Results Of Hog-Stress Study May Lead To Better Management Methods

May 04, 1998

CHAMPAIGN, Ill. -- Environmental stresses slow the rate at which pigs grow to market maturity. A new study has found that the stresses are additive and, therefore, predictable in their impact. Such knowledge, researchers say, may help improve management on hog farms.

Researchers subjected groups of Yorkshire and Hampshire crossbreds and purebred Durocs to three commonly occurring environmental stresses -- heat, overcrowded pens and regrouping -- in various combinations over four weeks. When all three conditions existed concurrently, the pigs' growth rate fell by 31 percent compared with pigs in the control group that was free of stressors. For pigs subjected to the three stressors individually, growth rates fell by 10 percent, 16 percent and 11 percent, respectively.

The University of Illinois study -- the first measuring the effects of more than two stressors occurring simultaneously on swine -- was published in the March issue of the Journal of Animal Science by Rodney W. Johnson, Mike Ellis and Y. Hyun of the U. of I. department of animal sciences and Gerald Riskowski, a professor of agricultural engineering. It was funded by the National Pork Producers Council and Cargill Inc.

Pigs often face a variety of other environmental stresses on hog farms, but the study clearly suggests that many stresses are additive in nature, thus predicting the detrimental effects of multiple stresses may now be possible, Johnson said.

"Animal environments are very complex," he said. "Of course, the ideal management strategy is to remove stressors from the environment. Pigs will eat more and grow faster as a result. However, the reality is that not all stressors are controllable."

Heat stress on summer days, in which temperatures in pig pens may reach 28 to 34 degrees Celsius (82 to 93 degrees Fahrenheit), is often uncontrollable in that applicable cooling systems are not entirely effective, and air-conditioning for an entire pig facility is financially improbable, Johnson said.

"Our data indicate that when the three stressors were imposed simultaneously, their detrimental effects to swine growth performance, in general, were additive," he said. "Therefore, if we know the effects of a number of individual stressors and recognize that the stressors are present, we may be able to predict the total effect on growth performance. The study also suggests that even if some stressors are uncontrollable, eliminating a single stressor can have significant beneficial effects."

The bottom line is that if pigs don't eat well because of stress, they don't grow and reach mature market weight quickly. Under optimum conditions, they can reach that weight in about 140 days. The U.S. average is 180 days, Johnson said.

The study was modeled after a study on chickens published in 1989 by U. of I. animal scientist Stanley Curtis, who found that six simultaneously occurring environmental stressors also had an additive effect.

University of Illinois at Urbana-Champaign

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