Evaluation of methods of rapid mass killing of segregated early weaned piglets

Abstract

The operational logistics of mass killing of healthy, surplus piglets by manual blunt force trauma, controlled blunt force trauma, intraperitoneal injection of barbiturate, and free bullet were recorded. Objective performance variables evaluated were, speed of application, human resource and input cost, animal restraint required, and failure rate. Subjective evaluation of esthetics and difficulty of application indicated manual blunt force trauma is an unacceptable technique. Under field conditions, physical methods of killing were superior to intraperitoneal injection of concentrated pentobarbital. Considering animal welfare metrics in isolation, controlled blunt force trauma was superior to all other techniques attempted.

Introduction

Foreign animal disease eradication operations require the ability to quickly and humanely destroy large numbers of healthy or infected livestock. The humane killing of healthy animals that could not be delivered to market (welfare slaughter) was a significant logistical problem and a cause of public concern in the 2001 foot-and-mouth disease outbreak in England (1) and in the 1997–1998 classical swine fever eradication in the Netherlands (2). Welfare slaughter is an animal welfare issue because of the logistic challenges of delivering mass killing humanely, but it is first and foremost an ethical dilemma in a world where food is abundant for some inhabitants and woefully lacking for others and in thwarting the natural intended purpose of farm animal production (3,4). The international veterinary community is searching for no-kill options to foreign animal disease eradication operational needs (3,5). This paper identifies the emergence of the multi-stage and just-in-time swine production complex in North America that may also have resulted in an unintended extreme sensitivity to animal movement restriction regardless of cause.

The risk and competing resource demands of welfare slaughter have been identified in planning for foreign animal disease eradication programs in Canada (6,7). In 3-site swine production systems (8) the 21-day-old 4.5 to 5.5 kg early weaned piglet has been identified as the most time sensitive stage of production and would be critically affected early in a foreign animal disease event (6).

A crucial downsizing of the North American pork production capacity occurred in 2008 and 2009 in response to a significant period of international non-profitability of the sector. During this period of downsizing there was a disproportionate decrease in the Canadian sow herd in comparison with the US sow herd for various reasons (9) (Figure 1).

Figure 1.

Quarterly estimated numbers of breeding swine for Canada and the United States from 1996 until the 3rd quarter 2009. The Canadian sow herd has been in continual decline since 2005 with a severe liquidation in 2008–2009.

The free market price of piglets has been difficult to establish in multi-site swine production as biosecurity programs prevent mixing and therefore sale by public auction. Most piglets are transferred between facilities owned by the same company or are traded under long-term contract arrangements. In the fall of 1997, The United States Department of Agriculture (USDA) Agricultural Marketing Services (AMS) began collecting and publishing a weekly price report for direct sales of weaned pigs (LW_LS255 report). This report summarizes cash market activity and provides a weekly spot market value for piglets weighing 10 to 12 lb (4.5 to 5.5 kg) (8). This price has fluctuated around 35.00 US$ for many years (10) (Figure 2). Feeder pig exports to the United States accounted for approximately 23% of Canada’s annual pig crop in 2008, up 30% from 2005 and accounted for 7.0 million head (11).

Figure 2.

Cash price of weaned pigs weighing 10 to 12 lb (4.5 to 5.5 kg). Data provided by the United States Department of Agriculture (USDA) Agricultural Marketing Services (AMS) weekly price report for direct sales of weaned pigs [National Direct Feeder Pig Report (Fri) LW_LS255 report].

In 2008 and 2009 the North American spot market price of segregated early weaned piglets (SEW) dropped below $10.00 (range: $4.00 to $15.00) on 3 occasions, April 2008, July 2008, and August 2009 (11). The primary market for Manitoba origin SEW piglets is Iowa (7) and the cost of veterinary certification, transport, and brokerage of a Manitoba SEW piglet to Iowa is about $4.00. When the spot market drops to $10.00 there are piglets with no value in Manitoba and they cannot be given away. The futures market conditions at these times are such that the cost of feed to grow a 5-kg piglet to market exceeds the future slaughter value; more money would be lost by putting the piglet on feed than by killing it.

On the 2 occasions where the spot market was below the $10.00 threshold for more than a single week, Manitoba producers requested assistance from the Office of the Chief Veterinarian in the humane disposal of surplus piglets. Veterinary and other staff assisted in the destruction of 2269 piglets in 2008 and 6121 piglets in 2009. During these time periods other producers killed their own surplus piglets without assistance from the province. The total number of surplus piglets removed from the market by killing in 2008 and 2009 is unknown.

The Office internationale des épizooties has published a standard for humane killing of animals for disease control purposes (12). Killing methods used in Manitoba in the 2008–2009 assisted operations were compliant with this chapter with 1 exception. The use of manual blunt force trauma is not approved by the OIE but has been previously evaluated and found acceptable (13). Methods of manual blunt force trauma are readily available to farmers. The use of manual blunt force trauma for the killing of piglets has been reported locally and in theory this technique may be required as a last resort in emergency welfare slaughter situations.

Materials and methods

In the 2008 operations piglets were killed on the farm of origin in 2 situations and at a commercial assembly yard. Participation of owners in the killing of piglets was limited to delivering the piglets to the place of killing and removal of the carcasses by use of a mechanical front-end bucket loader. Owners of farms preferred to pay to have the piglets removed for killing rather than involve farm workers in this task. In the 2009 operations all piglets were removed from the farms as usually scheduled and killed at an assembly point. The 2008 operation evaluated different options for killing while the 2009 operation measured repeatability and other performance measures of killing by free bullet.

Piglets were processed in batches defined by the pen as delivered by the producer or the assembly yard personnel. Pigs in a group were subjected to the technique and a short time period (2 to 5 min where trauma was applied and 60 min in the case of injection with pentobarbital) was allowed to lapse prior to the evaluation process.

During the evaluation phase, staff walked through the pen and piglets were individually examined and counted. Piglets were recorded as dead, failure to die, or conscious. A pig was considered dead if it had no spontaneous respiration or movement in trauma cases and no heart rate in chemical treatment. A failure to die pig was recumbent but maintained spontaneous respiration. A conscious pig was differentiated from a failure to die pig by voluntary movement or vocalization when the front foot was grasped. Piglets identified as conscious were re-stunned and exsanguinated. Piglets recorded as failure to die were killed by exsanguination accomplished by near removal of the front leg at the level of the ribcage causing severance of the brachial artery and vein. The time to apply the killing technique and the number of pigs were recorded per treatment group.

In the use of free bullet, a properly shot piglet would immediately exhibit extensor rigidity, swift transition into convulsions and die within 1 to 2 min. Free bullet shooting could fail in several ways; the target pig could be struck but fail to immediately go into convulsions (application failure as it resulted in a non-lethal injury); or, the projectile could pass through the target pig (killed) and strike a non-target pig (wounding). Under field conditions, it was not possible to clearly identify the non-target pig strikes and this failure rate was not recorded.

The lethal dose of pentobarbital in the dog is 40 to 60 mg/kg intravenously. Products containing concentrated pentobarbital solutions are viscous and large bore needles are used to facilitate injection. In field situations of slippery flooring and poor animal handling facilities, it was decided that a human operator weighing 80 kg should not handle more than 3200 mg (40 mg/kg) of pentobarbital in a syringe at any one time to avoid a lethal dose if accidentally self-injected. This is a physical volume of 13.3 mL of euthanyl (240 mg/mL) or 5.9 mL of euthanyl forte (540 mg/mL) (Bimeda-MTC, Cambridge, Ontario).

In this application, a 5-mL syringe with a 16-gauge needle was used for ease of operator handling and to not contain a lethal human dose. When euthanyl was used, 2 pigs were injected prior to re-filling the syringe; minimum dose 600 mg. When euthanyl forte was used the 5-mL dose was divided roughly between 3 piglets, varying with size of the piglet; average minimum dose 900 mg.

In killing by intra-peritoneal injection of barbiturate, pigs were separated into small groups and trapped behind a hinged gate. Individual pigs were lifted by the hind legs and held over a pen partition with the abdomen facing the second operator. The second operator individually injected in the lower abdomen. Injected pigs were immediately released into the holding pen where they walked away from the handlers’ position.

In killing by manual blunt force trauma, a blow to the dome of the skull was delivered by swinging an 8-oz (227-g) ball pien hammer. Specifically, 1 individual held the piglet horizontally by the hind legs and abdomen at near waist height, while the sternum and front legs were supported by a pen divider. The pig was struck on the poll of the head by a single blow delivered by a second operator. Operator failure was measured by repeated blows prior to releasing the piglet.

In application of controlled blunt force trauma, a modified Cash Special Captive Bolt Stunner was used (Accles & Shelvoke; Witton, Birmingham, W. Midlands, United Kingdom). A piglet was restrained by 1 operator by manually holding the piglet with 1 arm under the abdomen right to left and the second arm under the sternum left to right. The second operator applied the non-penetrating captive bolt to the poll of the skull. The brown load (73 J) was used to activate the captive bolt apparatus.

Shooting with free bullets was done by individuals certified in gun safety by slowly walking through the pen (2008 data, Table 1) or leaning over the wall of the pen and targeting the skull of piglets as they walked unrestrained in the pen (2009 data). Several types of .22 rim fire charges were tested with muzzle energy between 44 and 178 J.

Table 1.

Performance and costs of methods of killing piglets

Method	Staffa	Projectile energyb	Number of piglets in group	Real hour	Application failurec	Return to consciousness	Fail to die	Gross failure rate	Humane failure rate	Time/1000 pig (h)	Cost/1000 pigd
Short hollow point 1105 ft/s 27 grain, (shooter and loader)	2	99	300	0.42	13	2	1	5.3%	0.7%	1.39	$215.00
Ball round nose 710 ft/s 29 grain (shooter and loader)	2	44	194	0.68	8	1	10	9.8%	0.5%	3.52	$407.01
Ball round nose 710 ft/s 29 grain (shooter also loads)	1	44	168	1.10	16	9	6	18.5%	5.4%	6.55	$384.64
Lead round nose 710 ft/s 29 grain (shooter also loads)	1	44	178	1.10	19	5	3	15.2%	2.8%	6.18	$368.09
Subsonic HP 1050 ft/s 38 grain (shooter and loader)	2	129	249	0.65	13	1	3	6.8%	0.4%	2.61	$324.94
IP Euthanyl (piglet physical restraint)	2		240	1.08	0	5	11	6.7%	2.1%	4.51	$1194.79
Controlled blunt force trauma (piglet physical restraint)	2	73	108	0.45	0	0	0	0.0%	0.0%	4.17	$765.00
Manual blunt force trauma (piglet physical restraint)	2		50	0.23	6	1	5	24.0%	2.0%	4.67	$420.00
		Total	1487						Average	4.2 h	$509.93

^aNumber of staff required to apply the killing process to an individual pig.

^bProjectile energy in Joules was calculated from manufacturers information using the formula:

$$\text{E}=[\text{mass\hspace{0.17em}}(\text{in\hspace{0.17em}grains})]\times [\text{velocity\hspace{0.17em}}(\text{in\hspace{0.17em}ft}/\text{s})]/450400\times 1.355817948\hspace{0.17em}(\text{to\hspace{0.17em}convert}\hspace{0.17em}\text{ft}-\text{lbs\hspace{0.17em}to\hspace{0.17em}Joules}).$$

^cIn shooting, an application failure was immediate re-shooting a target piglet. In the use of manual blunt force trauma; a re-strike was recorded as application failure. 73 J is the manufacturer’s engineering calculation of the experimental model used with the manufacturer’s brown cartridge.

^dCost was calculated based on material consumed and veterinary time at $120.00/h, and non-veterinary staff time at $45.00/h.

The projectile kinetic energy is largely determined by muzzle velocity. Solid lead ball projectiles are available in a range of muzzle velocities. Cartridges marketed as subsonic or low noise loads are solid conical ball. Hollow point projectiles if fired with a muzzle velocity below 320 m/s (1050 ft/s) will not dependably expand on impact and are not manufactured for subsonic velocities.

In the 2008 operation, 6 piglets were selected from different areas of the pen for postmortem evaluation which was completed within 24 h of death. Piglets were returned to the laboratory and held in refrigeration and examined the next day. Carcasses were placed in sternal recumbency and the skull palpated. The skin was removed from the skull cap and the area was examined for extent of skull fracture and other evidence of damage. The skull cap and brain were sequentially removed and examined. Piglets killed by intra-peritoneal injection of barbiturate were not subjected to postmortem examination.

Cost of application of the technique was calculated on a per pig basis evaluating veterinary time at $120.00/h and non-veterinary time at $45.00/h. The cost of consumable materials was .22 projectiles $0.09 ea, sodium pentobarbital $0.45/mL, and blank cartridges for the non-penetrating captive bolt $0.39 ea. Piglets killed in the pentobarbital trial required disposal by burial on-farm. The additional cost of disposal by burial was not calculated.

In 2009 due to time constraints and accessibility of equipment, only free bullet was used to provide humane killing of surplus piglets. Subjective evaluation of the 2008 trials identified a preferred projectile as the 337 m/s, 99 J, hollow point cartridge (CCI short, 27gr, Hollow Point, muzzle velocity: 1105 FPS, Cascade Cartridge, Lewiston, Idaho, USA). This particular or similar cartridge could not be procured in sufficient quantity to meet the sudden demand of local operations in 2009. Several different loads were used (107 ± 44 J) which reflects the real situation in the event of an emergency resulting in interruption of free livestock movement in the North American swine industry.

Piglets killed by free bullet and other physical injury were disposed of by rendering. The rendering company preferred minimal bedding to be included with the dead piglets which were loaded by front-end loader. No bedding was used in the solid concrete floor killing pens prior to free bullet shooting. The use of free bullets in a concrete floor barn was considered a significant workplace health and safety issue. Operators wore heavy clothing and eye protection, and did not place themselves in line of fire of other operators.

Data were collected manually at pen side and information was keyed into a spreadsheet (Excel, Microsoft Corporation, Redmond, Washington, USA) for manipulation. Poisson, univarate and related data analysis were completed using a standard statistical analysis program (NCSS 2007, Number Cruncher Statistical System, Kaysville, Utah, USA).

Results

There were no human injuries related to free bullet use, chemical, or other methods of killing in these trials.

A preliminary trial of shooting with free bullets involved the use of .22 rimfire lead round nose, 29 grain muzzle velocity of 216 m/s (710 ft/s), kinetic energy of 44 J (32 ft-lbs). Two rifle operators walking through the pen remaining positioned back to back, killed 782 piglets in 3 h 20 min. The maximum muzzle velocity of this projectile is below the speed of sound and the auditory impression of discharge is similar to an air-rifle. In a conventional and in a curtain-sided barn, this repetitive sound caused no significant startle response in the piglets. A correctly struck piglet immediately convulsed, became recumbent and went on to cease movement and die within 1 to 3 min. In this group of pigs there was no postmortem evaluation; therefore, no data are included in Table 1.

The performance of individual methods in 2008 field application is summarized in Table 1. The failure rate of intra-peritoneal barbiturate was high in comparison with other methods reported. When examined 60 min after injection, 5 of 240 piglets were fully ambulatory and 11 were recumbent but continuing to breathe.

In the carcasses examined, all methods of inducing trauma created severe physical damage to the skull and brain tissue sufficient to render the animal immediately unconscious and to be lethal. On carcass examination, projectile fragments could not generally be found in animals killed. Flattened projectiles were frequently identified in the pen when piglets were being removed.

The use of manual blunt force trauma caused massive skull damage in the 6 carcasses examined. This technique proved to be difficult to apply in practice. A correctly delivered blow to the skull results in convulsion within seconds. Immediately after the blow, an unconscious convulsing piglet is difficult or impossible to differentiate from a conscious brain-injured piglet struggling in response to pain. Vocalization would identify a conscious piglet; however, the absence of vocalization was not considered as an assurance that the pig was unconscious. This uncertainty of the clinical status of a struck animal resulted in repeated blows (application failure) in many individual cases. The application of repeated blows to a convulsing piglet was dangerous for the operators physically and mentally.

In comparison, application of controlled blunt force trauma reliably resulted in a distinct, 3 to 5 mm deep circular indentation in the skull that was clearly visible as the piglet entered extensor rigidity prior to grand mal seizure and nasal hemorrhage. Operators had a high level of confidence that a piglet with a dramatic physical indentation in the dome of the skull was unconscious and could be placed on the floor. Controlled blunt force trauma induced convulsions were initiated and ceased similar to animals killed with perfect free bullet placement.

The average cost of killing a piglet was ~ $0.50, excluding the cost of transport to the killing pen, and removal of the carcasses and disposal (Table 1).

In the 2009 program the specialized equipment to deliver controlled blunt force trauma was not available and over 2 working days 6121 piglets were divided into 27 groups (mean 227 ± 69 piglets) and killed by free bullet. Baseline performance data were recorded. The average return to consciousness rate was 0.38 ± 0.78% and the average failure to die rate was 3.25 ± 3.17%. The average staff time required to kill 1000 pigs was 5.9 ± 3.09 h. A variety of ammunition loads was available and the shooting was delivered by 5 individuals. Piglets did not respond with significant flight with the use of higher velocity ammunition.

In a univariate Poisson regression analysis, projectiles having < 99 J kinetic energy were 1.94 times (P < 0.05) more likely to result in a conscious or failure to die piglet. Further univariate analysis also showed a statistically significant difference in piglet outcome by shooter, but not by projectile type (hollow point projectile versus solid ball). The data set was too small to allow multivariate investigation of the relationships and interactions between variables. Over-dispersion in the regression models was controlled for using the dispersion phi correction multiplier in NCCS 2007.

Discussion

Data presented in this study were collected as part of an actual emergency response and not from a controlled experiment. Bias may be present due to self recording of some variables, the lack of blinding, and lack of control groups. However, no other data related to mass killing of piglets under field conditions is available in the current literature.

Pentobarbital is approved for use as a euthanasia compound in dogs, cats, horses, cattle, mink, and birds by intravenous, intracardiac, and intrapulmonary injection with intravenous injection being the preferred method. Pentobarbital is not approved as a euthanasia agent in pigs. The intraperitoneal injection was chosen because of ease of administration and previous clinical experience using pentobarbital as an anesthetic by this route for ridgling surgery in young swine.

The apparent failure rate of pentobarbital may be explained by trans-abdominal injection into the bladder or into a fecal mass in the large intestine resulting in failure to absorb the agent or the agent being expelled. Also, individual pigs were not weighed prior to injection and a 15-kg pig may have received a sub-lethal dose (40 mg/kg). The estimated weight of the largest pigs handled was 12 kg.

An additional welfare risk observed in this use of pentobarbital was that animals becoming unconscious climbed upon and lay down on already recumbent animals. It was possible that unconscious individuals injected early in the process may have died due to crushing induced hypoxia rather than narcotic induced death.

A small number of piglets (n = 50) were subjected to killing by manual blunt force trauma primarily due to personal repugnance with the process. This process may be more humane than reflected in the data as failure of application in this technique is highly subjective. Carcasses examined postmortem had severe and fatal skull fractures.

The .22 caliber rifle and a broad range of ammunition are widely available in Canada and worldwide and is the caliber used in the olympic biathlon. The most common load available to the Canadian public is referred to as high power long rifle, indicating the power of the charge and length of the casing. This casing length and charge strength is designed to operate properly in semi-automatic firearms. The use of low velocity, sub-sonic ammunition required the use of manually operated rifles and repeaters with tube magazines to accommodate short casing length. This type of firearm is currently more difficult to purchase new.

In this study, even the lowest power loads available were found, with correct shot placement, to dependably transfer sufficient energy at a short distance of < 3 m to kill piglets. Using the lowest energy load minimizes the operator and non-target risk of accidental injury due to ricochet.

Projectiles that expand or shatter on contact with the target, such as hollow point, are designed to minimize the risk of penetrating through the target and to transfer all the kinetic energy of the projectile to the target. They are designed to be used in open field situations and at some distance from the target. Maximizing the energy transfer to a live target ensures the most probable immediate unconsciousness and progression to death. Sufficient kinetic energy of the projectile is required to force the expansion of the lead, and this projectile type is not available in sub-sonic muzzle velocities.

Many of the projectile charge combinations used in this study passed through the skull of the piglets and emerged. This was a welfare risk to other piglets placed behind the target and a health and safety risk to operators. Walking through the pen and placing a shot with the floor as a backstop or outdoor killing with soil as a backstop would minimize the risk to the operators and to non-target piglets associated with pass-through projectiles. Data from this study suggest that where it is safe to use, higher energy projectiles may compensate for less than perfect shot placement and have a welfare advantage.

In conclusion, the pork production complex in North America is highly efficient in cost of production and is very highly integrated, which makes it very sensitive to animal movement restriction. Welfare slaughter has been predicted as a major concern in the event of a foreign animal disease incursion and resultant animal movement restrictions in North America. Welfare slaughter as a result of pure market fluctuations has not been predicted nor previously reported in the literature. The preparation for emergency welfare slaughter should be extended beyond foreign animal disease contingency planning to include rapid shifts in market demand.

Current readily available equipment allows for imperfect but reasonable welfare assurance in the killing of surplus piglets. When using .22 caliber free bullets to kill piglets, the kinetic energy of the projectile should exceed 100 J. This study suggests that properly skilled and conscientious operators are the most important factor in assuring the humane death of animals. Risk for humane failure is expected to increase with time pressures on individuals and operator fatigue.

Research should be conducted into safer projectile design for use inside buildings and at close rage. There is also a need to develop better methods of humane killing of all sizes of swine under emergency situations.