Temple Grandin, PhD
Dept. of Animal Science
Colorado State University
Fort Collins, Colorado 80523 U.S.A.
Veterinarians need to be aware of these factors because such factors can cause animals to balk and become excited, which may result in excessive prodding. When a handling system is being evaluated, one must be careful to discriminate between a major design mistake and small distractions that can be easily corrected, but that can ruin the performance of the best systems.
A survey of 29 Canadian slaughter plants revealed that:
Practical experience and observations by the author in more than 200 beef and pork slaughter plants in the United States, Canada, Mexico, Europe, Australia, and New Zealand indicate that careful, quiet handling in the stunning chute will reduce PSE; dark, firm, and dry meat; and bruises. Cattle handled roughly had almost twice as many bruises, compared with those that had been handled gently4. In US and Canadian pork slaughter plants, the author has observed that moving swine quietly and reducing use of electric prods reduced PSE.
When a chute system design is being evaluated, one must determine whether handling problems such as balking and refusing to move are caused by a basic design mistake or by an easily correctable problem, such as untrained employees or small distractions. The author has observed that easily correctable faults in lighting or ventilation, or excessive high-pitched noise, can ruin the performance of a well—designed handling system. When animals balk, handlers are more likely to repeatedly poke them with electric prods. Electric prodding is stressful. A pig’s heart rate will increase with each successive application of an electric prod4. Elimination of electric prods reduced petechial hemorrhages in pigsb. Slick floors that cause animals to slip and fall also make humane handling difficult. A British study revealed that slick floors increased stress in cattle5.
The author has observed increasing problems with excitable swine and cattle6,7. These animals are more difficult to drive at the slaughter plant than are animals from calmer genetic lines. Observations by the author in the United States, Canada, Ireland, and the Netherlands indicate that there may be a relationship between indiscriminate selection for leanness and an excitable temperament. During these plant visits, the author worked with the employees driving thousands of animals. Some of the most difficult swine to drive are hybrids from halothane-positive hybrid boars. Although practical experience and research has revealed that swine that are homozygous or heterozygous for the halothane gene will be more likely to have PSE3, some breeders use boars with the halothane gene because the offspring will have larger loin—eye area and thinner backfat8. Unfortunately, the price for increased pork quantity is poorer quality. Interestingly, the author has never observed an excitability problem in Danish swine viewed in 7 Danish abattoirs. As a population, lean swine in Denmark have been bred to be almost free of the halothane gene.
Environmental factors during finishing can also affect excitability. Providing environmental enrichment to swine raised on slatted concrete floors resulted in calmer swine and facilitated their movement through a chute9. Environmental enrichment consisted of providing toys to chew and manipulate or people walking in the finishing pens every day during the entire finishing period. Practical experience on several farms indicates that swine will be easier to drive if the person walking through the pens moves in a different direction each day. Varying the routine during pen walking appears to train the swine to tolerate novelty.
Poor design can make quiet, calm animal handling difficult9,12,13. The most serious design mistake is constructing a single-file chute to the stunner that looks like a dead end. An animal approaching the entrance of the chute must be able to see that there is a place to go. When an animal stands in the forcing pen, it must be able to see at least 3 body lengths up the single-file chute. For cattle, curved chutes will work more efficiently than straight chutes, but they must be laid out correctly, so that the entrance to the chute does not appear to be a dead end9. Facilities for swine will work more efficiently if they are completely level. Ramps to the stunner will work well for cattle and sheep. The ramp must be located in the single-file chute. The forcing pen must never be built on a ramp or slope, or the animals will pile up against the rear crowd gate. Animal movement will be facilitated by installing solid sides on chutes, forcing pens, and restraint devices to prevent the animals from seeing outside the facility. Solid sides also prevent the animals from seeing people deep in their flight zones12,14.
The author has observed 5 important variables that impede animal movement in the slaughter plant. They are major mistakes in the design of chutes, re- strainers, stockyards, or other equipment; rough handling, caused by a lack of employee training or poor supervision of employees; distractions that cause balking, such as easily correctable faults in lighting or ventilation, or air hissing or high-pitched noise; poor maintenance of facilities or worn, smooth floors that cause animals to fall; and animals with an excitable temperament. Most of these faults can be corrected at minimal expense.
To determine the prevalence of easily correctable faults in animal handling facilities, the author visited 29 Canadian plants for slaughter of cattle, swine, lambs, horses, or sheep. The sample included the ll largest plants in Canada and a representative sample of small- and medium-sized plants. Data were collected on 33 slaughter lines in 29 plants. The number of plants with slick floors that would cause animals to fall was tabulated. The prevalence of distractions that caused obvious balking and impeded animal movement, including lighting at the stunning box or restrainer that was too dim or too bright, ventilation systems blowing air through the chute toward approaching animals, balking caused by seeing movement of people or movement of reflections on water or metal equipment, and high pitched motor noise or hissing air exhausts, were determined in 33 slaughter lines.
Slick floors and distractions that impeded the movement of animals were evident in a high percentage of the plants (Tables 1 and 2). Slick floors that caused animals to slip were located in the cattle stunning box or in high-trafhc areas where the rough finish had worn off the concrete. Approximately a quarter of the abattoirs surveyed had an easily correctable fault that caused balking. Ventilation air blowing down the chute into the faces of approaching animals caused swine and cattle to back up, which resulted in excessive use of electric prods. In 1 large beef plant, cattle balked at the entrance of the conveyor restrainer because the sun shone in their eyes and air blew out the entrance. An electric prod had to be used on almost every animal. In the afternoon at that plant, the wind changed direction and negated the effects of the positive-pressure ventilation system, and the setting sun no longer shone into the eyes of approaching cattle. The combination of a change in direction of the sun and the air flow greatly facilitated cattle movement, and electric prodding was greatly reduced. The author has corrected distractions that caused balking and has improved animal movement in many plants in the United States and Canada. In 1 surveyed beef plant and 2 unsurveyed pork plants with new, state-of-the-art chute systems, there was severe balking at the restrainer conveyor entrance because of air blowing toward the animals. Reversing air flow at the restrainer entrance greatly improved animal movement. In another beef plant, multiple electric prods were used on each animal before, and a single prod on < 10% of the cattle after, the ventilation system was modified.
|Type of Distraction||No. of affected slaughter lines (%)|
|Lighting problems (too dim or too bright)||5 (15)|
|Ventilation blowing toward approaching animals||3 (9)|
|Seeing movement of people or moving, sparkling reflections||8 (24)|
|High pitched motor noise or missing air exhausts||8 (24)|
|Flooring Condition||No. of affected slaughter lines (%)|
|Excellent, nonslip||8 (27)|
|Slick, not acceptable||6 (21)|
In 2 other beef plants, cattle movement was facilitated by increasing lighting at the restrainer entrance. When the system was new, it had adequate illumina- tion from overhead sodium lamps. As the lamps dimmed with age, balking increased. The addition of more light improved animal movement. Cattle and swine tend to move from a darker place to a more brightly illuminated place9,13. In 1 beef plant and 2 pork plants, moving an overhead light sideways so that it was off the center line of the single-file chute eliminated sparkling reflections that caused balking. Animals may balk if they see movement: moving people or moving, sparkling reflections. At 2 beef plants and 1 pork plant, animal movement was facilitated by installing shields that prevented the animals from seeing people ahead. Animals may also balk at jiggling objects. In 2 plants, swine and cattle balked at a jiggling gate and a moving chain that hung down in the chute. Removal of the wiggling chain and bracing a jiggling gate reduced balking.
High-pitched noise causes agitation and increases balking. Animals are more sensitive to high-pitched noise than are human beings15,16. Sheep slaughtered in a noisy commercial abattoir had higher blood cortisol concentrations than sheep slaughtered in a quiet research abattoir17. Observations indicate that high-pitched noise is more disturbing to animals than is the low-pitched rumble of conveyor chains. In 1 beef plant, replacement of undersized plumbing in a hydraulic system facilitated animal movement because a high-pitched whine was eliminated. In another plant, cattle movement was improved and visible signs of agitation were almost eliminated when silencers were installed on a hissing air valve located on a stunning-box gate.
Improvements in lighting and elimination of air hissing also will improve the operation of head-restraint devices. In 1 beef plant, placement of a light over a head-restraint yoke attracted the animal so that it voluntarily placed its head in the restraint yoke. In England, head-restraint devices are required by legislation to hold a bovid’s head for captive bolt stunning. In some circumstances, this restraint can increase stress8. Blood cortisol concentrations were higher in cattle with use of a head-restraint device, compared with those with use of a conventional single-animal stunning box18. A mean time of 32 seconds was needed to induce the animal to enter the head-restraint device. Low cortisol blood concentrations were found in cattle with use of a well-designed head restraint, in which the animal entered without balking and was stunned immediately after the head was caught19.
The author has observed that detecting the distractions that cause balking in calm animals is easy. A calm pig or cow will stop and look directly at a jiggling chain or a sparkling reflection. Small distractions appear to be a greater impediment to animal movement when animals with an excitable temperament are driven.
Plant design and staff expertise affected stress levels in swine20. The author has observed that untrained, poorly supervised employees will often handle animals roughly. High stress levels will be observed in well-designed facilities if supervision is lax. The most common mistake made by handlers is putting too many animals in the forcing pen. Forcing pens will work best when filled only half-full. Another factor is line speed. A design that works well at a slow line speed may work poorly at a high line speed. In British abattoirs, swine were more stressed in abattoirs with single-file races, compared with those in plants where small groups were electrically stunned on the floor1. Electrical stunning on the floor is most practical for abattoirs that slaughter < 240 pigs/h. The author has observed that floor stunning becomes rough and sloppy at higher speeds. The author also has observed that stunning swine with CO2 in a group avoided the stress of lining them up in single file. In such a system in Denmark, each group of 5 pigs quietly entered the stunning compartments, without squealing. Single-file chutes and restrainers work well for cattle because they have the behavioral trait of walking in single file. During cattle drives in "the Old West," the animals were led, rather than driven, and they often moved in single file21. On range land in the western United States, single-file cow paths are worn into the pastures.
To make an accurate determination of the cause of preslaughter stress, veterinarians must differentiate between stress caused by equipment design and stress caused by other factors. A number of plants may have easily correctable problems that would impede animal movement, such as slick floors; sudden, loud noises; or ventilation and lighting mistakes.
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