Biology of dairy cows during the transition period : the final frontier?

https://www.webpages.uidaho.edu/ruminant_nutrition/Reading%20materials%20411/dietary%20factors%20affecting%20feed%20intake-Allen2000.pdf

Effects of Diet on Short-Term Regulation of Feed Intake by Lactating Dairy Cattle

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.

/pdf/regulation-of-organic-nutrient-metabolism-during-transition-3cjtw7rd0r.pdf

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

Certain diets cause a marked reduction in milk fat production in ruminants. Commonly referred to as milk fat depression (MFD), the mechanism involves an interrelationship between rumen microbial processes and tissue metabolism. Numerous theories to explain this interrelationship have been proposed and investigations offer little support for theories that are based on a limitation in the supply of lipogenic precursors. Rather, the basis involves alterations in rumen biohydrogenation of dietary polyunsaturated fatty acids and a specific inhibition of mammary synthesis of milk fat. The biohydrogenation theory proposes that under certain dietary conditions, typical pathways of rumen biohydrogenation are altered to produce unique fatty acid intermediates that inhibit milk fat synthesis. Trans-10, cis-12 conjugated linoleic acid (CLA) has been identified as one example that is correlated with the reduction in milk fat. Investigations with pure isomers have shown that trans-10, cis-12 CLA is a potent inhibitor of milk fat synthesis, and similar to diet-induced MFD, the mechanism involves a coordinated reduction in mRNA abundance for key enzymes involved in the biochemical pathways of fat synthesis. A more complete identification of these naturally produced inhibitors of fat synthesis and delineation of cellular mechanisms may offer broader opportunities for application and understanding of the regulation of lipid metabolism.

/pdf/nutritional-regulation-of-milk-fat-synthesis-2ltygj39ak.pdf

Nutritional regulation of milk fat synthesis.

The Biologically Active Isomers of Conjugated Linoleic Acid

Description d'un protocole en une etape d'extraction-interesterification avant dosage par chromatographie gazeuse. Application a des graines oleagineuses, de la matiere grasse du lait, des aliments du betail, des dejections, du savon

Rapid method for determination of total fatty acid content and composition of feedstuffs and feces

Fat in lactation rations: review.

Publisher Summary This chapter discusses the biosynthesis of conjugated linoleic acid (CLA) in ruminants and humans. Conjugated linoleic acid is a mixture of positional and geometric isomers of linoleic acid with a conjugated double-bond system. Because of its potential to improve human health, there is great interest to increase the amount of CLA in the human food supply. This has caused great effort to be expended toward increasing the concentration of CLA, and more specifically rumenic acid (RA), in the milk and tissues of ruminant foods because these are the predominant source of CLA in human diets. RA is the predominant CLA isomer present in ruminant products, and the major source of its occurrence is endogenous synthesis via desaturation of vaccenic acid (VA) by ∆-9-desaturase. The chapter focuses on improving the understanding of biohydrogenation in the rumen and examining milk and tissue CLA responses to a range of diets. The diversity of various BH intermediates in digesta, milk, and tissues indicates the complexity of the BH processes as a whole and the population dynamics of the ruminal bacteria involved. Predicting the outcome of changes in the diet is complicated by the interactions of the ruminal environment, substrate supply and forms of dietary lipids, all of which influence the BH process simultaneously.

D.L. Palmquist

Papers

Rapid method for determination of total fatty acid content and composition of feedstuffs and feces

Fat in lactation rations: review.

Biosynthesis of conjugated linoleic acid in ruminants and humans.

Effect of Fatty Acids or Calcium Soaps on Rumen and Total Nutrient Digestibility of Dairy Rations

Ruminal synthesis, biohydrogenation, and digestibility of fatty acids by dairy cows