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Journal of Dairy Science Vol. 35 No. 2 128-139
© 1952 by American Dairy Science Association ®
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Nutritive Values of Crops and Cows' Milk as Affected by Soil Fertility. II. The Essential Amino Acids in Colostrum and Milk Proteins1,2

C. W. Duncan, Gertrude I. Watson, K. M. Dunn3 and R. E. Ely4

Departments of Agricultural Chemistry and Dairy, Michigan Agricultural Experiment Station, East Lansing

ABSTRACT

The essential amino acids in colostrum and milk proteins of cows maintained on feeds grown on highly fertilized and on highly depleted soil of the same type have been determined.

There was no essential difference between the amino acid pattern of the "first" colostrum and that obtained 24 hr. postpartum when the values are expressed as per cent of the crude protein, except that the arginine content was higher in the colostrum secreted by the cows receiving the unfertilized feed. The amount of crude protein in colostrum declined approximately 50 per cent within 24 hr. postpartum. The genetic differences between cows appear to be greater than differences between groups.

The amino acid concentrations of the 60-day composite milk samples obtained from each group of cows varied less than ± 10 per cent, except that the methionine content of the milk produced by the cows receiving the unfertilized feeds was 12 per cent higher than that produced by the cows receiving the fertilized feeds. The average amount of total crude protein in the milk was almost identical in both groups. Individual cow differences were larger than group differences.

The average amino acid values in the terminal milk proteins from each group of cows deviated less than ± 10 per cent, except that the leucine content of the milk produced by the cows receiving the unfertilized feeds was consistently higher than that produced by the cows receiving the fertilized feeds. The average total protein content in the milk produced by both groups was approximately the same.

The amounts of isoleucine and methionine increased as lactation progressed, whereas arginine and tryptophan decreased progressively from colostrum to terminal milk. Threonine decreased markedly during the first 60 days postpartum and then increased slightly as lactation progressed. The other amino acids were relatively unchanged.

The concepts that badly depleted soils produce crops of lower nutritive value than highly fertilized soils or that commercial fertilizers decrease the nutritive properties of crops are not confirmed by this investigation. Insofar as the amino acid composition of milk proteins is concerned, evidence is lacking which indicates that the nutritive value of feeds is dependent chiefly on soil fertility.

FOOTNOTES

1 Published with the approval of the Director of the Michigan Agricultural Experiment Station as Journal article no. 1269.

2 This work is supported in part by a grant from the National Dairy Council on behalf of the American Dairy Association and was presented in part at the forty-fifth annual meeting of the American Dairy Science Association, Ithaca, N. Y., June, 1950.

3 Deceased.

4 Present address: Bureau of Dairy Industry, U. S. D. A., Washington 25, D. C.






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Copyright © 1952 by the American Dairy Science Association ®.