Using these estimates, energy requirements for maintenance, maternal weight gain and fetal gain are converted into daily feed intake nutritional requirements that are easily calculated in a spreadsheet (www.ksuswine.org). This grid can be customized using the spreadsheet to adjust for the total born litter size, environmental temperature and dietary energy density.

Another feature of this spreadsheet is its ability to translate the grid into actual feed box settings. Thus, if the feed box setting is not the same as the weight delivered, farm staff does not need to make the conversions. It is important to periodically update these settings if the bulk density of the diet changes from the addition of different ingredients or changes in the test weight of grain.

The latest challenge we have been addressing is the variability in amount of feed delivered at various feed box settings due to the positioning of the drop and the type of drop.

Based on these studies, we have found that feed drop style definitely influences the accuracy of the amount of feed dropped at various settings. Also, we have found that some designs are more variable due to positioning than others.

Milk Production Drives Nutrient Needs

Milk production and hence litter growth rates are the main determinants of the nutrient needs of the lactating sow. Milk production represents 70-95% of the requirements for energy and amino acids, and is used as the basis for determining energy and lysine requirements.

To customize lactation diets based on sow productivity, an appropriate dietary lysine level can be calculated if average litter weaning weight and sow feed intake averaged over the entire lactation period are known.

The first step is to get a good estimate of average daily feed intake of lactating sows. For example, over a six-month period, a 3,000-sow farm with 450 farrowing crates farrows 3,615 litters with an average litter weaning weight of 101 lb. at 19 days of age. During this time, 419 tons of lactation feed were delivered to the farm.

Two simple calculations help determine actual lactation feed intake. The first method (above) uses crate days and feed disappearance.

The second method (above) uses number of lactating days and feed disappearance.

The first method should underestimate average lactation feed intake because of days that crates are empty or contain sows that are eating lactation feed but have not farrowed. The second method overestimates lactation feed intake because the feed to prefarrowing sows is counted as feed fed to lactating sows.

The average of these two values should be used as the feed intake estimate. In this example, the daily lactation feed intake should be between 10.2 and 12.2 lb.

Once an accurate estimate of feed intake is determined, the next step is to determine dietary lysine levels. Since milk production accounts for a major portion of the lysine requirement, and litter growth rate is an indirect reflection of milk production, litter weight gain can be used to customize lysine levels based on the level of litter weaning weight.

Sows require about 11.9 grams of lysine per pound of daily litter weight gain plus 2 grams for maintenance; thus, the next step is to determine daily litter weight gain, which can be calculated by dividing litter weaning weight by lactation length.

Based on average daily feed intake and litter weight gain, the dietary lysine level can be customized to accommodate the herd's average milk production. If the previous lactation diet being fed on the farm is higher in lysine than the recommended level, it may be possible to reduce the dietary lysine level without sacrificing performance.

If the previous lysine level being fed is lower or the same as the recommendation, the producer may want to increase the lysine (protein) level and reexamine performance records to determine whether litter weaning weight increases. This relatively simple approach allows the sow lactation diet to be customized to an individual farm.

First Parity Focus

First-parity sows require special consideration when formulating lactation diets. Usually their feed intake level is about 20% below the herd average. To maintain the same level of litter weaning weight, first-parity sows require about 0.20% higher lysine lactation diet (Table 2).

Also, researchers have demonstrated that first-parity sows require higher lysine levels for maximum reproductive performance than is required for maximal milk production.

Other essential amino acids critical to lactation performance that may become limiting include: isoleucine, methionine, threonine and valine.