Quantification of cooling effects on basic tissue measurements and exposed cross-sectional brain area of cadaver heads from Holstein cows > 30 mo of age

Penetrating captive bolt (PCB) is the primary method of preslaughter stunning for cattle and is also used for on-farm euthanasia. The objective of this study was to quantify the impact of cooling on the soft tissue thickness, cranial thickness, total tissue thickness, and cross-sectional brain area of cadaver heads collected from mature (> 30 mo of age) dairy cows following the application of a PCB stun in a frontal placement. Hide-on cadaver heads were obtained from culled dairy cows (N = 37) stunned in a frontal location using a handheld PCB device (Jarvis Model PAS—Type C 0.25R Caliber Captive Bolt, Long Bolt) at a commercial slaughter establishment. Following transport to the University of Wisconsin—River Falls, heads were split at midline along the bolt path by a bandsaw and then underwent FRESH, CHILL24, CHILL48, and CHILL72 refrigeration treatments. The FRESH treatment involved images collected immediately after splitting each head, the CHILL24 treatment involved images collected after 24 h of refrigeration, the CHIL48 treatment involved images collected after 48 h of refrigeration, and the CHILL72 treatment involved images collected after 72 h of refrigeration. Measurements of soft tissue thickness, cranial thickness, total tissue thickness, and cross-sectional brain area were recorded for each refrigeration treatment. Soft tissue thickness did not differ caudal to (P = 0.3751) or rostral to (P = 0.2555) the bolt path. Cranial thickness did not differ caudal to (P = 0.9281) or rostral to (P = 0.9051) the bolt path. Total tissue thickness did not differ caudal to (P = 0.9225; FRESH: 24.77 mm, CHILL24: 23.93 mm, CHILL48: 24.27 mm, CHILL72: 42.30, SE: 0.86) or rostral to (P = 0.8931; FRESH: 24.09 mm, CHILL24: 23.99, CHILL48: 24.26, CHILL72: 24.43 mm, SE: 0.79 mm) the bolt path. Cross-sectional brain area was not different (P = 0.0971) between refrigeration treatments (FRESH: 9,829.65 ± 163.87 mm², CHILL24: 10,012.00 ± 163.87 mm², CHILL48: 9,672.43 ± 163.87 mm², CHILL72: 10,235.00 ± 166.34 mm²). This study demonstrated that FRESH tissue parameters can be determined from cattle cadaver heads refrigerated for 24, 48, or 72 h. Lay Summary Euthanasia and preslaughter stunning are important to animal welfare. Penetrating captive bolt (PCB) is the primary method of preslaughter stunning for cattle and is also used for euthanasia. PCB causes severe brain damage by passing a metal bolt through the skull and into the brain of the animal. An immediate loss of consciousness should result from this process. There has been a growing interest in understanding various aspects of PCB stunning and euthanasia for cattle, including the impacts of bolt length and PCB placement. Much of the literature in this space includes the assessment of brain damage. The brain is a semifluid structure, which makes it difficult to assess brain damage after splitting cadaver heads with a bandsaw without refrigeration. It is unknown whether refrigerated cow heads can be used as a model for fresh heads, or if refrigeration significantly modifies the tissues. This study evaluated the impact of four refrigeration periods (0, 24, 48, and 72 h) on tissue parameters associated with the frontal PCB placement using cadaver heads from culled dairy cows. Refrigeration time did not change the tissue parameters, suggesting that a refrigeration period can be used to improve brain rigidity without mathematical adjustments to tissue parameters.