The sow herd is the engine that drives a pork production system. When things do not go well in the sow herd, the consequences ripple, and sometimes crash, through the rest of the production system for the next six months or more.

We all know that every engine needs fuel to perform properly, and the sow herd's primary fuel is feed. Sows need high-quality feed in the right form and amount to perform at optimal levels.

Concepts of Sow Nutrition

Two overriding concepts of sow nutrition must be recognized to achieve performance goals.

First, realize there is no one set of diet formulations that satisfy the needs of all sow herds. Diet formulations in gestation need to be based on physical size of the sows, their expected pregnancy weight gain, expected litter size at farrowing and the desired feeding level.

During lactation, diet formulations are based primarily on the number of pigs nursed and the expected voluntary feed intake of sows. Since these traits are not the same across all sow herds, diet formulations will vary. It is important for producers to use herd-specific diet formulations.

The second important concept of sow nutrition is that phases of the sow's reproductive cycle are interrelated.

For example, lactation feeding programs are designed to maximize the sow's milk production to produce large, heavy litters at weaning. However, if this objective is achieved by mobilizing nutrients from the sow's body, she will be thin at weaning and her return to estrus will be delayed or even fail.

That is why we feed sows for current performance with the intent of setting the stage for future performance.

Keeping Sows in Condition

Gestation is a good time to get sows in proper body condition and prepare them for the challenges of lactation.

Pregnant sows have nutrient requirements for body maintenance, development of the products of conception (fetuses, placenta, uterus, mammary glands) and maternal body weight gain. Energy requirements for body maintenance are directly related to sow size and account for 75% to 85% of the sow's total energy requirements. Requirements for the developing litter are relatively small, but have a very high priority.

Once requirements for maintenance and fetal growth are satisfied, any leftover nutrients are directed to growth of maternal body tissues. These tissues, fat and muscle, are what we evaluate when determining body condition of sows.

These tissues serve as reservoirs of energy (fat tissue) and protein (muscle tissue) to support the nutritional needs for milk production in the coming lactation period.

Continue Reading on next page: Feeding During Gestation

Feeding During Gestation

Determining the proper feed allowance is crucial to the success of a gestational feeding program. The proper feed allowance will ensure large, healthy litters and allow adequate body tissue reserves.

To achieve this objective, gilts (Parity 0) should gain 80 to 100 lb. of weight during their first gestation. Parity 1-4 sows should gain 60-80 lb. Mature sows (Parity 5+) should gain about 55 lb. from conception to farrowing.

Target backfat thickness at the 10th rib should be 0.7-0.8 in. at farrowing. Some very lean genotypes will have difficulty achieving this level of backfat thickness.

Young sows (gilts through mating for the third litter) deserve special attention during gestation and lactation. These young sows are still growing and require different quantities of nutrients than older sows.

Generally speaking, if young sows remain in the herd through farrowing their third litter, there is a pretty good chance they'll be around for a fifth or sixth parity. Producers serious about meeting the needs of young sows will feed them at different levels than older sows, and they will install a second feed bin to allow feeding a diet tailored to the needs of the young, gestating sows in the herd.

There are several ways to monitor sow body condition and effectiveness of the gestational feeding program. Subjective condition scoring is often used, but is not considered very accurate because sows with the same condition score can have drastically different backfat levels. A direct measure of backfat thickness with an ultrasonic probe is more accurate than condition scoring, but does not account for changes in body weight.

Weighing Gestating Sows

Since sow body weight determines the majority of nutrient requirements of a gestating sow, it is very important to accurately determine body weight of sows. The best way to do this is to weigh sows with a livestock scale. The only true replacement for a livestock scale is another livestock scale! Visual assessments of body weight are not accurate.

On many farms, installing a scale in a common hallway between gestation and farrowing rooms allows workers to weigh sows as they enter the farrowing room and again when they leave at weaning. Weighing requires extra labor, but this information is extremely important for evaluating the gestation and lactation feeding programs, as well as an aid in fine-tuning sow feeding programs.

Every sow does not have to be weighed. Farms can select smaller groups of sows, maybe one week's production during each season of the year, to monitor weight changes. Weighing sows after a change in the feeding program will also help evaluate the effectiveness of the change.

In the absence of a livestock scale, producers can estimate sow weight with a flank-to-flank tape measurement. To record this measurement, a cloth tape measure is stretched from one rear flank over the sow's back to the opposite rear flank. This flank-to-flank measurement is used in the following equation, developed by workers at Kansas State University, to estimate sow weight:

Sow weight, lb. = 26.85 × (flank measurement, in.) — 628.

This approach properly assigned sows into 75-lb. body weight categories about 70% of the time. While not as accurate as a scale, it certainly is more accurate than “eyeballing” sow weight. Using this method can help producers determine sow weight and ultimately the proper feed allowance for sows.

The consequences of incorrect feed allocations and body condition can be significant. If sows receive too much feed and become overweight, they will have depressed feed intake during the subsequent lactation period (Figure 1), and may have reduced sow longevity. In addition, high feeding levels may cause sows to get too big to fit comfortably into individual gestation stalls and farrowing crates.

In contrast, underfed sows won't maintain adequate tissue reserves to support a normal lactation, especially if management or environmental factors limit voluntary feed intake. This will lead to an increased wean-to-estrus interval and reduced prolificacy.

Continue Reading on next page: Feeding During Lactation

Feeding During Lactation

In contrast to the goal of controlled feed intake during gestation, the goal in lactation is to maximize sow feed intake. Achieving this goal minimizes loss of body condition, supports heavy weaning weights, promotes prompt return to estrus and boosts the size of the subsequent litter.

A recent study of performance records in the University of Minnesota's sow research unit revealed the importance of feed intake during early lactation. In this study, the odds that a sow would be culled from the herd before the next parity increased significantly if she averaged less than 7.5 lb. of feed/day or had at least one day with zero feed intake during the first 14 days of lactation.

An earlier study at the University of Minnesota demonstrated that the sooner after farrowing a sow reaches peak daily feed intake, the more total feed she will consume during lactation, and the more likely she is to return promptly to estrus.

Therefore, feed lactating sows aggressively after farrowing. Bring lactating sows to full feed by Day 4 or 5 after farrowing to encourage maximum feed intake.

Ideally, sows will experience no loss of body weight from farrowing to weaning to optimize subsequent reproductive performance and longevity in the herd. Small weight losses of 10-20 lb. should have no negative consequences.

Compromised reproductive performance can result if the sow experiences depressed feed intake and the associated negative nutrient balance during any period of lactation.

It is especially important for young sows to consume large quantities of feed during lactation, because they are more susceptible to negative nutrient balance than older sows. Diets with higher nutrient concentration and specialized ingredients might be warranted in many herds to meet the needs of these young sows.

Recent studies suggest that low levels of spray-dried animal plasma encourage increased feed intake by young sows, especially during summer. Specialized diets for young sows may require an additional feed bin to supply these lactation diets.

Focus management of lactating sows on maximizing feed intake by:

  • Keeping room temperatures as close to 65°F as possible to maintain optimum sow comfort;

  • Feeding multiple times/day to ensure feed is always available;

  • Keeping feed fresh and clean; and

  • Assuring that an ample water supply is available.

If sows are hand-fed, be sure to record feed offered on a stall card. This allows workers to track how the sows are doing, and encourages communication among workers regarding how sows are being fed.

Some producers have installed automatic feeding systems for lactating sows that allow the sows to choose when they want to eat and how wet they want their feed to be. These systems provide all of the feed sows want from a couple of days after farrowing until weaning.

One study conducted during the fall and winter seasons correlated increases in sow feed intake, weight gain during lactation and piglet weaning weight with automatic feeding systems (Table 1).

In hot weather, use drip coolers, shift feedings to the cooler times of the day and add water to the feed, but be sure remaining feed does not sour. Talk with your nutritionist about special formulations for hot weather.

Continue Reading on next page: Water, Feeding Methods

Don't Forget Water

Water is the most important nutrient in the sow's diet. Farm staffs often ignore water because cups or nipples supply it automatically. The workers don't have to expend any effort to get water to the sows, so it is easy to forget about it.

Pregnant sows will consume 3-6 gal. of water daily, while lactating sows can consume up to 9 gal. daily. These large amounts of water require a supply system that ensures ready availability to sows. Water flow rate from cups or nipple drinkers should be at least 4 cups/min. (1,000 ml/min.). Restricted flow rates will reduce feed intake and increase weight loss of lactating sows (Table 2).

Water quality is also important. Poor-quality water might depress intake and compromise sow performance. The National Academy of Sciences and others have recommended water quality standards for livestock (Table 3). Water should be tested annually.

Feed Delivery Methods

The primary objective of a feed delivery system is to guarantee that each sow receives her daily allotment of feed. Regardless of the method employed, accuracy of feed delivery equipment is important. Commonly used automated feed drops must be calibrated regularly to ensure sows receive the proper amount of feed. Most feed drops are based on volume, so changes in bulk density of feed can have an important impact on quantity of feed delivered to sows.

Remember, sows eat pounds, not quarts or gallons of feed. Ideally, feed drops should be calibrated monthly. At the very least, calibrate them with each change of feed ingredients, which could influence bulk density and change of season.

Feeding Frequency

Some advisors have suggested feeding sows multiple times daily during gestation to decrease boredom; reduce occurrence of stereotypic behaviors such as sham chewing, bar biting and vacuum chewing; and possibly improve efficiency of diet utilization. Reports from the field suggest that sows are calmer when fed multiple times/day.

However, work at the University of Minnesota showed no difference in occurrence of stereotypic behaviors or digestibility of dietary energy and protein when sows were fed once compared to twice daily. Similarly, researchers at Kansas State University found no benefit of feeding sows six times/day compared with twice/day.

Electronic sow feeders (ESFs) are not a new idea, but they have received renewed interest as producers consider group housing of pregnant sows more seriously. ESFs allow group-housed sows to be fed individually. Sows can consume their total daily allotment at one feeding or spread intake out over multiple feedings.

Like any sow housing and management system, group housing with an ESF can result in sow performance comparable to gestation stalls if managed properly. There are labor requirements for training gilts to use the system; monitoring daily intake of sows; replacing lost ear tags; and maintaining the computer, feeding station and air compressor that controls gates.

Pigs require nutrients, not ingredients, in their diets. Less expensive sources of nutrients may be considered.

In the search for alternative ingredients, one must consider a wide range of attributes before including them in sow diets (Table 4). Be especially cautious to avoid any disruptions in the performance of the pork operation's engine (the sow herd).

The recent explosion in ethanol production has created a mountain of its co-product, distiller's dried grains with solubles (DDGS). Numerous research studies have been conducted to evaluate DDGS as a component of grow-finish pig diets. However, relatively little work has been reported on feeding DDGS to sows.

Continue Reading on next page: Alternative Feed Ingredients, Take Home Message, Reference Tables

Our first study evaluated diets containing 50% DDGS in gestation and 20% DDGS in lactation. This study demonstrated that 50% DDGS in gestation diets supported sow performance equal to a corn-soybean meal control diet. Including 20% DDGS in the lactation diet supported performance equal to the control diet. However, sows should be transitioned onto a high DDGS diet gradually to allow time for them to adapt to the new diet.

A more recent study, completed in 2006, investigated inclusion of up to 30% DDGS in diets for lactating sows. Up to 30% DDGS in the diet supported lactation performance that equaled that of sows fed the corn-soybean meal control diet (Table 5).

Production of ethanol does not destroy mycotoxins that might be present in the source corn, but rather concentrates them by a factor of three. This has raised concerns among nutritionists and pork producers.

However, there seems to be only a small risk of mycotoxin contamination of DDGS because most ethanol plants screen incoming corn for quality and reject moldy, off-quality grain. Producers need to work with their DDGS supplier to ensure mycotoxins are not a problem in the DDGS product being fed.

Currently, it appears that producers can include up to 50% DDGS in gestation diets and 30% in lactation diets without negatively affecting sow performance.

The drive to use more biofuels has bolstered interest in biodiesel. In the production of biodiesel, a variety of fats are mixed with methanol and a catalyst to strip the fatty acids from the glycerin. The fatty acids are used in biodiesel and the glycerin is left for other uses.

Soybean oil is the predominant fat being used for biodiesel production, but other fats can also be used. Glycerin can be incorporated in swine diets as an energy source.

Early studies with nursery and grow-finish pigs suggest glycerin has an energy value very similar to corn. Crude glycerin may contain high levels of methanol and salt, which need to be considered in diet formulations. But at high inclusion rates, feed may not flow easily through commercial handling and feeding equipment. The value of glycerin in sow diets has not yet been determined. The swine nutrition research group at the University of Minnesota is currently studying the use of crude glycerin in lactating sow diets.

Societal concerns for the welfare of limit-fed gestating sows have led some to consider high-fiber diets for pregnant sows. Limit-feeding gestating sows to control weight gain can lead to stereotypic, repetitive behaviors that some people equate to compromised welfare.

European researchers have significantly reduced expression of these behaviors with very high (over 45%) inclusion rates of fibrous feedstuffs, such as sugar beet pulp, oat hulls, wheat bran and others. These results suggest that pregnant sows may have a behavioral requirement that high-fiber diets can satisfy without making them fat.

Unfortunately, diets that successfully control stereotypical behaviors do not flow well in U.S. feeding systems. We were not successful in decreasing these undesirable behaviors when sows were fed a diet containing 40% soy hulls that did flow through a commercial feed handling system. Future research will determine how best to utilize fiber in sow diets under U.S. conditions.

Take-Home Message

Feeding the sow herd is a complex venture that requires consideration of numerous factors. Attention to detail throughout the feeding program is important for success. Proper feeding during gestation and lactation sets the stage for optimal performance in subsequent phases of the reproductive cycle.

All sow herds are not alike. Producers must be open to new ideas and evaluate nutrition and management approaches that make economic sense in their herds.

Table 1. Influence of Automatic Feeding System for Lactating Sows
Trait Hand-fed Self-fed
Feed intake, lb./day 11.9 13.0
Sow weight change, lb. 1.3 13.7
Pig weaning weight, lb. 13.5 14.6
Peng et al. (2007)
Table 2. Effect of Water Flow Rate on Feed Intake and Weight Loss of Sows Through Day 21 of Lactation
Winter Summer
Water flow rate (cups/min.)
Item 3 0.3 3 0.3
Feed intake, lb./day 11.3 9.3 8.9 8.0
Sow weight loss, lb. 11.6 31.0 30.5 46.3
Leibbrandt et al. (2001)
Table 3. Recommended Water Quality Standards for Breeding Swine
Trait Recommended Maximum
Total dissolved solids <5,000 ppm
Nitrate N + Nitrite N <440 ppm
Nitrite N <33 ppm
Total coliforms <50 per ml
NRC (1998); EPA (1973)
Table 4. Attributes to Consider in Selecting Alternative Feed Ingredients
Nutrient profile Cost per unit of nutrient supplied
Presence of anti-nutritional factors Ease of handling
Presence of toxic compounds Digestibility of nutrients
Palatability Availability
Consistency
Table 5. Performance of Lactating Sows Fed Distiller's Dried Grains with Solubles (DDGS)
Dietary DDGS (%)
Trait 0 10 20 30
Sow feed intake, lb./day 14.3 14.5 15.4 14.7
Litter size weaned 9.7 9.6 9.9 9.8
Litter weight gain, lb. 100.3 103.3 103.1 100.4
Song (2007)