Fearful and associated responses of White Leghorn hens: effects of cage environments and genetic stocks.

Three measures of fearfulness were evaluated for hens of four genetic stocks after they had been kept in single-, 4-, and 6-bird cages for 26 or more weeks. Twelve hens of each stock and cage-environment combination were used (a total of 144 birds). Two tests involved latency of hungry hens to feed when confronted with fear-stimulating objects and one test was for latency to recover from induced tonic immobility. Results for the genetic stocks were inconsistent; strains identified as more fearful by a particular criterion were in some cases less fearful by another or did not differ. Hens kept in single-bird cages were either less fearful or showed a nonsignificant tendency, suggesting less fearfulness by all three criteria. Hens kept in 4-bird cages were typically similar in fearfulness to those in 6-bird cages. Fear-related responses were not clearly associated with plasma corticosteroids, body weights, mortality, or number of eggs laid. However, feather loss (in one test) was associated with escape and avoidance behavior of groups; stepwise increases in fearfulness with increasing group size were associated with similar increases in loss of feathers.