The Effects of Physical Feed Restriction on Body Composition and Reproductive Performance of Commercial Large White Turkey Breeder Hens and Its Subsequent Economic Impact

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Title: The Effects of Physical Feed Restriction on Body Composition and Reproductive Performance of Commercial Large White Turkey Breeder Hens and Its Subsequent Economic Impact
Author: Crouch, Andrew Neil
Advisors: Vern Christensen, Chair
Jesse Grimes, Co-Chair
Kenneth Krueger, Member
Tom Johnson, Member
Abstract: Large White turkey breeder hens were tested in a 4 X 3 factorial design to evaluate the effect of three different levels of physical feed restriction on subsequent reproductive performance. The feed treatments comprised: Control Control (CC) - ad libitum fed throughout the study, Control Restricted (CR) - feed restricted from 16-24 WOA, Restricted Control (RC) - feed restricted from 3-16 WOA and Restricted Restricted (RR) - feed restricted from 3-24 WOA. Feed restriction was implemented so that restricted fed hens achieved a 45% reduction in BW as compared to Control hens at 16 WOA. From 16-24 WOA restriction was implemented to maintain a slight increase in BW. At the completion of the respective restriction period, hens were gradually released back to ad libitum feeding. At the time of photostimulation (30 WOA) all treatments were divided into sub-treatments by weight: HEAVY, MEDIUM and LIGHT, resulting in four treatments with three sub-treatments within each. All hens continued on ad libitum feeding throughout a 20 wk lay cycle. Body weight (BW) for all treatments differed significantly (P<.05) at 16 and 30 WOA. At the end of lay (53 WOA) treatment CR no longer significantly differed in BW from treatment CC as did treatment RR no longer significantly differ in BW from treatment RC. Treatment CC reached maximum feed consumption at 12-15 WOA, whereas restricted treatments CR, RC and RR did not reach maximum feed consumption until just prior to photostimulation (30 WOA). At the end of the study, cumulative feed consumption was significantly less for restricted treatments. Previous research reported (Trial 1), concluded that restricting hens early in rearing preceding a lay cycle in the Winter season resulted in numerical increases in egg production. The time period for this study (Trial 2) was inverted from that of Trial 1, in that hens were photostimulated for Summer season egg production. For Trial 2, RC and RR hens laid significantly more eggs than did CC and CR hens for the first 1-5 weeks of lay (wol). However, within Trial 2, once house temperature increased to over 80-85 oF RC and RR egg production suffered dramatically, cumulating in a significant decrease in production. Hens restricted early in rearing (3-16 WOA) also cumulatively laid more soft shelled eggs and reported a decrease in hatch of fertile eggs for Trial 2. Determining why hens restricted fed early in rearing decreased egg quality and production soon after peak lay in the Summer season was a focal point of this study. Due to the fact that hens considered 'out-of-production' had circulating levels of prolactin up to 5 times less than that of hens 'in-production', incubation behavior and broodiness were not considered to be a factor. Therefore, body composition, carcass conformation and hormonal and enzyme activity were analyzed to determine the effect feed restriction had on each of these variables. Early feed restriction reduced the percent body fat of breeder candidates while increasing the percentage of moisture and ash. Relative weights of organ and tissues samples revealed that early feed restriction resulted in a larger percentage of crop, liver and total visera for restricted fed hens. Early feed restriction also increased the percentage of bone structure regarding femur and keel bone development. However, treatments which were restricted fed early exhibited a significant reduction in absolute and relative weight of breast and thigh muscles in comparison to ad libitum fed hens at 15 WOA. Although these differences were not reported at 30 WOA on a relative basis, absolute weights remained significantly different with respect to breast muscle. This same variation with regards to breast muscle was then noted throughout the 20 wk lay cycle. The sub-treatment 'weight', LIGHT, MEDIUM and HEAVY hens responded very much in the same manner irrespective of their initial treatment (CC, CR, RC and RR). This analysis results in the conclusion that a LIGHT hen is destined to be a LIGHT hen irrespective of her feed allotment. This phenomena is more than likely attributed to the genetic material compiled by each hen. LIGHT hens within each treatment exhibited a greater tendency for compensatory growth as compared to MEDIUM and HEAVY hens. However, egg production suffered within LIGHT hens as these hens at times laid a significantly smaller and undesirable quality of an egg. MEDIUM hens expressed a larger portion of BW through breast muscle, therefore appearing to make them the more reproductively oriented sub-treatment. In fact, MEDIUM hens did lay at a numerically higher hen housed production percentage. In conclusion, if turkey breeder hens are to lay in the Winter season, restricting feed early in rearing can prove economically beneficial. However, if hens are to lay during the Summer season, feed restriction early in rearing appears to be detrimental to subsequent reproduction in that initial breast and fat loss is never fully recuperated for the lay cycle. Therefore, feed restriction should be limited to later in rearing if any economic benefits are to be reported.
Date: 2000-10-10
Degree: MS
Discipline: Poultry Science

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