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Wean-to-First Service Interval is a Key to Greater Output

This month’s column will take an in-depth look at wean-to-first service interval and its effect on several production parameters. Wean-to-first service interval marks the days from weaning until the female is bred the first time.

This month’s column will take an in-depth look at wean-to-first service interval and its effect on several production parameters. Wean-to-first service interval marks the days from weaning until the female is bred the first time.

Most farms follow this definition, although there are a few farms that alter this number based on plans to skip heats when they don’t need sows bred that week or when they are in poor body condition. There are also some farms that heat check sows, but delay breeding for 12-24 hours to reduce semen usage or to do a better job of timing the first insemination. And, with more farms going to batch farrowing, some sows may be skipped or placed on Matrix to delay estrus so they can be bred to farrow during a specific week. All of these procedures would artificially increase wean-to-first service interval.

Over the last several years we have seen some shift to weaned sows cycling sooner. Several farms have average wean-to-first service intervals less than five days. This is probably due to later weaning ages, the use of more nurse sows , beginning heat checking sooner after weaning, increased daily feed intake in lactation, supplemental cooling systems in farrowing and gestation, and more aggressive feeding from weaning to breeding.

The 602 farms in the dataset had 20+ pigs weaned/mated female/year for the last 52 weeks records were available. These farms had an average of 6.9 days from weaning to cycling, with a range of 4.1 to 12.7 days. The Bottom 10% of the farms in the dataset averaged 10.1 days. The question is why? Is it due to when heat checking starts, low feed intakes in farrowing, poorly trained staff, poor recordkeeping, etc.?

In Table 1, the data is broken down to Top 10%, Top 25%, Top 50%, Total Farms, Bottom 50%, Bottom 25%, and Bottom 10% with the ranking based on wean-to-first service interval.

For this discussion, we will focus on pigs weaned/mated female/year, percent bred by 7 days postweaning, percent repeat services, farrowing rate, total born, piglet survival and weaning age.

Pigs weaned/mated female/year average was 24.47 pigs, with the Top 10% (60 farms) averaging 5.2 days to cycle at 25.91 pigs and the Bottom 10% (60 farms) dropping to 23.53 pigs. This shows that wean-to-first service interval is one of the drivers affecting increased pigs weaned/mated female.

We were also interested to see how much wean-to-first service interval affected some production areas. The seven charts (attached) look at these areas with 602 farms charted.

In Chart 1, pigs weaned/mated female/year, there is a definite drop in pigs produced as wean-to-first service interval increases. However, there is a lot of variation from farm to farm.

Chart 2, total born, shows about 0.50 pig increase in total pigs born when comparing the Top 10% with the Bottom 10%.

In Chart 3, farrowing rate, we were surprised to see only a 1.1% spread. Previous studies had shown a 6-8% spread. Higher quality boar semen or a more skilled staff may be the reason this spread has narrowed.

Chart 4, percent bred by 7 days after weaning, shows a lot of variation, which we would expect with the Top 10% averaging 93.6%, while the Bottom 10% farms averaged only 75%. The average of all herds was 85.9%.

In Chart 5, percent repeat services, we see an average of 8% and range from less than 1% to over 20%. In farms we review on a regular basis, we see more culling of repeats after one service, especially if the farm has a good supply of replacement gilts.

Chart 6, piglet survival, is calculated by subtracting stillborn percentage and preweaning death loss percentage from 100. The average is 79.8%, with wide variation from farm to farm, although there is very little influence from wean-to-first-service interval.

Chart 7, weaning age, shows an average of 19.97 days of age, with the Top 10% at only 19.81 days and the Bottom 10% at 19.78 days. As more farms move above 19 days of age at weaning, there is probably less influence on wean-to-first-service interval.

Clearly, farms with lower wean-to-first-service interval produce more pigs, have more sows bred by 7 days, higher farrowing rate, and there are fewer repeat females to find and deal with. Wean-to-first-service interval has less influence on total pigs born, piglet survival and weaning age.

To lower wean-to-first-service interval, newly weaned sows should be exposed to a boar on Day 1 and bred when found in heat. Weaned sows should receive extra feed from weaning until breeding. Lactation feed intake should be monitored to make sure sows are eating at least 14 lb. of feed per day, which may mean feeding more times per day, adding an automated feeding system, or installing a feed hopper system so lactating sows are self-feed. Always make sure water flow rate in farrowing is at least 2 quarts/min.

The trend lines show if you want your farm to wean more pigs per year, you must keep wean-to-first-service interval low.

Key Performance Indicators
Tables 2 and 3 (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