EFFECTS OF TEMPERATURE

The effects of temperature on reproductive performance have been examined by a number of researchers. Although the specifics may be debated, there is general agreement about the impact of temperature.¹ In general, increases in temperature above a critical level cause a decline in reproductive performance. In sows and gilts, the reduction in reproductive performance is expressed primarily as establishment of fewer pregnancies when heat stress is not severe. If heat stress is severe during breeding and early gestation, declines in reproductive performance also can be expressed as decreased embryo survival. Semen quality of boars is reduced by heat stress, but that effect may not become apparent for up to 40 days.¹ Boars exposed to a period of significant heat stress exhibit diminished semen quality for a limited period of time. The effects of heat stress on semen quality dissipate after a lag time of about 60 days after the heat stress ends.

Severe heat stress usually is characterized by sustained increases in rectal temperature. If rectal temperatures remain elevated, methods to reduce heat stress should be implemented. Such measures may include use of evaporative cooling pads, drippers and foggers, and circulating fans. To fully understand the effects of temperature, the concepts of effective environmental temperature (EET) and lower critical temperature (LCT) must be understood. EET is the temperature that a pig actually feels. EET includes the effects of air speed (drafts), floor type, building insulation, and supplemental cooling. The LCT is the EET at which pigs must increase metabolism to maintain body temperature and production.² If sufficient energy intake is not maintained, pigs use body reserves to increase metabolism. LCT also is defined as the EET at which cold stress begins to occur.³ To prevent cold stress in sows, the EET should be above 15.5° C. EET can be used to evaluate the various methods for reducing heat stress.

Feed intake and subsequent metabolism in gestating sows or gilts provides energy for maintenance (i.e., basic life processes and body temperature control), pregnancy, and body condition or growth. Energy for metabolism must come from feed intake. Metabolic energy will be allocated to maintenance first, then to pregnancy maintenance and development, and last to body conditioning and growth. If sufficient energy intake is not provided, a sow or gilt will lose body condition. To stop loss of body condition, the EET must be raised or feed intake must be increased. If a number of animals are losing body condition, the EET should be raised if possible. If only a few animals are losing body condition, their energy intake should be increased. If the EET is increased for a few animals, the remaining animals in the same environment may become heat stressed. If an animal is heat stressed, it either will use additional energy to dissipate heat or will decrease energy intake. With constant energy intake, a heat-stressed sow could lose body condition because additional energy is used to dissipate body heat, through panting, for example.

EFFECTS OF HUMIDITY

Relative humidity (RH) should be maintained between 40% and 60% but must be maintained below 80%.⁴ An environment that provides an RH between 40% and 60% is healthiest for sows. Most bacteria and other microorganisms thrive in an environment with high humidity. An RH between 40% and 60% minimizes the proliferation of bacteria while providing a level of humidity that is practical to obtain with typical ventilation and heating equipment. If the environment gets too dry, dust levels tend to increase. If the inside environment gets too wet (RH above 80%), moisture condensation problems typically occur when the outside weather is cold. During some periods during the year, it is nearly impossible or very impractical to maintain RH within the 40% to 60% range. During these periods, 70% RH should be the upper maximum, and good management practices, such as stringent sanitation, should be emphasized to help ensure a healthy environment for the sows.

Swine are less sensitive to humidity than to air temperature. A temperature-humidity index combines the effect of temperature, using the dry bulb temperature, and humidity, using the wet bulb temperature, into one numeric value. A temperature-humidity index for swine has been developed based on the physiologic responses of swine to various thermal environments.⁵ The coefficients of the temperature-humidity index are 0.75 for dry bulb temperature and 0.25 for wet bulb temperature for adult swine. Because the coefficient for dry bulb temperature is considerably larger than the coefficient for wet bulb temperature, adult swine are more sensitive to air temperature than to humidity. This fact is readily apparent in practice because evaporative cooling pads are extensively used in swine facilities to reduce heat stress. An evaporative cooling pad system converts energy in air based on dry bulb temperature to energy in air based on wet bulb temperature (humidity). By shifting the energy in air from a component to which large swine are highly sensitive to a component to which swine are less sensitive, the thermal environment the pig “feels” due to heat is minimized, and the environment is less stressful to the animal. If evaporative cooling pads are used, good management must be practiced so that adverse health effects due to high humidity are minimized.

EFFECTS OF LIGHT

Light frequency and intensity for swine housing typically are based on the needs of the workers and the activities they perform,⁶ rather than on providing the best physiologic situation for the animals, largely because little research has been done on the influence of light, and the results of what has been done are conflicting.^7–12 The general level of illumination recommended for breeding and gestation facilities is 15 foot-candles. The level of illumination should be increased to 20 foot-candles for animal handling and inspection. For the breeding area, this would correspond to the times when hand mating activities are being conducted.

Despite conflicting research results, the effects of light on swine reproduction are beginning to be understood. Gilts attain puberty normally with a minimum of 9 hours of light per day. Boars exposed to 15 hours of light per day had better semen quality at 8 months of age than did boars exposed to natural short-day photoperiods.² Long photoperiods during lactation may or may not improve the wean-to-service interval (WSI) or postweaning reproductive performance. Long photoperiods during late gestation may predispose to longer WSIs.¹³ A long photoperiod has been shown to increase the length of the estrous period in gilts by about 1/2 to 1 day.¹⁴ One study has suggested that supplemental light during lactation (16 total hours of light versus normal daylength patterns in controls) synchronized the onset of postweaning estrus in sows, and a higher proportion of treated sows than control sows had WSIs of 5 days or less.¹² Other studies have shown no effect.^7–11

EFFECTS OF AIR CONTAMINANTS

Air contaminants that typically are found in swine facilities include ammonia, dust, hydrogen sulfide, and carbon monoxide. High levels of these contaminants, such as ammonia levels above 100 parts per million (ppm), have been shown to decrease production levels and cause health problems.¹ The swine industry is rapidly moving to improve air quality in swine confinement facilities, however, to benefit the health of the animal caregivers.¹⁵ The air quality in swine breeding and gestation facilities should be maintained within the standards for gases defined by the National Institute for Occupational Safety and Health (NIOSH). No worker health standards are currently in effect for agricultural workers. The current NIOSH standards for industrial workers are used only as a guide for agricultural workers. If gas contaminant levels are kept within these standards, air quality should not have any adverse effects on worker health. Air quality in modern breeding and gestation facilities should not adversely affect sow reproductive performance if the air quality is adequate for the workers inside the facility.

The manure management system has a major impact on the air quality inside a swine facility. Manure management systems affect the levels of ammonia, hydrogen sulfide, and methane. Ammonia levels in buildings with scraper systems can average about 25 ppm¹⁶ or higher, and buildings with scraper systems have a difficult time maintaining air quality that is acceptable for worker health as just described. Therefore, scraper systems probably should not be considered as an acceptable method of manure removal. Deep pit buildings can have average ammonia levels that are acceptable,¹⁷ but when pits are emptied, ammonia levels, along with hydrogen sulfide and methane levels, usually are not acceptable and can reach dangerous levels for both workers and pigs. Acceptable ammonia levels can be achieved with the use of flush systems and pit recharge systems. These systems either quickly remove manure from the building or immediately submerge manure in water. Another acceptable manure handling system is a gravity-drain, liquid manure system (hairpin gutters). This system submerges manure in liquid and then periodically removes manure from the building. When manure is either quickly removed from the building or submerged in water along with periodic removal of the liquid, air quality inside a facility usually is acceptable.