Nutritive Values of Crops and Cows’ Milk as Affected by Soil Fertility. II. The Essential Amino Acids in Colostrum and Milk Proteins

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Abstract
Crops grown on natural soils seriously depleted of mineral nutrients and the same soil with adequate amts. of mineral fertilizers and minor elements constituted the sole ration for 2 groups of cows. Ten pairs of half-sisters were used, one in each group. There was no essential difference between "first" colostrum and that obtained 24 hrs. post partum, except that arginine content was higher in colostrum secreted by cows receiving unfertilized feed. Differences between cows was greater than differences between groups. The avg. amt. of total crude protein in the milk was almost identical in both groups. The methionine content in the 60-day composite sample from the group receiving unfertilized feeds was 12% higher than the other group. The avg. amino acid values of the terminal milk proteins from each group deviated less than + 10%, except that leucine content of milk produced from cows fed crops grown on unfertilized soil was consistently higher than those receiving feed grown on fertilized soil. Isoleucine and methionine increased as lactation progressed, whereas arginine and tryptophan decreased. 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.