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Vitamin C and reducing fear-based behavior

Vitamin C and Reducing Fear-Based Behavior

Fear is a vital defense mechanism for self-preservation of birds in the wild, but in the controlled environment of a commercial poultry operation, it's generally counterproductive. Panic, hysteria, attempts to flee and other fearful responses can quickly compromise a bird's welfare and performance, whether the response is prompted by exposure to people, new birds or environmental changes.

A growing body of research has shown significantly dampened fear in poultry receiving supplemental vitamin C compared to unsupplemented controls. Researchers have no hard estimates of the total value of this reduced fearfulness to producers, but studies have shown a significant benefit even when the results are limited to better feed efficiency.

Jones (1996) noted that in two studies involving 22 commercial units, feed:gain ratios were significantly correlated to fearfulness, in this case from exposure to humans. Feed efficiency in these operations ranged from 1.79 to 2.10, and the researchers reported that 28 percent of the variation could be attributed to fear of humans. Thus, an improvement of 0.09 unit in feed conversion would be possible if the farm with the most fearful birds reduced response levels to those of the least fearful.

Studies with vitamin C and fear-related behavior have generally begun supplementation 24 hours before the birds would face a fear-inducing stimulus. The stimuli used have included exposure to a novel object, placement in a new environment and brief manual restraint to induce "tonic immobility"--the instinctive response of basically playing dead that is characterized by both motor inhibition and loss of the righting response. The length of time that poultry remain tonically immobile is directly related to the intensity of their fear when restrained.

Typical of the studies to date is one with broiler chicks (Satterlee et al., 1994) in which both the length and the intensity of fearful responses were reduced in vitamin C-supplemented birds compared with unsupplemented controls. Vitamin C was administered at the level of 1,000 ppm in the drinking water for at least 24 hours, and the researchers induced fear either by placing the chicks in a new environment or by holding them down for 15 seconds to induce tonic immobility.

In the new environment, fear was measured by the time that the chicks remained frozen or made no sound (Table 1). The supplemented birds began moving again almost twice as quickly (P < 0.03) as controls, and they began vocalizing about 33 percent quicker (P < 0.05). There was also a tendency for the supplemented birds to resume walking sooner, and to walk more, after they were placed in the new environment.

Following restraint to induce tonic immobility, supplemented birds were also much quicker to resume movement than the controls. The time from onset until the first head movement was 44 percent less (P < 0.04) in the supplemented chicks, and these chicks righted themselves about twice as quickly. The results showed significant reductions in nonspecific, underlying fearfulness in the vitamin C-supplemented birds, the researchers reported. This study did not measure possible variations with different innate levels of fearfulness. In more recent work with Japanese quail, which are a particularly useful model for other domestic poultry, Jones et al. (1999) assessed vitamin C supplementation in two genetic lines, which had been identified for either low or high innate fearfulness.

Supplementation was again 1,000 ppm of vitamin C in the drinking water for 24 hours, and the researchers measured fear by placing each chick in a dark, sheltered compartment and then raising a door so the bird could enter an exposed, illuminated area.

Fearfulness was determined by the speed with which the birds poked their head through the door, emerged fully into the light compartment and also vocalized. Reduced timidity in the supplemented birds was noted in both genetic lines of quail, with no significant difference between them. For example, the supplemented birds from the low- and high-fear lines poked their heads through the door about 20 to 25 percent faster, respectively, than the unsupplemented controls.

The authors noted that "because poultry flocks are likely to include low-, moderate- and high-fear birds, these findings have additional practical relevance in that vitamin C supplementation would probably benefit all members."

These results paralleled those from earlier studies with Japanese quail, such as Jones et al. (1996), in which the birds were introduced to a novel object in their feed troughs. Supplemented birds were significantly less likely (P < 0.05) to avoid the object than unsupplemented birds. They were also significantly faster to regain movement after the researchers induced tonic immobility--averaging 69 seconds compared with 176 seconds for the unsupplemented controls.

The precise mechanisms underpinning these behavioral modifications are unclear, and they may be very different from the mechanisms explaining research observations of improved health and performance with vitamin C supplementation during other forms of stress.

Simply stated, stress conditions such as fear are believed to reduce vitamin C levels in the tissues of the bird. Consequently, the responses described in this article are believed to be due to the restoration of these levels by vitamin C supplementation.

More explicitly, scientists such as Pardue and Thaxton (1984) have suggested that the metabolic requirements for this antioxidant vitamin may exceed the bird's synthesizing capacity during periods of stress.

Since the response to vitamin C supplementation occurred at the same time as the birds were exposed to frightening stimuli, the biochemistry of their reaction to a stress condition such as fear may be involved. Jones et al. (1999) noted the apparent regulatory effects of ascorbic acid on various neurochemical substances and events such as catecholamine synthesis and conversion of dopamine to norepinephrine, which are associated with behavioral responses to stimuli. These effects are similar to those reported by Satterlee et al. (1993) in that ascorbic acid apparently modulated corticosteroid levels.

Whatever the mechanism may be, Jones et al. (1999) noted that the important point was that vitamin C supplementation with a stable source for 24 hours before a frightening event was accompanied by reduced flightiness or panic and the expression of more orderly behavior. To better ensure these results, the researchers added, it is important to use a stabilized form of the vitamin, such as ascorbyl-2-polyphosphate, which is available commercially as Rovimix® Stay-C® 35.

References:

Jones, R.B. 1996. Fear and adaptability in poultry: insights, implications and imperatives. World Poultry Sci. J. 52:131.
Jones, R.B., et al., 1996. Vitamin C supplementation and fear reduction in Japanese quail: short-term cumulative effects. Brit. Poultry Sci. 37:33.
Jones, R.B., et al., 1999. Timidity in Japanese quail: effects of vitamin C and divergent selection for adrenocortical response. Physiology and Behavior (in press).
Pardue, S.L., and J.P. Thaxton. 1984. Evidence for amelioration of steroid-mediated immunosuppression by ascorbic acid. Poultry Sci. 63:1262.
Satterlee, D.G., et al., 1993. Effects of vitamin C supplementation on the adrenocortical and tonic immobility fear reactions of Japanese quail genetically selected for high corticosterone response to stress. Applied Animal Behaviour Science. 35:347.
Satterlee, D.G., et al., 1994. Effects of ascorbyl-2-polyphosphate on adrenocortical activation and fear-related behavior in broiler chicks. Poultry Sci. 73:194.