Influence de l'équilibre en acides aminés de trois protéines infusées dans l'intestin grêle, sur la production laitière de la vache

International audienc

Effet de la nature des aliments concentrés sur les lieux de la digestion d'une ration à base d'ensilage de maïs chez la vache laitière

International audienc

Détermination de certains acides aminés limitants chez la vache laitière par la méthode des administrations post-ruminales

International audienc

Effects of Graded Amounts of Duodenal Infusions of Methionine on the Mammary Uptake of Major Milk Precursors In Dairy Cows

International audienc

Lactational responses of grazing dairy cows to rumen-protected methionine

International audienc

Effect of Graded Levels of Duodenal Infusions of Casein on Mammary Uptake in Lactating Cows. 2. Individual Amino Acids

International audienceThe experiment examined patterns of mammary uptake of individual AA when graded amounts of calcium caseinate (0, 177, 362, and 762 g/d) were infused duodenally into four lactating cows. Six blood samples were collected over 12 h from the subcutaneous abdominal vein and the carotid. Mammary blood flow was measured by an ultrasonic flow probe implanted around the external pudic artery. Infusions of casein linearly increased the arterial concentrations of all essential AA and several nonessential AA (Pro, Tyr, Orn, and Cit) and increased, or tended to increase, linearly the mammary arteriovenous differences of all AA except Glu and Ala. Absorption ability of the mammary gland was not reduced in vivo. Relationships between mammary arteriovenous differences and arterial concentrations were positive and linear in every cow for all AA except Asn, Ser, Gly, and Ala. Some essential AA (Lys, Arg, and branched-chain AA) were therefore taken up in excess of their output into milk proteins, but others (His, Thr, Met, and Phe) were almost exclusively extracted by the udder in a direct ratio to their output. As infusions of casein increase, Phe becomes probably the most critical AA for milk synthesis

Effects of Graded Amounts of Duodenal Infusions of Lysine on the Mammary Uptake of Major Milk Precursors in Dairy Cows

International audienceEffects of providing a limiting AA on milk secretion and mammary nutrient uptake were investigated using four lactating dairy cows given duodenal infusions of graded amounts of L-Lys.HCl (0, 9, 27, and 63 g/d). Infusions were administered over 4-d periods according to a Latin square design. Diets consisted of a 70:30 corn silage:concentrate ratio supplemented with 1.5 kg of DM/d as dehydrated alfalfa. The basal diet met requirements for energy and protein and was deficient in Lys. Cows were fitted with indwelling catheters inserted into the left carotid and left subcutaneous abdominal veins, and a transit-time flow probe was implanted around the left external pudic artery. Milk, fat, and protein yields were unaffected by infusions of Lys. Milk protein content increased to a maximum with the third treatment, and fat content showed opposite variation. Although arterial concentrations and arteriovenous differences of Lys increased to a plateau with the third treatment, the relationship between arteriovenous differences and arterial concentrations was curvilinear. Infusions of Lys tended to increase the efficiency of N utilization and the mammary extraction rates of AA to synthesize more milk proteins. Initially, Lys was extracted in a direct ratio to its milk output and then taken up in excess by the secretory cells, suggesting that Lys was no longer a limiting factor in milk protein synthesis

Effects of dietary concentrates on the metabolism of energetic compounds in the portal-drained viscera (PDV) and in the liver in lactating dairy cows

International audienc