Degree Type


Date of Award


Degree Name

Master of Science


Animal Science

First Advisor

Kristjan Bregendahl

Second Advisor

Anna K. Johnson


Commercial laying hens are typically induced to molt in an effort to cease egg production and extend their productive life for a second egg laying cycle. Furthermore, egg quality is improved and egg production is higher post-molt compared to pre-molt levels. This practice has been traditionally induced by a period of feed withdrawal ranging from 4 to 14 days accompanied by light restriction. However, there has been recent concern about the feed withdrawal method and its effects on laying hen well-being. Therefore, alternative methods have been examined. Low-energy molt diets are currently the most common method for inducing molt in laying hens, but they are not as effective at decreasing egg production during molt as feed withdrawal. For these reasons, we examined a 1-wk calcium pre-molt treatment that was followed 2 low-energy molt diets (soybean hulls and wheat middlings) compared to a 7 d feed withdrawal. During the calcium pre-molt treatment, hens were fed either a combination of fine (0.14 mm mean diameter) and coarse (2.27 mm mean diameter) CaCO3 or all-fine CaCO3, such that only the particle size of the calcium provided in the diets differed between the 2 treatments. When calcium is given to the hen in a fine particle size, it is more readily solubilized in the digestive tract and then hen may be deficient in calcium at night when it is needed for eggshell formation. Therefore, our hypothesis was that the fine-calcium pre-molt treatment would result in a more efficient molt compared to the traditional coarse-calcium treatment. The objectives of our study were to evaluate the effects of the calcium pre-molt treatment and low-energy molt diets or feed withdrawal on the behavior, production, and physiology of laying hens. We used a total of 981 Hy-Line W-36 laying hens (85 wk of age) that were housed 3 per cage with a 16 h photoperiod. During the calcium pre-molt treatment, hens had free access to feed and a 24 h photoperiod. During the 4 wk molt period, hens fed the low-energy diets had free access to feed, whereas the hens assigned to the feed withdrawal treatment had no feed for 7 d followed by restricted skip-a-day feeding (60 g/hen per feeding day). During the first 3 wk of molt the hens had an 8 h photoperiod and this was increased during the last week of molt to 12 h. Behavior was recorded for 4 h a day once during the baseline period, twice during molt, and twice post-molt for 2 postures (sitting and active) and 5 behaviors (feeding, drinking, non-nutritive pecking, preening, and aggression). Stress in the laying hens was assessed by a heterophil to lymphocyte ratio. Production data included egg production and related measures, feed consumption, body weight, and egg quality measures. Physiology data included measures of bone metabolism including bone-ash percentage and concentrations of plasma minerals, as well as fresh weights of the reproductive tract. Behavioral data was assessed using the PROC MIXED procedure of SAS, whereas the production and physiology data was assessed using ANOVA with JMP. A P-value ≤ 0.05 was considered significant in all comparisons. The calcium pre-molt treatment had no carryover effects on behaviors and postures of the laying hens during or post-molt. During molt, the hens assigned to the feed withdrawal treatment spent less time eating and drinking and more time being active compared to the hens fed the other 2 molt diets. However, there were no differences among the hens during the post-molt period for these behaviors. There were no differences in aggression, non-nutritive pecking, or preening. Overall, hens spent more time in non-nutritive pecking behavior during molt compared to post-molt. The treatments had no effect on the heterophil to lymphocyte ratios and they did not increase compared to baseline values. Comparing the production data, the fine-calcium pre-molt treatment was more efficient at inducing molt compared to the coarse-calcium pre-molt treatment by lowering egg production during molt and increasing egg production post-molt. This fine-calcium pre-molt treatment was successful regardless of which molt diet was fed. The feed withdrawal molt diet was the most efficient at decreasing egg production during molt. Between the 2 low-energy molt diets, the soybean hulls were more effective at inducing molt compared to the wheat middlings molt diet by decreasing egg production and reproductive tract weights during molt. There were no differences among the treatments in egg quality, however, these measures did increase post-molt compared to baseline levels. Additionally, any changes in bone metabolism measures during the molt period returned to baseline levels during the post-molt period, suggesting effects of molt are temporary. In conclusion, the treatments did not adversely affect the behaviors or postures of laying hens. The fine-calcium pre-molt treatment was effective at inducing a more efficient molt when used in combination with a low-energy molt diet or feed withdrawal. The low-energy molt diets, specifically the soybean hulls, were effective at inducing molt and can therefore be considered as alternatives to feed withdrawal for inducing molt.

Copyright Owner

Emily Rebecca Dickey



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107 pages