Vascular sources of amino acids for milk protein synthesis in goats at two stages of lactation

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Vascular sources of amino acids for milk protein synthesis in goats at two stages of lactation

Year: 

2002

Source of publication :

Journal of Dairy Science

Authors :

Mabjeesh, Sameer Jermaya

.

Volume :

Co-Authors: 

Mabjeesh, S.J., Rowett Research Institute, Greenburn Road, Bucksburn, Aberdeen AB21 9SB, United Kingdom, Department of Animal Science, Faculty of Agricultural, Food and Environ. Quality Sciences, P. O. Box 12, Rehovot 76100, Israel
Kyle, C.E., Rowett Research Institute, Greenburn Road, Bucksburn, Aberdeen AB21 9SB, United Kingdom
MacRae, J.C., Rowett Research Institute, Greenburn Road, Bucksburn, Aberdeen AB21 9SB, United Kingdom
Hanigan, M.D., Dairy Research Group, Purina Mills Inc., St. Louis, MO 63144, United States
Bequette, B.J., Rowett Research Institute, Greenburn Road, Bucksburn, Aberdeen AB21 9SB, United Kingdom, Dept. of Animal and Avian Sciences, University of Maryland, College Park, MD 20742, United States

From page: 

919

To page: 

929

(

Total pages: 

11

)

Link :

Vascular sources of amino acids for milk protein synthesis in goats at two stages of lactation

Abstract: 

An arteriovenous technique, combined with a 30-h i.v. infusion of [5- 13CH3]Met and [5,5,5-2H]Leu, was used to monitor mammary uptake of free amino acid (AA) and to estimate the proportion of casein synthesized from circulating peptides in goats in early and late lactation. At both stages, kinetics was performed on the last day of consecutive 5.5-d periods. The first period was an i.v. infusion of saline and the second an i.v. infusion of lysine (8.9 g/h) plus methionine (2 g/h). Net uptake of essential AA and protein yields were higher in early than in late lactation. Uptake of free Met, His, and Pro was less than, uptake of Tyr and Lys was equal to, and uptake of Arg, Leu, Val, and Ile was greater than milk protein synthesis. Peptide uptake, estimated from the difference in casein and plasma free AA enrichment, accounted for a larger fraction of casein-Met (17 vs. 8%) and casein-Leu (27 vs. 12%) in late than in early lactation. Small decreases in mammary blood flow, AA transport activity, and AA concentrations accounted for the lower uptake of AA in late compared with early lactation. Based on our studies of several AA, the utilization of circulating peptides for casein synthesis appears to be a general phenomenon.