets to allow calculation of flow rates of duodenal and fecal dry matter. Assayed ratios of nitrogen to diaminopimelic acid in ruminal bacteria and duodenal digesta or fecal bacteria and feces were used to calculate duodenal and fecal bacterial nitrogen flows respectively. Ratios of nitrogen to diaminopimelic acid in ruminal and fecal bacteria averaged 4.15 and 2.38 g/mmol. Apparent digestibility of organic matter in the forestomachs and whole tract averaged 43.7 and 66.4%. 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. Bacterial nitrogen flows averaged 255 and 91 g/day at the duodenum and in the feces. Bacterial nitrogen yield in the rumen averaged 36.6 g/kg organic matter apparently digested in the forestomachs. Frequency of feeding had no effect on almost all 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.