Effect of Selection for 12-Day Litter Weight on Lactational Performance in Mice

Abstract

The effect of selection for increased 12-day litter weight on lactational performance at days 8, 10, and 12 post partum was examined using mice drawn from two replicate selected lines and two replicate control lines. The components of lactational performance examined were milk yield and percentage composition with respect to total solids, lipid, and protein. Selection was found to have had no direct effect on the components of lactational performance measured. Milk yield, percentage solids, and percentage lipid increased linearly from lactation day 8 to 12 (P < 0'05). Using the estimates of the components of variance for 12·day litter weight obtained by Eisen, Legates, and Robison (1970) for the mice used, the correlation between 12-day litter weight and the additive genotype for lactational performance was estimated to be 0·45.