Swine Nutrition Guide: Nutrient Sources - Energy

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An essential part of a sound feeding strategy is to make good decisions on which ingredients to use in the diet. Ingredients provide nutrients that pigs require for normal performance. Pigs do not require specific ingredients in their diet, but instead require energy and nutrients such as amino acids, minerals and vitamins. There are numerous ingredients available to use in pig feed. Information in this section is intended to help people make good decisions on sources of nutrients.

Energy
Pigs need energy for maintenance, growth, reproduction and lactation. The bulk of the pig’s energy requirement is met by carbohydrates and fats. Fats and oils are dense sources of energy, containing about 2.25 times more calories than carbohydrates. The energy content of feedstuffs and energy requirements of pigs are commonly expressed as metabolizable energy (ME). The ME content of a feedstuff is determined by subtracting energy lost in the feces, urine and gasses from the gross energy in the feedstuff. Although many cereal grains can provide economical sources of energy for pigs in the Midwest, corn is used extensively in Nebraska and South Dakota. However, economic conditions can change, making other energy sources attractive for inclusion in pig diets.

How does one know whether another energy source is more economical?
Focus on the relative feeding value of energy sources shown in Table 1 rather than on achieving a certain feed efficiency or growth rate when evaluating alternative energy sources. Substituting milo for corn, for example, likely will reduce feed efficiency, but may reduce the cost of gain also. The feeding values were calculated using the ME, digestible lysine and available phosphorus content of feedstuffs. Corn, soybean meal (44% CP) and dicalcium phosphate were used as reference feedstuffs.

Corn is assumed to have a feeding value of 100%. Grain sorghum (milo), for example, has a feeding value about 95% that of corn. Thus, milo can replace corn in the diet when the price of milo is less than 95% of the price of the same weight of corn. For example, if corn costs $.04/lb, milo would become more economical to feed when it is less than $.038/lb ($.04/lb x .95 = $.038/lb). The feeding value of milo is slightly less than that of corn because it has less ME and digestible lysine. The relative feeding values apply when ingredients are included in diets in quantities no greater than those shown in Table 1.

When ingredients are included in diets at lower levels than indicated in Table 1, the feeding value may increase slightly. Average daily gain and reproductive performance will not normally be reduced by replacing corn with any of the energy sources at the levels shown in Table 1.

A range in feeding value is presented to account for variation in ingredient quality and individual producer goals. Also, be sure to consider factors such as storage costs and ingredient quality and availability.

Is carcass backfat affected by using alternate energy sources?
Backfat thickness may decrease by up to .1 inches when oats, barley, or other lower energy ingredients replace all the corn in the diet if fat is not added to make the diets isocaloric. Details on how added fat affects backfat are presented in the Practical Applications and Outcomes section of this publication. The fatty acid profile of backfat is made slightly more unsaturated when high-oil corn, full-fat soybeans and vegetable oils are included in the diet of finishing pigs. There has been no evidence that this has contributed to “soft pork” or a loss of carcass value. However, feeding more than 10% whole sunflower seeds to finishing pigs will result in “soft pork.” Adjustments for possible changes in carcass merit have not been made in the feeding values shown in Table 1.

How should alternate energy sources be included in the diet?
Two methods are acceptable. Check Table 1 to see if there is a suggested limitation on the quantity of the ingredient to include in the diet. The first method is to reformulate the diet on a total or digestible lysine basis. Formulating on a digestible lysine basis is more precise. The advantage of formulating on a lysine basis is that the additional lysine in wheat and barley, for example, can be taken advantage of. This means less supplemental protein is needed in the diet. Check the tryptophan, threonine and methionine levels of the diet during formulation to ensure they are adequate. The second method is to substitute the alternate energy source for corn on a pound-for-pound basis in the diet. This procedure is acceptable for all energy sources in Table 1, except fat and molasses. These energy sources contribute no protein or amino acids to the diet, so the diet must be reformulated. Do not formulate diets on a protein basis because the diet may be deficient in lysine, resulting in reduced pig performance.

What sources of fat are available?
Common sources of animal and vegetable fat and their ME values are listed in Table 29. Also available are blended combinations of animal fat, vegetable oil and refined or rerendered restaurant grease. Animal fat and soybean oil are the most common fat sources used in swine diets. Animal fats in the Midwest generally include tallow, choice white grease and yellow grease. These are solid at room temperature and must be heated to about 140 to 150oF before they can be blended into the diet. In contrast, vegetable oils are liquid at room temperature and can be added to the diet without heating. Also, in general, oils are preferred over animal fat in diets for pigs weighing less than 15 lb. Fats are available in a variety of forms including fats contained in complete diets, commercial supplements, dried fat products, whole soybeans and high-oil corn, in addition to fats obtained directly from refiners and renderers. Probably the easiest method of incorporating fat in diets made on the farm is to use fullfat soybeans or high-oil corn. Diets that contain full-fat soybeans as the sole supplemental protein source provide 3 to 4% extra fat. High-oil cornsoybean meal diets also contain 3 to 4% additional fat. Fat that is added to a swine diet should be stabilized with an antioxidant or preservative (e.g. BHT, BHA, or ethoxyquin) to avoid rancidity.

Are some energy sources better suited for pigs in the summer than winter?
Yes. Fat will improve pig performance more when provided in the summer than in the winter. Less heat is produced by pigs when they digest fat compared with starch or fiber. This allows pigs fed diets with added fat to continue to consume large amounts of energy during hot weather when feed intake is normally reduced. Thus, fat is generally more cost effective when fed in the summer than in the winter. In contrast, when low-energy, highfiber feedstuffs such as alfalfa, barley and oats are digested by pigs, heat production is increased. This extra heat can be used to help maintain body temperature during the winter. Energy sources with a high fiber content are therefore more cost effective for pigs fed during winter than summer.

Does low protein corn have a lower feeding value than normal corn?
Not likely. Results from several studies indicate that the relationship between the crude protein content and lysine content of corn is poor. Thus, corn containing 7 to 7.5% CP may have the same amount of lysine as 8.5% CP corn. The lack of a good correlation between corn crude protein and lysine content indicates that one should not automatically increase the amount of protein supplement or crystalline lysine in the diet when using low protein corn. Moreover, in a 1994 study of corn produced in the Midwest, 77% of the samples contained between .23 and .28% lysine. If the lysine content of corn in a finisher diet formulated to contain .65% lysine ranges from .23 to .28%, the lysine concentration in the complete diet ranges from only .63 to .67%.

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