RELATIVE IMPORTANCE OF PRE-PARTUM AND POSTPARTUM FACTORS IN THE CONTROL OF MILK-YIELD IN THE GUINEA-PIG

Examination of data pertaining to milk yield and litter growth rate of guinea pigs at peak lactation showed that milk yield increased with increasing number of pups carried by the dam during pregnancy and with increasing maternal weight. There was a significant linear correlation (P < 0.05) of mammary gland weight (expressed per unit of maternal body weight) with litter size. Increasing litter size within 18 h of parturition from 1 to 5 pups did not elicit a response in milk yield. Decreasing litter size from 5 pups to 1 pup reduced milk yield to the level expected of a monotocous dam. The ability of the guinea pig pup to survive from birth without access to milk and the inadequacy of milk supply to meet litter requirements when the litter size is > 2 pups is shown. The mechanisms controlling lactation in the guinea pig are discussed in relation to data obtained in other species.