Fats

(b) Pure fat is often the cheapest available energy source. The economy of using fat is often enhanced by the increased growth rate and the shorter time required for production; also the addition of fat permits the inclusion of other low-energy, low-cost materials. 

(c) Some of the fatty acids are essential to animals. For this reason it may be necessary to add pure fat in some formulas, especially calf rations. 

(d) Fats increase palatability.

(e) Fats eliminate dustiness in compounded feeds and reduce wear on pelleting dies. 

(f) Experiments indicate that it is possible to decrease the amount of excrement to less than one half by adding about 7% fat to feed for monogastric animals, thereby minimizing waste disposal problems. 
ANTIOXIDANTS. These substances are added to fats to prevent them from becoming rancid. Rancid fats are unpalatable to animals and may even be toxic. This is usually manifested in the form of diarrhoea, liver problems or encephalitis. Vegetable fats and oils are usually extracted with antioxidants which occur naturally in plants. It is necessary to add an antioxidant to animal fats, such as BHA (butylated hydroxyanisole), BHT (butylated hydroxytoluene) or ethoxyquin; the usual amount is 125-200 g per ton of fat. 

Antioxidants are effective only in newly extracted fats. These chemicals break the chain reaction of fat oxidation, in which process the antioxidants themselves are consumed. When all of the antioxidant is consumed, the fat turns rancid. It is not possible to increase the keeping quality of fat by adding more of the antioxidant because all excess will, on the contrary, speed up the process. The rapid consumption of antioxidants can be slowed down by adding 50-100 g of citric acid per ton of fat to regenerate the consumed antioxidants and by adding EDTA (ethylene-diamine-tetra- acetic acid) to conjugate mineral traces that initiate oxidative chain reactions. The addition of EDTA is especially recommended if the fat will come into contact with copper, nickel, cobalt, manganese or, to a lesser degree, zinc or iron. 

Stabilized animal fat in compounded feeds will keep fresh for at least four months if a mineral mix is not included. In a feed containing a mineral mix the keeping quality of fat is rather poor. 
DIFFERENT KINDS OF FAT. Fat is described by its origin, melting point (titre), amount of free fatty acids, colour and impurities. Animal fats are described as tallows when they are solid above 40 C, as lards when they are solid between 20 C and 40 C, and as oils when they are liquid below 20 C. Generally, tallows come from cattle or sheep, lards from hogs, horses or bones of all kinds, and oils from marine animals or vegetables. The lard from pigs and poultry can be highly variable depending on the diet. The water content of lard should be checked, as it is possible by using certain chemicals to make it take up extra water. 

Fish-liver oil, especially cod-liver oil, was formerly widely used as a source of vitamins A and D. It has been found, however, that it oxidizes very quickly in mixed feed and loses its potency within a few days; thus its inclusion in mixed feeds is wasteful. Fish-liver oil is of value in animal nutrition, but to retain its vitamin content it must be kept in a cool, airtight container and away from strong light. 

Palm oil is very rich in beta-carotene. The amount varies greatly depending on the method of processing and stage of maturity of the fruit. Unripe fruit contains about 1 mg of beta-carotene per kilogram, while ripe and overripe fruit have about 3 mg and 2.5 mg per kilogram. For cattle this corresponds to 600, 1900 and 1600 i.u. of vitamin, respectively. 

Soapstock is a by-product of the refining of crude vegetable oil, which contains free fatty acids and traces of protein that must be removed before the oil is sold for eating. After adding sodium hydroxide, the oil is heated. At a certain temperature, the sodium reacts with the free fatty acids and combines with heat- coagulated protein in globules which settle to the bottom of the vessel. The clear refined oil is siphoned off the top. This material is known as soapstock because it is used in the production of soaps. It is rich in free fatty acids, usually containing more than 35%. Soybean soapstock also contains xanthophyll. In one experiment 6% soybean soapstock gave egg yolks a good colouring. Small amounts of soapstock have been included in pig and poultry diets. It has no harmful effects and can be used in the same way as fat. 
USE. Much research has been done on the effect of added fat in dairy feeds. The results have varied greatly and have indicated that it is not advisable to allow the total fat content to exceed 8-10%. The brown lard is added to feed for ruminants as they can usually consume low-priced fats, although acceptability may decrease after the first few days. The use of artificial milk containing 14-30% fat in intensive feeding is rapidly spreading. Milk replacer starters (for calves and lambs up to a month old) contain 14-18% fat. Generally these products have a base of skim milk powder, to which homogenized fat is added together with minerals, antibiotics and emulsifiers (usually soya lecithin at a level of 6-9% of the total fat). Milk replacers for finishing beef cattle may contain up to 30% fat. It is advisable to use only stabilized fat in these types of feed. 

In pig rations the type of fat is more important than the amount. Rancid fats or fish oils should not be fed to pigs, with the possible exception of breeding animals. The softening effect of fat on pork depends mainly on the degree of saturation of the fatty acids in the fat included in the diet. The following table gives the approximate percentage of polyunsaturated fatty acids in the more common fats: 

				Percent						Percent
	Butter oil................    5							Olive oil..........       .. 8
	Cocoa fat................. 3							Palm oil.............      10
	Coconut oil .............. 1							Rapeseed oil.........   70
	Cod-liver oil.............80							Sesame seed oil...... 40
	Cottonseed oil..........50							Soybean oil..........    60
	Groundnut oil...........30							Sunflower seed oil... 65
	Herring oil............... 80							Walnut oil...........     75
	Lard.......................  10							Whale oil............     40
	Maize germ oil......... 55							Tallow ..............        3

When the ration is properly balanced in protein and other nutrients, the addition of fat to the pig diet modifies the thickness of the backfat very little. It is advisable as a general rule to increase the protein level 0.5-1 % for each percent increase in the amount of fat added. It is also important to increase the supply of minerals and vitamins by the same amount. Generally the feed conversion of a diet with added fat increases by the same percentage as the fat added (up to a maximum depending on species, other ingredients, etc.), and it is necessary to increase the contents of proteins, minerals and vitamins by the same percentage so that the proportion or the dosage received by the animal will not be reduced. Vitamin B, choline, calcium and magnesium should be increased by greater amounts than is usually indicated by the change in feed conversion alone. This applies also to poultry diets. 

With the inclusion of fat in poultry diets it is possible to increase the energy content and at the same time have a high level of other nutrients. In this way the genetic potential for rapid growth is better exploited. Broiler diets with up to 34% fat have been used, and for broilers the fat dosage seems to be limited only by economic considerations. Using fat in broiler diets may also be a method of overcoming the poor performance of broilers in hot environments, as it has been shown that fats have a lower heat increment than carbohydrates and proteins. It is therefore possible to improve the performance of chickens during high temperature stress by replacing carbohydrate calories with fat calories and by reducing the total protein while maintaining appropriate rations of amino acids and energy. As a rule the first 3-4% of fat added will pay with the double advantage of growth stimulation and improved feed utilization; above this level only the advantage of improved feed utilization remains. In practical feed formulations the economic level of fat addition is 5-6%. By increasing the protein, mineral and vitamin contents and adding fat, smaller amounts of the feed need to be eaten and the presence of fat inhibits the heat- producing conversion of carbohydrate to body fat. For layers the addition of fat must be proportional to egg production. When production is less than 30% (30 eggs per day from 100 layers), no more than 3% should be used. When production is over 70%, up to 6% may be used. 

The digestibility of animal fat is about 80% for monogastric animals and 85% for ruminants. The energy value on a dry matter basis is 190% TDN for ruminants and 180% TDN for pigs. Homogenized animal fat is about 92% digestible, and the energy value is 207% TDN for ruminants. Animal fat contains no minerals or vitamins. 

References

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