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Vitamin E in broiler health and performance

The importance of vitamin E adequacy to a strong immune response has been well documented--as has the reduction in immunocompetence with marginal vitamin E status. Now, university researchers continue to explore modes of action, while field work on commercial poultry operations is quantifying the economic returns that result from increased dietary vitamin E supplementation.

A study by Erf and Bottje (1996) concentrated on vitamin E status and specific immunity as measured by the proliferation and responsiveness of lymphocytes. The researchers noted that other work has reported interactions between vitamin E status and a wide spectrum of specific and nonspecific immune system components, ranging from structural aspects of lymphoid organs to the functional abilities of various immune cell populations. Researchers have also demonstrated improved response to a wide variety of organisms and diseases, including E. coli, Newcastle disease and infectious bursal disease (IBD), with increased vitamin E supplementation.

In this study, Erf and Bottje measured changes in lymphocyte development and function for both the B cells that develop in the bursa of Fabricius and the T cells that develop in the thymus. The treatments, starting on the day of hatch, included a basal diet supplemented with four levels of vitamin E: 0, 10,000, 50,000 and 100,000 IU per ton of feed (0, 11, 55 and 110 IU per kg).

The researchers reported three changes in immune development and function with increased levels of vitamin E. First, T cell proliferation in response to mitogenic stimulation increased significantly with increased vitamin E supplementation (Figure 1). Although this in vitro test does not directly test a T cell's ability to respond to an antigen, the researchers noted that mitogen responsiveness is an important diagnostic indicator of cell-mediated immunity.

By one measure (using phytohemagglutinin-P as the mitogen), lymphocyte proliferation was more than 90 percent greater in the birds receiving the highest level of vitamin E supplementation (100,000 IU per ton) than in those receiving no supplementation. Compared to the chicks receiving the control level of 10,000 IU per ton, birds receiving this highest level of dietary vitamin E had 15 percent greater lymphocyte proliferation.

Second, increasing dietary vitamin E supplementation appeared to influence the development of T cells as shown by the greater proportions of helper to killer T cells in the thymus, spleen and blood. The researchers noted that helper T cells produce cytokines that are required for the activation of both B cells and killer T cells. In addition, helper T cytokines also influence the class of antibody produced by the B cells, such as immunoglobulin (Ig) G or A, and can activate components of nonspecific immunity (especially macrophages) to increase the efficiency of that line of defense.

Third, there was a significant improvement in B cell activation with increased vitamin E supplementation when the broilers were injected with S. pullorum, a B cell antigen, at six weeks of age. Ten days later, the antibody response in chicks receiving the 100,000 IU/ton level was 29 percent greater than in those receiving no dietary vitamin E supplementation and 13 percent greater than in the chicks receiving 10,000 IU per ton.

Based on these results, the researchers said that increased vitamin E supplementation promises to better support immunocompetence, especially in young birds and those with a compromised immune system. That point also comes through clearly in field studies that measured improvements in health, performance and profitability with increased vitamin E supplementation in commercial operations.

Boren and Bond (1996) reported field work in which 1.52 million broiler chicks received either of two levels of dietary vitamin E supplementation in their starter feed: the standard 30,000 IU or 218,000 IU per ton of starter feed (33 or 240 ppm). Whole bird condemnations, septicemia-toxemia and inflammatory process were 34, 25 and 61 percent lower, respectively, in the broilers receiving the higher vitamin E level. Also, the feed-to-gain ratio was 2.3 percent (an average of five points) lower for birds receiving the increased supplementation.

These results were then calculated in economic terms for a complex with 1 million birds and typical feed costs, conversion rates and marketing weights. The reduced condemnation rate would produce savings of $7,668 per week, assuming a value of $0.3545 per pound of dressed broiler meat. These savings in themselves would pay for the $7,312 weekly cost of the increased vitamin E supplementation for 1 million birds. Then, the five point difference in feed-to-gain ratio would be worth an additional $25,750 per week for 1 million birds, assuming an average overall feed cost of $200 per ton. Even if feed cost only $150 per ton, the five-point improvement in feed efficiency would still save $19,315 per week for 1 million birds.

In a field study in Northern Ireland, McIlroy et al. (1993) measured the profitability of increased vitamin E supplementation when broilers were under far less disease pressure. In this work, 43 flocks (categories C and D in Table 1) exhibited no clinical signs of any disease, but bursal samples did show subclinical IBD. The birds received either 161,800 IU of vitamin E per ton of feed (178 IU per kg) or the operation's standard supplementation level of 43,600 IU per ton (48 IU per kg), with each treatment fed throughout the life of the birds. Performance was measured only by percentages to maintain confidentiality.

The researchers reported a significant 1.45 percent improvement in feed efficiency (P < 0.01) and a significant 2.2 percent increase in weight gains (P < 0.05) in the birds receiving the higher level of vitamin E supplementation. Because of the improved performance, these flocks also produced 10.3 percent greater net income (P < 0.05) than the flocks receiving the operation's standard supplementation level. In this work, the researchers also assessed the benefits of vitamin E in 36 flocks (A and B in Table 1) that faced even less disease challenge. Indeed, the researchers found neither subclinical IBD nor clinical signs of other diseases in these broilers. The performance and profitability differences by vitamin E supplementation level were less pronounced in these flocks, but the broilers receiving the increased vitamin E supplementation still produced 2 percent greater net profits.

The design of this study enabled the researchers to distinguish between returns from increased vitamin E supplementation by level of disease exposure, even though there were no clinical signs of disease. From a more practical standpoint for commercial production, the researchers also analyzed returns for the flocks as a whole--without the benefit of identifying which flocks had subclinical IBD from the outset.

By this analysis, the improved returns with increased vitamin E supplementation were similar to those for the flocks with subclinical IBD. Feed conversion and weight gains were improved 1.18 percent (P < 0.01) and 2.9 percent (P < 0.05), respectively, for all the flocks receiving increased vitamin E compared to those receiving the operation's standard supplementation level. Net returns were 9 percent greater (P < 0.05) with increased supplementation.

Other, still unpublished field studies have also found significant improvements in health and performance with increased dietary vitamin E supplementation. In one, feed conversion was improved by two points (1.1 percent) and infectious process was 25 percent less in the birds receiving 100,000 IU of vitamin E per ton of starter feed (110 IU per kg), compared to broilers receiving 17,500 IU per ton (19.25 IU per kg). Another company reported 26 percent less infectious process in birds that received 100,000 IU per ton of feed than in those that received 15,000 IU per ton (16.5 IU per kg).

Whitehead (1997) noted that field trials such as these "confirm the overall benefit from using higher levels of vitamins E supplementation routinely in broiler production. The extra cost of vitamin E can give an economic return by alleviating the immunological stresses universally present in modern commercial broiler systems."

The optimum levels and duration of feeding are difficult to establish precisely. The degree of protection necessary may depend upon the severity and type of immunological pressures induced by different vaccination, environmental and feeding programs as well as disease challenges. Nevertheless, it is now well established that the most efficient approach to vitamin E nutrition is to aim for enhanced histological status rather than merely avoidance of vitamin E deficiency.

References:

Boren, B., and P. Bond. 1996. Vitamin E and immunocompetence. Broiler Industry. Nov. 96.
Erf, G.F., and W.G. Bottje. 1996. Nutrition and immune function in chickens: benefits of dietary vitamin E supplementation. Proc. Arkansas Nutri. Conf., p. 113.
McIlroy, S.G., et al., 1993. Improved performance in commercial broiler flocks with subclinical infectious bursal disease when fed diets containing increased concentrations of vitamin E. Avian Pathology. 22:81.
Whitehead, C. 1997. Vitamin Nutrition for Broilers. RCD 9543, p.21.