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Nitrogen Constituents of Sow's Milk as Affected by Ration and Stage of Lactation¹

Departments of Animal Husbandry, Biochemistry, and Dairy Industry, University of Wisconsin, Madison

The effect of ration and stage of lactation on total protein, casein, and non-protein nitrogen in the milk of the sow was studied. A detailed analysis of sow's milk with emphasis on the nitrogenous constituents was made.

The additions of B₁₂, tankage or fish solubles to an all-plant protein ration did not result in significant changes in the total protein or casein content of the colostrum of sows previously maintained on a corn, soybean oil meal, 5% alfalfa (C.S.A.) ration, when the total protein of the ration was the same. Similarly, the source of protein had no effect on the amount of total or casein protein in the 15- and 30-day milk of sows in lots II, III, IV, and V.

The total protein content dropped sharply from colostrum to 15-day milk, but rose slightly in 30-day milk. The casein content values behaved similarly but the changes were not as marked. The decrease from colostrum to 15-day milk was highly significant in both instances.

The non-protein nitrogen increased significantly from colostrum to 15-day milk and there was a further increase in 30-day milk.

The mean values of sow's milk constituents (7th week of lactation) were as follows: 19.2% total solids, 7.13% fat, 5.7% lactose, 6.4% protein (N x 6.38), sulfur 67.1 mg %, pH 6.99, specific gravity 1.038, and freezing point — 0.563°C. Of the 6.4% protein, casein accounted for 57 to 58%, albumin 7.8%, globulin 10%, proteoses-peptones 17 to 18%, and non-protein nitrogen 7 to 8%. Alpha amino and urea nitrogen fractions made up about 85% of the accounted-for non-protein nitrogen.

² Present address: Department of Animal Husbandry, Cornell University, Ithaca, New York.

Manuscript received 10 March 1952.