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Recognizing Stress Factors

Brian Cotton, Swine Specialist, Brandon

Stress in pigs can be caused by many factors. Depending on how the pig adapts to stress, it may have a deleterious effect or it could be an instrument of training and hardening. Stress has three stages: mobilization (alarm reaction), resistance or adaptation, and exhaustion.

Heat & Cold Stress

Heat stress above 32C, depresses feed intake in sows and feeder pigs. Milk yield in nursing sows is decreased and piglet growth slower. High temperatures in early pregnancy can cause embryonic death and delay sexual maturity in gilts. Heat stress has negative effects on sperm production in boars. This may result in a decrease of 50-60% sperm mobility after 2-6 weeks of a period of hot weather. Decreased fertilization and litter size may show up as a problem after a period of hot weather.

Feeder pigs suffering from heat stress also do not eat as well and growth rates slow down. Longer days to market and barn throughput can be the results in feeder operations.

Young pigs are particularly sensitive to variations in temperature as their thermal comfort zone ranges only 1-2C. Cool temperatures and draughts result in poor weight gains and increased energy expenditure on the maintenance of relatively constant normal body temperatures.

Transportation Stress

Market hogs are susceptible to stress at marketing time as they are moved from pen to truck, mixed with other pigs, often crowded and heat stressed. Some strains of pigs succumb to over-exertion at this time. It is very important to handle pigs properly at this time to prevent market losses.

Properly designed or bedded transportation, travelling during the cooler part of the day, not overcrowding and careful handling are all important when moving pigs.

Social Stress Social stress is usually due to poor management. Every time a group of pigs is mixed together there is a struggle for leadership and increased aggression. Fighting, injury cannibalism may occur as dominant pigs harass low ranking pigs. These low ranking pigs struggle to eat and are often the poor doers in the pen. All-in-all-out management per pen is very important. A higher level of aggression accompanied by increasing stocking density is due to social discomfort caused by a lower familiarity of individuals coming from different groups. The aggressors often have to be identified an taken out of the pen and raised separately.

Nutritional Stress

Nutritional factors such as excessive or insufficient nutrition adversely affect the entire body function. In rapidly growing pigs the rate of weight gain can exceed the development of the control and adaptation systems. As a result, the body resistance to disease is decreased while the susceptibility of the animal to infection increases. Young animals are more sensitive to nutritional stress because their adaptive mechanisms are still poorly developed.

Over feeding and changing feeding patterns can cause stress and result in ulcers in pigs. Feeding times and amounts shouldn't vary sharply from day to day.

Poor quality drinking water containing high levels of dissolved minerals, including sulphates, increases the incidence of diarrhea and worsens post-weaning growth in piglets.

Post stress factors cannot be completely eliminated in modern hog barns. Recognizing what some of the stress-inducing factors are, and managing to reduce them, will ultimately help to increase production and throughput in your operation. Hunt, David (MAFRD) ;


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