Relationship between litter size at birth and within-litter birth weight characteristics in laboratory mice as pilot animal for pig.

We investigated the relationship between litter size at birth and within-litter birth weight (BW) characteristics of laboratory mice as a pilot mammal for pig. We obtained records of number born alive (NBA) and total and mean litter BW (LWB, MWB), and maximum and minimum values of within-litter BW (MaxIWB, MinIWB), range and standard deviation (Range, SDIWB), skewness (Skew), and kurtosis (Kurt) of within-litter BW for 656 litters at first parity. Pearson's correlations of NBA were highly positive with LWB (0.92), weakly negative with MWB (-0.31), MaxIWB (-0.19), and MinIBW (-0.33), and those of MWB were negligible with Range, SDIWB, Skew, and Kurt (-0.10 to 0.06). Estimated heritabilities, treated as dam traits, were 0.32 for NBA, 0.39 for LWB, 0.24 for MWB, 0.28 for MaxIWB, 0.05 for MinIWB, 0.16 for Range, 0.17 for SDIWB, and 0.00 for Skew and Kurt. Estimated genetic correlation between NBA and LWB was high (0.95). Therefore, LWB could be promising for efficiently improving NBA. The estimated genetic correlation of NBA was negligible with MWB (0.00), positive with MaxIWB (0.10), Range (0.48), and SDIWB (0.36), and negative with MinIWB (-0.36), suggesting that selection for increased NBA brings larger SDIWB and lighter MinIWB.