Recently I looked at two head restraint devices for beef cattle used in plants. In both systems, the head restraint device was correctly designed but both had the wrong type of pneumatic controls. In one of these systems, this resulted in high vocalization scores and many cattle bellowed. The cattle bellowed because the head holder applied excessive pressure. It was also impossible for the operator to control the amount of pressure applied to the animal. There are two ways to fix this problem: Either install new control valves or an additional pressure regulator.
One common mistake is running a pneumatic-powered restraint device with a single pressure regulator. Devices, such as a neck stanchion or a chin lift that press directly against the animal, require less pressure. Other parts of the device, such as a heavy door, require a higher maximum pressure to operate. A chin lift or neck stanchion will need to have its own separate pressure regulator that is set at a lower pressure. In one plant, reducing the pressure applied to the neck reduced their vocalization score from 23% to 0%. The pressure regulator was set at a lower maximum pressure. To determine the correct air pressure, the bovine should remain silent when the head is restrained. The head-holding device must also be inspected to ensure that it has no sharp edges or skin pinch points.
Another method to prevent excessive pressure being applied to the animal is to replace the pneumatic control valves. There are two types of valves. The worst valves have only two settings. They are either full air pressure on, or all air pressure is off. When the valve is moved, the device will always apply the full pressure that is set at the pressure regulator. The best type of pneumatic valves have mid-stroke position control. When the operator lets go of the valve, it will return to a midpoint between either fully extended or fully retracted. To make this type of system work may require the installation of check valves to prevent the system from bouncing. To install this method will require a more extensive knowledge of pneumatic controls compared to the previously mentioned method.
Speed controls are small valves that are used by the airlines to control the speed that an air cylinder moves. The speed can be set by turning a knob. A common mistake is confusing speed controls (also called flow controls) with a pressure regulator. Pressure and the speed that a cylinder moves are two separate things. Setting a speed control at a slower speed does not change the maximum pressure that can be applied by the system. I can vividly remember telling one person that slowing down the speed will just make the system slowly squeeze the animal too hard. The use of speed controls will greatly improve a system by preventing sudden jerky motions that frighten animals.
In conclusion, there are many existing restraint systems where animal welfare could be greatly improved by either the installation of an additional pressure regulator or using different control valves.