Litters/mated female/year is a key number in measuring female productivity. It is behind only pigs weaned/mated female/year and tied with pigs weaned/female farrowed in importance in the Swine Management Services (SMS) Production Index.

The farms selected for the data set had to be in production for more than three years and weaning a minimum of 22 pigs weaned/mated female/year during the prescribed time period. There were 397 farms out of 619 (64%) that met these criteria.

The Swine Management Services, LLC data set was divided into four groups:

• Under 1,000 mated females (141 farms) with average size at 650 females;

• 1,000 to 1,999 mated females (130 farms) with average size at 1,393 females;

• 2,000 to 2,999 mated females (94 farms) with average size at 2,579 females; and

• Over 3,000 mated females (32) with average size at 4,596 females. Litters/Mated Female/Year is the number of females farrowed divided by days in the period times 365 days divided by the average mated female inventory in the period. The theoretical maximum number for litters/mated female/year is 2.60 (115 days of gestation, 19 days weaning age, 6 days wean to 1st service interval, 100% farrowing rate, 0% death loss and all female culls have to be removed on weaning day). The calculation works very well when the average mated female inventory is constant from the time the females are bred until they farrow. If the mated female inventory is increasing, then this number will be understated and if the mated female inventory is decreasing, then it will be overstated.

Example 1: 48 females farrowed per week divided by an average mated female inventory of 1000 is 2.50 litters/mated female/year.

Example 2: The decision was made to reduce the female inventory by 20% over a 16-week period. All of the pregnant females were farrowed and culling came from open and weaned females; 48 females were farrowed per week, the ending mated female inventory was 800, but the average mated female inventory was 900. This would calculate to 2.78 litters/mated female/year, above the theoretical maximum of 2.60. Anytime you are analyzing numbers calculated with average mated female inventory, you also need to look for any changes in the mated female inventory during the period used in the calculation. This would include pigs weaned/mated female/year.

The trend for litters/mated female/year over the last four years using the entire database (Graph 1) shows very little change (less .02 over four years). The average number for the last four years is 2.35.

The difference is not significant between the different sizes of farms from 2.39 to 2.42 litters/mated female/year shown in Table 1. However, the difference is significant when you look at the top 10% depicted in Table 2. The under 1,000 average female mated inventory is 2.51, the 1,000-1,999 is 2.44, the 2,000-2,999 is 2.49 and the over 3,000 average female mated inventory is 2.43.

When looking at improving litters/mated female/year, all the numbers we mentioned in the theoretical maximum need to be looked at, starting with farrowing rate. Each 1% increase in farrowing rate has the potential to raise litters/mated female/year by .03. Each day that the weaning age is lengthened has the potential to lower the number by .02. Each day that wean to 1st service interval is lowered has the potential to raise litters/mated female/year by .02. And each week that the cull sows are held on the farm has the potential to lower the number of litters/mated female/year by .03.

Key Performance Indicators

Tables 3 and 4 (below) provide 52-week and 13-week rolling averages for key performance indicators (KPI) of breeding herd performance. These tables reflect the most current quarterly data available and are presented with each column. The KPI’s can be used as general guidelines to measure the productivity of your herd compared to the top 10% and top 25% of farms, the average performance for all farms and the bottom 25% of farms in the SMS database.

If you have questions or comments about these columns, or if you have a specific performance measurement that you would like to see benchmarked in our database, please address them to: or

Click to view graphs.

Mark Rix and Ron Ketchem
Swine Management Services LLC