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Fluctuating asymmetry (FA, i.e., deviations from symmetry in otherwise symmetrical bilateral traits) has been suggested as an integrated indicator of an animal’s ability to cope with the sum of challenges it experiences during its development. The validity of FA as a welfare indicator for broiler chickens is controversial, since some previous studies found that FA levels were lower under conditions that could be expected to improve welfare, whereas other studies did not find such an effect. Thus, the relation between FA and welfare in broiler chickens requires further study. We evaluated how FA was affected by a stressor (i.e., increasing stocking density) previously found to impact on several other welfare indicators measured on the same flocks. Birds were stocked at 2.4, 5.8, 8.8, 12.1, 13.6, 15.5, 18.5, and 21.8 birds/ m2 (4 pens per density). At 39 days of age, 8 birds were selected randomly per pen, plus an additional 11, 17, and 17 birds from each replicate of the 5.8, 13.6, and 21.8 birds/m2 treatment, respectively. After euthanasia, FA of 3D head configuration, 3D tarsometatarsus configuration, eye size, wattle size, outer toe length, middle toe length, shank length, tarsometatarsus length, and tarsometatarsus width (at the joint, spur and slimmest point) was determined. A mixed linear model (fixed factors: density, bodyweight, sex, and their interactions, random factors: replicate and pen) was used to evaluate the effects on the separate characters and a composite index of FA (combining data on all characters). FA of middle-toe length was the only separate character that increased with increasing density (F1,12.9=9, P=0.01, 0.46 vs. 0.59 mm at the lowest and highest density, respectively). Nevertheless, the composite index tended to increase with density (F1,21.7=4, P=0.06, -0.06 vs. 0.04 at the lowest and highest density, respectively), which may indicate decreased welfare. However, one of the assumptions of fluctuating asymmetry is that the animal is subjected to the same environmental influences on both sides. This assumption may not be fulfilled when leg deformations occur, as these may lead to asymmetric changes in bone growth by altering the division of force over the 2 legs. This raises some concerns on the applicability of FA analysis of broiler chicken legs, especially because stocking density did not affect the asymmetry of the head.
Originele taal-2Engels
TitelBook of Abstracts. 9th European Symposium on Poultry Welfare
Aantal pagina's1
Plaats productieUppsala
UitgeverijWorld's Poultry Science Association
StatusGepubliceerd - 17-jun-2013
Event9th European Symposium on Poultry Welfare - Uppsala, Zweden
Duur: 17-jun-201320-jun-2013

ID: 2166645