Body Size and Milk Production

The senior author has suggested (1) that in general the total efficiency of energy utilization by animals energy in the product (milk, eggs, etc.) energy in the food is independent of body size. Involved in this theory is the assumption that an animal's capacity to take in food per day is, as a rule, a certain multiple of its maintenance requirement or also its rate of fasting katabolism. This assumption was supported by some data on the food capacity of baby chicks, rabbits, sheep, swine, and steers, which indicated that the rate of intake of total food energy in these animals was four to six times as great as their rate of fasting katabolism. According to this theory the capacity for rate of production (energy in meat, milk, or eggs per unit of time) of large and small animals should be proportional to their respective rate of fasting katabolism; or, since this metabolic rate is proportional to the 3~ power of body weight (2), the capacity for rate of production should also be proportional to the a/~ power of body weight. Thus the rate of lactation per unit of metabolic body size (kg.~)* should be the same for large and small animals.