Heterotic and maternal effects in L and S growth strain rats: I. Reproductive performance.

A diallel cross between two strains of rats, from the same genetic source, but varying greatly in body size, was made in order to evaluate the following litter traits: number born alive, litter birth weight, number at 21 d of age, 21 d-litter weight, survival from birth to weaning and average birth weight. Least-squares analyses of variance of traits indicated that number born alive, litter birth weight and litter 21 d-weight was influenced greatly by maternal lines and to a lesser extent by paternal lines. Litters from Large line females (L) had greater numbers born alive with heavier litter weights at birth and 21-d than litters from Small line females (S) regardless of sire line. Heterosis was measured as a difference in performance between the hybrids and the mean of the parental lines. Heterosis levels for maternal traits were generally nonsignificant. Analysis of this mating scheme suggested that in this cross between extremes for body size the maternal effects were so great, that any heterotic effects present were not evident.