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. Accurate information on the amount of feed consumed is critical for adequate and economical management of nutrient supply. Estimates that underpredict feed consumption will lead to an excess of nutrient fortification economic loss, while overprediction of feed consumption will potentially contribute to nutrient inaccuracies.
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, nutrient adequacy, environmental temperature and humidity, sex, animal stocking density, and feed quality (eg, absence of molds), as well as a host of other management factors, such as feeder design, flooring conditions, ventilation, and pen cleanliness.
Major Feed Ingredients for Pigs
A fundamental principle of the economics of pork production is to feed the most economical cereal grains and correct deficiencies by supplementation with good-quality protein sources, minerals, and vitamins. Dependable mineral and vitamin premixes or complete manufactured supplements are commercially available. Less expensive, fortified corn-soybean meal diets are very common in swine enterprises, but other cereals and protein sources can be used.
Corn (maize) grain is by far the most widely used grain for feeding pigs in the US. Corn is very palatable and has a high energy density but possesses a relatively low protein content with a poor amino acid profile. Corn grain 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 regions of the US. The protein content is variable, depending on several agronomic factors. In general, grain sorghum can be substituted for corn; however, because the metabolizable energy (ME) value is slightly lower than that of corn, a decrease in feed efficiency is expected. Economic decisions must include an estimate of the increased consumption required to achieve an equal amount of growth.
Wheat has approximately the same energy content as corn and contains 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. Substitution on an equal protein basis will result in a lysine deficiency. Wheat can constitute all of the grain in a swine diet; however, the feed processing method for wheat should be considered. A fine grind of wheat grain may affect pig feed consumption and feed flow in storage bins and feeders. The two main types of wheat grown in the US, hard red winter and soft red winter, have equivalent nutritional value.
Barley has approximately 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 due to concerns for mold and mycotoxins.
Whole oat grains have a relatively low energy content and, therefore, should not account for more than 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 oat groats are sometimes used in starter diets because of their excellent palatability and digestible fiber content.
Cereal grains should be ground or rolled to maximize their feeding value. Corn and grain sorghum should be ground to a medium-fine particle size (550–600 mcm). Wheat should be ground more coarsely (650–700 mcm) to prevent "pasting" as pigs consume fine-ground wheat. Fine grinding improves feed conversion; however, too fine a grind may lead to 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. Depending on the level in the feed, aflatoxins, vomitoxin, zearalenone, fumonisins, and other mycotoxins can decrease animal performance and can especially cause reproductive problems in breeding animals.
Soybean meal accounts for > 90% of the supplemental protein ingredients fed to pigs in the US. Soybean meal 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 heat treatment (by extrusion or roasting) to inactivate the trypsin inhibitors and other heat-labile antinutritional factors.
Miscellaneous protein ingredients, including canola meal, 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 amino acids because of the lower lysine content or an imbalance of other essential amino acids. Animal protein sources such as meat meal, meat and bone meal, or fish meal can supply a portion of the supplemental amino acids in swine diets. Diets including these protein ingredients are commonly fortified with feed-grade amino acids using least-cost formulations.
Distillers dried grains with solubles (DDGS) is a coproduct of the ethanol fermentation industry. This coproduct is an excellent and generally economical feed ingredient for swine. Although DDGS has essentially no starch and considerably more fiber than corn, the ingredient has a higher fat (corn oil) content; hence, the ME content of DDGS containing 9–12% fat is similar to that of corn. The amino acid profile generally reflects corn amino acid profiles, and diets must be formulated to meet the essential amino acid requirements. Multiple new coproducts have been generated as ethanol fermentation plants continue to refine processing methods and strive to extract a greater portion of energy products for fuel. These coproducts include ingredients such as “low-fat” DDGS (generally 5–9% fat), “de-oiled" DDGS (< 5% fat), etc. Because much of the fat is removed, these ingredients have substantially lower ME and thus a lower feeding value.
DDGS and related coproducts are economical ingredients for pig diets when they are properly formulated. Diets containing 20–25% DDGS are well utilized by pigs. However, diets with > 30% DDGS fed to finishing pigs result in carcasses with “soft fat” as the body fat of pigs becomes more unsaturated, as evidenced by higher iodine values. The softer fat results in more flexible bellies that are more difficult to process into bacon slices and affects consumer acceptance. 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 weeks of the finishing period.
Feeding Management of Sows and Litters
The economically available ingredients commonly fed in the US result in diets that oversupply energy requirements for gestation. Thus, gestating sows must be limit-fed rather than allowed free access to feed. The necessity for limit-feeding creates a management dilemma for sow housing. Individual housing in gestation stalls offers an option for limit-feeding yet creates welfare concerns. It is difficult to provide limited feeding to pigs in group housing, due to social aggressive-recessive behaviors that compromise sound animal management, unless options for individual feed delivery, such as electronic feeders, are provided for group housing.
Gestation diets must be adequate in all nutrients for sows to produce healthy, vigorous pigs. Sows' body condition should be regulated by adjustments in gestation feed allotment to prevent sows at farrowing from being either too fat or too thin. Fat sows tend to have more problems at farrowing and will consume less feed during lactation, which delays return to estrus after weaning. Thin sows have a greater risk of pelvic organ prolapse and an increased risk of death during lactation or at weaning.
After farrowing, sows should be returned to full feed as soon as possible. Lactation diets typically contain lower concentrations of nutrients than gestation diets. However, because lactating sows consume a greater amount of feed than during gestation, the amounts of nutrients consumed per day are greater. Attention to the amount of feed consumed during lactation is critical for milk production and piglet health. Environmental temperature is a challenge during lactation because the thermoneutral zones for sows (13–18°C [55–65°F]) and baby pigs (29–35°C [85–95°F]) are drastically different.
Heat stress decreases sow feed consumption, thus reducing milk production, and potentially increases piglet death. Cold stress also increases piglet death. Thus, housing designs to provide zonal environments and decrease drafts for the piglets and lower overall room temperatures for sows are ideal designs. Additional management factors (eg, strict all-in-all-out management practices, room sanitation procedures, and vaccination protocols) ensure sow health and decrease subclinical health concerns that alter sow feed consumption.
Other issues, such as constipation in sows, are 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 or 10% if constipation is a problem. Chemical laxatives, such as potassium chloride or magnesium sulfate, can be included in the lactation diet at 0.75–1%; however, management efforts should be applied to limit dependencies on these approaches.
Newly farrowed pigs should be checked to ensure that each piglet has consumed colostrum. Small-weight or weak pigs may benefit from oral doses of artificial milk, but success depends on good management and sanitation. For overall piglet health, more successful, less labor-intense practices are approaches directed toward care of the sow as previously described. For sows with delayed milk let-down, milk flow may be stimulated by administering oxytocin to the sow. Nutritional anemia should be prevented by giving an iron injection before 3 days of age.
Pigs from large litters may be transferred to sows with a smaller number of piglets after they have consumed colostrum; however, the transfer should be done within the first 24 hours after birth. Best practices are to transfer the larger piglets, with efforts to make the litters more uniform in weight. A palatable pig starter diet, provided at 3 weeks, may increase piglet growth if pigs are weaned later than 3 weeks of age. (See also Health-Management Interaction: Pigs and Management of Reproduction: Pigs.)
Feeding Management of Weanling and Growing Pigs
Pigs are typically weaned at 18 to 25 days because this age optimizes sow rebreeding and reproductive efficiency. Weaned pigs grow best if they are allowed free access to a complex starter diet for 3–7 days after weaning, then transitioned to 2 or 3 less expensive diets for a 4- to 5-week nursery phase. Typically, nursery diets contain multiple sources of more digestible protein ingredients than those in grower diets and lower concentrations of soybean meal. Nursery diets' more expensive ingredients include milk-based products such as dried whey, lactose, and other coproducts from the food industry. Additionally, animal protein sources, such as dried blood and plasma products, are included, with caution to source ingredients from vendors that maintain quality control procedures to ensure nonpathogenic, high-quality products. These more expensive ingredients are balanced with feed-grade synthetic amino acids that include lysine, tryptophan, threonine, methionine, isoleucine, and valine to assure an optimum balance of amino acids in the complete diet. The gradual transition to less expensive nursery diets eventually progresses to the corn-soybean meal diets typically fed to growing pigs.
Because 60–80% of the total production cost for swine enterprises is feed costs, opportunities to minimize feed cost and maximize profits are most likely realized during the growing and finishing phase of production. The nutritional needs of growing-finishing pigs are best met by allowing free access to less expensive corn-soybean meal diets formulated on a least-cost basis with feed-grade synthetic amino acids. Alternate major feed ingredients were discussed above. Decisions to use alternate energy and protein ingredients, assuming correct formulations, are driven by ingredient costs. Limit-feeding decreases 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 waste or restricted growth.
Growth Stimulants for Pigs
Historically, antimicrobials and other chemotherapeutic agents were commonly added to swine diets to promote growth and feed efficiency, decrease deaths and morbidity, and improve health. The greatest responses to these growth-promotant compounds were observed in young pigs, with lesser responses as pigs progressed in age and weight. Improvements in herd health, facility designs, and management practices have lessened the economic benefits of these products. Furthermore, current use of these additives now requires a Veterinary Feed Directive following guides regulated by the FDA. (See also Growth Promotants and Production Enhancers.)
This FDA action has changed how antimicrobials can be used. According to the FDA's Guidance for Industry 213 and the 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 antimicrobials used in feed or water.
Microbials (probiotics) that are directly fed, such as live cultures of Lactobacillus acidophilus, Streptococcus faecium, and Saccharomyces cerevisiae, have been evaluated as possible substitutes for antimicrobials, but consistent beneficial responses from their inclusion have not been documented. In some instances, specific sugars (mannanoligosaccharides, fructooligosaccharides [also called prebiotics]) have shown promise as possible alternatives to antimicrobials for young pigs; however, growth responses are less consistent and of lower magnitude than from the inclusion of antimicrobials. 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.
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 also effective growth stimulants in young pigs.
