Who doesn't love summer? It's a welcome relief from winter's challenges. But summer comes with some challenges of its own, and seasonal infertility in breeding herds is at the top of the list.

Heat stress poses a particular challenge to a sow or gilt because her body is programmed first to survive and then to reproduce. To help avoid potential breeding-herd problems this summer, three North Carolina State University swine specialists – Billy, Flowers, Kevin Rozeboom and Todd See – offer some practical advice.

Ventilation is No. 1: In hot weather, moving fresh air through the building is vital in all phases of a sow's reproductive cycle. Unless ventilation is adequate, your other hot-weather-fighting measures will have little effect.

If you have not conducted a maintenance inspection already this year, wait no longer. Doing a ventilation test run will show if your system is moving air at or above recommended rates: 500 cubic feet per minute for sows and litters; 300 CFM for breeding females and boars; 180 CFM for gestating sows and gilts. (In the hot, humid Southeast, some producers have found it pays to double these rates.)

Fresh air must enter a room at 600 to 1,000 CFM per minute to circulate well and to prevent cold drafts from falling on animals. An effective year-round air-inlet speed is 900 CFM. If the building has cool cells, check to make sure they are functioning properly. If a farrowing room has nose coolers, test each to see that air flows freely onto the sow's nose.

Provide a drip or spray: In sow facilities, provide a water drip or spray in conjunction with circulating fans to enhance cooling. Either is preferable to fogging. That's because water on an animal's skin evaporates and cools; whereas fogging first has to cool the air, then it cools the skin.

Check to make sure that each spray nozzle delivers at least 0.02 gallons of water per hour per gilt or sow. A low-pressure drip system in the farrowing house should be rated for 0.5 to 1 gallon per hour.

Heat-lamp management: For nursing gilts and sows to get the most benefit from the cooling system, you have to manage heat lamps properly. Position lamps as far as possible from the sow's head, and replace heat lamps with ordinary 100-watt incandescent bulbs. This will reduce heat while providing necessary light for animals. A timer can conveniently turn on lamps in the evening and off in the morning. (If the building interior is not light all day, keep some lights on because total, continuous darkness can cause a sow to quit producing milk.)

Comfort zone for gilts: This is a good idea because high ambient temperatures can disrupt a gilt's reproductive cycle. Delayed estrus cuts into the estrus period and lowers conception rates. This can be avoided by paying special attention to replacement gilts' comfort. It is especially important to house them in a section of the building with good ventilation. Also allow ample floor space per gilt.

Putting the gilt in this area for as little as a day or two may return her to normal cycling. However, with some animals it may take as long as 2 or 3 weeks. Therefore, the area may need to be large enough to accommodate several animals comfortably. (In a high-humidity area if anestrus problems persist with more than 10 percent of gilts, some type of air conditioning may be justified as a last resort)

Natural ventilation: In breeding and gestation buildings that open up, managing air movement in hot weather is especially important. Make sure that side-wall curtains, ridge openings and side-wall air inlets are completely open.

Because people tend to adjust ventilation for human comfort at 3 or 4 feet above the animal's level, adding air-deflecting panels often improve air circulation in the animal zone.

Circulating fans and evaporative cooling make a naturally ventilated structure more comfortable. This is especially true if the building is not positioned east to west for maximum air flow or it has limited air-intake openings.

Water supply: When ambient temperatures go from 54°F to 60°F up to 86°F to 95°F, an animal increases its water consumption by 50 percent. A gestating sow needs to consume 3 to 5 gallons a day; a nursing sow needs 8 to 10.5 gallons.

The system should deliver 0.25 gallon to 0.5 gallon per minute. Water temperature and quality also are important. In hot weather, consumption of cool, 50°F water is almost double that of warm, 80¦F water.

n First 30 days after breeding This is when embryo loss is greatest. So, when gilts or sows are under heat-related stress it is imperative to take these steps:

1. Avoid inseminating in late estrus.

2. Mix females only at weaning.

3. Refrain from or stop moving females to different locations.

4. During and after breeding maintain an adequate level of nutrition for at least 30 days. (A sound strategy throughout the year.)

Lactating sows' body condition: To maintain body condition to promote on-schedule cycling and conception, consider adopting one of these approaches:

1. Reduce lactation period – as short as nine days for third-parity or older sows. However, first-parity gilts appear to need 14 days, the specialists say. Second-parity sows need 21 days.

2. In lactation periods of 28 days or more, split weaning conserves the sow's body fat. However, some studies show that removing two or three pigs earlier than three days prior to weaning may cause the sow to cycle while she's still lactating.

Breed more gilts: Anticipating a reduced, hot-weather conception rate, you may want to breed extra gilts. Of course, you need to have adequate space in your facilities to handle them without crowding. It is unwise to increase your gilt pool for summer breeding without allowing adequate floor space. Otherwise, you may create an even more serious problem – such as hot-weather stress that delays estrus in many gilts.

Scheduling chores: Rather than performing daily tasks in the gestating barn and farrowing house during the heat of the day, do as much as possible in early morning and evening. This makes hot weather easier to handle for workers and animals

Nursing sows' feed intake: All three specialists agree, this is the biggest single factor affecting seasonal infertility. Digestion creates heat, and it can be especially bad when sows are in a hot environment. The challenge is to keep sows consuming as much nutrition as they need, but in a moderate quantity at each feeding. Recommended management steps to accomplish this are:

1. Feed more frequently. Sows fed three times a day in summer instead of two usually consume 10 percent to 15 percent more per day. (Some North Carolina operations have found it pays to feed four times a day or more.)

When feeding multiple times a day, reduce the amount per feeding to avoid over-feeding. Smaller meals help keep feed fresh, too.

2. Liquid feeding may boost lactating sows' feed intake by as much as 15 percent. But it may require you to clean the feeders more frequently to prevent mold development. Also because it helps if animals are accustomed to wet feed, consider introducing it to them toward the end of gestation and continue after farrowing.

3. Add fat. To maintain a nursing sow's body energy balance in hot weather, consider using 7 percent to 10 percent animal or vegetable fat in the lactation ration. If you do, be sure to boost essential vitamins and minerals to maintain adequate daily consumption per sow.

Also keep in mind that a ration containing this much fat becomes rancid more quickly than one with only 1 percent or 2 percent fat, and that sows will not eat spoiled feed. So, at each feeding, smell leftover feed to see if it needs to be cleaned out of the feeder.

Hormone treatments: Gonadotropins and progestins may be used with gilts and sows to help cut the reproductive lag associated with heat stress and negative body-energy balances. However, these treatments are expensive and usually are cost-effective only when wean-to-estrus length is more than 10 days or there is a high frequency of delayed estrus.

If you are not familiar with these treatments, consult with your veterinarian or swine specialist.

Time for new genetics?: While strategies outlined in this article can alleviate some seasonal-infertility problems, their influence may be limited due to your animals' inherited ability to perform in hot environments. If you sense this to be the case in your herd, consult with a geneticist or swine specialist to see what options you should investigate.

Feeling the Affects

Your breeding herd's summer performance can be harmed five ways:

  • Delay coming into heat, also known as anestrus
  • Extended weaning-to-estrus intervals
  • High embryo death rate
  • Poor conception
  • Small litters

Easy Tips to Check for Overheating

  • Select a resting, calm animal.
  • For 60 seconds, count the number of times its rib cage moves in and out.
  • If you reach 40 counts or more, the animal is at risk of heat stress.
  • If breathing is more than 60 counts, the animal is probably suffering from heat stress.

    Don't Forget to Check Your Boars
    A boar's performance also suffers from hot-weather stress, and any declines there will have a major impact on your breeding herd's performance. Here's what can happen when a boar suffers heat stress.

    • Lower sperm output. Sperm production can stop temporarily.
    • Poorer sperm mobility.
    • Increased morphological abnormalities.

    It takes 6 or 7 weeks for most heat-stressed boars to recover. Prevention is far more cost-effective than the cure.