Lactation performance and mammary amino acid metabolism in lactating dairy goats when complete or met lacking amino acid mixtures were infused into the jugular vein

To investigate the compensatory responses of mammary gland tissues to deficiency amino acid (AA) supply, two AA mixtures were infused into the jugular vein of lactating dairy goats. Complete AA mixture (mixture 1, +M) contained all the constituents of casein and mixture 1 minus methionine (Met) was used as the deficiency AA supply treatment (−M). The results indicated that deficiency AA infusion decreased milk yield (P < 0.01), milk protein content (P < 0.05) and yield (P < 0.01), but increased mammary plasma flow (P < 0.01). Deficiency of Met decreased its arterial concentration (P < 0.05) while increased concentration of isoleucine (Ile), leucine (Leu), valine (Val), and phenylalanine (Phe) (P < 0.05) or had no significant effect on concentration of lysine (Lys), histidine (His), and argnine (Arg) (P > 0.05). The uptake Met by the mammary gland from arterial plasma were increased (P < 0.05), and those of other EAA were not changed (P > 0.05), except that uptake ratio of Ile was significantly lowered (P < 0.05) when −M was infused. Results from this study showed that the capacity of Met absorption by mammary gland could be elevated under the Met shortage condition.