Welfare of calves - 1. Investigations into some aspects of calf slaughter

The relationship between carotid occlusion, systemic blood pressure and brain function following electrical stunning and exsanguination (sticking) in slaughter calves (< 10 weeks) was assessed. Electrocorticograms, systemic blood pressure and evoked responses were measured in the chloralose. anaesthetised and the unanaesthetised states. Electrical stunning produced relatively short periods of measurable epilepsy in slaughter calves (18 s average). The pattern of decline in blood pressure after sticking showed variations between animals. However, the results indicated that two groups of animals could be recognised: a carotid occlusion (ballooning group) and no carotid occlusion (non-ballooning) group. The animals with ballooning (six out of 15 = 40%) developed occlusions of the caudal severed ends of the carotid arteries. These swellings, the so-called 'ballooning' effect, were characterised by large clots forming plugs at the severed ends of the arteries. When this phenomenon occurred the haemorrhaging was clearly impeded. This was reflected in the blood pressure traces which showed recovery episodes coinciding with the occurrence of the carotid occlusions. Our study indicates that in the worst possible case the development of a restriction to the outflow of blood can delay the rate of haemorrhaging and the decline in blood pressure. This can lead in turn to sustained brain function as evidenced by the continued presence of evoked responses following stun recovery and a long time to onset of the isoelectrical state in the electrocorticogram.