Paul Warriss and his associates at the University of Bristol in England have worked with sound measuring equipment to quantify the relationship between pigs squealing in the stunning chute and stress. They used a meter to measure the continuous sound level throughout a five-minute period. The researchers found there is a highly significant relationship between physiologic measures of stress and sound level. They also determined squealing pigs have a greater likelihood of producing P.S.E. meat.
While conducting the U.S. Dept. of Agriculture's 1996 Survey of Stunning and Handling Livestock in Federally Inspected Beef, Veal, Pork and Sheep Slaughter plants, a sound meter was not available to measure the intensity of pig squeals. To compensate, the number of pigs squealing while held in conveyor restrainers was counted in seven plants. In six plants squealing varied from 0 percent to 2 percent of the pigs. One plant had an elevated percentage of pigs squealing; 14 percent of the pigs squealed in the restrainer. This finding may be attributed to the condition of the restrainer, which had a missing part with conveyor sides on a different angle compared to other restrainers. The elevated percentage of squealing pigs may also indicate meat quality problems.
This particular plant had problems with bloodsplash in hams. When animals struggle and attempt to escape from a restrainer, bloodsplash may increase. Struggling against restraint may break small blood vessels. Excessive pressure exerted by a restraint device, powered by either hydraulic or pneumatic cylinders, will also increase bloodsplash. To reduce struggling in the restrainer, both sides must run at the same speed.
Vocalization scores in seven beef plants ranged from 0 percent of the cattle to 35 percent. Three of the plants had vocalization scores of 3 percent or less. The chain speeds in these plants varied from 75 head of cattle to more than 200 head per hour. Electric prodding was the cause of more than half of the vocalizations. In two of the plants electric prods were used excessively. The vocalization scores in these two plants were 12 percent and 32 percent of the cattle. In two other plants the main cause of vocalization was excessive pressure applied by a restraining device powered by an air cylinder. Slipping on a slick stunning box floor also caused animals to vocalize. With the exception of two animals, all of the vocalizations in the stunning chute area were caused by a stressful event such as electric prodding, slipping on the floor, excessive pressure exerted by a restraint device or missed captive bolt stuns.
In the two plants with excessive prodding, vocalizations significantly declined after the employees were instructed to tap the animals on the rear before resorting to an electric prod. Vocalizations declined from 12 percent to 3 percent in the first plant and from 32 percent to 13 percent in the second plant.
For acceptable welfare, vocalization scores for cattle should be 3 percent or less. Since conducting the survey, I visited four large beef plants with chain speeds of more than 150 head per hour. Three of these plants easily achieved the criteria of 3 percent or less of the cattle vocalizing. In one plant the estimated vocalization score was about 8 percent. This was due to lighting problems and equipment difficulties that were easily fixed. (See 'Troubleshooting handling problems," M&P, December 1994, page 62, for ways to eliminate distractions that cause balking.)
Since the survey was conducted, data from large numbers of cattle were tabulated to determine a sensible criteria for vocalization in plants that conduct ritual slaughter. In a plant with a well-designed head holding device run by a well-trained operator, 3.7 percent of the cattle vocalized. Most of the vocalizations were in response to pressure from a restraint device. Because the pressure was set correctly, the vocalizations were probably due to pinching. Slight modification of the neck brace would probably lower these scores.
In summary, vocalization scoring can be used in both pigs and cattle as a simple measure of animal stress. Achieving low vocalization scores improves both humane treatment of animals and meat quality.
The author operates Grandin Livestock Handling Systems, Inc., Ft. Collins, Colo., and is an Assistant Professor of Animal Science at Colorado State University.
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