Partitioning of Nutrients During Pregnancy and Lactation: A Review of Mechanisms Involving Homeostasis and Homeorhesis

Toxicity, metabolism, and impact of mycotoxins on humans and animals.

Conceptus energy and nitrogen de- mands in late pregnancy are mostly met by placental uptake of maternal glucose and amino acids. The resulting 30 to 50% increase in maternal requirements for these nutrients is met partly by increased volun- tary intake and partly by an array of maternal metabolic adaptations. The latter include increased hepatic gluconeogenesis from endogenous substrates, decreased peripheral tissue glucose utilization, in- creased fatty acid mobilization from adipose tissue, and, possibly, increased amino acid mobilization from muscle. Within 4 d of parturition, mammary demands for glucose, amino acids, and fatty acids are several- fold those of the pregnant uterus before term. Even unusual postparturient increases in voluntary intake cannot satisfy this increased nutrient demand. There- fore, rates of hepatic gluconeogenesis and adipose fat mobilization are greatly accelerated. Concomitant changes in amino acid metabolism include increased hepatic protein synthesis and, possibly, decreased amino acid catabolism, and increased peripheral mobilization of amino acids. Insulin resistance in adipose tissue and muscle, developed during late pregnancy, continues postpartum; adipose lipolytic responsiveness and sensitivity to adrenergic agents are increased postpartum beyond their levels during late pregnancy. Before parturition, these homeorhetic adjustments may be coordinated with lactogenesis by increased secretion of estradiol and prolactin. Their amplification and reinforcement at and soon after parturition may be regulated mostly by somatotropin.

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Regulation of organic nutrient metabolism during transition from late pregnancy to early lactation

Microencapsulation is a relatively new technology that is used for protection, stabilization, and slow release of food ingredients. The encapsulating or wall materials used generally consist of starch, starch derivatives, proteins, gums, lipids, or any combination of them. Methods of encapsulation of food ingredients include spray-drying, freeze-drying, fluidized bed-coating, extrusion, cocrystallization, molecular inclusion, and coacervation. This paper reviews techniques for preparation of microencapsulated food ingredients and choices of coating material. Characterization of microcapsules, mechanisms of controlled release, and efficiency of protection/stabilization of encapsulated food ingredients are also presented.

Encapsulation of food ingredients

Site of Digestion of Starch in the Gastrointestinal Tract of Dairy Cows and Its Effect on Milk Yield and Composition

E ARLY in 1963 the authors introduced a net energy system designed for use in the growing and finishing phase of the beef cattle industry (Lofgreen, 1963a, b, c). The system separated the requirements for maintenance from that for body weight gain and expressed a net energy value of the feed for these two functions. Such a system of expression was suggested to the Nutrition Committee of the National Research Council and was included in the first printing of the N.R.C. Bulletin of suggested energy terminOlogy as an errata sheet replacing the original terminology (Harris, 1962). For the past 4 years the suggested method has been tested under various conditions at this station, in commercial feedlots, and by nutrition consultants working with the cattle feeding industry and its adaptability to practice has been demonstrated. I t is the purpose of this paper to present the proposed system in the scientific literature, describe the experimental data upon which it is based, and discuss its application. The terminology used herein is that suggested in the first revision of the N.R.C. Bulletin on energy terms (Harris, 1966).

A system for expressing net energy requirements and feed values for growing and finishing beef cattle.

Growth, development and composition of the ovine conceptus and mammary gland during pregnancy.

The comparative energy requirements of sheep and cattle for maintenance and gain.

Forty-six Hereford heifers were slaughtered at different stages of gestation. Udders and gravid uteri were removed. Each gravid uterus was dissected into fetus, fetal membranes, fetal fluids and uterus. Fresh weights, dry matter, ether extract, ash, nitrogen and gross energy contents of the various tissues were determined. Weights and compositions of udders and uteri from 36 non-pregnant heifers were also determined. Relationships of the type W = Woe (b~-b2t) t where t is the number of days after mating, Wo is the amount of constituent on the day of mating and W is the amount of constituent on day t of gestation were derived to describe growth of different constituents of the gravid uterus during gestation. Udder development was most rapid after 234 days of gestation as indicated by ash and nitrogen contents. Udders of pregnant heifers contained approximately 48, 60, 67 and 102 g nitrogen at 134, 189, 237 and 264 days of gestation, respectively and udders of non-pregnant heifers contained approximately 37 g nitrogen. No net accumulation of energy occurred in udders of pregnant heifers re/ative to that gained in udders of non-pregnant heifers. Fetuses averaged 1.58, 7.53, 20.8 and 31.6 kg and contained 1.20, 1.60, 2.07 and 2.52% nitrogen at 134, 189, 237 and 264 days of gestation, respectively. Gross energy contents of fetuses were .54, .88, 1.17 and 1.32 kcal/g fresh weight at each of these times. Rates of nitrogen and energy storage in the gravid uterus were estimated to be .76, 2.79, 8.95 and 25.0 g/day and 36.0, 143,457 and 1,167 kcal/day at 100, 160, 220 and 280 days of gestation, respectively. None of these values was affected by fetal sex or maternal energy intake (150 or

W. N. Garrett

Papers

A system for expressing net energy requirements and feed values for growing and finishing beef cattle.

Growth, development and composition of the ovine conceptus and mammary gland during pregnancy.

The comparative energy requirements of sheep and cattle for maintenance and gain.

Growth, development and composition of the udder and gravid uterus of beef heifers during pregnancy.

Re-Evaluation of the Relationship between Carcass Density and Body Composition of Beef Steers