Effect of number of young born (litter size) on milk yield of goats: role for placental lactogen.

Relationships of number of fetuses, placental mass, and lactogenic activity of plasma to development of mammary gland during pregnancy and of litter size to milk yield were examined in British Saanen goats. In late pregnancy lactogenic activity, measured in plasma by radioreceptor assay, increased with number of fetuses. Total weight of placentomes increased with total fetal weight and, hence, fetal number. The weight of the lobulo-alveolar component of the udders was correlated positively with placental mass and fetal number. In hand -milked goats which bore triplets or twins, mean milk yield was 47% and 27%, respectively, higher than in mothers of single kids after correction for lactation number. Milk yield was correlated with the weekly mean of placental lactogen titers between wk 11 and term. This supports the view that placental lactogen has a significant role in the control of normal mammary development and function in goats.