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The swine industry has changed considerably in recent years, resulting in a need to re-evaluate the traditional management practices, and in particular the management of end of cycle boars in a way that is economical and meets welfare concerns. Boar meat has a low value in the North American pork chain and there is no processing facility in Canada which harvests this class of animal, thereby increasing the transportation cost associated with moving Canadian boars to the United States for slaughter. Assembly and transport of previously unacquainted mature boars is a significant welfare risk due to aggression. Current industry standards and codes of practice have attempted to alleviate the problems associated with shipping cull boars for slaughter by requiring individual segregation and detusking, but welfare concerns remain. On-farm euthanasia is the best option for managing end-of-cycle boars.
Boars are used in modern swine production as a source of semen for artificial insemination programs and as “teaser” boars on sow farms to detect estrus and increase fertility. Today, very few boars are used to naturally breed sows or gilts. Although the overall ratio of boars used per pig produced per year has decreased dramatically, boars are still a dynamic sub-population of the national swine production herd.
An effective boar culling program should be a part of any good breeding herd management program and a necessity for proper care of boars. The rapid cycling of boars, by continuously bringing in younger boars as part of the strategy to enhance the genetic potential available in modern swine production, means there is a constant flux of cull boars leaving the production cycle. How producers handle the end-of-cycle boars is becoming an increasingly important issue, particularly with growing public concern about the unintended consequences of intensive livestock production.
A study which evaluated reasons for culling boars in swine herds in Minnesota (1) showed that most boar removal was the result of the animals being overweight (47%), which also included old age, followed by reproductive problems (18%), including low fertility, poor libido, and poor reproductive performance. Since cull boars are otherwise healthy animals, producers are often of the opinion that they should try to salvage some value from them.
Cull boars from Saskatchewan are shipped to a number of assembly yards, primarily in Manitoba, where they are sorted and regrouped with other cull boars according to weight and then transported in groups to the United States for slaughter (ending up primarily in sausage and pet foods). Similarly in Alberta, almost all boars are collected at either large assembly yards or privately owned assembly points, and then transported to yards in Manitoba. From Manitoba they are again assembled with other boars and shipped to the United States for slaughter. How long these boars are in transit and how many of them die in transit is uncertain since there are no current data collection or monitoring systems in the North American cull swine marketing complex to document the time in transit or mortality associated with end-of-cycle sows and boars.
It has been well documented that the mixing of unfamiliar groups of pigs results in increased aggressive behavior and fighting among the animals in order to establish a new dominance hierarchy (2–4). The most severe aggression normally occurs during the first 30 to 90 min after the groups have been mixed (2,5), and although the overt aggressive acts are not seen commonly after the first 24 h of mixing, low levels of fighting can be observed up to 8 d after regrouping, indicating ongoing social conflicts and stresses sufficient to cause a reduction in performance (3). A study in Australia showed that mixing a relatively small number of boars during lairage induced fighting among the pigs, resulting in a high incidence of skin lesions and inferior pork quality (4).
During the pre-slaughter handling of pigs, unfamiliar groups of pigs will often be mixed together. Currently, the Health of Animals Regulations of Canada prohibits the transportation of groups of animals that are “incompatible by nature.” Part XII (Transportation of Animals) Section 141, subsection 5 states that “Groups of bulls, de-tusked boars, rams and goat bucks, if mature, shall be segregated from all other animals during transport.” (6). Although not specific, this suggests that cull boars being transported in groups are to be detusked prior to mixing and if not, must be transported in individual compartments.
Additionally, the Recommended Code of Practice for the Care and Handling of Farm Animals — Pigs (7), states that the industry will not tolerate inhumane handling of boars. Boars must be handled in the most humane way possible and the industry will pursue a policy of segregation and separation (7). Boars must not be controlled by hitting them on the nose to keep them from fighting. At times it may be necessary to use some force to keep them from doing physical harm to each other; in these cases the handler must take appropriate corrective measures (7). Particular attention in the Code of Practice has been focused on the management of cull boars prior to and during transport, including the following recommendations:
There are no studies on the behavior or handling of boars from the time they leave the farm to when they arrive at slaughter and no available data on boar mortality or morbidity. It is unclear whether or not Canadian transport regulations are widely followed in the industry and if they have helped prevent undue aggression and injury among recently mixed boars. Paetkau and Whiting (8) evaluated the need to tusk trim cull boars on arrival at assembly yards in Manitoba. All the boars had been loaded, transported and held in sorting pens prior to initial skin scoring, but despite this recent handling, overall initial skin scores were very low (minor scratches). The boars included in the study (150) were skin scored upon arrival and after an average of 1.4 h after having being mixed with other boars of similar weight (8). This study suggested that tusk trimming in mature teaser and AI boars is widely practiced in western Canada (8).
Boars with prominent tusks were not protected from being scratched nor did the presence of tusks alter the nature of aversive interactions between boars (as evidenced by a change in skin score) (8). Although full thickness skin lacerations appeared to be rare in assembled boars in this study, in every case where a full thickness skin laceration was observed, a different boar with a tusk score of 3 (extending beyond margin of lip > 3 cm) was present in the pen (8). Paetkau and Whiting (8) concluded that serious skin injuries are thus more likely to occur when boars did not have their tusks trimmed close to the time of transport (8), even though they found a low incidence of aggression among the animals.
The low level of inter-boar aggression is contradictory to documented evidence of aggressive behavior and subsequent lesions among recently mixed unfamiliar pigs (2–4,8). Paetkau and Whiting (8) suggested that the boars may already be exhausted at the time of entry into the study, or that loading and transport are significantly novel experiences that suppress aggressive behavior. It may be possible that mature boars behave differently than younger animals and sows (8); however, swine in general and boars in particular are innately programmed to fight other unfamiliar swine, so there was likely some factor underlying this unexpected finding. The boars may have been sedated, or possibly the tusk trimming or some other recent traumatic experience caused sufficient pain to suppress the aggressive behavior. Some of the cull boars observed in the study may have been too old or too sick to fight. Nevertheless, the study’s findings raise serious questions as to the cause of the unnaturally low level of aggression observed among newly mixed mature boars.
The Recommended Code of Practice for the Care and Handling of Farm Animals — Pigs (7) states that all mature boars (> 135 kg or showing signs of tusks) must be detusked before co-mingling and transport (7). This Code does not provide specific methods of tusk trimming, it states that, “only acceptable procedures must be used.” In Australia, according to the Model Code of Practice for the Welfare of Animals, tusk trimming is part of general good management and should be conducted using embryotomy wire (9). Other commonly used methods of tusk trimming include bolt cutters, hoof nippers, and hack saws. Whether all or some of these procedures are painful for the boar or whether certain tools and procedures for detusking are more welfare friendly than others has not been determined through comparative research.
An evaluation of the degree of gingivitis present and pulp tissue exposure of 102 tusks from culled boar mandibles suggested that if tusks are trimmed as per the current industry standard of within 2 mm of the gingiva, the pulp chamber will be exposed about half the time (10). In addition 44% of the mandibles examined also had scores associated with moderate to severe gum inflammation.
The innervation of the tusk of the domestic pig (Sus domesticus) has not been well documented (11). Detailed examination of the innervation of the tusk pulp in the African elephant indicated that the structure of the tusk pulp is completely different from that found in human teeth (12). Our understanding gained from human dentistry of the pain associated with exposed pulp in human teeth may or may not be relevant.
Tusk trimming methods that result in exposed pulp have the potential to cause pain in the boars, either through nociceptors within the pulp or as a result of associated gingival inflammation. It is possible that recent tusk trimming prior to mixing could potentially be a cause of reduced inter-boar aggression during assembly and lairage, and may partially explain the field observations of lower than expected aggression in assembled boars (6).
Sedation of the animals prior to and during transport may decrease the risk of intraspecific aggression in assembled and transported boars, but may not be a viable option. Currently, Stresnil (azaperone; Merial Canada, Baie d’Urfé, Quebec) is a sedative-tranquilizer indicated for the prevention of aggressiveness when mixing or regrouping pigs (13). Clinical trials indicated that although azaperone altered the pattern of aggression in previously unacquainted boars, the effect was not sufficient to prevent significant injury being inflicted on the animals if the tusks had not been removed (14). In addition, Stresnil has a meat withdrawal period of 24 h and is not for the use in animals for transport to slaughter (13). Thus, Stresnil is not a viable alternative for controlling aggression in mixed boars due to meat residue problems and an overall lack of effectiveness.
There has been a steady decline in the value of western Canadian end-of-cycle boars since 1997 (Figure 1). Part of this decline in farm gate value may be explained by the escalating transportation costs during the same period (15). Today the current USDA market prices (16) indicate that cull boars > 300 lb (136 kg) are valued between $5.00 to $12.00 US/cwt; that puts the total value of a 500-lb (227-kg) boar between $25 to $60 US.
The average cost of transporting a cull boar from Saskatoon, Saskatchewan to Brandon, Manitoba is roughly $25 to $35/boar, and from the assembly yards in Brandon to Chicago, Illinois where a large number of Canadian cull boars are slaughtered is about $40 to $50/boar (17). The total cost of shipping a cull boar from Saskatoon to Chicago, therefore, would run between $65 to $85/boar. At these prices, the value of the boar is unlikely to cover the costs of shipping the animal to United States for slaughter.
Although the ideal situation to prevent aggression among cull boars during transit would be to ship all boars in separate individual compartments, this is not likely a viable option that would be pursued by the industry, since individual compartments would result in even greater transportation costs. Also, a vehicle designed for the sole purpose of transporting boars in separate compartments (though ideal) would have limited use for other stock, particular considering only a very small proportion of pig transport is occupied by boars.
An interesting concept is to mix mature boars (1 or 2) with slaughter-weight pigs prior to and during lairage, which has been shown to greatly reduce the incidence and the intensity of fighting among recently mixed pigs prior to slaughter (18). However this idea violates the Health of Animals Regulation stating that animals of substantially different weights or ages must be penned separately during transportation and marketing. Additionally, if producers were capable of employing the concept of adding boars to groups of market hogs, the slaughter plants are often specialized and likely unable to deal with both age and weight classes.
On-farm euthanasia of cull boars is currently the most viable alternative to shipping Canadian boars to the United States for slaughter. It avoids the current monetary loss between salvage value and transportation costs and it circumvents the potential for reduced welfare associated with mixing and preparing boars for live transport.
However, on-farm euthanasia of mature end-of-cycle boars may come at a psychological cost to farm workers. Killing of end-of-cycle boars may be highly aversive to farm staff who have had daily contact with both teaser boars and boars they used for semen collection. Also, farm workers involved in the production of human food may find the destruction of animals that could be salvaged for human consumption an irresponsible action and culturally repugnant. In addition, humane killing on-farm is difficult to assure and carcass disposal is challenging.
The euthanasia method must ensure that the boars are humanely killed with minimal pain and distress. The best methods to achieve this in mature boars, without drug residues, is either by gunshot or with a captive bolt, keeping in mind that the captive bolt must be capable of penetrating a skull which is thicker than the typical cull sow’s.
Once the end-of-cycle boar has been humanely euthanized, disposal of the carcass must be addressed. Disposal via rendering is an environmentally safe way to deal with on-farm mortalities and allows some value of that carcass to be recovered, which would otherwise become waste (19). The cost of dead stock removal in Saskatchewan is $0.20/kg ($0.09/lb) for pick-up, which averages about $45/boar.
Burial of the carcass on the farm is an alternative to paying for dead stock removal. However, animal carcass burial may require adherence to local environmental regulations, and requires a backhoe or equivalent heavy machinery. Burial is typically done using the trench method which involves excavating a trough in the earth, placing carcasses in the trench and covering them with the excavated material (backfill) (19). It requires relatively little expertise and it is convenient and quick, but not practical during winter months. Since it can be done on-farm, this method is much more economical for the producer since it eliminates the need for transportation and is estimated to cost only about $7 to $8/hog (19). Burial is considered a convenient method for routine mortality disposal with minimal environmental impact when used sparingly (20). There is a potential for detrimental environmental effects, particularly water quality issues, and this option may be limited by regulatory constraints or a lack of suitable sites for burial. Unfortunately, it does not generate a useable by-product of any value (20).
In some aspects it requires a philosophical change to move away from the tradition of trying to salvage cull boars via transporting them to slaughter, towards a more pragmatic and welfare conscious decision to practice on-farm euthanasia and disposal of end-of-cycle boars. Nevertheless, in our opinion, this is an inevitable outcome under current conditions. The more intensified livestock systems become and the more the public gains awareness and interest in the welfare of domestic livestock then the more important it becomes to reassess how we deal with end-of-cycle livestock in swine and many of our livestock production systems. A social consensus is forming that shifts the traditional approach of salvaging all potential edible meat to a newer moral obligation to avoid animal suffering. Recent news stories confirm that the avoidance of animal suffering trumps the sin of discarding salvageable meat from cull animals (21). Some within the poultry industry have already made the change and now grind spent fowl instead of trying to salvage meat from these birds. From an animal welfare perspective, and based on economic analysis, this change in the poultry industry was necessary. A similar approach needs to be considered by the swine industry. Veterinarians working in swine production systems need to encourage producers to evaluate their practices related to end-of-cycle boar management. Consideration should be given to societal expectations of animal welfare and compassion for animals that have served their steward well.
Considering the cost of transport, the declining value of cull boars and the potential for reduced animal welfare in preparing (detusking) and transporting cull boars to slaughter in an aggression-free environment, the most logical and ethical alternative for managing end-of-cycle boars is to use on-farm euthanasia.
The authors gratefully acknowledge guidance and comments from Dr. Terry Whiting on an early draft of this manuscript. Direct and indirect financial support was received from the Natural Sciences and Engineering Research Council of Canada.
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