Effects of graded duodenal infusions of glucose on yield and composition of milk from dairy cows. 1. Diets based on corn silage.
Four fistulated Holstein cows were arranged in a 4 x 4 Latin square design to study the effects of graded amounts of glucose (0, 500, 750, and 1500 g/d) infused in the duodenum on milk yield and composition and plasma metabolites. Cows were fed a basal diet of 50% corn silage, 17% dehydrated alfalfa, and 33% concentrate. The treatments (feed plus infusions) were isoenergetic. Increased amounts of glucose did not affect milk yield or protein content. Fat yield and content decreased in a curvilinear manner; the lowest fat content was obtained with about 750 g of glucose. The decrease in milk fat resulted from a reduced yield of long-chain fatty acids (C16 and C18), probably caused by lower mobilization of fat. The glucose treatments significantly affected profiles of medium-chain fatty acids, which promoted the elongation process. The most important change in the plasma concentration of amino acids concerned decreased branched-chain amino acids. The lactose content was not greatly affected by infusions of glucose despite a significant linear increase in the concentration of milk glucose. In conclusion, an increase in the supply of glucose had no effect on milk yield and had a slight, positive effect on protein yield but induced a dramatic decrease in fat yield.
Hurtaud
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C
Institut National de la Recherche Agronomique, Station de Recherches sur la Vache Laitière, Saint-Gilles, France.
Rulquin
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Verite
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R
D000596:Amino Acids / Q000097:blood; D000597:Amino Acids, Branched-Chain / Q000097:blood; D000818:Animals; D002417:Cattle / Q000378:metabolism*; D004032:Diet; D004386:Duodenum; D002149:Energy Intake; D005227:Fatty Acids / Q000032:analysis; D005260:Female; D005947:Glucose / Q000008:administration & dosage*; D007774:Lactation / Q000187:drug effects*; D008055:Lipids / Q000032:analysis; D000455:Medicago sativa; D008892:Milk / Q000737:chemistry*; D008894:Milk Proteins / Q000032:analysis; D012820:Silage; D013025:Glycine max; D003313:Zea mays
D000596:Amino Acids; D000597:Amino Acids, Branched-Chain; D005227:Fatty Acids; D008055:Lipids; D008894:Milk Proteins; D005947:Glucose