THE ONTOGENY OF THERMAL NOCICEPTION IN DOMESTIC-FOWL - THERMAL STIMULUS-INTENSITY AND ISOLATION EFFECTS

Socially housed leghorn cockerels were confined to a heated grid (55, 57, or 59°C, Experiment 1; 59, 61, or 63°C, Experiment 2) and tested at posthatch ages of 14 days (Experiment 1) and 1, 3, 7, or 14 days (Experiment 2). In Experiment 1, chicks performed a discrete jump response only at 59°C. In Experiment 2, jump latency was inversely related to temperature at each age but significantly so only at 7 and 14 days posthatch. At the highest temperature, jump latency did not differ significantly across ages. At medium and low temperatures, latency increased from 1 and 3 to 7 days posthatch (antinociceptive effect) and decreased thereafter. Chicks raised in isolation from hatch to 7 days posthatch (Experiment 3) did not display the increased jump latency (antinociceptive effect) displayed by socially raised chicks. Developmental increases in jump latency may reflect stress‐induced antinociceptive concomitants of neophobia that emerge with age in this precocial species and social experience may be required for the normal development of this stress‐induced antinociception. Copyright © 1990 John Wiley & Sons, Inc.