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On-farm slaughter and killing

How do practitioners apply the science of killing to arrange or deliver on-farm killing in a safe and humane manner?

03 September 2020, at 8:10am

The first article of this series (Veterinary Practice, June 2020) dealt with the principles of humane euthanasia or slaughter on-farm and its legal framework. This second article will explore the practicalities of stunning and killing on-farm to achieve slaughter or euthanasia in a humane and safe way.

When faced with a need for on-farm slaughter or euthanasia of an animal, making the right decisions for the welfare of the animal can be daunting. This series of articles aims to make this less so as, with sufficient knowledge, the veterinarian and client can be confident of a successful and satisfactory outcome for the animal.

Before facilitating or carrying out slaughter or euthanasia on-farm, there will be a number of considerations: crucially that the method chosen maximises the probability of immediate success and minimises risk to personnel. When working with humans and animals, there is always a possibility of the unexpected. However, preparation for the “reasonably foreseeable” is essential. So important are these preparatory arrangements, they are a legal requirement in PATOK. When presented with an animal requiring slaughter or euthanasia, initial assessments of the animal, its potential to enter the food chain, the facilities and resources available will determine which methods are best suited to the situation.

If the animal is expected to enter the food chain, an RCVS registered vet must be present at or immediately before slaughter to perform an ante-mortem inspection and be prepared to sign a template form (BCVA, 2010) to that effect. The vet must verify that the animal displays no signs of systemic illness and has experienced an acute and recent catastrophic injury (eg broken leg). Under no circumstances should a vet be tempted to perform the inspection remotely.

Successful killing or stunning requires selection of the correct type of device and power of cartridge to cause brain dysfunction (see part one of this article). In all cattle and larger pigs, care must be taken to select a device which has sufficient power to perform an effective stun on animals with considerable depth of frontal sinus and bone. So, in all instances, refer to the manufacturer’s instructions for type of device and cartridge, and always err slightly on the side of caution.

If in any doubt of the anticipated efficacy of a captive bolt, a free-projectile device is a suitable alternative, providing the operator is competent and holds the appropriate firearms licence. Handguns, humane killers and shotguns must not be used on unrestrained large animals more than one metre distant. Such animals must be killed using a rifle and ammunition appropriate to the given range. Only a well-maintained stunning or killing device should be used and cartridges must be stored in a dry environment. It is worth noting that the law (WATOK) states that a captive bolt gun where the bolt does not “retract to its full extent” may not be used as it is unlikely to deliver an effective stun.

Once a suitable device has been selected, it must be applied in the correct firing position on the skull, as shown in the previous article. Captive bolt devices should generally be applied in contact with the skull, whereas free-projectile firearms are effective at a firing distance of 5 to 30cm for a shotgun, handgun or humane killer, and up to 100 metres with an appropriately powered rifle (HSA, 2016).

To restrain any animal for accurate application of the stunning or killing process, the head should be immobilised using either a handling crush or strong halter tied to a fixed point, or manual restraint, depending on species. Free-standing shots of fractious animals at distance using a rifle must only be undertaken by experienced marksmen due to the inherent risks of animal movement and mis-shots.

Most cattle are only safely handled, unless moribund, in a well-maintained handling crush, but the operator must also have safe access to use the stunning or killing device correctly and subsequently bleed or pith the animal.

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Sheep and goats may be restrained more easily using a halter or manual restraint against a solid surface by an assistant. Pigs are less easily restrained in this way, due to their independent nature, although guiding a pig into a corner using a board is appropriate. Sedation may assist in euthanasia, but precludes human consumption. Pig snares are not considered suitable, due to the distress and additional suffering caused, and should only be used as a last resort to permit. If using a free-projectile killing device for any animal, manual restraint by an assistant would be unsafe and must not be considered.

Before restraint, the guns must be loaded, with the safety on and in a safe place within easy reach. Spare cartridges must also be immediately to hand in case of a failed first shot. Wherever possible, cartridges of a higher power load should be available if a second shot is needed, and an alter-native captive bolt stunner, in case of mechanical failure with the first. It is recognised, however, that this would not always be the norm when animals are killed on-farm. Where the animal requires bleeding or pithing to follow stunning, or bleeding for human consumption, these tools must also be immediately to hand. To aid correct disposal of animal by-products, a suitable means of collecting blood should be available and all reasonable attempts made to ensure it cannot drain away.

Once the animal is effectively restrained, it must be killed or stunned without delay, the aim being to minimise restless behaviour which might impair accuracy. Effective stunning or killing is recognised by immediate loss of posture, absence of rhythmic breathing and fixed glazed expression; this will be followed by uncontrolled clonic kicking and paddling. In pigs, the movements follow very soon after stunning and are particularly violent; operators and bystanders must take care to avoid personal injury.

Eye movement, corneal reflex, incorrect body posture and presence (or return) of rhythmic breathing indicate a failed stun or kill, or recovery. In both situations, the animal must be immediately re-stunned or re-shot, in a position just above and to the side of the initial shot to deliver a renewed concussive impact to the skull, causing further brain dysfunction and mechanical destruction. Delivering a second shot through the initial point of penetration will not deliver an effective stun.

Clonic kicking as a result of uncontrolled spinal activity presents a challenge in all species. Wherever possible, if the animal is not a ruminant destined for human consumption, it should be pithed to minimise kicking – also killing it through manual destruction of brain and spinal cord. Ruminants must not be pithed if intended for human consumption (The Restriction on Pithing (England) Regulations 2001). But if pithed it will not then be necessary to bleed the animal – removing the need for handling of a necessarily sharp knife and improving operator safety.

Animals which are not free-projectile killed or pithed must be bled, to interrupt the blood supply to the brain causing cerebral death. Bleeding must follow captive bolt stunning without delay, since return to sensibility is possible until brain death is achieved. It is not necessary, or possible, to fully exsanguinate the animal, since blood drains under gravity in the absence of diastolic pressure. Roughly 50 percent of total circulating volume is lost during bleeding (Warris, 1984) and must be collected and disposed of as an animal by-product. For this reason, as well as operational ease, pithing is the preferred method when bleeding is not required for human or animal consumption.

“Sticking” must be performed using a very sharp, sterile knife to ensure that bilateral severance of carotid arteries or originating vessels is complete, facilitating a rapid bleed and fast brain death. A neck or chest cut can be performed, dependent on access to the ventral neck or thoracic inlet; however, it must be remembered that in cattle a neck cut will result in much longer times to brain death due to additional cerebral perfusion from the vertebral arteries. A chest cut in pigs and a neck cut in lambs and goats are favoured (Figure 1). Close monitoring for signs of possible stun recovery during bleeding is essential and if in any doubt as to the efficacy of the stun or bleed, animals must be re-stunned then re-bled.

In compliance with WATOK, no further dressing must be completed for at least 30 seconds after bleeding in cattle, and 20 seconds in pigs, goats, sheep and deer. This ensures that following a "good stick" brain death has been achieved. Heart activity may persist on auscultation for some time, but should not be confused with persistent signs of life.

Once dead, the animal may be prepared for collection and transport to the relevant processing facility. Animals intended for human consumption must be processed within two hours of slaughter to meet food safety requirements. However, if a carcass must be left for a period before collection it should be covered to prevent scavenger access and placed on a solid surface which can later be disinfected with a DEFRA-approved agent.

Responsibilities for coordinating or performing humane slaughter and killing generally end at the removal of the animal; however, it is nevertheless important to clean any used firearms and knives immediately, as well as clean and disinfect any PPE. Keepers have a statutory requirement to record and/or report the death of the animal and clean the site of operation. It may be of clinical interest to both vet and keeper to enquire of post-mortem findings with the operator or slaughterhouse Official Vet, and some hunt kennels or knackeries are also happy to welcome an informed bystander during processing.

The Humane Slaughter Association (HSA) is an independent charity recognised internationally for promoting scientific, technical and educational advances towards improving the welfare of food animals worldwide at slaughter, killing, marketing and transport. Its work includes researching, refining and demonstrating humane slaughter methods, publishing material such as guidelines, best practice, books and videos, funding research projects and the development of equipment. Specialist technical staff provide expert and practical advice on all welfare issues relating to food animals.
The HSA is funded by voluntary donations, subscriptions and legacies. For more information about their work call 01582 831919, email info@hsa.org.uk or visit their website.