Date Published: May 28, 2012
Publisher: BioMed Central
Author(s): Linda J Keeling, Anna Wallenbeck, Anne Larsen, Nils Holmgren.
There is increasing interest in recording tail damage in pigs at slaughter to identify problem farms for advisory purposes, but also for benchmarking within and between countries as part of systematic monitoring of animal welfare. However, it is difficult to draw conclusions when comparing prevalence’s between studies and countries partly due to differences in management (e.g. differences in tail docking and enrichment routines) and partly due to differences in the definition of tail damage.
Tail damage and tail length was recorded for 15,068 pigs slaughtered during three and four consecutive days at two slaughterhouses in Sweden. Tail damage was visually scored according to a 6-point scale and tail length was both visually scored according to a 5-point scale and recorded as tail length in centimetres for pigs with injured or shortened tails.
The total prevalence of injury or shortening of the tail was 7.0% and 7.2% in slaughterhouse A and B, respectively. When only considering pigs with half or less of the tail left, these percentages were 1.5% and 1.9%, which is in line with the prevalence estimated from the routine recordings at slaughter in Sweden. A higher percentage of males had injured and/or shortened tails, and males had more severely bitten tails than females.
While the current method to record tail damage in Sweden was found to be reliable as a method to identify problem farms, it clearly underestimates the actual prevalence of tail damage. For monitoring and benchmarking purposes, both in Sweden and internationally, we propose that a three graded scale including both old and new tail damage would be more appropriate. The scale consists of one class for no tail damage, one for mild tail damage (injured or shortened tail with more than half of the tail remaining) and one for severe tail damage (half or less of the tail remaining).
Tail biting can be described as the chewing and biting of another pig’s tail. Besides pain from acute injuries on the damaged tail, receivers often suffer from secondary infections leading to abscesses. Consequently, carcasses from tail bitten pigs are in many cases partly or fully condemned at slaughter [1-3]. Thus in addition to being a welfare problem for the bitten pig, tail biting is also an economic problem for the farmer. When large numbers of animals are considered in a representative sample, the prevalence of tail biting can also be a reflection of the housing systems and management practices in a region or country and hence an indicator of the welfare of the pigs in general.
Tail injury, tail length and sex were recorded for all pigs slaughtered over four days (16–19 June, 2003) at slaughterhouse A (western Sweden) and over three days (19–21 August, 2003) at slaughterhouse B (southern Sweden). The recording period of three or four days was chosen to maximise the number of pigs scored, but reduce the risk that the sample was dominated by pigs from only a few farms.
A total of 15,068 pigs, 6,837 and 8,231 pigs in slaughterhouse A and B respectively, were scored. Of these, 50.8% were male in slaughterhouse A and 50.7% in slaughterhouse B. The total prevalence of any type of injury and/or shortening of the tail was 7.0% (8.5% males; 5.5% females) in slaughterhouse A and 7.2% (9.1% males; 5.2% females) in slaughterhouse B. In slaughterhouse A, there was a small difference (0.7%) in the frequency of pigs with injured and/or shortened tails if all injury scores on the scale were used (scores 1–5) compared to when only major injury (scores 3–5) was used. However, there was no difference in frequency of injured pigs depending on the scale used in slaughterhouse B. If only pigs with half or less of the tail remaining were considered, the percentages were 1.5% and 1.9% slaughterhouse A and B respectively (Table 1). According to the slaughterhouse’s own routine recordings, monthly averages corresponding to the time of the data collection in the present study were 1.2% and 1.6% at slaughterhouses A and B respectively.
The number of pigs with tail damage (injury or shortened tails) at slaughter was found to be considerably higher than indicated by the remarks from routine recordings from the same time period. According to the classification used in this study, around 7% of the pigs had some form of tail damage. When only cases with half or less of the tail remaining were considered in the current study, the percentage of pigs (between 1-2%) was in agreement with the monthly averages of tail damaged pigs per slaughterhouse, despite some evidence of inter observer variability in the scoring of tail length. This finding suggests that the routine recordings of tail damage at slaughter in Sweden reflects the number of pigs with half or more of the tail missing rather than pigs with damaged, but longer tails. Thus they leave a considerable amount of tail damage unseen in the reported statistics from slaughterhouses.
Tail damage recorded routinely at slaughterhouses in Sweden, as an indication of tail biting and hence general pig welfare, underestimates the actual prevalence. More detailed observations estimated the prevalence to be four times higher and our findings suggest that this is because, in practice, it is mainly cases with half or less of the tail remaining that are recorded. In specific studies or in animal welfare assessment systems for benchmarking purposes nationally or internationally, we suggest a three graded scale with one class for no tail damage, one intermediate class for minor tail damage i.e. either injured with no shortening of the tail or injured with some shortening of the tail but still with more than half of the tail remaining, and one class for major tail damage i.e. with less than half of the tail remaining irrespective of whether or not the tail has any apparent injury. This study supports that tail damage is more common in males than in females, but also adds that the damage is more severe in males than females.
Although one author (NH) was employed by the national organisation that, among other things, advises the pig sector, none of the authors of this paper has a financial or personal relationship with other people or organisations that could inappropriately influence or bias the concept of the paper.
LK, AL and NH planned the design of the study and carried out the practical data collection. AW carried out the statistical analyses. LK and AW drafted the manuscript and all authors read and approved the manuscript.