Adding Used Cooking Oil to Feed Rations
Fats and Oils
Fats and oils are commonly added to the diets of domestic animals. Nutritionally, fats and oils are a source of essential fatty acids and energy. Generally, the natural feedstuffs consumed by domestic animals will fulfill their dietary fatty acid requirement. Therefore, the primary nutritional function of fats and oils is to provide energy. Fats and oils are concentrated energy sources; one unit provides approximately 2.25 times more digestible energy than either carbohydrates or proteins. In addition to providing energy, fats and oils are also added to the diet for other reasons. As a result of the relatively low heat increment during digestion, fats and oils aid animals during heat stress. In addition, fats and oils are also digestible and may improve overall digestibility of the ration. Addition to the ration also improves the efficiency of feed processing. Fats and oils act as lubricants, aid in pelleting, bind smaller feed particles, and reduce dust. Addition of fats and oils to the diet will increase the palatability of the ration and promote feed intake. Fats and oils also influence the absorption of lipid soluble compounds. They will increase the absorption of lipid soluble vitamins and may decrease the absorption of minerals such as phosphorus. As fats and oils are an expensive feed source, cost is often the factor that limits inclusion into the ration.
Feeding fats originate from a variety of sources. The discarded animal fats from processing and rendering plants are a source of animal feed fats. The primary animal feed fats are tallow, lard, mixed fats, and grease. Grease is an animal fat with a lower melting point compared to tallow. Animal fats and vegetable oils are used to prepare human foods, are recycled, and used as animal feeds. Generally, cost prohibits the use of the original vegetable oils. Examples of common vegetable oils include corn, cottonseed, soybean, olive, safflower, sunflower, canola, and peanut oil.
Figure 5.11 illustrates vegetable oil.
Acidulated vegetable soapstock is another animal feed fat. Vegetable soapstock is primarily composed of free fatty acids. It is a by-product of the vegetable oil industry.
In the industry, feed fats are supplied by renderers, blenders, and/or brokers. Blenders often purchase, process, and sell the fats and oils. Brokers purchase the fats and oils processed and then sell the fats and oils.
The official names of feed fats are listed on page 82 of the text. Some of the more common products in the animal feed industry include animal fat and vegetable fat or oils. Nutritional value and components of fats and oils potentially vary greatly by source and over time. It is important to purchase fats and oils based on specifications and also to verify the nutritional value of the fat and oil added to the ration. The following standards state the required nutritional value of the feed fats and oils: 1) at least 90% fatty acids; 2) maximum 2.5% unsaponifiable matter; and 3) maximum 1.0% insolubles. The fat must also be free from toxic or detrimental compounds.
A specific classification system and nutritional standards for feed fats and oils have not been established.
Table 5.2 states a proposed classification system and description of each category in the classification system.
| Classification | Description |
|---|---|
| Animal fat | Rendered fats from beef or pork by-products; |
| Poultry fat | Fats from 100% poultry offal |
| Blended feed-grade | Blends of tallow, grease, poultry, and |
| Blended animal and | Blends of class 3 and vegetable fat |
| Feed-grade | Vegetable oil, acidulated vegetable |
Table 5.21 on page 82 of the text is the proposed classification system with suggested quality specifications for feed fats and oils. The primary objective of the classification system is to standardize the components and nutritional value of the feed fats and oils.
Rancidity is an issue to consider when feeding fats and oils, especially unsaturated sources. The double bond(s) of unsaturated fatty acids are susceptible to oxidation. Oxidation produces a number of volatile compounds. Oxidation of a fatty acid causes rancidity of the feed. Rancidity is spoilage of the feed, characterized by an off-odor and flavor. Rancidity will reduce palatability and may cause additional nutritional problems. Addition of antioxidants to the feed will minimize oxidation. Examples of antioxidants are vitamin E, butylated hydroxytoluene (BHT), and butylated hydroxyanisole (BHA). Antioxidants also protect vitamins from oxidation. Typically, antioxidants will be added to feeds containing fats and oils. Grinding of whole grains can also cause rancidity. Rancidity can be minimized by further processing the grain or the addition of an antioxidant.
To some degree, fats and oils are used for all species. The amount of fat added to a diet varies by species and physiological state. For monogastrics such as swine and poultry, the amount of fat added to the diet is largely based on energy requirements and associated production goals. It is also important to consider monogastrics will eat to fulfill their energy requirement. Therefore, increasing energy density may decrease intake and the ration will need to be balanced to achieve adequate consumption of other nutrients. For swine on creep diets, fat may be added at a rate of 5-10% of the ration. For sows, it is recommended to add about 5% fat to the ration in late gestation. In growing poultry rations, fat may be added at a rate up to 10%. For layers, fat may be added to increase production. For horses with a high energy requirement, it is recommended to add 5-10% fat to the ration. For young ruminants, milk replacers may contain up to 10-30% added fat. For ruminants, the amount of fat added to the diet is dependent on energy requirements and the rumen system. Feeding excessive dietary fats will reduce digestive efficiency and animal productivity. Therefore, for animals with a functional rumen, the maximum level of dietary fat is 7-8%. Typically, dietary fat is added to finishing and lactating cattle rations. For finishing beef cattle, it is recommended to add 2-5% fat to the ration. For lactating dairy cattle, it is recommended not to exceed 6% fat in the total ration. In contrast to other animals, it is important to consider the source of fat for lactating dairy cows. The recommended sources are either a fat, oil, or soapstock mixture and whole oilseeds. Whole high oil seeds may also be used as a feedstuff. Oilseeds such as cottonseeds and soybeans are high in fat and protein.
Figures 5.12 and 5.13 illustrate whole cottonseeds and soybeans, respectively.
For nonruminants, the seeds must be processed. For ruminants, the seeds may be fed either whole or processed.
In addition to fats discussed, rumen inert fats are available. Rumen inert fats by-pass rumen fermentation and are not detrimental to the digestive or rumen efficiency. Rumen inert fats can be added to dairy cattle rations at a rate of 2-3%.
Source: https://courses.ecampus.oregonstate.edu/ans312/two/fats_trans.htm
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