BEHAVIORAL, CARDIAC AND CORTISOL RESPONSES TO BRIEF PEER SEPARATION AND REUNION IN CATTLE

Behavioral, cardiac, and adrenal responses of heifers to short-term is olation and to subsequent reunion with familiar or nonfamiliar conspec ifics were measured. Two groups of heifers were studied according to t heir different social reactivity: Aubrac heifers (n = 12) reared under suckler conditions and Friesian heifers (n = 12) reared under dairy m anagement. Because these two groups could also react differently to hu man beings, testing social isolation was realized by removing pen mate s without handling the subject. Moreover, heifers were tested in confi nement to avoid an alteration of the cardiac response to isolation by an excessive motor activity. Although physical restraint can influence the reactions, this effect is assumed to be weak because heifers had been exposed to the experimental procedures, including confinement for 3 days before isolation test, in addition to brief periods of physica l restraint occurring regularly according to rearing practices. Result s show that social separation induced struggling and large increases i n vocalization, heart rate, and plasma cortisol concentrations in all heifers. Except for vocalization, these effects were more severe in Au brac than in Friesian heifers. For all heifers, isolation-induced dist ress was positively correlated with the duration of social contacts th ey engaged with the pen mates prior to separation. Behavioral response s, i.e., struggling and vocalization, decreased when conspecifics were brought back, independently of their familiarity to the subject. In c ontrast, the heart rate decline induced by the entrance of conspecific s was more pronounced in response to reintroduction of pen mates. Thes e findings indicate that social isolation is a severe psychological st ress in cattle and that the mere sight of conspecifics reduces behavio ral distress regardless of peer identity. The isolation-induced distre ss depends on the genetic and rearing backgrounds of the heifers witho ut allowing to differentiate their respective effects. (C) 1997 Elsevi er Science Inc.