Recently I have run into several places with problems caused by a head-holder or other devices applying excessive pressure to an animal. If cattle vocalize (moo, bellow) in direct response to restraining their heads in a head-holder, there is a problem that needs to be corrected. In both cattle and pigs, vocalization during handling and restraint is associated with physiological measures of stress, such as cortisol, glucose and lactate. Blood levels of these substances increase when animals are poked with electric prods or stressed by a restraint device. They are also an indicator that the animal has become agitated and excited. US Dept. of Agriculture regulations state that agitation and excitement must be minimized. Vocalization in a head-holder can be caused by one of four factors: Excessive pressure applied by equipment; sharp edges; animal is held too long; and over-use of electric prods.
To prevent vocalization caused by being held too long, either stunning or religious slaughter should occur within 15 seconds after the head is fully restrained. It is best if the animal is either cut or stunned immediately. It is also essential to check for sharp edges. Cattle will often vocalize in direct response to being pinched or when excessive pressure is applied.
Both hydraulic and pneumatic equipment have pressure-regulation devices that can control the force exerted against an animal’s body. These should be adjusted so the device automatically stops applying pressure before the animal starts to show signs of agitation or excitement, such as vocalization, or struggling. Excessive pressure may also cause injuries, such as broken bones or bruises on the carcass. Often, a restraint device will need more than one pressure control. Less hydraulic or air pressure is required to operate a head-holder compared to operation of a heavy door. If both the door and the head-holder are controlled from the same air regulator or pressure-relief valve, excessive pressure may be applied to the animal’s head. A device that is capable of doing this requires a very skilled operator to prevent possible broken bones. When a head-holder is equipped with its own pressure-limiting device, it should be adjusted so it will automatically stop before the animal shows indications of agitation and excitement. If a careless operator keeps pushing on the controls, the system will stop before enough force is applied to the animal.
Speed vs. pressure
A common mistake that is made by some maintenance people is mixing up pressure control with speed control. If a speed control is placed in either an air or a hydraulic line, the cylinder that activates the head-holder or rear-pusher gate will move more slowly. If the pressure control is set too high, the device will slowly apply too much pressure depending on the setting of the speed control. As a comparison, think of the pressure controls like a water faucet. Speed controls control the volume of flow through either a hydraulic or an air line. Turning the screw on a speed control is analogous to turning the knob on a faucet to reduce flow. The pressure regulator in a pneumatic air system or the pressure relief valve in a hydraulic system limits the maximum amount of pressure the system can apply. Speed controls have no effect on pressure.
Types of controls
On devices designed to hold animals, the best type of valves for controlling equipment, such as the head-holder and a rear-pusher gate, are hand-operated control levers. The advantage of this type of valve is that it has throttling ability, similar to the accelerator of a car. The speed that the head-holder moves depends on how far the lever is pushed. It is easy for the operator to move the head-holder at variable speeds. When valves controlled by solenoids (electric switches) are used, the system only has one speed. It is also essential to have mid-stroke position control of cylinders on systems powered by air. This enables the operator to stop the movement of the head-holder when a pneumatic cylinder is only partly extended.
Dr. Temple Grandin operates Grandin Livestock Systems Inc., Fort Collins, Colo., and is a faculty member in the animal science department at Colorado State Univ.