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Network analyses can assist in predicting the course of epidemics. Time-directed paths or ‘contact chains' provide a measure of host-connectedness across specified timeframes, and so represent potential pathways for spread of infections with different epidemiological characteristics. We analysed networks and contact chains of cattle farms in Great Britain using Cattle Tracing System data from 2001 to 2015. We focused on the potential for between-farm transmission of bovine tuberculosis, a chronic infection with potential for hidden spread through the network. Networks were characterized by scale-free type properties, where individual farms were found to be influential ‘hubs' in the network. We found a markedly bimodal distribution of farms with either small or very large ingoing and outgoing contact chains (ICCs and OCCs). As a result of their cattle purchases within 12-month periods, 47% of British farms were connected by ICCs to more than 1000 other farms and 16% were connected to more than 10 000 other farms. As a result of their cattle sales within 12-month periods, 66% of farms had OCCs that reached more than 1000 other farms and 15% reached more than 10 000 other farms. Over 19 000 farms had both ICCs and OCCs reaching more than 10 000 farms for two or more years. While farms with more contacts in their ICCs or OCCs might play an important role in disease spread, farms with extensive ICCs and OCCs might be particularly important by being at higher risk of both acquiring and disseminating infections.

This paper summarises the findings from five studies in eight countries on over 1,500 cattle slaughtered commercially by the halal or shechita methods without stunning. It reports the number of cuts applied to the neck, the cutting methods and the frequency of complications during the bleeding period. Complications during the bleeding period that occurred in some cattle included: (i) delay in the time to collapse, which was interpreted as late loss of consciousness; (ii) premature arrest of bleeding from the carotid arteries due to false aneurysm formation; and (iii) blood entering the respiratory tract during bleeding. These features are important as they determine or reflect the duration of consciousness following the cut and the potential for protracted suffering from wound nociception or blood irritating the respiratory tract. When cattle were not restrained following the halal cut, they took on average 20 s to collapse. Fourteen percent stood up again after an initial collapse, and 1.5% took more than 4 min before their final collapse. Eight percent took 60 s or longer to collapse, and those animals were more likely to have false aneurysms in the severed ends of the carotid arteries. False aneurysms, which were at least 3 cm in diameter, formed in the severed cardiac ends of the carotid arteries in 10% of cattle slaughtered by halal or shechita. Some false aneurysms formed in the severed ends of the carotid arteries within 7 s of the halal cut, and in 10% of the cattle bloodflow came to a halt in one of the arteries within 10 s. On average, the false aneurysms developed within 21 s. Nineteen percent of cattle slaughtered by shechita and 58% of cattle slaughtered by halal had blood lining the mucosa of the trachea. All animals had blood lining the glottis. In both situations there could be a sense of respiratory tract irritation from the blood. It is proposed that severing the carotids at the position in the neck which corresponds to C1 will reduce the frequency of false aneurysm formation and subsequent arrested bloodflow from the severed arteries, and it will deafferent the respiratory tract reducing the transmission of potentially unpleasant sensory signals associated with blood contaminating the upper and lower parts of the tract. Most cattle subjected to halal and shechita have the neck cut at a position which corresponds to C2 to C4, and changing to a cut at C1 could partly reduce the potential for suffering during slaughter without stunning.

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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