HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Foldager, J. Articles by Bergen, W. G. Search for Related Content PubMed PubMed Citation Articles by Foldager, J. Articles by Bergen, W. G.

Factors Affecting Amino Acids in Blood of Dairy Cows¹

Department of Dairy science

W. G. Bergen

Department of Animal Husbandry, Michigan State University, East Lansing 48824

ABSTRACT

Concentrations of amino acids in blood plasma were studied in two experiments with lactating Holstein cows. In Experiment 1, 30 cows were allotted to five treatments varying in protein percent and source. Cows were bled during wk 4 and 9 of treatment at 0, 2, and 5 h after feeding. In Experiment 2, 68 cows were assigned to four rations. One contained 12.5% crude protein from natural sources and another 16.0%. Two other rations contained 16.0% crude protein (12.2% natural and 3.8% from nonprotein nitrogen). Blood was collected at 42 days postpartum 2 to 3 h after feeding. Seven cows from each treatment also were sampled 14 days prepartum and 126 days postpartum.

Cows fed 9.3% crude protein had lower branched-chain amino acids and higher glycine in plasma than those fed 13 to 14%. High yielding cows in mid-lactation (140 to 220 days) showed decreased branched-chain amino acids and increased glycine in plasma compared to low yielders. Production did not alter amino acids in early lactation (42 days). Several significant changes in amino acids of plasma were related to stage of lactation, but groups of acids did not follow consistent patterns. Samplings 2 h after feeding had lower branched-chain and aromatic amino acids than samplings at 5 h. Ratios of essential to nonessential amino acids were depressed by rations of low natural protein, by high milk production in early lactation, and in samples taken 2 h postfeeding. Estimates of minimum blood flow to the mammary gland needed for output of amino acids in milk identified methionine, phenylalanine, threonine, and lysine (in that order) as those in lowest supply. Ratios of essential amino acids of plasma to milk also suggested limited availability of these amino acids.

¹ Published with approval of the Director of Agricultural Experiment Station as Journal Article No. 8951.

² National Institute of Animal Science, Department of Cattle and Sheep Experiments, 25 Rolighedsvej, DK-1958 Copenhagen V, Denmark.