Nutritional programs can certainly play a major role in the amount of weight variation within a common group of pigs. The ability to minimize this variation involves many management, nutritional and health decisions.

From a nutritional standpoint, there are numerous ways to minimize the variation within a common group of pigs by providing consistent, nutritionally adequate diets formulated for specific genders and weights. Historically, this has been accomplished by feeding simple cereal grain-soybean meal-based diets throughout the various production stages.

However, with current feed ingredient prices at record highs, any and all options to determine optimum use of alternative ingredients, as well as the most economical nutrient levels of various diets, are being explored.

As feed alternatives or lower-quality (less digestible) replacements for lactose, protein and energy are utilized in diets, the potential for increased variation in a common pig group is more likely.

The effect of increased variation generally is not evaluated when diet decisions are made. The decision to lower feed cost is commonly the overriding factor.

While limited research data has evaluated the impacts of different alternatives and lower-quality ingredients on total group weight variation, the effects can be pronounced if feed ingredients are of poor quality.

It is important to remember that increasing the growth rate of the entire group of pigs will not reduce variation in the group or the need to sort pigs at market. Increasing growth rate will, however, increase the weight of the slow-growing pigs, which is the main marketing issue.

Following are eight areas that producers should focus on as they attempt to increase the growth rate of an entire group of pigs:

  1. Use genetics capable of high growth rate in commercial conditions.

  2. Maintain high health status.

  3. Identify and use sows with high milk production.

  4. Aim for high lactation feed intake to increase weaning weight.

  5. Increase age at weaning.

  6. Increase energy density of the diet to increase growth rate.

  7. Feed correct amino acid levels.

  8. Optimize feeding of ractopamine (Paylean from Elanco Animal Health).

While this list provides a basis for improving the growth rate of an entire group, following are several areas where nutrition may have direct implications on reducing actual variation within a group of pigs.

  • Improve pig birth and weaning weights.

    Total pigs born/litter and number born alive/litter have increased dramatically in the last several years. Since 2000, the rate of progress has been approximately 0.2 pigs/litter each year.

    This dramatic increase in litter size has been achieved through the application of genetic improvement focusing on ovulation rate. While genetic selection for increased ovulation rate has increased litter size, unfortunately, it has also increased the number of stillborns/litter and lowered average pig birth weights.

    Many factors affect fetal growth and development, including sow ovulation rate, uterine capacity, genotype, nutrition and feeding regimens.

    Researchers are beginning to understand that uterine capacity, which determines the number of fetuses maintained during pregnancy, is one of the greatest limitations to litter size. And litter weight is directly related to litter size. Pigs born in large litters are lighter at term because of the decreased placental surface area available to each.

    Additionally, mobilization of energy substrates increases in sows with larger litters. Glucose is a major energy substrate for fetuses, and has been shown to decrease in sows with large litters, due to the high-energy requirement necessary to sustain the uterus and fetuses.

  • There are two approaches to help solve the variability in piglet birth weights — genetically or nutritionally. Genetically, producers could select for moderate ovulation rate with high embryonic survival to reduce lightweight fetuses. The nutritional approach is to increase nutrient availability to the lightest fetuses to increase their size.

    Research has shown secondary muscle fiber development, which is an important determinant of postnatal growth, can be improved by increasing sow feed intake from Day 25 to Day 50 of gestation or after Day 70 of gestation. But high-energy intake during gestation increases expense, decreases feed intake during lactation and impairs mammary gland development. And research shows that high intake in gestation doesn't always increase birth weight, secondary muscle fiber number or carcass parameters.

    The addition of L-carnitine, a water-soluble, vitamin-like compound, to gestation diets has consistently resulted in increased litter weights at birth and weaning.

    Other researchers have observed increased sow weight gain and improved average fetal weight at Day 70 of gestation in sows fed supplemental L-carnitine. These effects can be attributed to significant changes in gene expression due to L-carnitine supplementation, which is involved in the regulation of muscle fiber development of the fetus and, therefore, improves pig and litter weight at birth.

  • Increase weight gain of the smallest pigs in a farrowing group.

    Several procedures can be used to increase the weight gain of the smaller pigs in an attempt to reduce variation in a group. Split suckling, use of supplemental milk and shifting the smallest pigs to better milking sows are examples. These management techniques have been proven to slightly increase the weight gain of the small pigs and, thus, reduce variation at market weight. However, the impacts are all relatively small, so the economic payback must be carefully calculated before implementation.

    Split-nursing — allowing the smallest half of the litter access to the sow for two hours within a 24-hour period after farrowing — has been shown to reduce variation in average daily gain and, thus, numerically reduce the variation in weaning weight. But, again, the impact is relatively small (about 2% lower coefficient of variation [CV]).

    Research has also shown that offering milk replacer to nursing litters can effectively increase weaning weight and that weight is not lost during the nursery stage. Thus, the increased weight at weaning remains at market time, but it must pay for the entire cost of the milk replacer.

    Similarly, trials with complex nursery diets have demonstrated increased weight gain in the nursery. Although data has not been entirely consistent, the advantage often does not become larger during the finishing stage.

    These changes in pig weight are relatively small compared to the differences caused by weaning age, sex or health status.

  • Consider split-gender housing and feeding.

    Since barrows grow faster than gilts, raising pigs within a common group based on gender will reduce the variation within that group simply because the variation in growth rate compared to mixed-gender feeding is reduced. Because barrow and gilt growth rates differ, diets are often formulated for specific genders at given weights.

    Another approach is to feed barrows and gilts the same diets, but alter the feed budget to match their nutrient needs at different stages of growth.

    Although split-gender feeding is simple in concept, the production system must be large enough to fill a barn or site with one gender within a reasonable amount of time.

    If split-gender feeding is practiced, but it takes several weeks to fill the barn, the variation in pig weights within that barn will be greater than if the pigs were housed as mixed-gender groups from a common weaning group.

    Likewise, if a common barn is filled by gender in a short period of time, but the pigs come from multiple sow production sites, the health status of the pigs may be jeopardized, which may reduce growth rates of the entire barn.

    The bottom line is this — filling a site or barn over multiple weeks or from multiple sources produces other large sources of variation (weaning age, health status) that may overwhelm any advantage of single-gender housing. As a rule of thumb, if a barn cannot be filled with a single sex within seven days, pigs should be housed as mixed sex to improve facility utilization.

  • Feed multiple diets within a group.

    Grouping pigs by gender in order to feed higher amino acid levels to the gilts has been practiced in the industry for some time. However, simply dividing groups based on weight has not been commonly practiced.

  • Research has shown that feeding different energy level diets to the light pigs compared to heavy pigs can reduce final variation of a common group. In concept, the lightest 50% of pigs in a barn are fed a higher-energy diet than the heaviest 50% of pigs. Research clearly shows improved average daily gain when pigs are fed higher-energy diets, especially in the early finishing period.
  • Thus, feeding different diets based on initial body weight going into the finisher may help reduce the final variation in the barn.

    Another approach to increasing weight gain of the lighter pigs in a group is to bump amino acid levels. In reality, the lightest pigs may not actually have a higher amino acid requirement than the heavier pigs. Weight does not accurately depict the amino acid requirements within a population.

    Rate of protein accretion and feed intake are the major determinants of amino acid requirements. Therefore, the heavier, faster-growing pigs may actually have a higher amino acid requirement because they have higher protein deposition rates, even though they consume more feed. With current knowledge, we formulate diets for the light and heavy groups to have similar amino acid:calorie ratios based on their average weight.

  • Use alternative feed ingredients.

    The use of alternative feed ingredients that are cheaper than corn or soybean meal can lower diet costs. The challenge is to balance the lower cost with any other potential pitfalls that may come with the alternative ingredients.

    Before any alternative ingredient is used, the nutrient composition must be understood, and the aid of a professional nutritionist should be sought to minimize any negative effects and to capture the potential value.

    For example, the use of distiller's dried grains with solubles (DDGS) will lower diet cost in most situations. However, use of the ethanol by-product also reduces carcass yield, and has been shown to increase the variation in weight within a common group of pigs when fed through marketing.

    While less data is available on the effects of various bakery by-products, meat and bonemeal or fibrous ingredients, such as wheat middlings or soybean hulls, on variation of pig weight, producers need to be aware of the potential lost revenue if the alternative ingredients result in increased variation due to changes in feed intake patterns.

    In addition, the economic impact of the change in carcass yield or quality (carcass fat softness) must be taken into account when determining the value of alternative feed ingredients. With any alternative, increased sampling and ingredient testing must occur to determine nutrient variability. Then, an informed decision can be made relative to any potential negative impacts that the variability will have on pig performance.

  • Weigh health programs and antibiotic usage.

    Although “high-health systems” is a nebulous term, it is meant to encompass the many factors that improve the health status of pigs within a group.

    Research has shown that pigs reared in an all-in, all-out manner have less variation in growth rate and market weight (7.5% vs. 8.8% CV) than pigs reared in a continuous-flow manner.

    Other system design factors that can lead to sustained improvements in health status, such as reduction in sources of pigs, location of the source herd and location of the growing barns, would be expected to also reduce variation in weight gain.

    Promptly treating clinical disease to enhance recovery and reduce spread of the bacteria within the group will reduce the number of lightweight pigs at market and, thus, reduce variation.

    The use of feed-grade antibiotics has been cited as a means of reducing variation in final market weight. Published evidence is lacking that this phenomena actually occurs because the impact is relatively small. A large number of pigs or groups of pigs are required to experimentally prove or disprove the concept.

    However, there is evidence that in multi-site production systems, feeding antibiotics consistently results in improved growth rate of nursery pigs, but not in finishing pigs.

  • Consider pelleted feed.

    Pellets can be made of different lengths, diameters and degrees of hardness. The ingredients in the diet will influence pellet hardness and quality. Various studies suggest a 3-6% improvement in growth rate and feed efficiency when pigs are fed pelleted diets compared to a meal. The benefit appears to result from less feed wastage and the ability to use ingredients with smaller particle size.

    Pelleting appears to improve the nutritional value of high-fiber feed ingredients to a greater extent than that of low-fiber ingredients. This may be a result of increasing the bulk density of the feed. As with any feed processing method, the increased cost must be offset by the improved feed efficiency of pigs fed the pelleted diet.

    We are not aware of any data indicating that pelleting influences variation in growth rate.

  • Use nutrition to minimize seasonal variation.

    Although great strides have been made in managing the environment in barns, seasonal variation in growth rate remains a major obstacle within a production system. Pigs placed in the late summer through the early winter months grow faster than pigs placed in late winter and spring months (Figure 1). As a result, market weights are reduced by 6 to 13 lb. for pigs marketed in June through mid-September. Market price is normally highest during this same time period.

    For many production systems, 75 to 80% of the net profit for the year is derived during these summer months. The most profitable systems have determined methods to maintain market weights through the summer months. The only way that weights can be maintained is by increasing growth rate for groups of pigs finished during this time or by increasing days in the barn.

    Growth rate can be increased by one of two main feeding interventions. First, increase the energy density of the diet during summer months or for newly placed groups that will be marketed during the summer and early fall. Second, optimize ractopamine (Paylean) use by season of the year to assist in making market weights more uniform throughout the year.

    Because the response to ractopamine is consistent for pigs at various weights, it can also be used to increase the growth rate of the lightest pigs in the group to make them grow similar to the heaviest pigs. This is especially important during the summer months to maximize average daily gain of both the fastest and the slowest-growing pigs. In winter months, more emphasis is placed on slowest-growing pigs, as the growth rate of the entire group is higher.

    The difference between feeding ractopamine and increasing energy density of the diet is that feeding ractopamine is often economical regardless of whether the weight gain is needed or not. The economic value of feeding ractopamine is much greater in pigs that require the extra weight gain; however, the improvements in feed efficiency and carcass parameters (loin depth and yield) usually make it economical to feed to heavy pigs also. Thus, if ractopamine were only fed to the light pigs in the group, the potential increase in profit on the heavy pigs would be lost.

    If dietary energy is already at the economic maximum and ractopamine is already being used, pigs must be given more days to grow to achieve the same market weight in the summer due to the lower seasonal growth rate. Finding extra days is not easy, but the production system needs to be built with this flexibility.

    For example, wean-to-finish barns offer flexibility, as they can be double- or triple-stocked in the summer months to allow pigs in other barns more time before the facility is needed.

    Similarly, heavier stocking density in nurseries in summer months reduces the finishing barn requirements. Heavier stocking density will reduce growth rate of these pigs; however, they will be marketed during the winter months when space is normally not a problem.

  • Maximize water availability.

    As with all areas of production, clean, fresh water should be made available to pigs at all times. While this suggestion seems simple, it can be a source of concern if no one is paying attention to the pigs' water needs.

    Groups of pigs with insufficient access to water will have more variation. Plugged nipples, poorly designed water troughs or incomplete filling of gestation barn troughs caused by feed blockage can cause restricted water supply. Standard operating procedures on a farm should ensure that all pigs have proper access to feed and water.