The functional effects of the antioxidants as they affect nutrients and the animals' utilization of them can be summarized as follows:
1 Nutrient Deficiency Prevention
Dietary deficiencies of vitamins A and E seem to be ameliorated in certain circumstances and ethoxyquin promotes higher levels of vitamin A storage in the liver. Repletion/deletion experiments show that in both monogastric and ruminant animals, a diet containing an anti-oxidant protects fat soluble vitamins throughout ingestion and metabolism. The important benefit of antioxidants most probably lies in their conservation of essential nutrients and their improved utilization by the animal. Altogether too often, it is the practice to use levels of vitamin E far above the animals' nutrient requirement and the result is economically unfavourable. It has been shown in diets designed for chicken and turkey breeders that ethoxyquin has a vitamin E sparing effect.
2 Prevention of Rancid Oxidation of Fats
In lipid peroxidation, the unsaturated fatty acids undergo a loss of hydrogen, resulting in the formation of a free radical at the site of unsaturation. If the feed material in which this reaction is taking place does not contain vitamin E or some other effective antioxidant, the free radical is quickly converted to a fatty acid peroxide free radical and finally to a fatty acid hydroperoxide (Fig. 1). An antioxidant can block this peroxidation by supplying a hydrogen in the first free radical formed, thereby reconverting it to the original fatty acid. If the hydroperoxides are allowed to form, they continue to decompose by breaking down into a variety of aldehydes and ketones.
Fig. 1. Peroxidative Rancidity
Antioxidants prevent oxidative losses of vitamins A and E and pigmenters (oxy- and keto-cerotenoids) in stored mixed feeds. Antioxidants stabilize critical oxidation-susceptible nutrients that are naturally present in a fish feed composed of several feedstuffs so that losses are minimal from mixing and storing. If pigmenting substances are used, the anti-oxidants are definitely needed. The benefits of adequate, consistent use span all facets of fish production which include the processing and handling of feedstuffs, formulation, and fish cultural practices.
Some beneficial effects of ethoxyquin are described in Table 2.
Table 2 Some Effects of Ethoxyquin in Feeds
|Sample||Vitamin A activity, I.U.*||Change (%)|
|Feed A (no antioxidant added)||Initial 150 325|
|Final 77 800||- 48.2|
|Feed B (150 ppm Ethoxyquin)||Initial 151 366|
|Final 115 633||- 23.6|
|Sample||Extractable fat*||Iodine No.*||ME (cal/lb)*|
|Fish meal (unstabilized)||7.0||109||1 149|
|Fish meal (stabilized)||9.4||178||1 461|
|Hatchability of eggs from hens (12 weeks, 7% linoleic acid diet)|
|Supplementation||Egg hatchability (%)|
|Ethoxyquin, 125 ppm||78.96|
|Vitamin E, 16 mg/lb||82.11|
|Ethoxyquin, 125 ppm and Vitamin E, 16 mg/lb||79.15|
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