Cattle Breed and Head Dimension Effects on the Performance of a Captive Bolt Stunner Equipped with Three Different Length Bolts

Captive bolt stunning is commonly used as a means of quickly and effectively rendering cattle insensible prior to slaughter. Effective stunning of cattle is partially ensured by proper placement of the device, which may be breed-dependent. For Holsteins, stun placement is typically recommended 2.5 cm above common placement for other breeds. The purpose of this study was to determine if head dimensions and brain location differ between Holstein and non-Holstein breeds. This study also examined the effects of different bolt lengths on physical brain damage. It was hypothesized that head size and brain damage would not differ based on bolt length or breed. This study utilized a randomized, unbalanced block design, with treatment blocked by day. Experimental unit was animal, and analyses were performed using t-tests in SAS 9.4 (SAS Inc., Cary, NC). The stunner used was a Jarvis USSS-1 (Jarvis Products Corp., Middletown, CT), a penetrating, pneumatic captive bolt gun. For brain damage assessment, 292 heads were randomly sampled across three collection periods, with an approximately equal split between Holstein and non-Holstein breed. Each period was assigned either the control bolt (CON), medium bolt (MED), or long bolt (LON), with lengths of 15.2 cm, 16.5 cm, and 17.8 cm, respectively. Heads were were collected, immediately measured, and chilled for splitting and damage analysis at the CSU Necrology Laboratory (CSU VTH, Fort Collins, CO). For head dimension assessment, 426 heads equally distributed between Holstein and non-Holstein breed were sampled. Head width, poll to orbit, right orbit to poll, and left orbit to poll did not differ between breeds (P > 0.13). Head length and orbit to nose length were greater for Holsteins (P = 0.0046). Brain size, length, and width, as well as skull thickness did not differ between breeds (P > 0.32). Stunning metrics included bolt entrance hole diameter, which was greatest for LON, least for MED, and intermediate for CON (P < 0.0001). Bolt penetration depth was greatest for MED (P < 0.0001). Sagittal brain damage was least for CON, with greater damage measured on MED and LON (P < 0.0001). Dorsal damage was least for CON and increased for MED and LON (P < 0.0001). The data in this study suggest differing bolt lengths affect brain damage and head dimensions appear to be different between breeds in nose length only, indicating that current recommendations for differing stun placement based on breed may need to be reevaluated.