Body composition in non-reproductive adult males and females in a long-term selection experiment for litter size in mice

Earlier studies have shown that adult mice from a line selected for high li tter size (S-line), in particular females, had higher residual food intake (RFI) than mice from a non-selected control line (C-line). It was suggested bar this increase in RFI, in particular the mature selected females, may a nticipate the metabolically stressful periods of pregnancy and lactation. T he present study investigated whether body composition at maturity has been changed as a correlated response to selection, in order to support the off spring during pregnancy and lactation. Furthermore, part of the observed di fferences between individuals in RFI may be attributable to differing propo rtions of body protein and lipid. For these reasons, differences in body co mposition at maturity between males and females of the S-line and the C-lin e were investigated. Lipid percentage was similar for C-line animals and S- line females; S-line males had a significantly rower lipid percentage. Male s had a higher protein percentage than females, in particular S-line males. The results show that body composition in adult non-reproductive females h as not been affected as a correlated effect of selection for high litter si ze. Furthermore, the results suggest that the high lean content in S-line m ales may explain part of the high RFI compared with C-line animals. Body co mposition in S-line females probably does not explain the high RFI compared with S-line males and C-line animals. Factors other than protein and lipid levels must be responsible for the differences found between the lines and sexes in RFI.