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Adjust Breeding Targets in Hot Summer Months

As the weather warms up, you need to make sure your breeding crew adjusts weekly or batch group breeding targets to allow for a drop in farrowing rate of females bred during the summer breeding season.

Since we do analysis for a large number of sow farms in the United States and Canada, we decided to review data from the fall of 2009 to the fall of 2010. We selected farms with an average over 12.5 total pigs born per litter for the past two years. Forty-nine farms met that specification. Broken down by region, there were nine farms from the U.S. south region, 24 farms in the U.S. north region and 16 farms in Canada. The division for north and south was determined by the Mason-Dixon Line.

Chart 1 shows the farrowing rate (by breeding date). The data was adjusted to reflect the farrowing rate to the week bred. The 12-month farrowing rate for the 16 Canadian farms was 87.8%, 85.2% in the north region and 87.2% in the south region. Canadian farms are minimally affected by the heat. Farms in the north are affected the most, showing drops in farrowing rates to 82% in July, 81.9% in August, 80.9% in September, and starting back up in October (84.7%). We were surprised to see the south farms did not drop as much as the north farms, which were 85.3% in July, 83% in August, began coming back up in September at 86.7%, and in October at 87.9%. Farms in the south did not drop as low and did not last as long as the farms in the north region.

When we were selecting these farms, we did not select for supplemental cooling in gestation or farrowing. As Charts 2, 3 and 4 show, there is a lot of variation between the three regions. The greater variation in the farms for the north region was probably do to the larger number of farms in the average, with some farms that do not have cool cells.

We also studied the “repeat services” trend (Chart 5). The 52-week average for repeat services for Canada was 6.8%, for the north was 8.2%, and in the south was 6.0%. Canadian farms, because of reduced effect on farrowing rate, did not show much difference in number of repeats by month. Farms in the south started showing an increase in repeats in June, with a big increase in repeats in August – with a very good job of finding them and either rebreeding or culling them.

Farms in the north had three times the repeats in December, March, August, September and October. We think the increase in repeats in late summer was caused by the heat. The spikes in December and March could have been caused by lower breeding performance over the holidays or a health challenge at some of the farms.

Chart 6, wean-to-first service for the year, shows an average in Canadian farms at 6.9 days, in the north at 6.5 days, and in the south at 6.7 days. Wean-to-first service is a key to subsequent farrowing rate and litter size. If these days increase, most of the time farrowing rate and litter size will decline. The chart shows some wean-to-first service increase starting in late June, with another spike in August for farms in the north and south. Farms in Canada peak in September. Both Canadian and southern farms had an increase in wean-to-first service days in to October, which is probably due to keeping non-cycling, weaned sows longer in the breeding barn, trying to catch them in heat instead of culling.

Chart 7, Female Death Loss, reflects an increase in death loss due to heat in the summer months. Southern farms showed an increase from 5% in July to more than 13% in August. The surprising change is the Canadian farms show the highest 12-month average of 8.1% in January, late June and August. Most Canadian farms do not have cooling systems to use during the short summer heat periods.

There is some effect on farrowing rate, number of repeats, wean-to-first service interval and death loss in the summer months, so what’s the best approach to minimizing the summer heat’s impact on farrowing rate? Here are some suggestions:

• Breeding target. Based on your historical sow records, you need to establish a new breeding rate that may be 5-10% above your current target. Identify the date to start the increase. Be sure you have extra gilts to breed if you increase your breeding target.

• Boar semen. Make sure semen coolers are in an air-conditioned office set at 70° F. Check the temperature of semen at delivery with a temperature gun to make sure the semen has not be over-heated or cooled and place a high/low thermometer in the semen cooler and chart daily those temperatures. Fluctuations should not be over 2-3 degrees in a 24-hour period. Make sure that a cooler with cool packs is used to transport and store semen in the breeding barn and only take enough semen for that breeding session.

• Supplemental cooling. Be sure the barn’s cool cells are in good repair, free of debris (inside and outside), pumps are working, water flow is adequate for maximizing the cooling effects, and the unit is set to come on at about 75° F. Farms that do not have cool cells need drippers and stir fans set to come on at 75° F to cool the sows in lactation and gestation.

• Water consumption. In gestation is 2-4 gal./head/day; increase by up to 50% on hot days. In lactation, sows can consume up to 10-15 gal./day in peak hot weather days.

• Feeding. Lactation feed intake affects wean-to-first service and is the key to getting sows cycling again. Sows should have ad-lib access to feed starting the day after farrowing. If sows are hand-fed, someone should come back to the farm for a late-evening feeding when barns are cooler. Remember, in the summer some sows will eat over 42% of their daily diet between 6 p.m. and 6 a.m. You may want to increase the energy level of the lactation diet to help increase daily energy intake.

• Hormone therapy. Working with your veterinarian, you may want to consider giving young females at weaning a hormone injection to help get them cycling sooner.

• Gilt management. Getting gilts to cycle in the summer can be a big problem. Temperatures over 85° F can cause gilts to have irregular cycles or even stop cycling. Gilts that are actively being heat-checked and bred should be in a building with cool cells or some type of supplemental cooling. This helps prevent culling due to size and age.

• Breeding management. Try to breed in the cooler part of the day. To ensure sows will cycle after weaning, start boar exposure the day of weaning, rotate the boars used for heat checking and breeding every 1-2 hours, and allow boars extra time to stimulate the recently bred females. When heat checking and breeding, move the boars into the flow of air from the cool cells so the females are upwind to ensure the pheromones reach them before you get there to breed them. Remember, you have 5-15 minutes to get a female bred once she is in standing reflex – the prime time for breeding.

As the charts show, there is quite a lot of variation in farrowing rate, wean-to-first service interval, repeats and female deaths loss from farm-to-farm and in different geographic locations. Each 4% drop in farrowing rate reduces pigs/sow/year by 1.35 pigs. That’s why it is important to prepare for better breeding results during the hot summer months.

Key Performance Indicators
Tables 1 and 2 (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