Dietary Effect on Maternal Performance

Increasing the productivity of the sow herd continues to be a key objective of pork producers in order to enhance the profitability of swine operations. An important component of improving the productivity of a sow herd and profitability is providing optimum nutrition to gestating and lactating sows. Determining optimum nutrition has been an objective of the sow research at Kent Feeds Research Farm over the last decade.


Genetic companies have made great strides in selecting a maternal line with increased litter size. Iowa State researchers (Vonnahme et al., 2000) demonstrated this recently when they determined the ovulation rate of multiparous sows (ranging from 1 to 14) of PIC’s Camborough line. Ovulation rate of the Camborough line was 26.6 compared to 16-18 typically reported by university researchers in university herds. This disparity of ovulation rate between the Camborough line and the university lines astounded researchers.


These ISU data help us better understand the type of sow in commercial operations – much different than the 2-way cross or 3-way cross of ten years ago. Scientists, veterinarians, geneticists, and producers need to continue to explore better management techniques, nutritional needs, and ways to improve her health status.


In this paper we will explore the nutrient needs and nutrition management of today’s prolific sow.




There are differences in approaches to feeding gestating sows in the swine industry today. Some have chosen to feed gestating sow diets with nutrient levels similar to the NRC (1998) minimum requirements. Others have opted to feed diets significantly above NRC (1998) minimum requirements. At Kent Feeds, we attempt to base our recommended levels on scientific research with some safety margin.


Feeding management of sows has evolved over the past few years. With a majority of sows being housed inside (and mostly in crates) few producers alter nutrient concentrations of the diet by lowering protein, mineral, and vitamin levels for winter-time feeding when feed intake was increased. Most producers today have one gestation diet. Feeding rate is individualized based on the condition of each sow or pen of sows.


In the swine industry, there is little consensus on the crude protein (lysine) level required in the gestating sow diet. Recommendations (specifications) range from 12 to 16% crude protein (0.55% to 0.80% lys). At Kent Feeds we recommend 13% crude protein (0.58 to 0.60 lys) for multiparous herds. In the early ’90s, Kent Feeds conducted a gestating sow trial comparing 13 vs 16% crude protein. Increasing the crude protein in the gestating sow diet did not improve sow reproductive performance.


Mahan (1998) evaluated two levels of crude protein (13 vs 16%) in the gestatng sow diet of a high-producing genotype and concluded that primiparous sows require a higher gestation protein concentration, but a 13% crude protein diet was effective for older sows.


Researchers at the University of Nebraska (Casey and Johnson, 1999) studied the benefits of increasing the amounts of protein (11.6 vs 18.1%), vitamins, and certain minerals 50% during gilt development through lactation of 3 genetic lines of gilts that had been selected for large litter size. Number of pigs weaned was not significantly affected by gestation diet and lactation diet. Pigs of sows fed the high-nutrient diet during gestation were .95 lb (P <.05) heavier at weaning than pigs of control sows which the authors suggest was a carry-over affect of the gestation diet on milk production and pig growth.


There is some evidence that increasing the crude protein level in the gestating gilt diet to 15-16% in a start-up situation may be beneficial. In a sow herd of multiple parities, we believe it is most cost effective to feed a 13% CP (0.58-0.60% lys) gestation sow diet.


Another area of interest at Kent Feeds has been the addition of a fiber source in the diet of gestation sows. Reese (1997) reviewed the published literature on the benefit of fiber in the gestating sow diet. Sows fed the fiber-added diets compared to the controls farrowed and weaned more pigs, had greater lactation feed intake, less weight gain during gestation and reduced pig birth weight. French researchers (Ramonet et al., 1999) reported that sows fed high-fiber diets were quieter, and exhibited fewer nonfeeding oral behaviors which may be associated with improved welfare.


Many fiber sources including alfalfa meal, alfalfa haylage, corn gluten feed, distillers grains, oats, wheat straw, corn cobs, soy hulls, oat hulls, and sunflower hulls have been used as fiber sources in gestating sow diets. Many of these fiber sources are impractical to use in today’s feed handling systems. During the past decade Kent Feeds has conducted several trials to find an optimum fiber source and level that will benefit litter size and lactation feed intake, is economical, and can be conveyed in today’s feeding systems.


The two fiber sources that best meet the criteria describe above are soy hulls and oat hulls. In the early 1990s we conducted a trial comparing added oat hulls with a low-fiber diet. When all sows were included in the data base, the number of pigs born alive for all sows was increased 0.68 pigs (P <.05) with the added oat hulls in the diet. There was no difference in feed intake during lactation when feeding the added fiber in gestation; however, with parity 1 and 2 sows feed intake tended to be greater when oat hulls were included in the gestation diet.


In more recent trials, we have not observed any benefit of added fiber in the gestation diet on litter size. The lack of response in recent years may indicate that with “newer” genetics, there may be no effect on litter size. However, there is some indication that added fiber in gestation improves lactation intake. The following data are from a trial conducted at the Kent Research Farm in which two fiber sources were compared with a low-fiber control. Average feeding level during gestation was similar for all treatments.


Table 1. Fiber diet differences compared to low-fiber controls in gestation

  +Oat Hulls +Soy Hulls
No sows/treatment 49 56
No. pigs born alive +0.4 -0.14
Avg pig birth wt, lb -0.19 -0.06
Sow gest wt gain, lba -15 -18
Sow 14-d lact feed intake, lb/db +0.8 +0.5
Sow 14-d lact wt change, lb +3.1 -0.8

aControl vs +oat hulls, P=.07; Control vs +soy hulls, P=.02
bControl vs +oat hulls, P=.10


In this trial (table 1) including oat hulls and soy hulls in the gestating sow diet did not increase the pigs born alive, but did reduce gestation weight gain. Lactation feed intake of the sow was increased (P=.10) compared to the control sows.


Many sow units have successfully incorporated a fiber source in the gestating sow diet. The economic benefit of greater feed intake during lactation based on the added fiber source in the gestating sow diet is difficult to assess.




Based on the available data, Kent Feeds recommends the inclusion of chromium tripicolinate in the sow diet. With the recent drop in price of chromium tripicolinate, it is economically feasible to use. From a practical standpoint, the addition of 200 ppb chromium in sow diets can be easily accomplished. The recommendation is to start feeding chromium to replacement gilts from 50 lb on up. This not always possible because some farms do not receive their replacement gilts until they weigh 200-220 lb.




With the wide acceptance and use of 17- to 21-day weaning age in the US swine industry, producers have learned from research and experience that it is important to get as much feed into the lactating sow as possible. Several years ago there was a debate surrounding how best to feed sows – bring them up quickly (ad lib) or a slower step-up.


During this time, Kent Feeds conducted a trial to compare an ad lib feeding regimen (bring up to full feed within 3 days) or a step-up program (feeding level was increased slowly over 8 days).


Table 2. Lactating sow feeding management

  Ad lib Step-up
No. of litters 72 76
Pigs at 14 days 9.11 8.68
Avg pig 14-d wt gain, lba 5.73 5.25
Sow 14-d lact. wt change, lbb -5.2 -14.7
Sow 14-d lact. feed intake, lb/dc 12.2 9.1
Sow 14-d backfat change, mma -1.2 -3.4

aAd lib vs Step-up, P < .05
bAd lib vs Step-up, P < .10
cAd lib vs Step-up, P < .001


Limiting the potential feed intake of sows through a severe step-up program reduced pig weight gain, (P <.05), increased sow weight loss (P < .10) and backfat loss (P < .05) during lactation. As expected, the average feed intake during lactation was less with the step-up program.


Many producers are bringing up sows to full feed within 2-3 days and attempting to maximize feed intake. To do this requires sows to be fed 2-3 times daily in order to keep the feed fresh, prevent feed wastage, and stimulate feed intake. Not many producers are feeding 3 times per day because of the labor required to do so.


In the Midwest, producers who are adding fat to meal lactation diets, are typically adding 2-3%. Adding high levels of fat (5-8%) to lactation diets has not been in vogue – partly due to the difficulty in handling the complete meal feed.


In most farrowing units priority should be given to managing sows such that feed intake is increased rather than relying on the additional calories from fat. Increasing feed intake from 10 to 12 lb/d of a typical no-added-fat, corn-soy diet will increase ME intake 2960 Kcal/day. Adding 3% fat to the diet of sows eating 10 lb/day, increases energy intake approximately 470 Kcal/day. The reward of ME/day is much higher from increasing feed intake than adding fat.


More attention has been given by researchers in the last few years to the crude protein (amino acid) needs of prolific lactating sows than any other nutrient. With little consensus among researchers and the data on the practical required amino acid levels for prolific sows, we see a wide range of crude protein (lysine) levels being fed to lactating sows.


In the early l990s, trials demonstrated that prolific lactating sows required a higher level of crude protein (amino acids) than the 15% (0.68-0.70% lysine) that was being fed. Many published trials and Kent trials demonstrated the benefit of feeding higher levels of amino acids in the lactation diet. During the mid-1990s, the concept of minimum daily nutrient levels for lactating sows took hold. Feed companies based lactation diet recommendations on sow daily feed intake and/or number of pigs nursing. This strategy failed to catch on at the farm level, as it was impractical.


Today, most producers use one or two lactation diets. A start-up gilt herd may be fed higher CP (lysine) levels in some situations, than a herd of mixed parity sows. It is not unusual to see some producers feeding a 20-21% CP (1.3-1.4% lys) to a start-up gilt herd and 19-20% CP (1.2% lys) to a multiparous sow herd. The Kent Feeds recommended lactation program is 17.5-18% CP (.95% lys) for multiparous herds and 18-19% CP (1.0-1.05% lys) for gilt start-up herds.


It has been well established that young maturing gilts with a high potential for milk production, large litters, and generally low feed intake are extremely vulnerable to depletion of body stores, both energy and protein. Because intake of energy and protein are low, sows mobilize energy from fat reserves and amino acids from body protein. As a result, sow weight loss increases, nitrogen balance is negative, piglet growth rate decreases, weaning to estrus interval increases, and subsequent litter size may be decreased.


Based on trial work and computer models, the amino acid requirements of lactating sows of the 1998 NRC were increased considerably compared to those listed in the previous edition. Since the release of the 1998 NRC recommendations, researchers have attempted to verify the NRC levels of amino acid needs and determined if higher levels can be justified for high-producing gilts and sows.


Peters and Mahan (2001) concluded that feeding lysine levels above NRC (1998) recommendations does not affect sow or litter performance. Preliminary data from the Kent Research Farm suggest that increasing the crude protein level in the lactation diet from 17.5% to 20% (0.95% lys to 1.16% lys) by replacing corn with soybean meal does not improve litter weight gain (milk production) of multiparous sows. Moreover, at the higher protein concentration, feed intake (lb/d) of the sows decreased resulting in greater weight loss of the sows. We continue to accumulate numbers to verify this trend.


Summertime heat causes considerable stress on lactating sows resulting in reduced feed intake. Spencer et al. (2001) suggested that reducing the lactation length of heat-stressed sows (90°F) from 19 to 14 days can reduce the impact of sow tissue loss and future reproductive performance, especially in first-litter gilts. They also verified that heat stress can decrease subsequent litter size in both parity 1 and 2+ sows. In some situations weaning gilts early during hot weather to reduce additional tissue loss may be a management tool that can be employed.


We need to continue to support additional sow research on the nutritional needs and best management of today’s prolific sow in order to maximize reproductive performance and longevity in the herd.


Literature Cited


Casey, D.S. and R.K. Johnson. 1999. Response to Increasing Levels of Nutrients Fed During Gestation and Lactation to Control and Prolific Gilts. 1999 Nebraska Swine Report. University of Nebraska. 29-31.
Mahan, D.C. 1998. Relationship of Gestation Protein and Feed Intake Level over a FiveParity Period Using a High-Producing Sow Genotype. J. Anim. Sci. 76:533-541.
NRC, 1998. Nutrient Requirements of Swine (l0th Ed.). National Academy Press, Washington, DC.
Peters, J.C. and D.C. Mahan. 2001. Effects of dietary lactation lysine level, lysine source and dextrose on sow and litter performance. J. Anim. Sci. (Abstr)
Ramonet, Y., C. Meunier-Salaun, and J.Y. Dourmad. 1999. High-Fiber Diets in Pregnant Sows: Digestive Utilization and Effect on the Behavior of the Animals. 1999. J. Anim. Sci. 77:591-599.
Reese, D.E. 1997. Dietary Fiber In Sow Gestation Diets – A Review. 1997 Nebraska Swine Report. University of Nebraska. 23-25.
Spencer, J.D., R. Cabrera, R. Graves, R.D. Boyd, J. Vignes, and G.L. Allee. 2001. Effect of early-weaning (14 vs 19 d) on sow lactation performance during heat stress. I. Tissue loss, milk production and subsequent reproduction. J. Anim. Sci. (Abstr).
Vonnahme, K.A, S.P. Ford, M.E. Wilson, G.R. Foxcroft, G. Gourley, T. Wolf, and M. Quirk-Thomas. 2000. Controls of Litter Size-Do Conclusions Drawn from Institutional Herds Always Have Relevance to Commercial Swine Production? 2000 Swine Research Report. Iowa State University. 73-75.