生産性だけではない：英国のデュアルパーパス品種イクワースにおける竜骨骨折と福祉問題の調査

This study explores welfare concerns, with a focus on keel bone fractures (KBF), in the traditional British breed Ixworth, a non-commercial dual-purpose chicken. Although keel bone fractures were lately discussed in the context of high laying performances, 69.2 % of hens exhibited KBF, particularly in the caudal region, challenging the notion that lower-performing breeds are less prone to this issue. The location of these fractures indicates that incomplete bone ossification may play a crucial role. Notably, we found that egg size during critical ossification age (31, 34 and 35 weeks of age (woa)), rather than total egg count, was the primary risk factor for KBF. Beyond KBF, other welfare indicators such as plumage condition and footpad lesions were evaluated. Plumage damage peaked at 50 woa but showed recovery towards the end of the laying period. The prevalence of footpad lesions, however, increased with age, reaching a peak at 70 woa. A moderate correlation between egg production and footpad lesions was identified, suggesting increased laying may exacerbate this issue. Our findings demonstrate that traditional breeds like the Ixworth might also show welfare problems, including KBF and footpad lesions. These results emphasize that reduced productivity does not necessarily mitigate welfare risks. Instead, risk factors like egg size and bone development should be considered in future research and breeding. Expanding this investigation to other breeds could further enhance our understanding of welfare challenges in alternative poultry systems.