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Finding, Rebreeding Sows that Recycle Is a Key to Better Farrowing Rates

As we continue to look at the importance of finding sows that recycle after breeding and their impact on subsequent farrowing rate, we will continue to use a subset of 22 farms. These farms are collecting and recording more detailed information than most farms collect.

Two programs developed by Swine Management Services (SMS) – Breeding Technician Report and In-Depth Breeding Analysis Report – are used to analyze the data and provide the farms with more detailed information by tracking semen batch, breeding technician by number of matings, day of the week bred, time of day bred, when returns are being found, etc. (see accompanying charts and tables).

Table 1 and Chart 1, Farrowing Rate by Days to Return to Estrus, shows 10,000 females out of 122,407 females returned to estrus and were bred on the 22 farms over the most recent 52-week period. These farms vary by size, genetics and geographic location. The data is broken down by parity and into six groups by the days to return to estrus after breeding.

Days 11-17 and 25-38 are considered irregular returns. If females are found open during the early days (Days 11-17), there is usually an issue with technicians inseminating sows or gilts that are not in solid heat. Some AI technicians may have to be retrained to lower this number.

Irregular returns to estrus (Days 25-38) are females that probably conceived on the initial insemination, but for various reasons returned to estrus. Common causes include a single mating, a small litter developing in the uterus, under-conditioned sows or untreated infections.

Regular returns are commonly found at Days 18-24 and Days 39-45. These females did not conceive on their last breeding and will start having normal heat cycles every 16-25 days.

Farms that do a good job of identifying returns to estrus begin heat checking with boars on Day 14 after breeding, finding over 60% of the regular returns by Day 25. Returns found on Days 39-45 were probably missed as open on Days 18-24 after breeding. The recycles increase the farrow-to-farrow interval and open sow days. Returns after Day 46 can be regular or irregular and should have been found by heat or pregnancy checking. Most of these sows are classified as not-in-pig, aborts, deaths, or females that are culled in late pregnancy.

Table 2 and Chart 2, Farrowing Rate by Days to Return to Estrus, display 15 AI technicians from the 22 farms in the dataset. Farrowing rate is based on the day the return female was found and rebred. The overall farrowing rate for breeding returns was 69.4%, ranging from 56.8% to 78.3%. As you can see, there is a large variation in farrowing rate by technician and by the day they find and rebreed the returns. As Chart 2 points out, some AI technicians (e.g. A, B, D) are very consistent in finding and rebreeding sows that return to estrus. However, other technicians (e.g. I, K, M, O) struggle, especially finding too many early returns that probably are less fertile for rebreeding.

Table 3 and Chart 3, Farrowing Rate by Previous Lactation Length, show data from 84,962 farrowings. Data was broken down by lactation lengths of 1-7 days, 8-14 days, 15-21 days, and 21+ days. The average weaning age of the litters in the dataset was 19.2 days.

When broken down by parity, the data shows lower farrowing rate for sows weaned at 1-7 days (76.3%) and 8-14 days (81.7%). Weaning sows after 15 days of lactation improves farrowing rate. It is important to remember that it takes at least 15 days for the sow’s uterus to heal and shrink down after farrowing, before it is ready for the next litter to implant. If a litter must be weaned early (before 15 days), most farms make sure one heat is skipped before the sow is bred again. Along with improvement in farrowing rate, there will probably be an increase in total pigs born in the subsequent litter. It is interesting to note that the older parity sows are affected more by the early weaning litters at 1-7 days of age.

In summary, to rank in the Top 10% of the SMS Farm Benchmarking database, you need to have a farrowing rate of at least 89%, repeat services less than 5%, total pigs born/litter of 14+ pigs, and a piglet survival rate of at least 82%. To achieve this goal requires good genetics, nutrition, facilities and people – the biggest influence being the people. It is important to be able to record detailed information on each person and to show them the areas where they are strong in, as well as those that need improvement.

Key Performance Indicators
Tables 6 and 7 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