Carbohydrates and fats in the diet supply most of the pig's caloric needs. Today, energy requirements are expressed as kilocalories (kcal) of digestible (DE or metabolizable energy (ME) per pound of feed. Digestible energy is defined as the amount of energy in the feed minus the energy lost in the feces and urine.
Energy sources for swine are the cereal grains; corn, milo, wheat, barley, and their by-products. In addition, fat, which contains 2.25 times the amount of energy as cereal grains, is often used to increase the energy density of swine diets. Most common cereal grains and fats are quite palatable and digestible. However, cereal by-products tend to be more variable; therefore, their use in swine diets may be limited. Although cereal grains will provide carbohydrates to meet the pig's energy needs, they must be supplemented with amino acids (protein), vitamins, and minerals to meet the pig's requirements for these nutrients.
When formulating swine diets using the common cereal grains, producers do not balance for a specific energy level in the diet, because the pig will often eat to meet its energy requirement. However, when low-energy feeds are used, pigs are limit-fed (sows and gilts), or external factors limit feed intake, dietary energy levels must be checked to ensure adequate intake.
Both grains are excellent energy sources in swine diets. In North Carolina, however, milo is often a more economical source of energy. Because the energy content of corn is slightly higher than that of milo, feed efficiency of pigs fed corn diets will be slightly better than that of pigs fed milo, but average daily gains will be the same.
A general recommendation for swine diets is to replace corn with milo on a pound-for-pound basis or on a lysine basis. One disadvantage of milo is that it can be more variable in nutrient content than corn because of growing conditions. In addition, because a milo kernel is smaller and harder than a corn kernel, fine grinding, (1/8 or 5/32" screen) or rolling is suggested for best utilization.
Fats and oils such as lard, choice white grease, beef tallow, corn oil, and soybean oil contain about 2.25 times as much metabolizable energy as most of the cereal grains. Research indicates that the addition of 1 to 5 percent fat to growing-finishing swine diets will improve feed conversion and often average daily gain with no adverse effect on carcass quality. A reduction in the amount of dust will be evident and wear on mixing equipment and augers will be reduced with 2 to 3 percent added fat.
Addition of fat above 5 percent will further improve feed conversion, but physical handling problems such as bridging in the feeders and caking in the mixer may limit the use of these higher levels. Diets containing fat may become rancid during prolonged storage or when feed is exposed to high temperatures. Therefore, an antioxidant such as ethoxyquin, BHT, or BHA should be added to fat before mixing it into the rations.
Adding fat to swine diets is a matter of economics. Fat additions will usually increase the cost of the diet, which must be offset by an increase in pig performance. Several commercial supplements and complete feeds contain added fat. New commercial products that contain dried fat may reduce part of the mechanical problems of adding liquid fat on the farm, but the economic feasibility of using these products must be evaluated. Fat products that have limestone as the carrier should be avoided, because the calcium will decrease the digestibility of the fat.
Research with sows suggest that feeding a diet with 5 percent added fat at a rate of 5 lb/day for 10 days before farrowing has the potential to improve pig survivability if preweaning survival is below 8C percent. The reasons for the increase in survival rate appear to be increases in milk yield and milk fat content.
The potential benefits of fat addition must be evaluated in terms of economic considerations. When calculating what price you can pay for adding fat to a swine diet, the following equation can be used:
percent improvement in feed efficiency needed to offset added diet cost
For example, if adding fat will increase diet cost by 5 percent, you must get at least a 5 percent improvement in feed efficiency before it is economical. Fat may be added in summer diets to increase the energy density of the feed to offset low feed intake due to high temperatures. Feed efficiency is usually improved 2 percent for each 1 percent increment of added fat in growing-finishing pig diets.
Recent research shows that not all fat sources give similar improvements in pig performance, especially for baby pigs. This may be a result of the fat source's fatty acid profile or impurities from the rendering process. In general, fat sources such as soybean oil and choice white grease are considered higher quality than tallow and yellow grease. Evidence indicates that blends of soybean oil and coconut oil support excellent performance in baby pigs. Waste cooking oils may be used in swine diets but should also be checked for quality.
Fat sources of questionable quality should be analyzed for moisture, impurities, and unsaponafiable material (MIU), as well as free fatty acids. Moisture should not exceed 1 percent, free fatty acids 15 percent, impurities .5 percent, unsaponifiable material 1 percent, and total MIU 2.5 percent. If two fat sources are blended together, moisture should not exceed 1 percent, free fatty acids 30 percent, impurities .5 percent, unsaponifiable material 3.5 percent, and total MIU 5 percent.
There is no perfect feed ingredient that can be fed to pigs by itself. Some feeds, if added to the diets in excess amounts, will decrease performance. Some less commonly fed feedstuffs, such as millet and rye, should not exceed the recommended levels shown on Table 4.
Under adverse weather conditions, such as drought, floods, or early frosts, low test weight or sprout-damaged grain may be available for use in swine diets. As the degree of sprout damage increases or test weight decreases, the energy content of the grain is decreased. Therefore, the pig will need to eat more feed to meet its energy requirement. Although average daily gain will usually not be affected, feed efficiency will become poorer. Research has shown that his occurs when milo drops below 45 pounds per bushel test weight and wheat is below 50 pound test weight.
Furthermore, milo with up to 40 percent sprout damage can be effectively used by growing finishing pigs. When the test weight of milo and wheat drop below 45 and 50 pounds, respectively, or there is more than 40 percent sprout damage, average daily gain will begin to be affected. Blending low test weight or sprout-damaged grain (up to 50 percent) with normal grain is an effective way to utilize weather-damaged grain. It is extremely important to recalibrate volumetric mixing equipment when feeding low test weight grains.
Profitability the biggest disadvantage to weather-damaged grain is the increased potential for mold or aflatoxin contamination because of high moisture content. Therefore, weather damaged grains should always be tested for molds and aflatoxin and, if contaminated, these grains should not be fed to starter pigs or the breeding herd. If contaminated grains are used, they should be blended with normal grain and fed only to growing-finishing pigs in limited amounts. Several mold inhibitors have been shown to improve pig performance when mold-contaminated grains are fed.
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