The influence of age, carbohydrate-fat ratios of milk replacers, and development of ruminal function on growth, health, and blood glucose concentrations were evaluated in calves. Colostrum-fed, 3-day-old Holstein bull calves were fed to 12 wk on one of three dietary treatments: 1) a high carbohydrate, low fat (60.5% glucose, 9.5% lactose, and 3% lard) milk replacer; 2) a low carbohydrate, high fat (23% glucose, 12.5% lactose, and 30% lard) milk replacer; and 3) weaning at 6 wk of age from high-fat replacer to a standard calf starter. The high fat milk replacer was superior to low fat milk replacer for total weight gains and efficiency of feed conversion. Rates of weight gain of starter calves were similar to those of calves fed low fat. Calves fed the diet with low fat had a high incidence of diarrhea, an occasional outbreak of a yeast-related ethanol intoxication syndrome, and high concentrations of glucose in urine. Irrespective of milk replacer composition or development of ruminal function, plasma and whole blood glucose concentrations declined rapidly in the first 6 wk. Corpuscular glucose declined steadily with age in all calves. This age-related decrease of blood glucose concentration of calves seems to be a constitutive phenomenon.
In vitro rates of conversion of [1-14C]leucine to 4-methyl-2-oxo[1-14C]pentanoate and of oxidation of [1-14C] and [U-14C]leucine were measured for tissues from fed and starved (5 days) sheep. Slices of liver and kidney and preparations of adipose tissue and of fibre bundles of external intercostal muscle (EIC) were used. Skeletal muscle is likely the major site of leucine catabolism in sheep although adipose tissue is capable of substantial metabolism. Muscle and adipose tissue from fed sheep released 17 and 5% of the [1-14C]leucine transaminated as 4-methyl-2-oxo-[1-14C]pentanoate and upon starvation the proportions were increased (P less than 0.001) to 46 and 32%. Starvation reduced (P less than 0.01) leucine catabolism in all tissues except the kidney. The pattern of leucine catabolism in EIC muscle changed from extensive oxidation in the fed state to being limited essentially to transamination and decarboxylation in the starved state.
ABSTRACT. Rates of utilization of glucose, acetate, and cerning such changes in lipid metabolism have yet to be obtained. lactate and activities of selected enzymes were determined The present investigation involved studies of adipose tissue from in vitro to characterize the nature of lipogenesis and me-fetal and unsuckled newborn calves. Rates of utilization of tabolite utilization in perirenal adipose tissue from 6-to 7-glucose, acetate, and lactate, as substrates for oxidation and for month old fetal and 3-to 4-h-old unsuckled newborn calves. synthesis of fatty acids and glyceride glycerol, were determined Contribution of the pentose phosphate cycle to glucose in vitro to characterize the nature of lipogenesis and patterns of metabolism was estimated using specifically labeled glu-metabolite utilization. Specifically labeled glucose was employed cose. Rates of fatty acid synthesis from all three substrates to evaluate the contribution of the pentose phosphate cycle to and oxidation of glucose were much greater in fetal than glucose metabolism and to the reducing equivalents needed for in newborn adipose tissue. In fetal adipose tissue, acetate fatty acid synthesis. In addition, activities of selected enzymes and lactate were major sources of carbon for fatty acid related to lipogenesis in adipose tissue were also assayed. synthesis; glucose functioned mainly by metabolism via the pentose phosphate cycle to provide reducing equivalents for fatty acid synthesis and by incorporation into glyceride MATERIALS AND METHODS glycerol for fatty acid esterification. Pentose phosphatePerirenal adipose tissue samples were obtained from five fetal cycle contributed 58 and 12% to glucose metabolism in calves (180-2 10 days gestation or 64-75% of full term) and eight adipose tissue of fetal and newborn calves, respectively. newborn unsuckled calves (3-4 h after birth). Newborn calves Adipose tissue metabolism of newborn calves was charac-were sacrificed by exsanguination prior to tissue removal. ~d iterized by greatly depressed rates of fatty acid synthesis pose tissue samples were placed in warn saline (37" C) for despite high enzyme activities and elevated rates of gl~cer-transport to the laboratory, cleaned of connective tissue and ide glycerol synthesis. (Pediatr Res 20: 542-544, 1986) blood vessels, and cut into small (30-50 mg) pieces. Adipose tissue pieces weighing 50-100 mg were placed in siliconized 25-ml Erlenmeyer flasks containing 2 ml of incubation medium (Table 1). Concentrations of glucose, acetate, Iactate/pyruvate, M~~~ studies of fetal metabolism have been carried out in and insulin in the incubation medium were determined in the sheep with substrate utilization usually being determined on the preliminary experiment to achieve maximum rates of substrate basis of rates of oxygen consumption and uptake of different utilization. The flasks were gassed with a mixture of 95% O2 and substrates. Various acute and chronic preparations and tech-5% C02, capped with self-sealing rubber serum caps fitted wth niques suc...
Leucine (0.1 mM) was preferentially incorporated into proteins rather than being oxidized in intact external intercostal muscle fiber bundles from sheep. At higher leucine concentrations, oxidation became more important. Leucine metabolism in muscle was reduced by starvation. Leucine was not a significant precursor of fatty acids in sheep adipose tissue.
Rates of utilization of glucose, acetate, and lactate and activities of selected enzymes were determined in vitro to evaluate the effects of age and diet on lipogenesis in perirenal adipose tissue of calves. Three-day-old Holstein bull calves were fed up to 12 wk of age on one of three dietary treatments: a high carbohydrate milk replacer; a high fat milk replacer; and weaning at 6 wk of age from high fat replacer to calf starter. Adipose tissue biopsies were obtained from calves at 2, 5, 8, and 12 wk of age. Rates of fatty acid synthesis and activities of enzymes of the pentose phosphate and citrate cleavage pathways were increased in calves fed high carbohydrate milk replacer. These parameters were decreased in calves fed high fat replacer and were further depressed after weaning. Substrate preference for fatty acid synthesis in all calves was acetate, then lactate, then glucose. With increase in age from 2 to 12 wk, adipose tissue of calves fed milk replacer partitioned more acetate and lactate toward fatty acid synthesis and less toward oxidation. The pentose phosphate cycle was characterized by high rate of recycling and contributed at least 50% of reducing equivalents required for fatty acid synthesis. It appeared that several features of lipogenesis characteristic of functional ruminants are also shared by preruminant calves.
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