Spurred by the continuing quest to improve health and performance, a growing body of research is prompting the turkey industry to reconsider the basic concept of vitamin requirements. These were long considered to be the dietary levels necessary to prevent specific deficiency signs in a "typical" bird. Today, however, the desired vitamin requirements are more likely to be considered the dietary levels that permit optimum health and performance in turkeys produced under a variety of conditions.
The change is important, because vitamins are involved in all the biological functions that allow an animal to use feed components for health, growth, feed conversion and reproduction. For instance, the fine-tuning of amino acid and energy combinations for optimum performance will be largely wasted if vitamin intake isn't also optimum. As a result, the industry is recognizing that vitamin inadequacies do not have to approach clinical status before they compromise a producer's returns.
The industry is also recognizing that recommendations must be tailored to different situations when developing optimum vitamin allowances--the total vitamin levels from all dietary sources, including fortification (supplementation) and feedstuffs. Among the factors that influence these optimums are animal genetics, physiological makeup, nutritional and health status, stress levels, vitamin stability and bioavailability, feed management and environment. Optimum vitamin allowances will also contain margins of safety to ensure that intake does indeed meet projected levels.
The research underpinning this new approach has been conducted with most of the vitamins. One example is work with vitamin C. Under the old view of nutritional requirements, ascorbic acid was not considered an essential dietary nutrient in poultry and other species that can synthesize it. Yet studies with turkeys, broilers and also pigs have shown improved health and performance in animals receiving dietary vitamin C supplementation, especially during periods of stress.
Researchers at the University of Minnesota have reported significant improvements in the health and performance of turkey poults and breeding birds receiving vitamin C supplementation compared to unsupplemented controls. In the work with breeding birds, Noll et al. (1995) reported that hens receiving 200 ppm of vitamin C produced 6.5 percent more eggs (P < 0.10) than unsupplemented controls. Over the 24-week study, the supplemented hens produced six more eggs per hen, an increase that more than paid for the 15 cent per hen cost of the vitamin C. In the work with breeding toms, birds receiving 200 ppm of vitamin C had 12 to 15 percent greater concentrations of sperm (P < 0.05) than unsupplemented toms.
In the work with poults, Noll et al. (1996) studied vitamin C supplementation at 150 ppm in water during the two-week starter period. The supplemented poults had 6.5 percent greater feed intake (P < 0.10) and 5.5 percent greater water intake (P < 0.05) than controls. Such improvements are especially important during the starter phase, the researchers noted, because poults are under considerable stress, are often dehydrated and may have limited energy reserves in the remaining yolk sac. The poults given vitamin C also tended to be more uniform in body weight than controls.
Studies with increased supplementation of other vitamins have brought equally strong results. For example, the National Research Council (NRC) lists the vitamin E requirements of turkeys at 10,900 IU per ton of feed (12 IU per kg) to avoid clinical deficiency signs. However, vitamin E adequacy is also well recognized as necessary for a strong immune response, and reduced immunocompetence occurs before other signs of vitamin E inadequacy appear.
Ferket et al. (1993) reported that young poults which received 10 times the NRC requirement had increased phagocytic macrophages compared to those receiving the NRC requirement. It was not until vitamin E allowances were increased to 272,000 IU per ton, or 25 times the NRC requirement, that humoral immunity (to sheep red blood cells) was optimized.
In a recent survey of the turkey industry in North America, the average levels of vitamin supplementation were generally above the NRC requirements, suggesting that the industry recognizes these as baselines. However, much can still be done to improve vitamin intake levels or the efficiency with which vitamins are delivered to the birds.
A survey of turkey hatcheries by Grimes and Pardue (1996) found that 56 percent of them inject poults with vitamins post hatch. Although this shows that hatchery managers and other production personnel recognize the importance of vitamin adequacy, injection is also an expensive, labor-intensive method of delivery. Vitamin administration through the feed of both breeders and poults, and then continuing through the production period, would greatly reduce labor requirements and reduce the cost of vitamin delivery.
References:
- Ferket, P.R., et al., 1993. Vitamin E and performance, immunity and meat quality of turkeys. Proc. Carolina Poult. Nutri. Conf, p. 1.
- Grimes, J.L., and S.L. Pardue. 1996. A survey of commercial turkey hatcheries in the United States. J. Appl. Poult. Res. 5:231.
- National Research Council (NRC). 1994. Nutrient Requirements of Poultry. 9th rev. ed. National Academy Press.
- Noll, S.L., et al., 1995. Vitamin C supplementation in turkey breeder diets. Gobbles. 52 (8):6.
- Noll, S.L., et al., 1996. Vitamin C supplementation of poult drinking water. Gobbles. 53 (7):5.
