There are many differences between beef and bison in both the slaughter and processing operations. Bison are more flighty and fearful of humans compared with cattle; thus, transportation and handling of bison is particularly difficult due to their relatively large flight zone, strong herd instincts, and aggressive nature.
During transportation, bison will remain calmer if kept in a group during loading, unloading, and lairage. Dehorned and horned bison have to be segregated into different compartments or transported in different trucks to avoid goring as the damage to the hide and carcass results in a loss of yield and consequent loss of dollars to the producer. Most commercial bison herds are raised with their horns. If a producer chooses to dehorn, typically the entire herd is dehorned, so that there is not a mix of dehorned and horned animals together which would negate any advantage of dehorning by continuing a goring risk in the herd.
During the unloading process in the slaughter facility, bison tend to run in groups, so it is imperative to have pens with limited side visibility and long alleyways for the animals to exit the trailers. Some recommendations by Lanier and Grandin can be applied in the slaughter facility. For example, bison will remain calmer if each animal is brought up individually to the stunning box from the lairage pen. Bison waiting in the single file chute often become agitated and will stay calmer if they remain in a lairage pen with their mates.
The stunning box should have solid sides as well as a solid top to prevent bison from rearing and endangering worker. For animal welfare reasons, bison are typically stunned with a rifle (calibers from 0.22 magnum to 0.223 and larger) due to the thickness of the skull preventing proper stunning with a captive bolt. The Canada Food Inspection Agency offers stunning guidelines for bison when firearms are used to control the perforation and ricochet problems. Mobile abattoirs have been tested for use with bison to minimize the stress associated with transport.
Although some improvements to quality traits were noted using mobile abattoirs (fewer incidences of carcasses graded as dark, less bruising, and improved meat tenderness), the stress associated with assembling and stunning animals in home facilities varied depending on the amount of pre-stunning handling. Limits on size of the mobile facility (maximum capacity was 10 bison per day) and the high cost associated with cooling the carcasses to the required temperatures before off-loading made the cost per animal to the producer greater than a stationary abattoir.
The study concluded that mobile abattoirs may have a place for remote bison farms with low volume, high-value sales that have the value-added attributes of zero transport, improved animal welfare, and improved quality for the discerning consumer. However, on-farm handling facilities and methods would need to be standardized to provide welfare and quality guarantees.
From the stunning station, the carcass is taken to the dressing area where the head is skinned for inspection. This process is relatively slow compared with beef cattle, as the head of a bison is very large. The carcass is then moved to the hide removal station. Hides, particularly on the anterior portion of the animal, are thick and require a change in skinning equipment to handle the extra weight.
The hide on the posterior area of bison is very thin, requiring a slower pace on the rump areas so that the hide is not punctured and cross-contamination is not introduced before evisceration. Bison evisceration, similar to beef, removes the organs and contents of the abdominal and thoracic cavities, which are presented for inspection.
At the carcass splitting station, bison carcasses can be too large for standard beef splitting equipment, as the thoracic vertebrae of bison are larger than beef carcasses. Once the carcass has been split, the remainder of the processing (i.e., washing, weighing, and chilling) is very similar to beef.
Conventional chilling (0 ± 2°C until 24 hours post-mortem) and other chilling technologies have been evaluated for bison, such as blast chilling, spray chilling, and elevated temperature conditioning, but none of these are currently used commercially. Using these technologies, the increased cooling rate helped to minimize carcass shrinkage, which was reflected in the yield.
However, in the USA, Rinse & Chill (MPSC Inc., Hudson, WI) technology (vascular infusion with a chilled isotonic solution of sugars and salts) is being successfully used commercially to reduce the post-mortem pH and temperature earlier and more rapidly than the traditional slaughter practices and to thoroughly remove residual blood from the animal (Yancey et al., 2001). In addition, the technology is thought to contribute to improved/easier boning-out, leaving less meat on the bone.
Bison carcasses are fabricated into cuts similar to those from a beef carcass. The bison industry has “adopted” names, numbers, and standards that were developed for beef by both Canadian and U.S. regulatory bodies. The major subdivisions of the carcass include chuck, brisket, rib, short plate, short loin, sirloin, hip, and flank.
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