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Reallocation of body resources in lactating mice highly selected for litter size¹

W. M. Rauw^2,*, P. W. Knap, L. Gomez-Raya^*, L. Varona^* and J. L. Noguera^*

^* Àrea de Producció Animal, Centre UdL-IRTA, 177, 25198 Lleida, Spain and and PIC International Group, D-24826 Schleswig, Germany

² Correspondence:
phone: +34 973 70 26 30; fax: +34 973 23 83 01; E-mail:
wendy.rauw{at}irta.es.

The present study investigated differences in the allocation patterns of body stores in lactating female mice from a line selected for high litter size at birth (S-line, average litter size of 20) and dams from a nonselected control line (C-line, average litter size of 10). Body weight, litter size, litter weight, and absolute and relative lipid and protein mass were measured at peak lactation (2 wk in lactation) and at weaning (3 wk in lactation). Body size in S-line females has been increased as a correlated effect of selection for high litter size at birth, allowing for larger litters and higher absolute milk production. However, these dams produce larger litters relative to their own body weight. At peak lactation, lipid and protein percentage did not differ between lines. At weaning, S-line females had a higher protein percentage (P < 0.001) and lower lipid percentage (P < 0.05) than C-line females. Apparently, S-line females produce more offspring but at a greater cost to their own metabolism. This process was insufficient to supply the offspring with adequate resources, resulting in reduced (P < 0.0001) pup development and increased (P < 0.0001) preweaning mortality rates.

Key Words: Body Composition • Lactation • Mice • Resource Allocation • Selection

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