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Studies on Lactation^*

I. Production of Milk in the Dog as Influenced by Different Kinds of Food Proteins

(From the Department of Vital Economics, University of Rochester, Rochester, N. Y.)

Balanced diets, containing all of the known vitamins and other requirements, were fed to Boston bull females of the same breed and breeding. The diets were all based upon the following scheme: 0.7, to 0.8 gram of nitrogen per kilo., 75 to 80 calories per kilo., 30 per cent protein, 25 per cent fat, 40 per cent carbohydrate and 6 per cent ash. The only variable in the diets was the source of protein. Beef liver, round, kidney and dried hen's egg were the sources of protein.

The experimental diet was fed from the time of conception through the fifth week of lactation, the diet being increased to meet the demands of the growing pups.

The litters were all limited to three pups and the mothers given identical care.

The milk was collected by manual manipulation during the fifth week of lactation when the pups were not with the mother.

One dog was bred to the same sire and kept under identical conditions for four pregnancy-lactation periods. Egg was the source of protein in the first and third periods while liver was used in the second and fourth.

She showed a better nitrogen retention on liver both times. When fed liver she produced in the fifth week of lactation 1934 cc. of milk, containing 13.5 per cent fat in one experiment and 2156 cc. of milk, containing 13.25 per cent fat in the other. When fed egg she produced in the corresponding week, only 1361 cc. of milk containing 12.25 per cent fat. The pups of the liver experiments grew 1.34 times as fast as those of the egg experiments.

Another dog of a different breed and breeding, when fed round steak as the source of protein, produced in the fifth week of lactation 865 cc of milk containing 12.5 per cent fat. The growth of the pups was practically the same as on the egg experiment.

Owing to some unknown cause, no experiments were completed on kidney diet. This diet did not seem toxic and produced plenty of milk when fed to a lactating dog with five pups. It may have some effect on the intrauterine life of the pups, since none of the mothers fed on this diet during pregnancy delivered normally.

The chemical studies may be of some significance in the study of the physiology of lactation.

The work shows the degree of betterment in lactation that can be brought about by changing the source of protein in the diet. Liver is a much better source of protein for lactation than either egg or round steak.

Our conclusion that liver is the best source of protein (of those tried) for milk production in dogs, is borne out by the quantity of milk produced, the fat content of the milk, the nitrogen retention and the slope of the growth curve of the pups.

Manuscript received 27 February 1931.