Relation of animal vision, hearing and smell to stress and injury
Livestock behave in various ways, depending on circumstances and, to a large extent, species. A basic understanding of animal behaviour in typical circumstances from the farm to the market or slaughterhouse will assist handlers in the management of livestock and thereby prevent undue stress and injury.
For example, animals, which are unaccustomed to frequent contact with humans, such as ranched or extensively raised stock, will not allow people to approach or touch them easily. These animals will require more elaborate loading ramps, pens and handling races than tame ones. People loading extensively raised animals need to understand the psychology of the animal in order to prevent injury to either the animal or themselves. On the other hand, oxen, draught animals, those animals raised intensively or dipped regularly (for tick control) and animals living in close contact with humans, such as in rural areas, are generally more tame and easy to handle.
Ruminant animals can discriminate between different colours. The ruminant eye is most sensitive to yellow-green and blue light. Experience has shown that livestock, particularly cattle and pigs, as well as ostriches, are very sensitive to light contrast. This causes them to hesitate at and shy away from drains, gates, and changes from wet to dry or concrete to metal floors. Lighting should be even and diffuse and harsh contrasts of light and dark should be avoided. Ultraviolet or diffuse light has a calming effect on poultry and ostriches.
Some livestock species, e.g. cattle and ostriches have a wide angle of vision and to prevent them from becoming afraid of distractions outside confines, the holding pens, crowd races, stunning boxes and gates should have solid sides. Animals will also shy at moving things, as well as darkness and they may refuse to enter a dark place. Animals have a tendency to move from a darker to a lighter place. Extra, indirect lighting may help in moving animals in pens. Adding a light to illuminate a race entrance or removing a lamp to eliminate a sparkling reflection will often improve animal movement. All species of animals may hesitate and refuse to move when they see things in the race that scare them, such as sparkling reflections, dangling chains, moving people or equipment, shadows or water dripping. A calm animal will stop and look right at the distraction that scares it. If air is blowing towards the animal this should be changed. If animals hesitate, the distraction that causes this should be removed instead of increasing the force used to move them. Rapidly moving objects scare animals. Forcing them to quickly approach a vehicle, pen or building may cause them to panic.
Cattle, sheep and ostriches have very sensitive hearing, particularly to high frequency sound. Sounds that do not bother people, such as intermittent high-pitched noise, may hurt animals ears. Reducing noise from equipment and people will improve animal movement, reduce stress and the risk of injury. People should not yell, whistle or make loud noises. Clanging and banging of equipment will unsettle animals and can be reduced by installing rubber stops. Hissing air is one of the worst noises but also easy to eliminate. It must be said, however, that in many rural circumstances where cattle live in close proximity to humans and where they are mustered, kraaled every night and regularly dipped, some of these noises can be useful aids to droving. For example in rural Africa, where cattle are accustomed to yelling and loud noise it encourages movement.
However, generally it is obvious that noise increases physiological stress levels. This refers also to preslaughter handling and handling at point of slaughter. Slaughter in a small, quiet abattoir produces less stress hormones in animals compared to a large, noisy commercial plant.
With regard to smell, emitted odours, particularly strange smells, may cause animals to become unsettled and excited. This is noticeable in animals, which are strangers to each other or to surrounding conditions. Pre-mixing of these animals, or smearing pigs with litter from a single source will reduce tension and fighting amongst strangers. Many people interested in the welfare of livestock are concerned about animals smelling blood. Cattle will hesitate and sometimes refuse to enter a stunning box or restrainer if the ventilation system blows blood smells into their faces. An exhaust fan to suck away smells will facilitate entry into a stunning box. If an animal becomes agitated and frenzied during slaughter handling, subsequent animals often become agitated as well and an entire slaughter day can turn into a continuous chain reaction of excited animals. The next day, after the surrounds and equipment have been washed, the animals will be calm. A stress pheromone in the blood of severely stressed animals can be smelt by others and cause excitement. Blood from relatively low-stressed animals may have little effect on others. Research with cattle and pigs indicates that stress hormones are secreted in the saliva and urine. Pigs and cattle tend to avoid objects or places, which are contaminated with urine from a stressed animal.