Feeding for Reproductive Success

By Bob Goodband and Joel DeRouchey,
Kansas State University, Manhattan, KS

Interest in nutrition programs for developing gilts remains an area of focus for pork producers as sow lifetime productivity too often falls short of expectations. Because longevity is influenced by numerous overlaying variables, it is difficult to outline a single nutrition program that is best for all production systems.

Some farms have the capability to limit-feed developing gilts, while others full-feed them all the way to breeding.

The guiding principles behind any development strategy are that gilts should be mated at a moderate body weight (300 lb. or greater) and allowed to continue to grow through the first gestation period — reaching approximately 400 lb. at farrowing.

The objective of this report is to discuss the most important nutrients to consider in a gilt development program and to summarize some proposed feeding strategies.

Dietary Amino Acids

Dietary energy and amino acid (lysine, etc.) concentrations have the greatest impact on rate of protein and fat deposition, so they are the primary considerations when formulating diets for developing gilts.

It is important for producers to understand the lean and fat deposition rates of their replacement gilts in order to know the correct level of nutrients to supply. Most genetic suppliers can provide information on the nutrient requirements of replacement gilts from their maternal lines.

Historically, gilt development diets were often formulated to contain excess amino acid levels to encourage maximum protein deposition. Typically, producers not wanting animals to be short of nutrients at any stage of production had a tendency to simply increase the diet requirement over the animals’ actual needs, including amino acids.

Excess amino acids are wasteful, both from a cost and environmental perspective. Data from pork checkoff-supported studies indicates that excess amino acids may actually be detrimental for gilt longevity. In a trial, gilts were fed one of three different treatments: corn-soybean meal diet formulated to 0.95% lysine, corn-soybean meal diet with 5% added fat formulated to 0.60% lysine (fed from 150 to 250 lb.), or a high-protein diet restricted to 4 lb./day intake.

Gilts that were fed the moderate lysine level (0.60%) or were restricted to 4 lb./day feed intake had a higher probability of remaining in the herd through four parities (53% and 56%, respectively), than gilts with ad libitum access to the 0.95% lysine diet, where 33% completed four parities. Because fewer sows completed four parities, the number of total pigs born over the four parities was lower for gilts full-fed the 0.95% lysine diet compared with gilts fed the 0.60% lysine diet, or the gilts restricted in feed intake (22.2, 28.5 and 27.9 pigs, respectively). Clearly, there is no advantage to providing amino acids in excess of the gilts’ requirements.

Because the goal is to meet the needs of the gilt for normal lean accretion, formulating diets to meet the needs of the gilts on a gram-per-day basis will ensure the correct amount of amino acids are consumed daily, whether they are full-fed or on a restricted-feed intake system. Recommendations for dietary amino acid levels for replacement gilts can be found in the National Swine Nutrition Guide (2010) factsheet, “Replacement Gilt and Boar Nutrient Recommendations and Feeding Management,” available on the Pork Information Gateway Web site, www.porkgateway.org.

Dietary Energy Levels

Dietary energy intake of replacement gilt diets during the development period is more difficult to manage than the dietary amino acid levels.

The ultimate goal in gilt development is to prevent over-conditioned gilts at the time of breeding and during the first gestation period. Sows and gilts that are too fat have reproductive problems. Poor reproductive performance leads to a cascade of issues, including lower feed intake, greater weight loss in lactation, more feet and leg problems, earlier culling from the breeding herd and increased mortality rates.

Feeding management to prevent gilts from getting excessively heavy for breeding (300-lb. target, 200 days of age) is a challenge for many producers. While we know that limit-feeding gilts starting at 180 lb. is an effective means of preventing excessive body condition, this may be impractical for most producers.

Again, it is important to understand the lean and fat deposition potential of replacement gilts. Simply put, it may be unnecessary to place a high-lean maternal gilt on a low-energy diet because she is less likely to develop excessive body condition compared to a moderate- or low-lean maternal gilt that has a higher potential for fat deposition and becoming overly conditioned. In fact, some maternal gilt lines remain very lean up to 300 lb. on a full-fed system.

If more backfat is desired, research has shown that high-lean replacement gilts can be fed a slightly deficient amino acid diet, which will moderate lean accretion and increase fat deposition, and longevity can be improved. However, producers with medium- or low-lean gilts often attempt to feed a lower-energy diet starting at 50 lb. to reduce fat deposition levels that occur naturally. Research has demonstrated that gilts fed low-energy diets for a more moderate growth rate were retained in the herd for longer periods of time.

Vitamins and Minerals

Calcium (Ca) and available phosphorus (P) are two very important minerals that are needed for bone strength, and should be fortified above those recommendations for finishing pigs. Typically, we recommend Ca and P concentrations at approximately
0.10 percentage units greater than is found in finishing diets (Table 1).

Providing high levels of Ca and P will not affect growth rate, but will increase bone Ca and P concentrations. Higher concentrations also help buffer the demand for these nutrients during lactation. Diets should be formulated on an “available phosphorus” basis rather than a “total phosphorus” basis to minimize excess in the diet, as well as its effects on phosphorus concentration in swine manure.

Some additional vitamins and increased trace minerals are used in gilt developer diets compared to grow-finish diets due to their importance in reproduction. Examples of these vitamins include folic acid, biotin, choline and pyridoxine. For many of these vitamins, limited research is available to demonstrate their efficacy or appropriate level, much less the duration they should be fed before breeding. Typically, the diet(s) fed for the last 30 days prior to breeding contain similar vitamin levels as are formulated in gestation and lactation diets.

Trace mineral levels fed during gilt development are generally similar to levels fed in gestation and lactation diets as well. However, much less research data is available to support the ideal level of trace minerals for improved longevity in the breeding herd. Also, additional vitamins and trace minerals used in some breeding herd diets, such as carnitine and chromium, should be fed 30 days prior to
breeding.

Practical Gilt Diets

Practical diet recommendations for full-fed gilts are outlined in Table 2. Many producers do not have the ability to limit-feed gilts, so they typically full-feed developing gilts.

Diets fed to replacement gilts up to 50 lb. are usually identical to those fed to all nursery pigs, with the same amounts of lysine, Ca and P. However, from 50 lb. to approximately 300 lb., we suggest diets that meet estimated lysine requirements but with the extra Ca and P as previously described.

From a dietary energy standpoint, fat can be added when it is economical. However, if gilts are coming into the breeding herd too big, we sometimes add wheat middlings or soy hulls to the last developer diet to slow their growth.

Gilt Handling Protocols

The farm’s gilt management protocol will affect how gilts are handled before breeding (See Figure 1).

If gilts are moved directly from the developer barn to the gestation barn, they can be fed the regular gestation diet for a period of time at 4 to 4.5 lb./day, and then flushed by feeding 6 lb./day from 190 days of age to breeding. Providing an extra 2 lb./day of feed for two weeks before breeding has been shown to increase litter size as much as one pig per litter.

In some cases, gilts are moved to the gestation barn and limit-fed (Table 3). For example, if gilts are limit-fed from 250 to approximately 300 lb, they should be fed 6 lb./day or more for the last 14 to 21 days before mating to obtain the flushing response. Flushing before breeding is not necessary for full-fed gilts.

Regardless of the management program, after mating gilts should be limit-fed at approximately 4 lb./day for the first 7 to 14 days after breeding to prevent increased embryo mortality. During gestation, gilts should be fed to hit a target weight for farrowing.

Target Moderate Growth

Research has shown that developing gilts should be fed for a moderate growth rate. The goal for many different sow lines is to have a 300-lb. gilt at 200 days of age that is eligible for breeding. To achieve this goal, developing gilts can be fed diets similar to normal grow-finish diets, except calcium and available phosphorus levels should be higher to increase bone mineralization.

For at least the last 30 days before breeding, gilts should receive the same vitamin and trace mineral levels normally fed in sow diets. While overall data is limited on the ideal nutrition program to increase sow longevity, it is generally agreed that making sure gilts are not over-conditioned prior to breeding and farrowing will help keep them in the breeding herd longer.