Relationships between postnatal plasma oxytocin concentrations and social behaviors in cattle.

We examined the associations between natural individual variations in basal oxytocin (OXT) in postnatal cattle and social behavioral traits. At 1, 2 and 6 weeks of age, the basal OXT exhibited individual variability in 20 Holstein heifer calves. Cluster analysis of mean OXT for these time periods obtained two subgroups: high OXT (HOXT; n = 9) and low OXT (LOXT; n = 11). Social behaviors were observed for 2 days at week 6 after introduction into a four-peer group, and at 10-14 months of age (10 months) immediately and 1 week, 1 month and 5 months after introduction into 11-15 heifers. At week 6, the main effect of the OXT groups was not significant for all social behaviors. At 10 months, there tended to be interactions between the OXT groups and time periods with respect to the frequency of escape behaviors. LOXT heifers exhibited more escape behaviors than HOXT heifers on the first day of the second sociality tests. At 10 months, HOXT heifers exhibited both attacking and affiliative behavior for peers more than LOXT heifers during 5 months after the second social introduction. This suggests that postnatal OXT concentrations may have long-lasting effects on individual differences among social behavioral traits in cattle.