PRESENCE OF CUES FROM STRESSED CONSPECIFICS INCREASES REACTIVITY TO AVERSIVE EVENTS IN CATTLE - EVIDENCE FOR THE EXISTENCE OF ALARM SUBSTANCES IN URINE

In gregarious species like cattle, the presence of partners often affe cts fear-related reactions. The first experiment investigated whether behavioral and physiological responses to stress depend on the emotion al state of the partner. Aubrac heifers were presented with food in a novel environment. Compared to heifers in the presence of a companion that had been previously habituated to the environment without receivi ng shocks, those in the presence of a companion animal that had previo usly received electric shocks in that environment had a stronger incre ase of cortisol response (11.2 +/- 1.1 vs. 7.4 +/- 0.9 ng/mL), showed a significantly longer latency to feed (60.1 +/- 12.3 vs. 17.5 +/- 5.9 s), and fed more slowly (54.5 +/- 11.4 vs. 110 +/- 7.3 s), After repe ated exposure to the test conditions, when heifers of both treatments fed rapidly after entrance, response to an unexpected air blast from t he feeding bucket was measured. Heifers in the presence of a stressed companion showed an increased latency to feed again compared to those with a nonstressed companion (44.5 +/- 5.1 vs. 22.8 +/- 4.3 s). Stress ed companions urinated during tests; therefore the second experiment i nvestigated whether heifers respond differently to urine collected fro m stressed and nonstressed conspecifics. In a first test, heifers were presented with food on a grid in a bucket in a novel environment. The y had a longer latency to feed when the bucket contained urine from st ressed rather than from nonstressed conspecifics underneath the grid ( 128.1 +/- 9.6 vs. 108.2 +/- 4.9 s). In a second test, heifers were pre sented with a novel object in a familiar environment. Heifers showed a ion latency to explore the object when it had been sprayed with urine from stressed compared to urine from nonstressed conspecifics (215.2 +/- 45.0 vs. 25.8 +/- 8.6 s). The results show that heifers perceive t he state of increased stress of conspecifics and become more fearful a s a result. They further show that this perception is at least partly mediated by olfactory cues in the urine. (C) 1998 Elsevier Science Inc .