The metabolism of glucose, acetate, lipids and amino acids in lactating dairy cows

Abstract

Specialized techniques, previously used in surgically prepared goats, which simultaneously measure udder metabolism (arteriovenous difference of milk precursors x udder blood flow) and the whole body turnover of the milk precursors, have been successfully transferred to dairy cows. Methods of obtaining representative samples of arterial and mammary venous blood and of measuring udder blood flow are described.The rates of entry into the circulation, as determined by isotope dilution, of glucose, acetate and plasma free fatty acids were 3-3-4-0, 1-7-2-1 and 0-5 kg/day respectively. Acetate and glucose contributed 32-50 and 4-11% respectively of the total CO a output by the animal.Measurement of the uptake of precursors of milk constituents and their transfer into milk showed that there were substantial arteriovenous differences of glucose, acetate, triglyceride and /?-hydroxybutyrate which were not significantly different between breeds or related to milk yield. Isotopic and balance data confirm that glucose is the main precursor of lactose and that the oxidation and transfer of glucose into lactose accounted for 69-98 % of the glucose entry rate. As in the goat, plasma triglycerides and blood acetate accounted for 35-80 % and 25-50 % of the milk triglycerides respectively. Propionate was extracted from plasma but the uptake was only about 8 % of the value for acetate.There was no net arteriovenous difference of phospholipids, cholesterol esters or free fatty acids, but the fall in specific radioactivity of free fatty acids across the mammary gland indicated there was an exchange of free fatty acids between plasma and mammary tissue. In agreement with previous findings, acetate contributed to all the milk fatty acids up to a chain length of C 14 and part of the C 16 fatty acid. Plasma triglycerides contributed to the remainder of the C 16 fatty acid and all the milk fatty acids with a chain length of C 18 or higher.In contrast to the lactating goat, cow plasma contained very few chylomicrons. The majority of the triglycerides taken up by the udder were derived from the lowdensity lipoprotein fraction.The essential amino acids were extracted from blood in amounts sufficient to account for the essential amino acids secreted into milk protein. Although the plasma level of methionine was low, 52-72 % of the material reaching the mammary gland was taken up. The uptake of arginine was far in excess of the requirement for milk protein synthesis.been difficult to interpret such trials accurately because oi our relative ignorance of the complex The economic importance of the dairy cow has processes involved in the body's mechanisms reguled to numerous studies on the effect of diet on the lating the uptake and metabolism of milk preyield and composition of milk. Frequently it has cursors by the udder. However, in fed and fasted • Present address: Biochemistry Department, Lin-goats important quantitative data have been coin College, University of Canterbury, New Zealand. obtained by simultaneously measuring milk out-

Thyroid hormones, blood plasma metabolites and haematological parameters in relationship to milk yield in dairy cows

“…TG are an important source of long-chain fatty acids for milk fat synthesis (Bickerstaffe et al, 1974) and are mainly concentrated in the very low density lipoprotein fraction, which is higher in dry than in lactating cows (Palmquist, 1976). Also, TG are taken up by the mammary gland which could explain the negative relationship between milk yield and plasma TG concentrations in our study.…”

Effects of different energy intakes before and after calving on food intake, performance and blood hormones and metabolites in dairy cows

“…https://doi.org/10.1017/S0003356100025320 requirements, can be explained by the probably the consequence of high glucose somewhat slower rise of DM intake after requirements for lactose synthesis calving, and by the higher initial milk yields. (Bickerstaffe, Annison and Linzell, 1974). A good appetite after parturition is Because the energy-corrected milk yield of considered an important factor for the the three experimental groups was similar, prevention of ketosis (Baird et al, 1974).…”

Revue bibliographique : Variations quantitatives et métabolisme des lipides dans les tissus adipeux et le foie au cours du cycle gestation-lactation 2e partie : chez la brebis et la vache

“…En effet, les aliments qu'ils ingèrent, riches en parois végétales, séjournent pendant 15 à 48 h dans le rumen-réseau (dont le contenu est de 60 à 100 I chez le bovin adulte), où ils subissent une dégradation plus ou moins complète sous l'action des enzymes sécrétées par les micro-organismes qui y pullulent (10 10 par ml). Les (Raphaël et al, 1973 ;Bickerstaffe et al, 1974 ;Harrison et al, 1974 ;Leat et Harrison, 1975). Celle-ci résulte en outre du catabolisme très rapide des VLDL et surtout des chylomicrons (Puppione, 1978 ;Ferreri et Elbein, 1982).…”