A two-generation reproduction study to assess the effects of cows' milk on reproductive development in male and female rats

Objective: To examine whether the considerable quantities of increased female sex hormone levels found in modem milk as a result of modem dairy farming practices are safe for human consumption. Design: Males and females of the P generation were maintained on a diet containing milk for 10 weeks before mating. Exposure to milk was continued up to the end of weaning of the F2b offspring. Setting: Two-generation reproduction study. Animal(s): Male and female Wistar Galas rats. Intervention(s): P- and F1-generation rats were mated. Main Outcome Measure(s): Fertility, fecundity, and morphology and function of reproductive organs. Result(s): Although milk had growth-promoting effects in both parents and offspring, it caused no impairments in fertility, fecundity, or reproductive organ development in either generation. However, a whole litter from a dam of the P generation was born dead, three litters in total had a pup with skeletal abnormalities, and the AGD of F2a female pups was reduced. These events occurred only in the milk-treated rats. It is unknown whether these issues had any relevance to milk or only happened by chance. Conclusion(s): Further study is required to determine whether milk from pregnant cows is completely free from adverse effects on reproductive health. (C) 2004 by American Society for Reproductive Medicine.