Study on the Association between Tail Lesion Score, Cold Carcass Weight, and Viscera Condemnations in Slaughter Pigs

Tail biting is a serious animal welfare and economic problem in pig production. Tail docking, which reduces but does not eliminate tail biting, remains widespread. However, in the EU tail docking may not be used routinely, and some 'alternative' forms of pig production and certain countries do not allow tail docking at all. Against this background, using a novel approach focusing on research where tail injuries were quantified, we review the measures that can be used to control tail biting in pigs without tail docking. Using this strict criterion, there was good evidence that manipulable substrates and feeder space affect damaging tail biting. Only epidemiological evidence was available for effects of temperature and season, and the effect of stocking density was unclear. Studies suggest that group size has little effect, and the effects of nutrition, disease and breed require further investigation. The review identifies a number of knowledge gaps and promising avenues for future research into prevention and mitigation. We illustrate the diversity of hypotheses concerning how different proposed risk factors might increase tail biting through their effect on each other or on the proposed underlying processes of tail biting. A quantitative comparison of the efficacy of different methods of provision of manipulable materials, and a review of current practices in countries and assurance schemes where tail docking is banned, both suggest that daily provision of small quantities of destructible, manipulable natural materials can be of considerable benefit. Further comparative research is needed into materials, such as ropes, which are compatible with slatted floors. Also, materials which double as fuel for anaerobic digesters could be utilised. As well as optimising housing and management to reduce risk, it is important to detect and treat tail biting as soon as it occurs. Early warning signs before the first bloody tails appear, such as pigs holding their tails tucked under, could in future be automatically detected using precision livestock farming methods enabling earlier reaction and prevention of tail damage. However, there is a lack of scientific studies on how best to respond to outbreaks: the effectiveness of, for example, removing biters and/or bitten pigs, increasing enrichment, or applying substances to tails should be investigated. Finally, some breeding companies are exploring options for reducing the genetic propensity to tail bite. If these various approaches to reduce tail biting are implemented we propose that the need for tail docking will be reduced.

Two matched case-control studies were performed at an abattoir with a capacity of 780 pigs per hour, each study using the approximately 7000 pigs slaughtered on one day. In the first study, the severity of tail biting and pneumonia were recorded in pigs with bitten or intact tails. In the second study, the tail score, sex, and the presence of pleuritis, externally visible abscesses and trimming were recorded in pigs with bitten or intact tails. In study 1, there was no significant association between the tail score and the percentage of lung tissue affected by lesions typical of enzootic pneumonia, but there was a significant association between the severity of tail biting and the prevalence of lungs with abscesses and/or pleuritic lesions (P<0.0001). In study 2, there were significant associations between the severity of tail biting, and the prevalence of external carcase abscesses and carcase trimming; the carcases of castrated males had evidence of tail biting more frequently than the carcases of females (P<0.05).

Despite extensive utilisation in epidemiological investigations of animal health, to date there has been little consideration of the value of abattoir meat inspection as a pig welfare surveillance tool. This study measured the prevalence of tail-docking, tail biting, carcase condemnations and associated financial losses of the latter (Northern Ireland only) in 36,963 pigs slaughtered in six abattoirs from the Republic of Ireland and Northern Ireland in July and August 2010. Over 99 per cent of inspected pigs had been tail-docked, while 58.1 per cent and 1.03 per cent had detectable and severe tail lesions, respectively. Producer losses resulting from carcase condemnation were estimated to be €0.37 per pig slaughtered. Enhanced capture and utilisation of meat inspection data for use in animal welfare surveillance schemes has the potential to drive improvements in production efficiency and animal welfare. However, significant differences were detected in the prevalence of carcase condemnation conditions between abattoirs and judiciaries (Republic and Northern Ireland). This reflects variation in the criteria and methods of data capture used in meat inspection in different abattoirs. Thus, the meat inspection process needs to be standardised and reformed before it can be reliably utilised in large-scale pig welfare surveillance schemes.