Effects of dietary fatty acids on the social life of male Guinea pigs from adolescence to adulthood.

Dietary intake of polyunsaturated fatty acids (PUFAs) or saturated fatty acids (SFAs) differently modulates neurophysiological and behavioral functions in response to altered hypothalamic-pituitary-adrenal (HPA)-axis activity and an individual's development. In this context, an individual's social environment, including social interactions and social hierarchies, is closely related to hormone concentrations and possibly interacts with dietary fatty acid effects. We investigated if dietary supplementation with walnut oil (high in PUFAs) and coconut fat (high in SFAs), compared to a control group, affects body mass gain, cortisol and testosterone concentrations, plasma fatty acids, and social behavior in male domestic guinea pigs from adolescence to adulthood. For analyses of cortisol and testosterone concentrations, social interactions were included as covariates in order to consider effects of social behavior on hormone concentrations. Our results revealed that SFAs increased escalated conflicts like fights and stimulated cortisol and testosterone concentrations, which limited body mass gain and first-year survival. PUFAs did not remarkably affect social behavior and hormone concentrations, but enabled the strongest body mass gain, which probably resulted from an energetic advantage. Neither sociopositive nor agonistic behaviors explained age-specific differences in hormone concentrations between groups. However, a high number of subdominant individuals and lower testosterone concentrations were related to increased cortisol concentrations in adult PUFA males. Our findings demonstrate the importance of dietary fatty acids regarding behavioral and endocrine developmental processes and adaptations to the social environment by modulating HPA-axis function and body homeostasis.