Published online by Cambridge University Press: 18 August 2016
In the accompanying paper, specific genetic factors for body weight and food intake were identified in non-reproductive male and female mice of a line selected for high litter size at birth (average of 22 born per litter) and a non-selected control line (average of 10 born per litter). The existence of these factors are indicated by variation in efficiency parameters such as growth efficiency and maintenance requirements. Residual food intake (RFI) and Parks’ estimates of growth efficiency (AB) and maintenance requirements (MEm) were used to quantify these factors. In the growing period, females had a higher RFI (are less efficient) than males. At maturity, selected mice had higher RFI than control mice and selected females had higher RFI than selected males. AB was higher in selected-line mice than in control-line mice, and higher in males than in females. MEm was higher in selected-line mice than in control-line mice, and higher in females than in males. The results indicate the existence of specific genetic factors for both growth efficiency and maintenance requirements. Selected females may increase RFI in the adult state to anticipate the metabolically stressful periods of pregnancy and lactation, to support a genetically highly increased litter size.