Acclimation of growing pigs to climatic environment

In intensive pig production the climatic environment has an important impact on productivity and health of the animals. Since factors as draught and fluctuating temperatures are known to influence the incidence and severity of Haemophilus pleuropneumoniae infections in growing pigs at the beginning of the fattening period. These aspects of climatic environmment in young growing pigs were studied.

It is known that climatic factors influence metabolic rate and energy metabolism of animals. Moreover, acclimation to adverse conditions, e.g. low ambient temperature, may occur. This implicates that the outcome of infection might be related to time of occurrence of climatic stress. This was studied in chapter I. Pigs infected with Haemophilus pleuropneumoniae and exposed to climatic stress (fluctuating temperature and draught) thereafter had a higher mortality and morbidity rate compared with pigs exposed to thermoneutral conditions (25 °C). Specific serum antibody levels of pigs were increased at day 12 p.i. and higher for pigs exposed to climatic stress compared with pigs kept at 25 °C. Infection of pigs with Haemophilus pleuropneumoniae after 12 days of exposure to both conditions (25 °C). vs fluctuating temperature and draught) showed no distinct differences between both groups. Acclimation of pigs could be related to this.

Time and day of achievement of acclimation of pigs to different adverse climatic conditions was studied also. Exposure to ambient temperatures of either 25 °C or 15 °C influenced energy metabolism. Pigs housed at 15 °C reduced their ad libitum feed intake during the first 6 days after exposure compared with pigs at 25 °C. Heat production was equal to that of pigs at 25 °C. As a result maintenance requirement was increased by 11% and the amount of energy available for production was lowered. Daily gain and fat deposition were subsequently lowered at 15 °C. At day 11-12 after initial exposure to the climatic treatments differences between the temperature groups were no longer present. The effect of both ambient temperatures on heat production and activity was also studied. Day of acclimation was determined as that day after which heat production or activity-related heat production remained constant.

Besides ambient temperature, acclimation was also studied with respect to the occurrence of draught during the night period. Draught was applied at either constant ambient temperatures of 25 °C or 15 °C or fluctuating temperature (25 °C). during the day period and 15 °C). during the night period). Draught consisted of an increased air velocity from < 0.2 m/s to 0.8 m/s with a lower temperature of 5 °C. Acclimation estimated from heat production of pigs at a constant ambient temperature of 25 °C was achieved during the day period at day 5 after initial exposure. At a constant temperature of 15 °C and also at the fluctuating temperature acclimation was delayed with a few days as compared with a temperature of 25 °C and reached at day 8. During the night period acclimation at 25 °C could not be determined since heat production did not alter with increasing daynumber after initial exposure. Acclimation during the night period at 15 °C and at the fluctuating temperature was achieved at day 6 and 3 respectively. This showed that acclimation during the night period differed from that during the day period. Moreover with fluctuating temperature, the temperature during the day period (25 °C). influenced acclimation during the night period (15 °C).

The occurrence of draught delayed day of acclimation. At 15 °C and at the fluctuating temperature a "shift" in heat production and activity was found from the day period to the beginning of the night period. For the determination of the day of acclimation at 25 °C, 15 °C or fluctuating temperature this period was omitted first. Data in literature showed that an increase in heat production by 11 kJ per kg metabolic body weight (kg ^0.75) is equivalent to an increase in lower critical temperature (LCT) by about 1 °C. The effect of draught on heat production was expressed as change in LCT. At 25 °C draught increased LCT by 2.8 °C, at 15 °C by 4.2 °C and with fluctuating temperature by 4.5 °C when compared with control groups exposed to a similar temperature. Draught had thus a differential effect on the LCT, depending on the ambient temperature. Draught was applied during three 2-hour periods at night (21.00-23.00 h, 1.00-3.00 h and 5.00-7.00 h) and made it possible to estimate the effect of draught within nights. At 25 °C draught increased LCT by 3.2 °C, at 15 °C by 6.0 °C and with fluctuating temperature by 5.4 °C. It showed that, within nights, influences of draught on heat production were greater.

The effect of exposure to various climatic conditions on blood parameters was also studied. Pigs exposed to fluctuating temperature and draught had an increased percentage of lymphocytes and a decreased percentage of neutrophils in peripheral blood after 16 days of exposure.

Homeothermic animals maintain a constant ambient temperature. An increased heat loss to the environment will be compensated by an increase in heat production thus enabling body temperature to remain constant. With the use of telemetrical measurements of body temperature the effect of various climatic conditions on body temperature were determined. Results showed that body temperature was not affected by a constant ambient temperature. With application of draught body temperature was changed. A rhythm was found with the occurrence of draught at 25 °C, 15 °C and fluctuating temperature. A rhythm in heat production and activity-related heat production in relation to the occurrence of draught was also present. However rhythm of body temperature was not similar to that of heat production or activity-related heat production. Heat production and also activityrelated heat production were at their maximum directly after the onset of draught, whereas body temperature was lowered first and increased thereafter. Difference in the peak of heat production and body temperature was correlated with the effect of draught on heat production.

As a response to infection pigs will alter their set-point temperature and body temperature will incline. Consequently the defence mechanism is increased. Thus lowering body temperature due to sudden changes in climatic environment as with draught, will delay or diminish this enhancement. As a result of the effect of draught on body temperature the ability of animals to cope with infection is impaired.