Differential effects of handling on isolation-induced vocalizations, hypoalgesia, and hyperthermia in domestic fowl.

ABSTRACT

The effects of handling and subsequent brief isolation on vocalizations, thermal nociception, and thermoregulation were examined in 7-day-old cockerels. In Experiment 1, fifteen min of isolation elicited more vocalizations in handled than nonhandled chicks. Nonhandled chicks exhibited longer response latencies than handled chicks. In general, isolated chicks exhibited longer jump response latencies (i.e., hypoalgesia) on hot-plate tests than chicks tested immediately upon removal from the brooder. Compared to handled chicks tested immediately, all other groups exhibited increased core body temperatures. Experiment 2 examined these handling and isolation effects after 15 min of isolation with or without conspecifics. Chicks isolated alone vocalized more than chicks isolated with conspecifics. As in Experiment 1, handled chicks vocalized more than nonhandled chicks. Nonhandled chicks exhibited longer response latencies than handled chicks on hot-plate tests. Isolation-induced hypoalgesia was observed only in handled chicks that were isolated without conspecifics. Core body temperatures were highest in chicks isolates without conspecifics. Additionally, chicks isolated with conspecifics exhibited higher core body temperature than chicks tested immediately. Decreased core body temperature due to handling exposure was observed only in chicks tested immediately. These results demonstrate that isolation effects on vocalizations and nociception are primarily due to social isolation and that isolation effects on thermoregulation are a result of both social and environmental factors. Moreover, the increase in isolation-induced vocalizations in handled animals does not correlate well with the decrease in isolation-induced hypoalgesia and hyperthermia displayed by handled animals.