lymphocyte and reduced antibody response. The presence of rancid fat in the intestine increases the number of intestinal E. coli, which can cause an infection under the skin, and this is associated with respiratory disease in birds, which in severe cases leads to septicaemia and death.
Use of antioxidants Antioxidants are products added to animal feeds to prevent oxidation of fat or vitamins. In order for an antioxidant to be useful in feeding, it must have the following qualifications: - It should be effective in preserving animal and vegetable fats, vitamins, and other feed qualities subject to oxidative destruction
- It should be non-toxic to man and to farm animals - It should be effective at very low concentrations, and - It should be sufficiently inexpensive to be economically practical.
Of the chemical compounds that have been investigated thus far, three have been found to be extremely effective antioxidants for feeds and feed ingredients and these can be used both efficiently and economically (Table 1). Combi- nations of these antioxidants are normally found in com- mercially available products to take advantage of the differ- ent properties of each antioxidant. A number of natural antioxidants, such as tocopherols, rosemary extract and green tea extract, may also be used to prevent feed becoming rancid.
Practical recommendations For feeds containing added fat, the following points should be considered during handling and storage: - The degree of contact with air: oxidation cannot occur with- out oxygen, and proper storage and handling conditions can reduce the interaction between the fat source and air.
- Temperature: the rate of reaction of oxygen with fat can double with every 10 degrees C increase in temperature. By keeping fats in the coolest storage conditions possible or by avoiding overheating, this rate of reaction can be slowed.
- Presence of catalysts: contact with copper or iron should be avoided, and cleanliness can prevent contact between non-oxidised and oxidised fat.
- Light: exposure to light should be minimised in order to prevent photo-oxidation.
Feed formulation Lipid oxidation can take place during the steam flaking of ce- reals. This has been shown to reduce the bioavailability of methionine and tryptophan in wheat, rye, barley, and oats by as much as 26%. Feeding little and often will ensure that feeders are not overfilled with a feed that quickly turns rancid and unpalatable. It is also a good idea to limit feed orders to what can be consumed within no more than a month.
References are available from the author upon request. ▶ ALL ABOUT FEED | Volume 28, No. 5, 2020 13
Studies have shown that birds fed diets with rancid fats had low fertility and hatchability, as- sociated with several health disorders.
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