164. The nutritive value of milk supplemented with minerals as an exclusive diet for fats. Comparison of equal volumes of Summer and “winter” milk before and after laboratory pasteurization

Abstract

Milk was obtained simultaneously from cows on early pasture and from stall-fed cows receiving winter rations. By suitable blending of the morning's and evening's milkings of each milk the fat content of the two milks was equalized daily. A part of each milk was then pasteurized in the laboratory by a “holder” method. The total nutritive value of the milk was measured on rats in two separate experiments. In one the milks, supplemented with iron, copper and manganese, were fed as an exclusive diet. The four types of milk were given to twelve groups of litter-mate male rats, the intake being equalized within each group. The experiment lasted 8 weeks, and at the end no difference was found in gain in weight, body length, general appearance of the rats or composition of the carcasses. The palatability of the milks as gauged by the refusals of the rats was investigated by various statistical methods, which showed that summer milk was probably more palatable than “winter” milk, but that pasteurization had no effect. In the second experiment the intake of milk was limited to 20 ml. daily, but the rats were given in addition unlimited access to a basal diet of casein, sugar and salts. This experiment was also carried out on groups of four litter mates (four groups of does and seven groups of bucks). After 8 weeks 5% brewer's yeast was added to the basal diet, resulting in a marked increase of the growth rate of all the groups. At the end of the 8 weeks, the gains in weight, intakes of basal diet, and gains per gram of solids ingested were compared. The only statistically significant differences were in favour of pasteurized summer milk when compared with summer raw and with “winter” pasteurized.