Four Holstein cows in midlactation were equipped with ruminal and abomasal cannulas and used to study the effect of synchronized degradation of crude protein (CP) and organic matter (OM) and feeding frequency on digestion and outflow of nutrients. A 4 x 4 Latin square design was used. Diets were arranged in a 2 x 2 factorial design; the four diets contained high ruminally degradable OM and high ruminally degradable CP, high ruminally degradable OM and low ruminally degradable CP, low ruminally degradable OM and high ruminally degradable CP, and low ruminally degradable OM and low ruminally degradable CP. In each period, cows were fed four times daily from d 1 to 14 and two times daily from d 15 to 28. Mean daily ruminal ammonia N concentration was reduced by high ruminally degradable OM, low ruminally degradable CP, and twice daily feeding. Fluctuation in ruminal ammonia N was lower when cows were fed four times daily than when cows were fed twice daily. Plasma urea N concentrations were lower for cows fed diets that were high in ruminally degradable CP. Higher CP flow in the abomasum was found for cows fed the diet containing high ruminally degradable OM and low ruminally degradable CP. Microbial dry matter and CP flow to the abomasum were higher for cows fed twice daily than for cows fed four times daily. Flow of OM in the abomasum was not altered by concentrations of ruminally degradable OM or CP. These results suggest that the available energy in the rumen (ruminally degradable OM) is the most limiting factor for ruminal N utilization under our experimental conditions. Use of these data may improve the prediction of plasma urea N.

I. The changes in the solubility of calcium, magnesium and phosphorus in digesta flowing along the intestinal tract and the net movement across the intestinal wall of these elements were determined in six rams, each equipped with three T-shaped cannulas; cannulas were placed in a total of six different sites of the small intestine. CrzO, was used as a marker substance to measure the rate of flow of the digesta.2. The concentrations of soluble Ca, Mg and P decreased as digesta moved along the intestine. The greatest fall in soluble Ca occurred after the first 3 m of the intestine, while a significant decrease in soluble Mg was found only at 15 and 25 m from the pylorus. The concentration of soluble P in digesta decreased until the 7 m site and then remained stable. In the faeces, the level of soluble Mg was approximately 4 times higher than, and that of Ca equal to, the levels of Mg and Ca found in digesta flowing through the upper intestine. Unlike Ca and Mg, a very low concentration of soluble P was found in the faeces. 3.In the duodenum, 84, 78 and 62 yo of the total Ca, Mg and P respectively were soluble, whereas in the digesta flowing through the terminal ileum the corresponding values were 3.2, 7.2 and 19 % for Ca, Mg and P respectively. 4.The forestomachs and the colon were found to be the main sites of Mg net absorption;1.12 mmol/h was apparently absorbed from the stomach and 1.05 mmol/h from the colon.The upper small intestine (1-3 m from the pylorus) appeared to be the major site of Ca and P absorption. 5.In the last 10 m of the small intestine, considerable amounts of minerals were secreted; 4'70, 0.96 and 1.85 mmol Ca, Mg and P/h respectively were added to the digesta flowing between 15 and 25 m from the pylorus. The effect of the increase in the pH of digesta along the small intestine on the solubility of these minerals is discussed.

We partitioned the flow of amino acids (AA) to the abomasum among rumen undegradable protein (RUP) and bacterial, protozoal, and endogenous fractions using four Holstein cows in midlactation that were equipped with ruminal and abomasal cannulas. A 2 x 2 factorial design with four diets, combinations of high or low ruminally degradable organic matter, and rumen degradable protein, was employed. Crude protein (CP) and AA contents of ruminal bacteria and protozoa and abomasal digesta were determined. Equations for the source compositions and in vivo flows of CP and 16 AA were then solved simultaneously with a linear program to estimate the contribution of RUP, bacterial, protozoal, and endogenous CP to AA flows. The flows of RUP and bacterial AA were not affected by diet. Low dietary RDP increased the flow of protozoal AA to the abomasum, but the ruminally degradable organic matter content of the diet did not affect protozoal AA flow. Across diets, RUP, bacterial, protozoal, and endogenous fractions provided 55, 33, 11, and <1% of the CP, and 62, 26, 12, and <1% of the AA that reached the abomasum. The linear program was a useful tool for partitioning AA that flows to the abomasum. The technique may also allow dietary effects on ruminal microbes and the AA profile of protein flowing to the duodenum to be better understood and perhaps manipulated.

The effect of heating whole cottonseeds on the degradability of DM and CP in the rumen and the small intestine of lactating cows was determined in situ. Whole cottonseeds were heated for 1 or 2 h at 140, 160, or 180 degrees C prior to digestion. The degradation of DM and CP was determined in dacron bags suspended in the rumen for 3, 6, 9, 24, and 48 h. Bags incubated in the rumen for 24 h were introduced into the small intestine through a duodenal cannula and subsequently recovered in feces. The effective ruminal degradabilities of DM and of CP were evaluated, assuming a ruminal outflow rate of .08/h. Heating of whole cottonseeds decreased the degradability of DM and CP in the rumen with a corresponding increase in the amounts digested in the small intestine. The calculated temperature at which this effect was first observed was 130 degrees C. Following optimal heating amount of digestible CP reaching the small intestine more than doubled. The agreement between these findings and the results of previous in vivo experiments suggest that the dacron bag technique may reliably be used for determination of nutrient availability in the intestine.

This study analyzed the relationships among the effective degradabilities of organic matter (OM) in feedstuffs, which were assessed separately by an in situ method and a direct in vivo measurement of the rumen degradation of OM in the diets of Holstein dairy cows. For this comparison, 80 individual data points were used from studies of dairy cows that were in midlactation and that had been cannulated in the rumen and abomasum. In vivo evaluation of the true degradability of OM in the rumen was based on rare earth digesta markers. Purine N served as a microbial marker. Feed samples were incubated in the rumens of dairy cows for 3, 6, 9, 12, 24, 48, and 72 h, and effective rumen degradation was calculated from the percentage of residual OM for rumen outflow rates of 4, 6, and 8%/h. Evaluations of rumen degradability of OM by the in situ method were correlated with actual in vivo measurements of rumen degradability of OM (r2 = 0.31, 0.34, and 0.37; SE of the estimate = 4.1, 4.0, and 3.9%, respectively). We concluded that the in situ method is a useful tool for providing reliable estimates of rumen degradability of OM in dairy cows.

The object of this study was to evaluate the impact of monensin administration on the early lactation performance of cows maintained on a high-energy diet, and on health traits during the transition period. Cows (n = 168; parity 3.3 +/- 1.4, initial body condition score 3.1 +/- 0.08, and milk yield of 34.3 kg/d +/- 0.9 for multiparous cows in the preceding lactation) were divided into control and monensin treatment groups. A controlled-release capsule supplying 335 mg of monensin/d for 95 d was inserted into the rumen of monensin-treated cows 30 d before the expected calving. Blood samples were obtained 2 h after feeding on d 14 prepartum and on d 7, 14, and 50 postpartum. Plasma glucose concentration was 3% higher (58 +/- 0.5 vs. 56.4 +/- 0.5 mg/dL) and beta-hydroxybutyric acid was 17% (6.7 +/- 0.3 vs. 8.0 +/- 0.3 mg/dL) lower in monensin-treated than control cows. Plasma glucose was 10% higher (60.0 +/- 0.6 vs. 54.5 +/- 0.3 mg/dL) and beta-hydroxybutyric acid was 16% lower (6.8 +/- 0.3 vs. 7.9 +/- 0.2 mg/dL) in primiparous than multiparous cows. Plasma nonesterified fatty acid concentration (measured only in primiparous cows) was 17% lower (287 +/- 15 vs. 336 +/- 17 muEq/L) in treated than in control cows. Rate of ketosis incidence was 60% lower (8 vs. 21%) in monensin-treated than in control cows, and the proportion of control cows that required a supply of glucogenic precursors was 3-fold higher than in monensin-treated cows. The body condition score was 3.1 +/- 0.05, 2.7 +/- 0.05, and 2.4 +/- 0.05 on d 60 prepartum and d 7 and 50 postpartum, respectively, and was not affected by treatment. During the first 5 mo of lactation, milk yield was 7% higher (37.6 +/- 0.6 vs. 35.2 +/- 0.6 kg/d) in monensin-treated cows than in control cows. Our results showed that monensin administration, as a controlled-release capsule in prepartum cows, can be beneficial, even if these cows are maintained on a high-energy diet during the subsequent lactation.

The effect of infusing similar energy equivalents of starch into the rumen, or starch or oil into the abomasum was studied in four midlactation cows in a 4 x 4 Latin square design experiment; controls were ruminally infused with water. Cows were fitted with cannulas in the rumen, abomasum, and ileum, and nutrient digestion in the rumen and small intestine was evaluated with Cr as a digesta marker. Ruminal infusions of starch, or abomasal infusions of starch or oil, were associated with a decrease in voluntary feed organic matter intake. Overall energy intake was reduced in oil-infused, but not in starch-infused cows. Nonstructural carbohydrate digestibility in the rumen and in the small intestine was similar among treatments. In abomasally infused cows 3.4 kg/d of nonstructural carbohydrates was apparently digested in the small intestine. Milk production was reduced in oil-infused cows, but the efficiency of milk energy and protein yield was unaffected by treatments. Plasma glucose, insulin, and IGF-1 concentration, mammary glucose extraction rate, rumen ammonia and plasma urea, and arterial and mammary extraction rate of amino acids were all similar among treatments. Large quantities of starch can be digested in the rumen or small intestine of dairy cows. There appear to be no metabolic advantage to increasing the supply of starch to the rumen or the abomasum of mid-lactation dairy cows maintained on highly concentrated diets and exhibiting a positive energy balance.

A study was conducted to evaluate the effect of abomasal infusion of casein on post-ruminal digestibility of starch and on milk yield and composition. Six multiparous Israeli Holstein cows in mid lactation, fitted with ruminal and abomasal cannulas, were used in a 3 ✕ 3 Latin-square experiment. Each cow received 1600 g maize starch infused into the abomasum. Treatments were: abomasal infusion of sodium caseinate at 0, 350, or 700 g casein daily. Chromium mordant neutral-detergent fibre (NDF) was used as a digesta marker. Casein infusion was associated with increases in post-ruminal and total-tract digestibility of non-structural carbohydrates and protein. Concentrations of rumen ammonia and of plasma insulin, glucose and urea were higher in casein-infused cows. Concentrations of milk protein and lactose and milk protein yield increased with casein infusion. Results indicate that increased protein flow to the abomasum can improve the yield of milk constituents in dairy cows. Digestibility and yield responses to infusion of 350 g casein per day were similar to those at 700 g/day. There was a tendency toward reduced milk protein efficiency in casein-infused cows. It is suggested that part of the production response can be related to a direct effect of protein supply and the rest can be explained by the indirect effect of improved carbohydrate availability in the small intestine.