Increasing Turkey Egg Production and Reproductive Efficiency

As a result of selective breeding strategies to increase turkey production in recent decades, turkeys' growth rates and body size have been maximized at the expense of their reproductive efficiency. Turkeys currently have the shortest reproductive cycle and produce the fewest eggs of any poultry species.

Commercial turkey breeders rely on management procedures to extend turkey hens' egg-laying period and discourage nesting and incubation. The breeders have found it increasingly difficult, however, to identify and manage nesting hens in commercial operations that typically consist of 20,000 to 30,000 hens per flock. Current management procedures are time-consuming, labor-intensive, and only moderately effective in forestalling the onset of nesting behavior and subsequent drops in egg production.

Physiological Factors

With funding from the National Research Initiative (NRI) Competitive Grants Program, researchers at the University of Minnesota are investigating physiological factors that control nesting behavior in turkeys. The scientists have discovered that elevated circulating concentrations of the hormone prolactin inhibit hens' ovarian function, stimulate nesting behavior, and decrease egg production.

With the long-term goal of increasing egg production by controlling amounts of circulating prolactin, the investigators have undertaken additional studies to learn more about the physiological factors regulating prolactin synthesis and release. The regulatory mechanisms governing secretion of prolactin have been shown to involve the hypothalamus (a region of the brain) and the pituitary gland.

VIP Hormone

The scientists have developed sophisticated surgical techniques to collect blood from tiny vessels connecting the hypothalamus and the pituitary gland. These blood vessels transport a crucial hormone vasoactive intestinal peptide (VIP)—from the hypothalamus to the pituitary gland.

Although the neuromechanisms regulating reproductive behavior are not yet clearly understood, VIP is a known physiological stimulator of prolactin secretion in turkeys. Studies have demonstrated, for example, that turkeys displaying nesting behavior have elevated brain levels of the hormone.

Immunization

The University of Minnesota scientists have designed a strategy to "immunize" turkeys against the effects of VIP by injecting them with additional VIP. This causes the turkeys' immune systems to generate antibodies against the hormone.

The antibodies neutralize the effects of VIP on the reproductive system, thereby decreasing circulating concentrations of prolactin, decreasing nesting behavior, and increasing egg production. In two recent studies, immunization of turkey hens against VIP resulted in a production increase of more than 30 eggs per hen during a 21-week period.

Impact

The potential of VIP immunization to increase turkey egg production is clear. Researchers currently are seeking ways to generate large quantities of pure VIP through genetic engineering and recombinant DNA technology.

The scientists recently isolated the gene encoding VIP in turkeys and have initiated studies to determine whether recombinant turkey VIP will prevent nesting behavior in turkey hens and increase egg production as effectively as the natural VIP. The results of this research are expected to help benefit the turkey indus try and, ultimately, the consumer by helping growers increase avian reproductive efficiency and egg production.

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