The goats in Leon Kruger’s smallstock unit at the ARC’s Animal Production Institute, often seemed to become ill after being handled. “Animals are normally healthy and well-adapted to their environment and conditions,” he explains. “But as soon as they are in a trial involving handling and weighing, different feed or being separated from their peers, they become ill after two or three weeks.”
Kruger noted that, apart from the physical handling, no other variables could lead to the animals becoming ill. He therefore concluded that handling was an important stressor that could lead to illness. A stressor, he points out, is anything that disrupts an animal’s homeostasis, the system with which it self-regulates variables so that its internal body systems remain relatively stable.
If a potential predator (for example, a human) enters an animal’s safety zone, it triggers the fight, flight or freeze response, which results in the animal ceasing grazing and facing the potential threat. This response also triggers the release of the so-called stress hormone, cortisol, into the circulatory system. Cortisol is one of a group of steroid hormones released to enable an animal to escape a potentially dangerous situation if necessary. When it is present in the bloodstream of any animal, it can compromise the animal’s immune system.
“Opportunistic micro-organisms can multiply during a state of compromised immunity, leading to stress-related diseases such as pasteurellosis and coccidiosis,” Kruger says.
To confirm his observations, Kruger conducted tests to determine whether an animal suffered from high stress levels by measuring the cortisol level in its blood.
However, he first had to establish a basal cortisol level for the goats used in his research. To achieve this, a number of animals were brought to a crush every day and moved quietly and at their own pace to the handling area. Once they were in the crush, Kruger would calm each goat down by placing one hand under its chin and the other on its head, stroking it gently.
When all the goats were accustomed to being handled, he slowly inserted a needle into each goat and immediately pulled it out. In this way, the animal was gradually introduced to the procedure that would follow. “They became so used to this that they wouldn’t even flinch when I inserted the needle,” Kruger says. “Eventually they were calm enough for me to draw blood to determine the basal level of cortisol.”
Kruger established that this was between 40 nanomol/l and 60 nanomol/l for the goats in his trial – well within the normal values of 42 nanomol/l to 82 nanomol/l.
The trial, and its surprising results
Kruger’s research subjected the group of 36 goats to a number of stress-inducing situations, using eight goats at a time.
According to him, the results were rather unexpected. In the first trial, the goats entered the crush at their own pace and were then doused with water.
They exhibited an elevated cortisol value of 158 nanomol/l, significantly higher than the basal level (see graph 1). In the second trial, the animals were kept in the sun for three hours, and then vaccinated. Once again, the cortisol value was significantly higher than the basal level and persisted for more than 90 minutes (see graph 2).
In the third trial, the goats were left without food or water for 48 hours and then exposed to direct sunlight for three hours. They were not handled at all, and blood samples indicated that their cortisol levels were not significantly higher than the basal level. Kruger concluded that, in every trial, handling, and not the lack of food, water or sun exposure, was the variable that increased cortisol levels.
“If the cortisol level is increased for a short time, it will not necessarily affect an animal’s immunity.
But the cumulative effect of taking a goat from its camp, putting it into a crush and handling it, disrupts its homeostasis. This affects its psychological and physiological integrity, causing stress.”
Signs of stress in animals are difficult to detect: often the only indication is an increase in vocalisation.
“This is especially true in cattle. When they start milling around due to anxiety, you won’t get them to exit a gate. This is usually when they are prodded from behind, just making the situation worse,” Kruger explains. “I tell handlers to stand back so that the animals can get rid of their worst anxiety, see that there is an opening, and move out.”
As a veterinary technologist involved in vaccine development at the ARC, Kruger has considerable experience in working with animals and explains that it is simply a matter of approach.
“When you handle animals harshly, the resultant high level of cortisol released into the bloodstream compromises the immune system to such an extent that even vaccination doesn’t work,” he says. “No mammal can avoid this. Researchers have gone as far as measuring cortisol levels in the blood of students before an exam. The results show that even humans are susceptible to the immune-compromising levels of cortisol in the blood when under stress.
“A short duration stressor means that the release is quick and will not have an effect on the immune system.”
Handling the farm
Kruger has observed that commercial smallstock farmers often lack proper handling facilities such as a crush. Individual animals are often caught and dragged along by the leg, for example, leading to high levels of stress.
“The aim of this trial was to simulate a commercial smallstock enterprise,” he explains. “If there’s no handling chute and you work with a small number of 50 animals, just imagine how long it would take to get to the last one.
“When you catch an animal, it naturally tries to escape. The flock is milling around and there’s constant dust. Even guiding the flock to the handling chute, if there is one, is often accompanied by fear-evoking stimuli. Then, when in the handling chute, the frightened animal is expected to stand still for a procedure to be performed.
“Such activities are not traditionally considered stressful. But the research results show that in fact they cause significant stress to the animals as the cortisol level in the blood remains high for a longer period. It’s then that the immune system becomes compromised and opportunistic bacteria and micro-organisms multiply to cause disease.”
According to Kruger, many commercial farmers can improve this situation through better livestock handling techniques. The first task, he explains, is to understand animal behaviour. When animals are moved, they should be given time to become accustomed to their new environment and be allowed to calm down and overcome their anxiety.
“An animal has a ‘flight zone’ and it will determine how large that zone is. It also depends on how often it is handled. If
you work with an animal frequently and gently, this zone will become smaller. If it’s handled infrequently and roughly, the zone will become larger.”
In a more extensive farming operation, the flight zone will be large as the animals are not handled often. A farmer or farm worker will also find it more difficult to get them to enter a high-density area such as the handling chute. Animals recognise a barrier and see it as providing safety. If a person is on the outside of a fence, animals inside will not flee and are often curious and will come closer, Kruger explains.
“That’s why a crush is so important, even for smallstock. Animals see it as a safety zone between them and humans.”
Common diseases caused by stress
Various pathogenic bacteria such as Mannheimia haemolytica inhabit the upper respiratory tract where they do not normally cause disease as the animal’s immune system wards them off. But when the immune system is compromised due to stress and the subsequent release of cortisol, the bacteria multiply exponentially and cause the lung disease known as pasteurellosis. This is why this disease often occurs about two weeks after periods of high stress such as being transported or handled.
Most feedlots experience outbreaks of pasteurellosis and other lung diseases due to the stress associated with animals being transported to the feedlot and processed on arrival.
“A farmer is often advised to vaccinate before a stressful period. But if handling causes the animal stress, the increased cortisol level would compromise this acquired immunity. Proper and stress-free handling is as important, if not more important, than the vaccination itself.”
Coccidiosis is a disease normally confined to young animals. The immune system in older animals prevents the harmful organisms from causing clinical disease. If an older animal suffers from it, it may well be that a stressful incident had compromised its immune system, with subsequent cortisol release, as is the case with pasteurellosis.
“I think most farmers are aware of this. But we never knew its true extent. The research results have quantified it,” he says.
“We thought that when animals have food and water they are fine. But we now have proof that withholding food and water for a while is not as important a stressor as handling.
“We also sometimes hear that vaccines don’t work. That is not necessarily true. A vaccine goes through stringent quality assurance tests. There are several reasons why it may not be effective. Stressful handling is one of those reasons.”
“Handling should, where possible, be done by the same persons and in the same manner,” Kruger explains. “Animals get accustomed to a herdsman’s smell, appearance, behaviour and voice. The more accustomed the animals become to the herdsman, the smaller their flight and safety zones will be and the less stress they will experience when being handled.
An animal’s visual perception also determines the best way of handling it. A sheep and a goat, for example, both have a slit-shaped pupil that allows a wider field of vision, but it has a blind spot directly behind it. It does not have good depth perception and cannot determine accurately how far away a person or a predator is. It needs time to focus on the perceived threat.
“This is also why they often have to stop and look at something on the ground to identify it. It’s then when the handler erroneously starts prodding or chasing them. Livestock will also resist being taken from a well-lit area to a darker area such as the inside of a truck, because they can’t see what is inside.”
Another important aspect when working with animals is maintaining a point of balance, Kruger explains (see Figures 1 to 3).
Figures 1 to 3: When working with an animal in a crush, stand in front of its shoulder to make it move backwards and away from you. Stand behind its shoulder to make it move forward. Maintain a point of balance on the shoulder to allow it to see you. This will stop it from moving around when handled.
“If you work with an animal in a crush, standing in front of its shoulder will make it want to move backwards and away from you. Standing behind its shoulder will cause it to move forward. Maintaining a point of balance on the shoulder blade will mean that the animal will see you and not move away.
“Even a severely excited animal will eventually calm down if ‘gentled’ and will allow the handler to perform procedures without causing it stress.”
Repeated positive contact will make animal handling much easier, Kruger explains. ‘Gentling’ involves physically handling the animal, using your hands to ‘look at the animal. In this way, the farmer or worker will also be able to pick up abnormalities such as abscesses and poor body condition. An animal remembers ‘negative handling’ for a long time and will associate a particular handler with this negative experience. It will then be prone to stress every time it sees the handler.
Kruger stresses the importance of a farmer being aware and recognising animal behaviour – and using it to his advantage in an effort to prevent stress-related diseases. Research has also demonstrated the negative negative effect of stress on meat quality and tenderness.
Stress and reproductve problems
In addition, there is a marked relationship between cortisol levels and reproduction. Evidence shows that cortisol (corticosteroids) may be responsible for abortion and foetal resorption during the early stages of pregnancy, and that there is a link between stress and ovulation, and even semen quality.
“A stock farmer must see appropriate and stress-free handling in the same light as vaccination and dosing in preventing disease. Stress cannot be eliminated, but positive handling can reduce it,” Kruger concludes.
Phone Leon Kruger on 012 672 9169 or 082 663 2664, or email [email protected].