Dr Todd See Swine Genetics Specialist North Carolina State University

As temperature and humidity climb, you can expect to see increased death losses in the units and during trucking, reduced growth performance, reduced boar fertility, delayed heat, reduced ovulation rate, and increased embryonic death if animal comfort is not maintained. The Livestock Conservation Institute has developed a weather safety index that indicates producers should be on the Alert at temperatures greater than 75 degrees; the Danger Zone is anytime temperatures rise above 100 degrees, and the Emergency Zone covers temperatures above 100 degrees with 25 percent or greater humidity.

The following points should be checked and considered: Pig handling, inspection of watering systems, attention to ventilation and cooling equipment, trucking guidelines, and plans for seasonal infertility.

Pig handling

Pay extra attention to the movement of animals. Keep the pigs calm, move them slowly, and refrain from using electric prods. In addition, be certain to avoid loud noises and yelling and moving pigs too fast. Moving pigs in groups that are too large (more than five pigs) also causes pigs to become more excitable and hot. Finally, try to avoid excessive stationary periods when moving, loading, and hauling swine, especially in hot weather. Consider changing the pig movement schedule to early in the day or late in the evening when it is cooler. Heat will increase the stress on an animal during movement. Signs of pig stress to be aware of are:

• Open mouth breathing
• Vocalization (squealing)
• Blotchy skin
• Stiffness
• Muscle tremors
• Increased heart rate
• Increased body temperature

Nursery and finisher

Inspect and maintain cooling and ventilation systems: Fans, cool cell pads, drip-and-spray cooling systems, and air inlets should be checked to make sure they are functional. Take special care to check for worn fan belts that may dramatically reduce the ventilation rate. Also, the nozzles in drip-and-spray cooling systems may have become plugged with sediment from periods of inactivity. These nozzles should be checked and cleaned.

Provide adequate water: Water usage will increase for each type of animal in the summertime. A nursery pig will need 1 gallon per day and a finisher 5 gallons per day. Nipple waters should be checked for minimum flow rates to ensure that the animals can achieve their minimum water requirements. In the nursery the flow should be 1 to 1½ cups per minute, while in the finisher the flow rate should be at least 3 to 4 cups per minute.

Prevent overcrowding: Overcrowding of pigs will have a greater impact in the summer. Adequate space to reduce fighting and improve pig performance is more critical in warmer weather. Nursery pigs need 1.7 to 2.5 square feet per pig. In the finisher, space needs grow as the pig grows, starting at 5 square feet per pig at placement (50 pounds) and ending with 8 square feet per pig at 150 pounds to market.

Use care when trucking: When trucking animals, load and unload promptly and do not make stops. Animals should be wet prior to transport on hot days. Trucks should provide maximum ventilation, and using wet sand or wet shavings for bedding can be beneficial. For 250-pound hogs, you should have about 1.8 head per running foot of floor that is 92 inches wide.

The Livestock Conservation Institute suggests that in the Alert Zone 10 percent fewer hogs should be loaded, and deliveries should be made by 11 a.m. In the Danger Zone 20 percent fewer hogs should be loaded, and deliveries should be made at night. When the Emergency Zone is reached, trucking should be postponed if possible until the weather moderates.

Breeding herd

Seasonal infertility is well documented. If your herd has historically had a seasonal infertility problem, take steps to reach your breeding target. This can be accomplished by breeding up to 40 percent more females, depending on the decline you see in farrowing rate. Breeding targets should increase gradually through May, June, July, and August and decline through September to a normal level. High temperatures reduce feed intake, which impairs the female's ability to adequately recover from farrowing. This results in longer wean-to-estrus intervals and reduced ovulation rates.

Remember that keeping boars fertile is just as important as keeping the sow herd comfortable. Two weeks of exposure to 80-degree-plus Farenheit temperatures cause a dramatic increase in abnormal sperm and a reduction in motility. It will take the boar a minimum of four weeks to recover from heat stress. Boars may also become lethargic and have reduced libido during periods of hot weather. Temperatures that are greater than 85 degrees may reduce semen quality for 4 to 6 weeks. When temperatures rise, monitor the boars' respiration rates. Normal respiration is 25 to 35 breaths per minute, and heat stress is 75 to 100 breaths per minute. When the boars' respiration reaches 40 to 50 breaths per minute, intervene and take measures to cool the boars.

Feed consumption: Without question getting sows to maintain feed consumption or prevent it from decreasing during the summer months is the most critical management step for reducing the impact of heat stress and seasonal infertility. It is important during warm weather to maintain the breeding herd's feed intake.

1. Feed when temperatures are lowest: Feeding when temperatures are lowest in the early morning or evening can stimulate the sow's appetite. To accomplish this, a change in work schedule is often required.

2. Increase feeding frequency: Most producers experience a 10 to 15 percent increase in feed intake when they change from 2 to 3 times per day. There are some farms in North Carolina that actually feed 4 or more times per day in the summer. The main thing to remember here is that when you increase the frequency of feeding, you decrease the amount that you feed each time. For example, if you are currently feeding 6 pounds twice a day (12 pounds total), when you switch to feeding three times per day, you may want to offer the animals around 4.5 pounds at each feeding (13.5 pounds total). The reason this strategy works is based on the normal increase in body temperature that occurs after a sow consumes a meal.

Theoretically, there wouldn't be as big an increase in a sow's body temperature after she eats 4.5 pounds versus 6 pounds due to less feed to be digested, etc. Consequently, this could be very important for sows whose body temperature may be in the upper end of the thermo-neutral range due to elevated environmental temperatures.

3. Use fresh feed: Sows tend to be picky eaters, compared to most animals (contrary to popular belief). In warm conditions, feed is more likely to spoil, compared to cool conditions, especially if it contains high levels of fat. It is interesting to note that increasing the feeding frequency in conjunction with feeding slightly smaller meals at each feeding is actually an excellent way to keep feed fresh as well.

4. Try liquid diets: This practice can be implemented during lactation; but because of the short period of time that sows are actually in lactation, it may be more beneficial to acclimate females to this change of diet during late gestation. However, wet feeding reduces the time that feed may stay in the trough and be fresh. Success may vary greatly between operations, but this strategy has been reported to boost sow feed intakes as high 15 percent.

5. Add fat to the diet: As a result of poor feed intake, many sows are not able to meet the metabolic demands of lactation and revert to a negative energy balance. This factor probably accounts for most of the reproductive disorders during periods of elevated temperatures. One way ensure that sows are consuming enough energy, even though they are eating a smaller quantity of feed, is to add fat to the lactation diet. Supplemental fat (7 to 10 percent animal or vegetable fat) will increase the dietary metabolic energy content of the feed. However, there are two important considerations in adapting this practice. First, a diet containing high amounts of fat will become rancid more rapidly than a traditional diet with 1 to 2 percent fat. Sows will not eat rancid feed, and, therefore, feeding smaller quantities more often and smelling leftover feed in the sow feeder at each feeding should be a standard practice. Second, because sows are consuming less feed, dietary levels of essential vitamins and minerals will also need to be boosted to account for less feed consumed on a daily basis.

6. Provide constant water: High ambient temperatures will increase water requirements, particularly for sows. Increased water consumption coupled with increased urinary water loss is an effective mechanism by which pigs lose body heat. A change in ambient temperature from 54º-60º F to 86º-95º F gives an increase of >50 percent in water consumption. Nursing sows need to consume 8-10.5 gallons of water every day and gestating sows 3 to 5 gallons. One rule of thumb is a water-to-feed ratio of 5:1. Fresh and constant water supply is also critical during breeding and gestation. The watering system should deliver a minimum of 0.25 gallons per minute and ideally 0.5 gallons per minute. Sows will quickly become frustrated if the flow rate is low, and this will influence their appetite for dry feed. Water temperature and quality are also important. During periods of high ambient temperatures, pigs will consume almost double the quantity of cool (50º F) water than warm (80º F) water.

Check and maintain ventilation: The first step in reducing the impact of heat stress on sow fertility is to make sure that ventilation systems are in good working order and are providing adequate ventilation. Ventilation rates for a sow and litter, gestating sow, and breeding barn sow during the summer months are 500, 150, and 300 CFMs/hd. Following a thorough maintenance inspection, test the ventilation system to ensure that these rates are met. It is not uncommon to find that in even fairly new operations, ventilation systems do not operate as designed. Unless these systems are meeting the required ventilation rates, other management practices that we will describe will not be effective. Additionally, fresh air from the inlets must enter rooms at a speed between 600 to 1,000 ft/min. in order to distribute fresh air and prevent cold air from falling on animals (drafts). Don't overlook fresh air inlets. Adjustments should be made seasonally, and a good year-round air inlet speed goal is 900 ft/min.

Pigs are more sensitive to the combined effects of heat and relative humidity than humans are, since they do not sweat, and it is important to consider heat indexes and activation temperatures of supplemental cooling systems. For example, if it is 75º F in the barn, but the heat index is over 85º F due to high humidity, the supplemental cooling system needs to be active. It is imperative that supplemental cooling systems are in place in all phases of sow production. These could include evaporative drip or spray cooling and circulating fans. Sprinkling is preferred to fogging, which uses smaller water droplets. Sprinkling cools the skin surface by wetting the skin and allowing the water to evaporate, whereas fogging cools the air and then the air must cool the skin. Most systems will be designed to operate for a period of 1 to 2 minutes up to 4 times per hour. Spray nozzles should provide at least 0.02 gallons of water per hour per head. Low-pressure drip systems in the farrowing house should be rated for 0.5 to 1 gallon per hour. Most operations in the southern states also have installed components such as cool cells, which can be effective in keeping room temperatures 10 to 15 degrees cooler than outside temperatures. Another effective method to cool sows during lactation may be the installation of nose coolers. In farrowing rooms equipped with negative pressure systems using a plenum as an air inlet source, a tube can be connected to the plenum and directed to the bottom of the farrowing crate near the sow's nose while she is lying down. This supplies a constant air movement across her face when the ventilation system is activated.

Activation temperature for these systems should be set between 75º and 78º F, as opposed to between 80º and 85º degrees. While this practice may not be able to maintain a farrowing room between 75º and 78º degrees if the ambient temperature outside reaches 90º+ F, it does prolong the period over which the room temperature increases, since the cooling process begins sooner. Along with earlier activation of cooling systems, replacing heat lamps with regular "household" 100-watt incandescent bulbs will reduce the ambient temperature of the farrowing room. Furthermore, heat lamps may need to be shut off completely during periods when temperatures do not fall below 85º F to help reduce room temperatures. If this strategy is practiced, a source of light is needed somewhere in the room. Some producers report lactation failure if sows and litters are subjected to total darkness on a continual basis.

Prenatal mortality: Mortality at this stage may be as high as 40 percent. The bulk of this embryo loss occurs during the first 2 to 3 weeks following breeding. Factors associated with embryo loss include stage of pregnancy, disease, age of dam, genetic factors, nutrition, external environment, intrauterine environment, and stress. The following steps to avoid increased embryo mortality should be taken throughout the entire year; however, during a critical time when pigs are under extreme heat-related stress, following these suggestions is imperative:

1. Avoid late estrual inseminations: The simplest way to prevent late estrual inseminations is to ignore "target" number of inseminations and breed females totally on the basis on a strong standing heat response. Another way to reduce mistimed inseminations is to determine the average estrus length in your weaned sows, gilts, and repeat breeders and based on these averages, shorten the last insemination interval. For example if you normally can service sows AM-AM-AM, change your schedule to AM-AM/PM. Thorough heat-checking prior to performing subsequent inseminations will also help prevent poorly timed late artificial inseminations, which may interfere with uterine preparation for implantation.

2. Minimize unnecessary stress by mixing females only at weaning: Once fertilization occurs in the oviducts, pig embryos descend into the uterus very quickly; however, implantation does not occur until day 12 and full attachment until day 18. During this time, the pig is highly susceptible to stress factors, such as movement and temperature. If females are to be mixed, this should be performed on the day of weaning to prevent unnecessary stress on the animal. Any unnecessary stress following breeding can result in embryo detachment and loss.
3. Refrain from, or even stop, moving females in gestation to different locations: After breeding and around day 30 of pregnancy, females can be moved to a different location; however, mixing sows and gilts any time during or following breeding greatly increases the chances of subsequent embryo mortality. Temperature changes are likely to elevate embryo mortality, and steps to prevent environmental extremes should be taken to avoid unnecessary stress during early pregnancy.

4. Provide a good, level plane of nutrition before, during, and after breeding: Pre-mating nutritional status appears to be a greater determinant of embryo numbers and survival than the post-mating diet in gilts. This strategy requires "flushing" gilts with an extra 1 to 2 pounds of feed during the estrus cycle prior to mating. This can be attempted for sows as well, even though most post-weaned sows will voluntarily restrict their own feed intake. However, various studies have indicated that high feed intake during the first 30 days following breeding may also have a negative impact the embryo survival rates. Therefore, sows and gilts should be maintained on a level feed plane at or slightly above maintenance following breeding. There are no extra measures to take in feeding during periods of heat stress with the exception of ensuring that the female is consuming feed daily (hopefully around 4-5 pounds per feeding, depending on diet formulation). Appropriate action to boost appetite may be required, similar to procedures used during lactation.

Reproduced Courtesy