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Hedge poultry health bets with vitamin C

Because poultry synthesize vitamin C in their kidneys, supplementation has long been considered unnecessary. In an ideal world, that may be true. But few birds live in an ideal world, free from such stresses as heat and handling, which may affect the adequacy of the ascorbic acid that they synthesize.

Today, a host of research studies and field experience suggests that the average broiler, breeder, layer or turkey may come up short in responding to stress if it relies solely on its own vitamin C-synthesizing capacity. These studies suggest that dietary supplementation can help provide adequate tissue levels.

Although it has not been determined exactly how vitamin C supplementation helps negate the effects of stress, several avenues have been suggested:

  • Stress itself increases corticosterone production, which causes a depletion in adrenal vitamin C stores and hampers the immune system. Vitamin C also gives the immune system a boost by its involvement in collagen synthesis, wound healing and bone formation. Collagen is a component of epithelial tissue, an important natural barrier to pathogens.
  • In studies that measured the metabolic effects of heat stress on chickens, supplemental vitamin C also appeared to help restore plasma electrolyte levels associated with dehydration to normal levels, and to lessen the plasma protein response that indicates tissue protein catabolism. In other studies on carcass yields, vitamin C supplementation appeared to maintain tissue hydration by stabilizing plasma and tissue electrolyte levels in birds subjected to standard preslaughter stresses, such as cooping and feed and water deprivation.
  • Interest in the cellular antioxidant role of vitamin C is also spurring research on its effects on poultry health.

 

The level of dietary supplemental vitamin C needed to help combat the harmful effects of stress depends on a number of factors, including the type and severity of stress and the age and reproductive status of the bird. However, research results have not been sufficiently uniform to establish supplementation levels, says North Carolina State researcher Dr. Sam Pardue.

The poor stability of ascorbic acid has also made it difficult to conduct consistent research, Pardue notes. More stable forms of vitamin C, now on the market, should make instability a problem of the past.

 

Growing Birds and Vitamin C

Research on supplemental vitamin C for stressed growing birds shows benefits from beginning to end, and even beyond slaughter. Whether the stress comes from necessary management practices like beak trimming and vaccinations or from disease, heat stress or preslaughter cooping, studies have shown that the performance of growing birds receiving dietary vitamin C exceeds that of unsupplemented birds.

Without supplemental vitamin C, the young chick may be particularly handicapped in responding to stress, because the ability of poultry to synthesize vitamin C appears to be age related. It has been estimated that the day-old chick's ability to synthesize C is only one sixth to one third that of a three- to four-week-old bird.

North Carolina researchers (Pardue and Williams, 1990) found that ascorbyl phosphate injections of 1,000 µg per bird for chicks and 1,500 µg for poults helped reduce the stress resulting from beak trimming. Chicks and poults receiving supplemental vitamin C by injection or through drinking water showed increased early growth rates in this study (Figure 1).

 

Figure 1

As the birds grow and face new environmental and immunological stress, either alone or in combination, the benefits of supplemental vitamin C continue. Gross (1988c) reported that heat-induced mortality in Leghorn chicks fed 330 ppm of supplemental vitamin C was zero, compared to 40 percent in unsupplemented chicks. Levels above 330 ppm were not shown to favorably affect livability.

Because heat and other environmental stresses reduce immune response, vitamin C needs apparently increase in the presence of infectious disease. Pardue et al. (1985a) reported that antibody response to sheep red blood cells was suppressed during heat stress but increased when chicks received 1,000 ppm of dietary vitamin C. Other researchers found that pericarditis or death was significantly less when 300 ppm of vitamin C was added to the diet one day before  E. coli infection. In this study, chicks receiving 220, 440 or 660 ppm of vitamin C showed significant reductions in morbidity and mortality. The vitamin was most effective during periods of low to moderate stress; supplementation did not reduce the incidence of pericarditis or mortality during severe stress.

Other studies have found that broilers that were exposed to both heat stress and coccidiosis lost less weight when their diet was supplemented with 1,000 ppm of vitamin C. This is important because decreased feed intake tends to increase the susceptibility of chicks to infectious disease.

At the end of the production period, as broilers face the additional stresses of catching, cooping, feed and water withdrawal, and hauling, vitamin C remains important to production performance, according to various studies. The stresses of marketing appear to alter the birds' electrolyte balance, which in turn can cause the birds to dehydrate. Satterlee et al. (1989) reported that this dehydration was reduced when 1,200 ppm of vitamin C was added to the broilers' drinking water 24 hours before slaughter.

The positive benefits from this reduced shrink continue past slaughter. In three studies that added 488 to 1,200 ppm of supplemental vitamin C to drinking water 20 to 32 hours before slaughter, whole chilled carcass yields were significantly greater, ranging from 0.45 to 1.81 percent. In one study (Krautmann et al., 1990), breast meat yield was also significantly increased, by 0.86 to 1.36 percent, in vitamin C-supplemented birds (Figure 2).

 

Figure 2

Research into the interaction between simultaneous stressors and vitamin C levels continues. University of Illinois researchers are examining the cumulative effects of heat stress, disease (coccidiosis) and beak trimming on broiler performance and the role that vitamin C can play in alleviating these effects. In the studies to date, Dr. Paul Harrison and graduate student J.S. McKee have included 150 or 300 ppm of supplementary vitamin C in corn-soybean rations.

"Added vitamin C did not eliminate the effects of stress-the chicks still responded to the stress," Harrison says. "But the negative effects, from both a production and a biological standpoint, were reduced."

 

Breeders and Layers

Since ascorbic acid is involved in the synthesis of steroid hormones, including the sex hormones, it is not surprising that research has shown that supplemental vitamin C may favorably affect reproductive performance in poultry during stress.

Like other birds, breeding and laying hens exhibit heat stress in a number of ways. The metabolic abnormalities include elevated corticosteroid levels, altered acid-base balance and depressions in immune function and reproductive ability.

A 1990 Minnesota study (Cheng et al.) found that mortality was more than one percent less during a three-month period when older heat-stressed hens received 100 or 200 ppm of dietary ascorbic acid. Both levels of ascorbic acid also favorably affected internal egg quality and eggshell quality.

But the benefits appear to continue even when heat stress is absent or minimal. A North Carolina study (Peebles and Brake, 1985) reported benefits from vitamin C supplementation in both hot and cooler weather. With supplementation at 0, 50 and 100 ppm, egg production, hatch of fertile eggs and number of chicks increased during both parts of the study. The researchers say this indicates a role for supplemental vitamin C even when heat stress is not an issue.

The need for supplemental vitamin C has also been found in male birds. For example, Dobrescu (1987) reported that breeder toms whose feed was supplemented with 150 ppm had 28 percent greater semen volume and 31 percent higher sperm concentration.

 

References:

  • Cheng, T.K., et al., 1990. Effect of environmental stress on the ascorbic acid requirements of laying hens. Poultry Sci. 69:774.
  • Dobrescu, O. 1987. Vitamin C addition to breeder diets increases turkey semen production. Feedstuffs. 59:18.
  • Gross, W.B. 1988c. Effect of ascorbic acid on the mortality of Leghorn-type chickens due to overheating. Avian Dis. 32:561.
  • Krautmann et al., 1990. Practical applications of ascorbic acid for poultry. Ascorbic Acid in Domestic Animals, Proc. 2nd Symp., Kartause Ittingen, Switzerland. P. 292.
  • McKee, J.S., and P.C. Harrison. 1995. Effects of supplemental ascorbic acid on the performance of broiler chicks exposed to multiple concurrent stressors. University of Illinois.
  • Pardue, S.L., et al., 1985a. Role of ascorbic acid in chicks exposed to high environmental temperature. J. Appl. Physiol. 58:1511.
  • Pardue, S.L., and S.H. Williams. 1990. Ascorbic acid dynamics in avian neonates during stress. Ascorbic Acid in Domestic Animals, Proc. 2nd Symp., Kartause Ittingen, Switzerland. P. 28.
  • Peebles, E.D., and J. Brake, 1985. Relationship of dietary ascorbic acid to broiler breeder performance. Poultry Science. 64:2041.
  • Satterlee, D.G., et al., 1989. Vitamin C amelioration of the adrenal stress response in broilers being prepared for slaughter. Comp. Biochem. Physiol. 99:569.

 

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