By Michael S. Lilburn
The commercial breeding sector of the turkey industry has been very successful at continually improving the commercial traits (i.e. body weight, breast muscle yield) that are the economic drivers of the industry. It has been recognized for many years that the continual selection for traits of economic importance may have negative correlated effects on reproductive efficiency. The turkey industry has partially countered this via the use of artificial insemination to maintain high levels of fertility, but there is no simple, identified management tool for optimizing production efficiency in commercial breeder hens. It is accepted that body weight control of turkey hens during rearing is essential for optimizing egg production, but physical restriction of hens as practiced in broiler breeders is not an accepted option. Thus, there is a need for studies whose objective is to control body weight in replacement hens via ad libitum, controlled feeding of low nutrient dense diets.
The primary objective of the research reported herein was to create different body weight groups during rearing via dietary manipulation. This was followed by individual weighing of hens at 24 weeks and allocating them into replicate pens of Heavy, Medium and Light body weight hens.
These body weight treatments were designed to bracket the target body weights recommended by the primary breeder, Hybrid. In addition to hen-day egg production and egg weight determinations, a sample of hens from each treatment were euthanized for carcass, reproductive organ and selected skeletal measurements at one week (30 weeks) and three weeks post-photostimulation (32 weeks). The dietary rearing treatments resulted in hens that weighed 24.45 and 23.0 lbs at 24 weeks, 26.6 and 25.6 lbs at 30 weeks and 24.8 and 24.1 lbs at 42 weeks. The Heavy, Medium, and Light hens weighed 27.6, 26.3, and 24.3 lbs at 30 weeks and 25.6, 24.6, and 23.0 lbs at 42 weeks.
After the onset of hen-day egg production, the Light treatment hens had significantly better hen-day egg production than either the Medium or Heavy hens. The Heavy hens had approximately a 2 gram improvement in egg weight at 4, 8, and 10 weeks of egg production compared with the Light hens. The Medium weight hens were intermediate. At 30 weeks of age, hens in the Heavy, Medium and Light body weight groups had corresponding differences in carcass weight, but there were no significant effects on shank length, follicle number or reproductive tract weight. At 32 weeks, there were also no body weight treatment effects on follicle number or reproductive tract weight, but there was a progressive decrease in femur, tibia and shank length in the sampled hens as body weight declined.
Total carcass lipid (% DM) increased from 42% to 51% between 30 and 32 weeks of age, but there were no significant differences between body weight groups. The greatest increase in carcass lipid occurred in the Light body weight group (41.7% to 53.5%), and this resulted in a marginal age by body weight interaction (P < .087). Across all three body weight groups, there was a significant decline in body weight between 30 and 42 weeks of age.
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