Relation between mammary gland development and body weight.

Mammary gland indices including deoxyribonucleic acid, dry fat-free tissue, and wet weight were correlated with body weight in species having a range of 20,000 fold in body weight. Included were mice, hamsters, rats, guinea pigs, rabbits, sheep, and cattle. From limited data accumulated at Missouri, the relation of deoxyribonucleic acid of mammary gland (Y, mg) to bodyweight (X, g) was Y = .53X-79 at the peak of lactation, Y = .29X-82 at the end of pregnancy, and Y = .056X-84 at the beginning of pregnancy. Comparing mammary dry fat-free tissue (mg) to body weight resulted in: Y = 20X-80, Y = 9.7X-85, and Y = 2.6X-91 in the same order while equations for mammary gland wet weight (mg) and body weight were: Y = 135X-82, Y = 123X-79, and Y = 38X-85. The composite value for regression (b) when all data were combined was .80. These mammary indices relate to but are slightly higher than metabolic body weight which is accepted generally as body weight to the three-quarter power.