Supplementation of canthaxanthin antioxidant to breeder diets has a positive effect on flock fertility and hatchability. Moreover it increases chick viability and enhances the maturation of major physiological systems, including the immune system.
By Professor Peter Surai, Feed-Food, Scottish Agricultural College, Scotland, UK
Carotenoids are the most numerous and widespread group of pigments found in nature, with more than 750 types known. They are synthesized by higher plants, algae and some microorganisms and are accountable for the bright colours in the red/orange/ yellow family that are seen in nature. In nature, male birds allocate carotenoids to their plumage to indicate their health status, making them more successful in finding a mate, whereas females mainly invest carotenoids in the egg. Carotenoids are responsible for the colour of egg yolks and are thought to play a central role in avian embryonic development. Within the cells, the primary role of carotenoids is that of an antioxidant.
Antioxidants are required to protect the cell from damage by free radicals. These are highly reactive molecules, containing one or more unpaired electrons. Their high reactivity is a result of their trying to lose or gain an electron to achieve stability. Free radicals are produced during the normal processes of cell metabolism. Egg hatching is also considered to cause oxidative stress, having the potential to cause lipid peroxidation in the developing embryo. In fact, all biological molecules are susceptible to free radical damage, but lipids, proteins and DNA are particularly at risk. To protect the integrity of their cells, organisms require antioxidants.
Carotenoids are excellent antioxidants, acting to scavenge singlet oxygen (1O2) and peroxy and sulphur radicals. They also protect lipids against superoxide and hydroxyl radical attack. In this way, carotenoids are able to prevent lipid peroxidation. Both in vitro model systems and in vivo animal experiments have shown that canthaxanthin has a high antioxidant activity thanks to its characteristic double bonds and has been described as one of the most powerful lipid-soluble antioxidants in nature. It is able to react with a range of free radicals and is very effective in protecting against oxidative stress.
Egg antioxidant defences
The chicken egg consists primarily of yolk, white (albumin) and shell. The majority of the lipids are found in the egg yolk, where a range of fat soluble antioxidants are also located. The water soluble compounds such as Vitamin C are not accumulated in the egg yolk, therefore the only antioxidants present in high enough quantities to be of any protective use in the yolk are Vitamin E and carotenoids. Other compounds with antioxidant activity e.g. Coenzyme Q and Glutathionine are present only in very low concentrations, and therefore play a minor role in lipid protection. The concentration of both Vitamin E and carotenoids in the yolk is largely dietary dependent.
Canthaxanthin is successfully absorbed from the feed and efficiently transferred to the egg yolk and then further to the developing embryos. From there, it is transferred into the organs and tissues of the developing bird. Chick embryo development is associated with an accumulation of polyunsaturated fatty acids in tissue lipids, making them susceptible to lipid peroxidation. The antioxidant system is responsible for protection of the polyunsaturated fatty acids, proteins and DNA from damage caused by free radicals and toxic products produced during metabolism.
Oxidative damage is an important factor in embryonic mortality, particularly during the sensitive periods of hatching and immediately after. Breeder dietary supplementation with canthaxanthin significantly increases the anti-oxidative status of the egg yolk and newly hatched chicks and as a result the hatching rate of chicken eggs is significantly increased.
SOD (Superoxide Dismutase) activity increases in the plasma of newly hatched chicks hatching from canthaxanthin enriched eggs. Generally, the accumulation of TBARS (Thiobarbituric Acid Reactive Substances) is used to monitor lipid peroxidation or break down. Canthaxanthin has been shown to be very effective in prevention of TBARS formation in eggs and chicks. TBARs are also reduced in yolks from stored eggs from breeders fed canthaxanthin. This was seen in eggs on the same day of production as well as in eggs stored for 4, 8 and 12 days.
High carotenoid concentrations in the liver of newly hatched chicks are thought to be an important adaptive mechanism for the protection of tissues from the oxidative stress of hatching. This suggests that canthaxanthin provides a substantial benefit to chicken eggs, embryos and young chickens during early postnatal development. Increased canthaxanthin concentrations in the egg yolk and embryonic tissues have also been associated with higher vitamin E concentrations in the liver and plasma of day old chicks. It is thought that if the canthaxanthin scavenges free radicals, that fewer free radicals would be present to react with the vitamin E, leading to its increased availability and concentration in the chicks.
Studies have shown that the antioxidant capacity of newly hatched chicks is significantly increased and there is a significant decrease in MDA in the plasma of chicks. This is thought to be linked to the increase in plasma canthaxanthin and vitamin E levels. A decrease in mortality with canthaxanthin supplementation has also been found. Consequently, a positive effect of canthaxanthin in the maternal diet is seen in fertility, hatchability and embryonic mortality. Hand in hand with increased fertility, studies have shown that canthaxanthin supplementation also improves survival and storage of spermatozoa within the reproductive tract of the hen. It has also been shown that chicks hatched from eggs laid by breeders fed a canthaxanthin supplemented diet show a higher pigmentation colorimetric score for their shank skin, thought to be associated with canthaxanthin accumulation.
Gene expression modulator
Carotenoids are powerful immune-stimulants. Studies have been carried out to suggest that antioxidants, including carotenoids may affect gene expression during embryonic development. The concentration of carotenoids in the egg yolk was found to have a profound effect on the immune system development after hatching. It has been suggested that carotenoid depletion in the egg yolk may decrease the capacity for appropriate immune responses later in the life of the chicken. In mammals there are already several genes that have been described which are specifically regulated by carotenoids including canthaxanthin.
What does this mean?
The enhancement of the antioxidant system in the developing chick by supplementing the maternal diet offers a significant opportunity for poultry producers. The postnatal developmental period in the chicken is a critical time for the maturation of major physiological systems, including the immune system, as well as a time of high risk of lipid peroxidation. Therefore, increased supplementation of the maternal diet with canthaxanthin could help to maintain antioxidant system efficiency and therefore increase chick viability.
References are available from the author on request