In the previous paper it was demonstrated that skimmed milk powder was superior to casein as a source of protein for the growing rats.
The present experiment was conducted to find out whether the superiority of skimmed milk powder was attributable to the presence of lactose, albumin, or combined effects of both elements.
Thirty weaned rats were divided into 5 groups, each of which was fed for 20 days on (1) casein diet plus lactose (CL group), (2) casein diet plus albumin (CA group), (3) casein diet plus albumin and lactose (CAL group), (4) skimmed milk diet (Sk group), (5) whole milk diet (Wh group), respectively.
In order to evaluate the effects of those elements, the body weight, food intake, the nitrogen excretion in the urine, and the length, the weight, the ash and calcium contents of the bone were determined and compared with those of the skimmed milk diet group.
The addition of lactose to casein diet had on favorable effects either on the growth of animals, efficiency ratio of the diet, nitrogen utilization or on the bone development.
The growth of animals especially stayed significantly below the levels of the Sk group, and CL group showed the poorest results among these groups.
The supplement of albumin with casein diet produced marked improvement in the animal growth and the excretion of nitrogen, and induced the superior bone weight, ash and calcium contents to the Sk group.
By the further addition of lactose to the above diet the growth at the early and middle stages of the experimental period was accelerated, but this effect disappeared by the end of the experimental period. The bone attributes which were examined at the 20th day suggested more efficient ash and calcium utilization by the combined addition of albumin and lactose to the casein diet than by the single addition of albumin.
It seems that lactalbumin plays a prime role in keeping the high nutritive value of skimmed milk and lactose can exert its effect on the weight gain at the early stage of growth and on the bone development, only when casein is supplemented with albumin.
The whole milk diet group showed always better results either in growth, nitrogen utilization or the bone development.
It appears that the superiority of skimmed milk to casein as the source of protein for the young animal come mainly from its albumin content, and the effect of lactose is secondary and specific with the stage and the feature of the growth and development.
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