University of Guelph, Department of Animal and Poultry Science, Guelph, Ontario, Canada, N1G 2W1.
Poult Sci. 2010 Jan;89(1):96-107. doi: 10.3382/ps.2009-00294.
In the turkey industry, molting is traditionally achieved by reducing photoperiod and withdrawing feed and water for several days. Although it is the most effective method, this practice is discouraged in Canada and alternative strategies need to be established. Thyroid hormone levels naturally change during molt, and dietary thyroxine (T4) supplementation was previously shown to induce molt in chickens. This study aimed at evaluating the effectiveness of supplemental dietary T4 in inducing molt in spent turkey breeder hens. One hundred twenty 75-wk-old hens were randomly divided into 4 groups (5 floor pens/replicates, 5 hens each) with the control group kept under a 14-h photoperiod and fed a breeder's diet throughout, whereas hens from the 3 other groups were supplemented with 40 ppm (45.76 mg/kg) T4 for 10 d. One treatment group was maintained under 14 h of light and fed a breeder's diet, whereas the 2 others were subjected to a drop in photoperiod to 6 h during or after supplementation and then were fed a maintenance diet. Egg production, feed intake, BW, molt, and plasma levels of T4, prolactin, and luteinizing hormone were measured. All treated hens ceased laying by d 20; however, several individuals spontaneously returned to lay when left on 14 h of light, suggesting incomplete involution of the reproductive tract. Supplementation significantly reduced feed consumption and induced rapid BW loss. All hens returned to their initial weight by the end of the experiment. Most treated hens initiated molt by d 8 of supplementation and all completed molt by d 37. Plasma T4 in treated hens increased significantly by d 3 (P < 0.05) and remained significantly higher than in controls until d 9 (P < 0.01). Levels returned to initial values by d 35. Prolactin levels did not appear to be influenced by T4 but were mainly dependent on photoperiod and reproductive stage, whereas luteinizing hormone levels remained low throughout. In summary, dietary supplementation with 40 ppm (45.76 mg/kg) T4 was successful in inducing molt in turkey breeder hens. However, dropping the photoperiod was necessary to completely reset the reproductive system.
在火鸡产业中，传统的换羽方法是通过减少光照时间并停止投喂和供水数天来实现。尽管这是最有效的方法，但在加拿大，这种做法是不受鼓励的，因此需要建立其他替代策略。甲状腺激素水平在换羽期间会自然变化，并且先前的研究表明，日粮中添加甲状腺素（T4）可以诱导鸡换羽。本研究旨在评估补充日粮 T4 对淘汰种用火鸡母鸡换羽的效果。将 120 只 75 周龄的母鸡随机分为 4 组（每组 5 个鸡笼/重复，每个鸡笼 5 只母鸡），对照组母鸡保持 14 小时光照并全程投喂种鸡日粮，而其余 3 组母鸡则在 10 天内每天补充 40 ppm（45.76mg/kg）T4。其中一组处理组在 14 小时光照下继续投喂种鸡日粮，另外两组在补充期间或补充后光照时间减少至 6 小时，然后投喂维持日粮。测量产蛋、采食量、体重、换羽情况以及 T4、催乳素和促黄体生成素的血浆水平。所有接受处理的母鸡在第 20 天停止产蛋；然而，当将它们留在 14 小时光照下时，一些个体自发地恢复产卵，这表明生殖道的不完全退化。补充 T4 显著降低了采食量并导致体重迅速下降。所有母鸡在实验结束时体重恢复到初始水平。大多数接受处理的母鸡在补充后的第 8 天开始换羽，所有母鸡在第 37 天完成换羽。处理组母鸡的血浆 T4 水平在第 3 天（P<0.05）显著升高，并在第 9 天（P<0.01）前一直显著高于对照组。T4 水平在第 35 天恢复到初始值。催乳素水平似乎不受 T4 影响，但主要取决于光照时间和繁殖阶段，而促黄体生成素水平一直较低。总之，日粮中添加 40 ppm（45.76mg/kg）T4 成功诱导了淘汰种用火鸡母鸡换羽。然而，需要降低光照时间才能完全重置生殖系统。
