RESEARCH ▶▶▶
Rancidity of poultry feeds and ways of controlling it
Oxidation of fats and oils (rancidity) is a natural reaction that occurs when unsaturated fatty acids are exposed to free oxygen. Antioxidants could therefore be added to animal feeds to prevent oxidation.
BY DR SALAH HAMED ESMAIL, FREELANCE JOURNALIST D
uring the reaction between unsaturated fatty ac- ids and free oxygen, a peroxy radical is formed when the triglyceride free radical reacts with an oxygen molecule. The peroxy radical then reacts
with another triglyceride, forming hydroperoxides, which are very unstable and break down into a number of second- ary products such as aldehydes and alcohols, which contrib- ute to the unpleasant flavors associated with rancid fats. They may also form other polymers that are unavailable and therefore reduce the energy content of the fat and are capa- ble of affecting the absorption of, or even destroying, fat-soluble vitamins. Currently, there are no reliable stand- ards for measuring the level of rancidity of fats, but it is gen- erally accepted that fats with a peroxide value (PV) greater
than 100 m.eq/kg may affect performance. There are also concerns about the toxic secondary products of ox- idative decomposition, which adversely affect the immune function.
Effects on performance It has been shown that a PV higher than 100 m.eq/kg can re- duce feed intake, weight gain and feed efficiency, with as a consequence high mortality. In other studies, birds fed diets with rancid fats had low fertility and hatchability, which are associated with health disorders such as encephalomalacia. It is also known that vitamin E deficiency occurs under oxida- tive stress, which may lead to several forms of immune-in- competence, including the reduced proliferation of
Table 1 – Commonly use chemical antioxidants in poultry feeds. Antioxidant
Rate of application Ethoxyquin (1,2-dihydro-6-ethoxy-2,2,4- trimethylquinoline) 150 ppm BHA (butylated hydroxyanisole) BHT (butylated hydroxytoluene) 200 ppm 200 ppm Mode of action
- Stabilize free radicals and prevent them from undergoing further reactions
- Retard oxidation of carotene, xanthophyll, and vitamins A and E
- Promotes higher levels of vitamin A storage in the liver - Some antioxidants such as BHT have antiviral action prevent mortality in chickens exposed to virulent Newcastle disease virus
12 ▶ ALL ABOUT FEED | Volume 28, No. 5, 2020
PHOTO: HENK RISWICK
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