Studies on animal growth

In order to clarify some of the problems connected with a study of the growth of meat-producing animals an investigation of certain aspects of growth has been undertaken. Because of the difficulty of conducting large scale experiments with the common meat producing animals, the mouse was chosen for the present study. As a pilot to future work with larger animals, average age changes in body composition and metabolic rate of mice from birth to maturity have been determined. In addition, the effect of plane of nutrition on these two variables and on growth rate and feed efficiency have been investigated. The composition of the body varies in a regular manner with increasing body weight especially on a fat-free basis. Changes in the major constituents apparently exhibit differential growth. The protein to water ratio is suggested as a valid index of physiological age in all mammals. Metabolic rate does not bear a constant relationship to body weight, age, surface area, fat-free mass or protein mass in growing animals. It is, however, directly proportional to the fat-free mass divided by the protein to water ratio and to total body-water. The former expression is considered a valid index of physiologically active mass because it is a function of that fraction of the body which is metabolizing and of changes in its composition. It is the amount of metabolizing tissue corrected to a common physiological age. Plane of nutrition has an effect on growth rate, feed efficiency, body composition and metabolic rate. Restricted nutrition slows up the growth process such that the rate of physiological aging decreases. Thus, most of the changes in the growth complex resulting from restricted nutrition may be due to changes in the relative growth rates of the various body tissues.Land and Food Systems, Faculty ofGraduat