Method of stunning, handling of the animal during stunning and time taken for these operations are risk factors associated with the welfare of the animals before slaughter.
The stunning method should be efficient to make the animal unconscious and should also involve minimum handling of the animal. Slaughter plant management must be careful about the length of time horses spend in the stunning box and the competence of the personnel doing stunning. Maintaining a high standard of welfare requires constant management attention and vigilance. Employees should remain calm and avoid rough handling. The risk factors which affect the welfare of animals during slaughter are described below.
76 1.4.2.1. Handling
From a welfare standpoint, animals should be handled as little as possible in lairage and also during stunning. Handlers should be competent and the systems used should be designed to encourage smooth movement of the stock. Benign handling devices such as flags, flappers and bags should be used instead of electric goads/prods or sharp objects. If goads/prods are used, it is important that handlers do not become overzealous in their application of these devices to the point where they may cause harm, or may use them inappropriately. Rough handling can increase the risk of animals slipping and falling during handling and stunning. One study reported that plasma activity of CK in cattle was positively correlated with the time spent in the race and associated handling (Cockram and Corley, 1991). Regular training of the staff involved in handling has proved to be a good tool to improve handling and stunning (Grandin, 2010a).
1.4.2.2. Method of stunning
Horses intended for slaughter are stunned by a captive bolt (Micera et al., 2010) or shot using a rifle (Grandin, 1994). When properly applied, both cause trauma to the cerebral hemispheres and the brainstem, resulting in immediate unconsciousness (Werner and Gallo, 2008; Grandin, 1994). If exsanguination is performed immediately after stunning, then unconsciousness leads to a painless, humane death. Penetrating captive bolt instruments are powered by gunpowder or compressed air that provides sufficient energy to penetrate the horse's skull (AVMA, 2007). In Canada, some slaughter plants use a rifle shot for slaughter of horses while others use captive bolt. There are some studies carried out on rifle shot as a method of stunning which suggest that if performed properly, death is immediate (Blackmore et al., 1995). The optimal site of penetration of
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the horse's skull is one-half inch (4 cm) above the intersection of two diagonal lines: one diagonal line extends from the base of the right ear to the lateral corner of the opposite eye and the other line extends from the base of the left ear to the lateral corner of the opposite eye (OIE, 2012). The firearm should be aimed directly down the neck,
perpendicular to the front of the skull and held at least 2 to 6 inches away from the point of impact. A 0.22-caliber long rifle is adequate, but 9-mm or 0.38-caliber pistols have greater penetrating potential. If a shotgun is the only available firearm, a rifled slug is preferred (Werner and Gallo, 2008).
A significant welfare issue in the slaughter plant could be horses not being stunned properly. The numbers of stunning attempts needed to stun the animal and number of animals sensible or conscious after exsanguination are two variables studied to assess stunning efficiency. The Werner and Gallo (2008) study in Chile showed that only 85%
of horses became unconscious on the first attempt of stunning and the remaining 15%
needed a second attempt which could be attributed to improper stunning practises. The same study reported that 57.2% of horses stunned returned to consciousness. However, there are no published studies on the efficiency of horse stunning practices in North America.
Micera et al. (2010) showed significant elevation of plasma cortisol, epinephrine and nor-epinephrine concentrations in blood collected by venepuncture after stunning
procedure than that in blood collected 45 minutes before stunning, thereby indicating the stressful nature of stunning. Another similar study found that physiological variables such as blood lactate concentration, blood glucose concentration, plasma creatine kinase activity, cortisol and PCV were significantly higher after stunning compared to
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stunning (Werner and Gallo, 2008). At this point, it is hard to differentiate whether these physiological variables are responding to the stunning procedure itself or whether their increase is due to a stressful situation such as handling during the stunning process.
However, these studies indicate the importance of a scientifically evaluated method of stunning in order to reduce the risk of poor welfare in horses. Unfortunately, there is no scientific literature comparing the efficiency of captive bolt and rifle for stunning horses.
When horses are shot, the noise created can induce fear in the other horses waiting to be stunned or shot. Noise can be an issue both with captive bolt and rifle shot. Gregory et al., (2007) suggested that the captive bolt (possibly air driven captive bolts) produces less noise (less than 111dB), but was also associated with a shallow depth of concussion in cattle. So it is important to strike a balance.
Handling before stunning is also an important procedure which can have an impact on the welfare of horses during slaughter procedure. Training the personnel involved in handling of horses during stunning about flight distance of horses and practical ways to make them move forward without evoking a negative response are good strategies to improve welfare.
1.4.2.3. Time taken for stunning and exsanguination
Time taken for stunning and exsanguination procedures has a significant effect on the welfare of the animal. Generally, the length of time an animal spends in the stunning box is related to the speed of the slaughter line which in turn depends on the speed and efficiency of operators (Werner and Gallo, 2008). When these variables were recorded in a horse slaughter plant in Chile, mean time in the stunning box was 9 minutes and 48
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seconds (Werner and Gallo, 2008). Even though, the Meat Inspection Act and associated Regulations of Canada do not specify any limits for the time taken between stunning and exsanguination, research has shown that cattle can in some circumstances, regain
consciousness after stunning with captive bolt (Appelt and Sperry, 2007) and hence exsanguination has to be carried out within a minute to reduce this chance. It is relevant to note here that United Kingdom regulations allow only 30 seconds between stunning and exsanguination for bovines and 20 seconds for smaller animals, such as sheep goats and pigs (Government of United Kingdom, 1995) however, there was no time limit mentioned about horses in this legislation.