THE MERCK VETERINARY MANUAL
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Feeding Levels and Practices in Pigs

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Performance of weanling, growing, and finishing pigs; gestating sows; and lactating sows and their nursing pigs is related to both the quality of the diet and the amount consumed on a daily basis. Knowing the amount of feed animals consume is important in the overall feeding management process. Weanling, growing, and finishing pigs are ordinarily allowed to consume feed ad lib, and the amount consumed is affected by the energy density of the diet, environmental temperature, gender, and feed quality (eg, absence of molds), as well as a host of other management factors such as feeder design, crowding, etc.

Daily feed intakes of various weight classes of growing-finishing pigs fed a diet containing 3,300 kcal of ME/kg (typical of a corn-soybean meal diet) as estimated by the NRC growth model are shown in Table 1: Pigs:Dietary Nutrient Requirements of Growing Pigs Allowed Ad Lib Feed (90% dry matter)Tables. These intake levels represent an average for barrows and gilts. Feed intakes will be slightly higher for barrows and slightly less for gilts weighing 50–135 kg. Preventing overcrowding and cooling pigs with automatic water sprayers during hot weather help to alleviate reduced feed intake. These intake levels can be used as a guide to project total feed requirements or prescribe in-feed medication.

For gestating gilts and sows, the NRC estimates that a feeding level of approximately 4.7–4.9 lb/day (2.1–2.2 kg/day) during the first 90 days of gestation and 5.6–5.7 lb/day (2.5–2.6 kg/day) for the final 25 days to farrowing of a corn-soybean meal diet (3,300 kcal ME/kg) provides sufficient energy for maintenance; some lean and fat tissue accretion (particularly in gilts); and the energy needs of the developing fetuses, placenta, and other supporting tissues (see Table 2: Pigs:Reproductive Measures and Dietary Nutrient Requirements of Gestating and Lactating SowsTables). Mature sows do not need more energy than that required for maintenance and some increase in body weight. If gestation diets contain oats, alfalfa meal, or other energy diluents, higher feeding levels will be needed to meet the sow's daily energy requirement. Attempts to limit voluntary feed intake during gestation by allowing ad lib access to extremely high-fiber diets has not been successful; invariably, excess weight gain occurs.

Producers should adjust the feeding level of pregnant gilts and sows to keep them in good condition. Excess body condition at the end of gestation is often associated with reduced feed intake during lactation and sometimes results in reduced litter size, greater incidence of dystocia, more pig overlay, and a greater incidence of postpartum dysgalactia syndrome (see Postpartum Dysgalactia Syndrome and Mastitis in Sows). Poor body condition results in a greater incidence of shoulder sores in sows, lower birth weights, and thin sows at weaning with delayed return to postweaning estrus (or even anestrus). Litter size at the subsequent farrowing can also be negatively affected if sows are in poor condition at breeding.

The amino acid requirements of first-litter gilts are higher than those for sows. Both gilts and sows require higher levels of dietary amino acids during the latter stage of gestation than in the initial 90 days of gestation. (see Pigs:Reproductive Measures and Dietary Nutrient Requirements of Gestating and Lactating SowsTables.)

The NRC estimates that lactating gilts and sows nursing 11–11.5 pigs that gain 240 g/day during a 21-day lactation require 13.1–14.6 lb (6.0–6.6 kg) of feed (3,300 kcal of ME/kg) daily to meet their energy requirements (see Table 2: Pigs:Reproductive Measures and Dietary Nutrient Requirements of Gestating and Lactating SowsTables). The amount of energy and feed depends on number of pigs nursed, weight gain of the pigs (both of these factors influence milk production), and weight loss of the sow. High-energy diets should be self-fed to sows during lactation, or sows should be hand-fed all they will consume three times daily. Proper temperature regulation in the farrowing room and the use of drip-coolers during hot weather help to alleviate low feed intake.

If feed intake is too low, sows will lose excessive weight during lactation (see Lactating Gilts and Sows). If this is a problem, including 3%–6% fat in the lactation diet or top-dressing the lactation feed with additional fat should be considered. If problems persist, more energy during the final 3–6 wk of pregnancy may be helpful.

Diets high in protein and amino acids should be fed to prolific sows nursing large litters to maximize milk production and to prevent excessive weight loss of the sow. Such sows may require diets containing 16%–18% or more crude protein (minimum of 0.9% lysine). If energy intake is sufficient, high-protein lactation diets will minimize or even eliminate weight loss in sows during lactation.

Major Feed Ingredients

A fundamental principle of the economics of pork production is to feed the most economical cereal grains and to correct the deficiencies by supplementation with good-quality protein sources, minerals, and vitamins. Dependable mineral and vitamin premixes or complete manufactured supplements are commercially available. Fortified corn-soybean meal diets are very popular in pig operations, but other cereals and protein sources can be used.

Corn (maize) is by far the most widely used grain for feeding pigs in the USA. It is very palatable and high in energy but relatively low in crude protein. In addition, corn is deficient in lysine, tryptophan, threonine, and several other essential amino acids, as well as vitamins and minerals.

Grain sorghum is a major energy source for pigs in western and southwestern USA. The protein content is variable depending on factors such as variety, whether the crop was grown on irrigated or dry land, amount of fertilizer used, and other environmental factors. In general, grain sorghum can be substituted for corn on an equal-weight basis, but because the ME value is slightly lower than that of corn, a poorer feed conversion should be expected.

Wheat has about the same energy content as corn and contains 2%–3% more protein and 0.05%–0.1% more lysine than corn. Wheat can be substituted for corn on either an equal-weight basis or on a lysine basis, but not on a crude protein basis or it will result in a lysine deficiency. Wheat can constitute all of the grain in a swine diet. The two main types of wheat grown in the USA, hard red winter and soft red winter, have equivalent nutritional value.

Barley has ~85%–90% of the feeding value of corn, even though it usually contains 2%–3% more protein. Scabby barley should not be fed to pigs.

Oats have a relatively low energy content and, therefore, should not account for >20%–25% of the cereal grain in the diet. Generally, when oats are included in the diet, the rate and efficiency of gain should be expected to decline. Rolled oats groats are sometimes used in starter diets because of their excellent palatability.

Cereal grains should be ground or rolled to maximize their feeding value. Corn and grain sorghum should be reduced to a medium-fine particle size (550–600 microns). Wheat should be ground more coarsely (650–700 microns) to prevent pasting. Fine grinding improves feed conversion, but excessive reduction in particle size may lead to an increased incidence of gastric ulcers. Pelleting of diets may result in a small improvement in gain and especially feed efficiency. In general, the benefit is greatest with pelleted diets that contain high levels of fiber, such as barley-based diets. Cereal grains should be as free as possible from mycotoxins. Aflatoxins, vomitoxin, zearalenone, fumonisins, and other mycotoxins can reduce animal performance, depending on level in the feed, and can especially cause reproductive problems in breeding animals.

Soybean meal accounts for >90% of the supplemental protein fed to pigs in the USA. It is very palatable and has an excellent amino acid profile that complements the amino acid pattern in cereal grains. Ground, full-fat soybeans can also be fed to swine but only after they are heated (by extrusion or roasting) to inactivate the trypsin inhibitors and other heat-labile antinutritional factors.

Canola meal also is an excellent protein source. Low-gossypol cottonseed meal (<100 ppm free gossypol), peanut meal, sunflower meal, and other oilseed-based meals can be used in swine feed but generally not as the sole source of supplemental protein because of the lower lysine content of their protein. Animal protein sources such as meat meal, meat and bone meal, or fish meal can supply a portion of the supplemental protein in swine diets.

Distillers dried grains with solubles (DDGS) is a byproduct that has received a lot of attention in recent years because of the increased number of ethanol plants that use corn to produce ethanol for fuel. This byproduct is an excellent and generally economical feed ingredient for swine. Although DDGS has essentially no starch and considerably more fiber than corn, it is considerably higher in fat (corn oil); hence, the ME content of DDGS containing 9%–12% fat is similar to that of corn. Recently, some ethanol plants extract a portion of the oil from the solubles before adding the solubles back to the dried grains. This results in a “low-fat” DDGS, generally 5%–9% fat, which has slightly less ME than conventional DDGS. Further removal of fat, called “de-oiled DDGS” (<5% fat) has substantially less ME than either of the other types of DDGS, so it has a lower feeding value. DDGS is also higher in protein than corn, but the quality of protein (ie, balance of amino acids), like corn protein, is poor.

A considerable amount of research has been done with DDGS in recent years. Diets containing 20%–25% DDGS are well utilized by pigs, but when high levels (>30%) of DDGS are fed in finishing diets, body fat of pigs becomes more unsaturated, as evidenced by higher iodine values. This results in softer, more flexible bellies that are more difficult to process into bacon slices. To overcome this problem, producers should consider either removing DDGS from the late finishing diet or reducing the level of DDGS to 10% during the final 3–4 wk of the finishing period.

Feeding Management of Sows and Litters

Gestation diets adequate in all nutrients should be fed to sows to produce healthy, vigorous pigs. Sows should be fed so that they are in good body condition at farrowing—not too fat or too thin. Thin sows tend to farrow smaller pigs that have a poorer chance of survival than larger, more vigorous pigs. After farrowing, the sow should be returned to full feed as soon as possible. Constipation in sows is generally not a problem if the sow is eating well. Wheat bran or dried beet pulp can be included in the farrowing diet at 5%–10% if constipation is a problem, or chemical laxatives such as potassium chloride or magnesium sulfate can be included in the diet at 0.75%–1.%.

Newly farrowed pigs should be checked to ensure that each has nursed. If necessary, milk flow may be stimulated by giving oxytocin. If the sow is slow in coming into milk, weak pigs may benefit from receiving artificial milk, but success depends on good management and sanitation. Nutritional anemia should be prevented by giving an iron injection before 3 days of age or by other means discussed previously. Pigs from large litters may be transferred to sows with smaller litters after they receive colostrum; however, the transfer should be done within the first 24 hr after birth. A palatable pig starter diet should be provided beginning at 2–3 wk if pigs are weaned later than 3 wk of age. (Also see Pigs and see Pigs.)

Feeding Management of Weanling Pigs

Pigs weaned at an early age (3–4 wk) perform best if fed a complex starter diet for 1–2 wk after weaning. Typically, the starter diet contains dried whey and/or lactose, dried blood products, and a high level of lysine. Some producers use a medicated early weaning program or segregated early weaning program to produce healthier pigs. This entails weaning at 10–16 days of age and requires excellent nutritional management. Such diets should contain even higher levels of lysine as well as high levels of lactose (as the sugar or from dried whey) and 3%–7% dried animal plasma. A gradual transition should eventually be made to less expensive starter diets and then to corn-soybean meal diets.

The nutritional needs of growing-finishing pigs are best met by a full-feeding program. Limit-feeding reduces the rate and efficiency of gain but may improve carcass quality of finishing pigs. Proper design and adjustment of self- feeders is necessary to prevent feed wastage or restricted growth.

Growth Stimulants

For many years, antibiotics and other chemotherapeutic agents have commonly been added to swine diets to promote growth and feed efficiency, reduce mortality and morbidity, and improve health. The greatest response to these growth enhancing agents is in young pigs, with lesser responses as pigs progress in age and weight. The levels of antibiotics fed and drug withdrawal requirements should be in accordance with manufacturers' recommendations and legal restrictions. (Also see Growth Promotants and Production Enhancers.)

The antibiotics approved as feed additives for swine include bacitracin methylene disalicylate, bacitracin zinc, bambermycins, chlortetracycline, lincomycin, neomycin, oxytetracycline, penicillin, tiamulin, tylosin, and virginiamycin. Chemotherapeutic agents include carbadox, roxarsone, sulfamethazine, and sulfathiazole. Several of these are approved only in combination with certain other additives. Apramycin also is approved for use as a water medication. Also, pharmaceutical levels of zinc (1,500–3,000 ppm) as zinc oxide, or copper (100–250 ppm) as copper sulfate or tribasic copper chloride are effective growth stimulants in young pigs.

However, FDA action in 2013 changed how antibiotics can be used. According to Final Guidance 213 and the proposed Veterinary Feed Directive (VFD) rule, antimicrobials medically important in human medicine (this includes all of the antimicrobials approved for swine except carbadox, bacitracin, and bambermycins) previously used at subtherapeutic levels for production purposes (improved growth and efficiency) are no longer allowed for that purpose. Instead, they are allowed only for disease prevention and only under veterinary supervision and oversight. This regulation applies to antibiotics used in feed or water. Companies that produce those antimicrobials are asked to voluntarily remove the production improvement claim on their product labels. These products will no longer be available to producers on an “over-the-counter” basis; they will only be available on a VFD basis. The FDA gave the industry 3 years to implement the changes.

Microbials that are directly fed (once referred to as probiotics), such as live cultures of Lactobacillus acidophilus, Streptococcus faecium, and Saccharomyces cerevisiae, have been evaluated as possible substitutes for antibiotics, but controlled studies have not shown consistent, beneficial responses from their inclusion. In some instances, inclusion of specific sugars (mannanoligosaccharides, fructooligosaccharides [also called prebiotics]) have shown promise as possible alternatives to antibiotics for young pigs, but growth responses are less consistent and of lower magnitude than from the inclusion of antibiotics. The direct-fed microbials and oligosaccharides are thought to encourage growth of desirable microorganisms in the GI tract, such as lactobacilli species and bifidobacteria that partially displace some of the less desirable microorganisms, including some pathogenic microbes.

Certain “repartitioning agents” have been tested with finishing swine and found to be very effective in improving growth rate, feed conversion, and carcass leanness. Examples are β-agonists, such as ractopamine and porcine somatotropin. Presently, ractopamine is the only such agent approved for use in pigs in the USA. These agents affect nutrient requirements, in particular by increasing the dietary requirements for amino acids.

Last full review/revision March 2015 by Gary L. Cromwell, PhD

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