Hormones and behavior in rhesus macaque abusive and nonabusive mothers. 2. Mother-infant interactions.

This study investigated the differences in parenting style and hormonal variables in abusive and nonabusive rhesus macaque mothers during the first 2 months of lactation. All subjects lived in large social groups in outdoor corrals. Abusive mothers were more protective and more rejecting of their infants than nonabusive mothers, particularly in the first month. Abusive and nonabusive mothers did not differ in levels of circulating estradiol (E2) and progesterone (P) during the periparturitional period except that the decrease in P after parturition was less marked in abusive than in nonabusive mothers. Individual differences in periparturitional E2 or P were not correlated with differences in parenting style. Mothers with higher frequencies of abuse, however, had significantly higher values of the E2-to-P ratio in the last week of pregnancy and significantly lower values of P in the first week of lactation than mothers with lower frequencies of abuse. Although pregnancy or lactation hormones are unlikely to be one of the main determinants of abusive behavior, endocrine variables may interact with personality characteristics or environmental factors in causing this phenomenon.