Four lactating Holstein cows were used in a 4 X 4 Latin Square design to determine the effects of postruminally administering sodium caseinate and/or glucose on milk production, milk composition, nitrogen utilization, amino acid utilization by the lactating mammary gland and glucose turnover rate. An 8.5% increase in milk yield and a 13.3% increase in milk protein production were obtained during infusion of sodium caseinate. No significant production responses were attributed to abomasal infusion of glucose. Arterial concentrations of most essential amino acids were increased during infusion of sodium caseinate. Uptake of phenylalanine, methionine and lysine by the mammary gland most closely paralleled their output in milk. The relative concentrations of methionine, lysine and phenylalanine in arterial plasma were considerably less than their concentrations in milk which resulted in a large percentage extraction of these amino acids by the mammary gland. If the availability of essential amino acids to the mammary gland, per se, was limiting the synthesis of milk protein, methionine, lysine and phenylalanine may have been the three amino acids most limiting. Measurements of glucose entry rate showed a trend toward increased glucose flux when either glucose, sodium caseinate or glucose plus sodium caseinate were infused abomasally. The similarity in glucose entry rates obtained during infusion of glucose and sodium caseinate suggest that the increase in milk production was not due totally to increased glucose flux resulting from sodium caseinate infusion.
Three experiments, each utilizing three ponies, were conducted using a mixed VFA solution of [1J4CI acetate, [1JaC] propionate and [2-33H] butyrate to determine VFA production rates in the cecum of the pony. Diet A used in experiment 1, contained a forage to grain ratio of 1:2, while diet B, used in experiments 2 and 3, contained a forage to grain ratio of 3:1. Experiment 1, in which a constant infusion technique was used, resulted in net VFA production rates (mmoles/min) of 3.667 to 3.977 (3=3.836) for acetate, .410 to 1.664 (3=1.213) for propionate and .342 to 1.124 (2=.629) for butyrate. The wide variation in rates was due to extreme values found with one animal. Experiments 2 and 3 were single injection experiments with calculated production rates in mmoles/min ranging from 3.956 to 5.778 (7=4.638) for acetate, 1.035 to 1.560 (3=1.299) for propionate and .403 to .629 (3=.450) for butyrate. Interconversion of the VFA, calculated from data of experiment 1, demonstrated that approximately one-half of the butyrate was derived from acetate, while only 2 to 4% of the acetate was derived from the butyrate. VFA production within the cecum accounted for approximately 30% of the digestible energy intake. (
Five lactating, rumen-fistulated Holstein cows were used to obtain additional information concerning the effects of postruminal infusion of sodium caseinate on milk production and amino acid utilization. A 7-day continuous abomasal infusion of approximately 450 g/day of sodium caseinate was preceded and followed by 7-day infusions of an isonitrogenous-isocaloric solution of glucose, monosodium glutamate, and urea. Total collections of milk, urine, and feces were obtained during the last 5 days of each infusion period. On the last day of each period, arterial and mammary venous blood samples were obtained for analysis of plasma free amino acids. During infusion of sodium caseinate, milk production, milk protein (N times 6.38) production, and efficiency of nitrogen utilization for milk crude protein production were increased. Arterial plasma concentrations of free histidine, isoleucine, phenylalanine, valine, and total essential amino acids were elevated above control levels during infusion of sodium caseinate, while ornithine and tryrosine were decreased. Calculation of the relative concentration of essential amino acids in arterial plasma and in milk protein indicated that methionine and lysine were least abundant in plasma relative to their requirement for milk protein synthesis. A high precentage extraction from arterial plasma by the mammary gland also suggested that methionine and lysine may have been the essential amino acids in most critical supply for milk protein synthesis. Calculation of uptake to output ratios of individual plasma amino acids by the mammary gland suggested that significant quantities of extracted arginine, isoleucine, leucine, threonine, and valine were utilized in pathways other than direct incorporation into milk protein.
Isotope dilution techniques were used to study steady-state glucose kinetics in four rumen-fistulated Holstein steers and to study the effect of rapid absorption of ammonia from the rumen on glucose metabolism. Steers were fed a high-concentrate diet at hourly intervals from automatic feeders. Plasma glucose specific activity curves following single intravenous injection of [2-3H]glucose were used to construct a two-compartment model of the glucose pool with inflow and outflow from compartment one. Primed continuous infusion of [2-3H]glucose was used to determine the steady-state turnover rate of glucose and to monitor changes in the rates of inflow and outflow of glucose from the glucose pool following a single dosage of urea (0.4 g/kg body weight) into the rumen. Compartment sizes of the glucose pool were 65.6 and 33.5 g for compartments 1 and 2, respectively. Glucose turnover rate during steady-state was 15.4 mg/minute/kg body weight 0.75 and transfer rate of glucose between compartments was 17.9 mg/minute/kg body weight 0.75. Concentrations of rumen ammonia-nitrogen, plasma ammonia-nitrogen and plasma urea-nitrogen were 6.1, 0.5 and 4.0 mg/100 ml, respectively, before urea dosage. Rumen ammonia-nitrogen, plasma ammonia-nitrogen increased after urea dosage and reached peak concentrations, 170.0 and 1.2 mg/100 ml, respectively, approximately 120 minutes after urea dosage. Plasma urea-nitrogen increased linearly throughout the 4-hour sampling period and reached 12.0 mg/100 ml at end of the experiment. Concentration of glucose in plasma increased from 98.2 mg/100 ml before urea dosage to 114.6 mg/100 ml at 100 minutes after urea dosage. Estimates of glucose production and utilization indicated that the increased concentration of glucose in plasma in all steers was due, at least partially, to a decrease in the rate of glucose utilization. A rapid rate of glycogenolysis which resulted in a marked increase in the plasma glucose concentration also was evident in one steer.
One thousand twenty steers and heifers were used in six feeding trials to examine the influence of laidlomycin propionate on feedlot performance and to determine the most efficacious dietary concentrations of that ionophore. Cattle were fed diets ranging in energy content from 1.08 to 1.49 Mcal NEg/kg of DM. Laidlomycin propionate improved rate of gain and feed conversion in both steers and heifers. Improvements in performance were not evident when laidlomycin propionate was fed at only 3 mg/kg. However, both average daily gain and feed conversion were improved by laidlomycin propionate within the range of 6 to 12 mg/kg of DM (P less than .001). Feed consumption was not substantially affected by inclusion of laidlomycin propionate in the diet. Improvements in ADG and feed conversion were greater on lower-energy diets than on higher-energy diets, but both these performance characteristics were improved regardless of the type of diet fed. Average daily gain was maximized with laidlomycin propionate at 6 mg/kg, whereas improvements in feed conversion were sustained through 12 mg/kg. Carcasses of cattle fed diets containing 6 to 12 mg/kg of laidlomycin propionate weighed 7.3 kg more (P less than .001) than carcasses of cattle fed the control diets. Yield grade and quality grade were not affected by laidlomycin propionate (P greater than .05).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.