Farmer's Weekly (South Africa)
Understanding the effects of stress
Animals can suffer stress even during ‘normal’ handling, making them more susceptible to disease.
Stress is defined as an external influence on the balance (homeostasis) of a system, which has the potential to trigger a negative reaction.
Homeostasis maintains the stability of the body’s internal environment in response to changes in external conditions. On a very hot day, for example, an animal seeks to maintain stability by keeping in the shade, drinking more water and eating less. The scientific name for this is ‘thermoregulation’; if successful, the animal will suffer no stress.
Thermoregulation is easier during hot spells than cold spells, which is one reason why more stress-related diseases are encountered during the change from autumn to winter.
Recent research shows that even routine handling can cause stress in cattle.
When animals (including humans) are stressed, the steroid hormone cortisol is released. It supplies energy in the form of glucose and enables the animal to escape from the stressor.
In this respect, it benefits the animal, but the release of cortisol can also have major negative consequences.
In livestock, too much cortisol due to constant stress can hamper successful reproduction and increase susceptibility to disease due to compromised immunity.
Farmers will often say a vaccine is not working efficiently, when the truth is that an animal with a high concentration of circulating cortisol cannot mount an efficient immune response.
MAIN DISEASES
Diseases typically associated with stress are Mannheimia haemolytica and Pasteurella multocida (pasteurellosis), which are both related lung diseases, and coccidiosis. Most of the pathogens that cause these diseases are opportunistic and occur under natural circumstances in livestock, but are kept under control by the immune system.
Immunity develops either through vaccination or continuous exposure to non-fatal doses. But stress (high cortisol levels) can lower this immunity to such an extent that the animal succumbs to the disease.
• M. haemolytica and P. multocida
M. haemolytica causes a form of pneumonia, while P. multocida causes a form of broncho-pneumonia.
They are an important cause of economic loss in the ruminant industry and often encountered in feedlots and bull-testing centres around the country after seasonal changes from high temperatures to low temperatures. Occurrence is prevalent in young, growing cattle, and particularly in calves placed in feedlots after weaning.
Symptoms include morbidity and anorexia due to fever; coughing; and a nasal discharge. Abnormal lung sounds can be heard through
a stethoscope, and animals also tend to breathe more rapidly.
An initial diagnosis can be based on the history of the case and on the reaction to treatment. Diagnosis can be confirmed by sending nasal swabs to a laboratory.
Antibiotics are used for treatment. The sooner the treatment, the better the chances of survival.
Management is of the utmost importance to ensure control, and stress should be kept to the minimum. As adverse weather conditions cannot be controlled, it is important that animals are vaccinated well in advance of expected stressor periods.
Farmworkers responsible for the animals should be trained in the proper handling procedures.
• Coccidiosis
Coccidiosis in cattle is caused by Eimeria parasites and is common in young animals that are moved from pasture to feedlots.
Affected animals usually present with a high morbidity but low fatality rate. Poor production also often occurs in recovering animals.
Symptoms include diarrhoea with or without blood and mucous; dehydration; emaciation; and malaise.
Diagnosis is based to a large extent on the history of the case, and can also be confirmed by testing the faeces.
The disease is transmitted by means of the faecal-oral route. Therefore treat all animals in the group with coccidiostats (sulphanomides; sulphadimidines; diclazurils). This is particularly important under unhygienic conditions.
Give affected animals additional fluids to prevent dehydration and to replace minerals and electrolytes.
Please take note, the foregoing is merely intended as an overview of stress-related diseases.
Speak to your veterinarian or animal health technician for more information.
• See Shane Brody’s Communal Farming column on page 29 for advice on dealing with heat stress in pigs. • Source: Kruger, L. 2014. ‘The effect of environmental factors on stress in cattle’ (arc.agric.za > search ‘ARC Animal Production Institute, Newsletter No. 103’).