A case of clubbed down syndrome in broilers

This study presents a case of clubbed down syndrome in conventional broilers. During the first week of life, severe growth retardation was observed in approximately 25% of the flock. The growth-retarded chicks weighed only 45 g and showed a typical feather disorder which was most apparent on their abdomen and was defined in literature as typical for clubbed down syndrome. Necropsies, histology, biochemical analysis of blood and liver samples, serology and different PCR tests were performed in broilers to assess the aetiology of the clinical signs that were present in the affected broiler farm. Because of the suspicion of a possible link with the broiler-breeder farms, different investigations including serology, PCR and feed analysis were also performed on these farms. The results suggest that an accidentally excessive amount of calcium and iron in the feed of broiler-breeders, 3 weeks prior to first clinical signs in broilers, led to the development of clubbed down in the offspring, because of a relative Zn-deficiency in broiler-breeders and an absolute Zn-deficiency in the hatching eggs that were produced during this period. This appeared to be a reversible process as no clinical signs were observed in younger offspring of these broiler-breeders after they had consumed more of the new batch of feed. A potential involvement of Astrovirus could not be completely ruled out. This study demonstrates the importance of correct mineral concentrations in broiler-breeder feed and the impact it can have on the development of the offspring.

本研究报道了一例常规养殖肉鸡的棍棒状羽毛综合征（clubbed down syndrome）病例。在肉鸡出壳后的第一周，鸡群中约25%的个体出现严重生长迟缓症状。生长迟缓的雏鸡体重仅为45克，表现出典型的羽毛异常，该异常以腹部最为显著，文献中将其定义为棍棒状羽毛综合征的典型特征。研究人员对患病肉鸡场的肉鸡开展了尸检、组织学检测、血液与肝脏样本生化分析、血清学检测及多种聚合酶链式反应（PCR）检测，以明确该临床症状的病因。由于怀疑该病症与肉鸡种鸡场存在关联，研究人员同样对该类种鸡场开展了血清学检测、PCR检测及饲料成分分析等多项调查。研究结果显示，在肉鸡首次出现临床症状的前3周，种鸡饲料中钙与铁含量意外超标，造成种鸡出现相对锌缺乏，同期产出的孵化蛋则存在绝对锌缺乏，最终导致子代肉鸡发生棍棒状羽毛综合征。该过程具备可逆性：当种鸡更换为新批次饲料后，其后续产出的子代肉鸡未再出现临床症状。星状病毒（Astrovirus）的潜在致病作用无法完全排除。本研究证实了肉鸡种鸡饲料中矿物质浓度配比合理的重要性，以及该配比对子代生长发育的显著影响。