| Popis: |
Feather pecking and cannibalism in laying hens continues to be a serious welfare and economic problem in the egg industry, and presents a major obstacle to the adoption of non-cage production systems. This project examined internal and environmental factors involved in the development of feather pecking and cannibalism in one commercial laying strain (ISA Brown), with particular attention to changes associated with sexual maturation at about 16 weeks of age. A detailed study of behavioural and hormonal development in pen-housed pullets under constant environmental conditions revealed age-related changes in the same number, type and targeting of bird-to-bird pecks. Feather pecking, which began in juvenile birds between 5 and 10 weeks of age, was associated (on a per pen basis) with more severe pecking damage after the onset of lay. This resulted from increased vigorous feather pecking/pulling, vent pecking and aggressive pecking. Times spent preening and dustbathing also increased at sexual maturity. Increased pecking damage at the onset of lay coincided with physiological changes, most closely with increased plasma progesterone concentration. Large variability between pens in the extent of pecking damage illustrated the unpredictability of pecking problems. Investigation of the circumstantial link between damaging pecking and hormonal state (through experimental manipulations of the latter) proved to be problematic, and a direct causal link could not be demonstrated. The only evidence supporting such a link was from an experiment where acute administration of the anti-oestrogen tamoxifen resulted in reduced vigorous pecking and pulling (but not gentle pecking) at a novel pecking device (a bunch of string). There was no evidence of a relationship between birds' individual plasma hormone levels at 25 weeks of age and their feather pecking behaviour before or after sexual maturity. |
