by Temple Grandin (Updated March 2007)

There have been some questions about whether or not a captive bolt actually kills an animal. Practical experience in slaughter plants indicates that cattle shot correctly with a penetrating captive bolt have irreversible damage to their brain and they will not revive. If a non-penetrating captive bolt is used the animal may revive unless it is bled promptly.

These photos show correctly applied captive bolt stunning. The animal is instantly rendered insensible to pain.

There has been renewed interest in the use of non-penetrating captive bolt due to concerns about BSE (Bovine spongiform encephalopathy). The elimination of stunners that injected air into the brain greatly reduced the amount of brain or spinal cord tissue that could be spread to other parts of the body. However, research has shown that even when air injection had been removed, small amounts of brain tissue may enter the body and brain tissue may contaminate plant equipment. The effective use of non-penetrating captive bolt requires much more accurate aim than a penetrating captive bolt. This may require the use of equipment to hold the animal's head. Designs for head holders can be found in the religious slaughter section of www.grandin.com and in the restraint for stunning section. Mushroom head non-penetrating captive bolt stunners inflict varying degrees of damage to the skull. Non-penetrating captive bolt that fractures the skull is more effective than a stunner that does not fracture the skull. Effectiveness increases as the degree of skull fracturing increases. It is likely that reducing the spread of at risk brain material is reduced when fracturing is minimized. Unfortunately, effective stunning and reducing skull fracturing are two opposite goals. As the amount of damage to the skull is reduced, placement of the shot must become more and more precise to achieve instantaneous insensibility. Shooting on a slight angle may result in failure to induce instantaneous insensibility. A mushroom head with a larger diameter may be more effective with less fracturing than a mushroom head with a small diameter.

In plants using a non-penetrating captive bolt animal welfare should be evaluated with the American Meat Institute scoring system in the same manner as penetrating captive bolt. The plant must be able to stun 95% or more of the cattle correctly with a single shot. They must be able to attain an acceptable score of 75% of the cattle moved with no electric prod and 3% or less of the cattle vocalizing. If a head restraint is used, a vocalization score of 5% is acceptable.

Heavy mature bulls are more difficult to stun with captive bolt compared to cows or fed beef. Practical experience in plants indicates that heavy bulls are most effectively stunned with either a perfectly maintained cartridge fired penetrating captive bolt stunner, a fire arm with a free bullet, or one of the new powerful pneumatic penetrating captive bolt stunners. Stunning mature bulls correctly has been a continuous problem that has repeatedly shown up in restaurant audits. The stunning of bulls with a non-penetrating stunner will need to be carefully monitored and audited to maintain a high standard of animal welfare.

For large bulls and other heavy livestock such as bison, some plants routinely shoot them twice with a captive bolt. To verify that 95% or more are rendered insensible with one shot, the auditor or inspector should check for signs of return to sensibility BEFORE the second shot is done. A stunner shot that shoots in the air and does not touch the animal does not count. If the bolt of the stunner touches or partially penetrates the animal it is counted as a missed shot.

The issue of stunner problems with brain tissue contamination must be kept in perspective. The carcass splitting saw also spreads spinal cord tissue on the carcass. Splitting saw contamination may possibly be worse than contamination from a standard penetrating captive bolt.

Studies done under good commercial conditions show that contamination from brain proteins is low. A study done by Rovira et al (2005) at Colorado State University indicated that only one animal out of 360 had a positive GFAP immuno assay for brain protein in the blood after penetrating captive bolt. Thirty cattle were sampled in 12 commercial plants. In 10 out of the 12 plants, the animals were shot with a single shot. The one positive sample occurred in a plant where the kill floor layout made it impossible to verify that the animal was shot with a single shot. A study done at the University of Bristol by Coore et al (2005) showed much higher levels of contamination. They used methods that may have confounded their results. The cattle were anesthetized and a catheter with a balloon was inserted into the jugular vein. There is a possibility that this device may have slowed down bleedout and changed blood flow patterns in the brain. Another study done under commercial conditions had results similar to the Colorado State study (Lucker et al, 2005).

References:

Coore, R.R., et al, 2005. Brain tissue fragments in jugular vein blood of cattle stunned by use of penetrating and non-penetrating captive bolt guns. Journal of Food Protection, 68:882-884.

Lucker, E. et al, 2002. Studies of contamination of beef with tissues from the central nervous system (CNS) as pertaining to slaughter technology and human BSE exposure risk. Berl Munch Tierarztl Wochenscher, 115:118-121.

Predergast, D.M., et al. 2003. Dissemination of central nervous system tissue from the brain and spinal cord of cattle after captive bolt stunning and carcass splitting. Meat Science. 65: 1201-1209.

Rovira, P. et al, 2005. Identification of humane cattle stunning systems that minimize possibility of central nervous system tissue entering the circulatory system. Colorado State University, Animal Science, Swift Graduate Seminar.

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