Use of dietary thyroxin as an alternative moulting procedure in turkey breeder hens

换羽是一种自然的过程，在繁殖季节结束后，在迁徙之前促进羽毛的更换。由于在繁殖周期之间也需要这种生理事件，因此已经开发了人工换羽技术来诱导家禽的第二个产卵期。然而，大多数方法都是基于饲料和水的提取，虽然非常有效，但这种方法会造成严重的压力和严重的健康和福利问题。因此，加拿大不鼓励使用这种做法，在每个繁殖期后更换种鸡群。这不是一个问题，只要替代育种持续可用。然而，疾病爆发通常会导致立即禁止禽鸟迁徙，从而扰乱受精卵供应链，迅速使整个行业崩溃。强制换羽可能是唯一的选择。然而，出于对动物健康和福利的考虑，需要建立新的、有效的、负担得起的和可接受的替代饲料和水限制技术。根据本实验站的初步试验和笼养鸡试验结果，饲粮中添加甲状腺素可诱导脱毛，且对鸡的健康和福利影响最小。然而，在火鸡中，所需的最低剂量和饮食中甲状腺素对第二次生殖周期的影响仍有待确定。因此，本研究旨在设计饲粮中添加甲状腺素诱导雏火鸡种鸡换羽的方案。反过来，这项研究的结果将有助于制定新的战略，这些战略将在经济上可行，在伦理上可接受，以延长火鸡群的繁殖寿命。

Moulting is a natural process which promotes the replacement of feathers at the end of a breeding season before migration. Since this physiological event is also required in-between reproductive cycles, artificial moulting techniques have been developed to induce a second egg-laying period in domestic birds. However, most methods are based on feed and water withdrawal, and although very efficient, such protocols result in severe stress and serious health and welfare problems. Thus, the use of this practice is discouraged in Canada and breeder flocks are replaced after each reproductive period. This has not been a problem, as long as replacement breeders are continuously available. However, disease outbreaks usually result in an immediate ban on bird movement, and would thus disrupt the fertile-egg supply chain, rapidly collapsing the entire industry. Force moulting might then be the only alternative. Nonetheless, due to animal health and welfare concerns, new effective, affordable, and acceptable alternatives to feed and water restriction techniques need to be established. Based on a preliminary trial performed in our research station and results obtained in caged chickens, dietary thyroxin supplementation can induce moult with minimal impacts on birds' health and welfare. However, in turkeys, the minimum dose required and the impact of dietary thyroxin on the second reproductive cycle still remain to be determined. Thus, this study aims at designing protocols to induce moult in spent turkey breeder hens using dietary thyroxin supplementation. In turn, results from this study will help develop new strategies that will be economically feasible and ethically acceptable to extend the reproductive life of turkey flocks.