Utilisation des produits terminaux de la digestion par la mamelle chez la vache laitière

Abstract

Summary. Use of the end-products of digestion by the udder of the dairy cow.Relations between mammary arterio-venous (AV) differences and arterial level were studied for glucose, acetate and beta-hydroxybutyrate on 172 samples and for blood essential amino acids on 20 samples, pooled by day and by cow. The data were obtained from 32 experiments on 5 cows eating various diets (Rulquin, 1981(Rulquin, , 1983. AV differences in acetate and beta-hydroxybutyrate were highly related to the arterial levels (R = 0.97 and 0.86) and averaged 74 and 41 % of these levels ( fig. 11. On the other hand, the AV difference in glucose was poorly (R = 0.5) related to the arterial levels.Among the essential amino acids, only AV differences in phenylalanine, leucine, arginine, isoleucine and histidine were linearly related to the arterial levels (R = 0. 78, 0.73, 0.68, 0.63, 0.60) (fig. 2). AV differences in lysine, methionine, valine and threonine were more related to the AV differences of other amino acids than to the arterial levels ( fig. 3).These results have been discussed in connection with different mammary metabolic transport systems and with the ability to modify mammary nutrient input by dietary manipulation.Introduction.

Nutritive value of barley/kale bi‐crop silage for lactating dairy cows

“…Reductions in milk fat concentrations and yields from cows offered the Bi-crop diet agree with one previous report of dairy cows offered whole-crop cereals (Sutton et al, 1998), but not others, when no differences between dairy cows offered grass silage or wholecrop silage were found (Leaver and Hill, 1995;Sutton et al, 1998). Acetate and b-hydroxybutyrate are the major precursors of milk fatty acids, and their uptake and utilization by the mammary gland is highly correlated with arterial concentrations (Rulquin, 1986;Miller et al, 1991), and the combined plasma concentrations of these two metabolites were higher in dairy cows offered the Grass and Mix diets (which also produced the greatest quantities of milk fat) than that of dairy cows offered the Bi-crop diet. Acetate and b-hydroxybutyrate are the major precursors of milk fatty acids, and their uptake and utilization by the mammary gland is highly correlated with arterial concentrations (Rulquin, 1986;Miller et al, 1991), and the combined plasma concentrations of these two metabolites were higher in dairy cows offered the Grass and Mix diets (which also produced the greatest quantities of milk fat) than that of dairy cows offered the Bi-crop diet.…”

“…Differences in milk fat production in this study are likely to have been caused by reduced fibre digestibility and differences in the rumen uptake of acetate and butyrate, the latter being converted to b-hydroxybutyrate by the rumen epithelium in the presence of ammonium ions (Britton and Krehbiel, 1993). Acetate and b-hydroxybutyrate are the major precursors of milk fatty acids, and their uptake and utilization by the mammary gland is highly correlated with arterial concentrations (Rulquin, 1986;Miller et al, 1991), and the combined plasma concentrations of these two metabolites were higher in dairy cows offered the Grass and Mix diets (which also produced the greatest quantities of milk fat) than that of dairy cows offered the Bi-crop diet.…”