Abstract
It has been known for some time that milk production can be materially increased by dietary treatment. This increase was first accomplished by increasing the protein content of the diet, then later by using good quality animal proteins such as liver. The vitamins, especially the B complex, are of considerable importance as well.
In the present study the growth of approximately 350 litters of suckling rats was used as a criterion of milk production. Only the growth period from the fourth to the seventeenth day of life was considered. The logarithmic functions of the daily weight of litters of 6 were plotted against time. The slopes of the resultant curves were compared, and expressed as lactation indices.
The basal diet of the lactating rats consisted of casein, 15 parts; salt mixture, 5; agar agar, 2; starch, 76; lard, 14; wheat germ oil, 5 drops per day; cod liver oil, 6 drops per day; and irradiated yeast, 3 gm. per day. To this basal ration were added daily supplements of various fractions of liver or egg. When dried substances such as amino acids were used they were incorporated in the basal ration replacing part of the casein.
The lactation promoting factor was found to be present in considerable amounts in the following: liver, egg, water extract of autolysed liver or egg; 25% level of casein, Witte's peptone, blood fibrin, cystine. The best results were obtained when one part of cystine replaced one part of casein in the basal ration. This is a rather low protein diet for a rat, especially a lactating rat, and the results suggest that cystine plays a specific rôle in stimulating milk production either as such or as a constituent of glutathione which in turn may influence the production of milk.
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