Edited by: Stephanie Torrey, Independent Researcher, Guelph, Canada
Reviewed by: Nienke Van Staaveren, University of Guelph, Canada; Jen-Yun Chou, University of Pennsylvania, United States
This article was submitted to Animal Behavior and Welfare, a section of the journal Frontiers in Veterinary Science
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The prevalence of tail lesions evaluated at the slaughterhouse varies considerably between herds. These lesions result mainly from tail biting, a harmful behavior with multifactorial origin. This study sought to investigate if a batchwise inspection of tails at slaughterhouse could be a useful method to estimate the animal welfare situation in finishing pig herds, and if so, what type and detail of tail scoring such an inspection should utilize. We investigated the distribution of different types of tail lesions and how well their scoring at slaughterhouse was associated with the situation recorded on-farm by a veterinarian as part of routine herd health visits. We also wanted to determine if animal welfare-related herd-level parameters, recorded by herd veterinarians during herd health visits, are associated with tail scoring at the slaughterhouse. A total of 10,517 pigtails from 84 herds were scored for this study. Herd data were collected from the national health classification register for pig farms in Finland and also included annual herd production quality data collected by the slaughterhouse. The scores of the tails varied considerably between the herds. On average, 48.1% (sd = 19.3) of the tails with an average length of 30.4 cm (sd = 2.7) were fully intact, 37.3% (13.9) had healed (length = 26.4, sd = 5.1 cm), 12.4% (9.0) (length = 28.9, sd = 4.3 cm) had minor acute wounds, and 2.3% (2.1) (length = 24.2, sd = 6.0 cm) had major acute wounds. Proportions of different tail lesions at slaughterhouse were associated with or tended to be associated with the following herd-level parameters in regression models: use of wood as enrichment (
Tail biting (TB) is a major welfare concern in pig production (
The prevalence of TL varies considerably in scientific studies and has been estimated to be 2–4 fold higher in pigs with undocked tails than those with docked tails (
Our aim was to investigate if a batchwise, thorough inspection of tails at the slaughterhouse could be a useful method to estimate the animal welfare situation in finishing pig herds, and if so, what type and detail of tail scoring such an inspection should utilize. To achieve this, we investigated (a) how the distribution of different types of intact and damaged tails vary between farms, (b) how well TL scoring at the slaughterhouse is associated with the herd-level situation of tails scored during a single herd health visit, and (c) how long term production parameters (annual mortality, annual total, and partial carcass condemnations) are associated with tail scores in the slaughterhouse. In addition, to further evaluate the value of TL scoring at the slaughterhouse as a proxy measure of on-farm conditions: (d) we tested if certain relevant, and available, risk factors for tail biting (mainly related to health and use of enrichment), recorded by herd veterinarians during herd health visits, are associated with tail scoring at the slaughterhouse. We hypothesized that by recording only the severely bitten pigs at the slaughterhouse we could estimate the total TL level in the herd, both in the long and short term. We also hypothesized that certain herd-level parameters, such as animal health and management features, are associated with the level of tail damage scored at the slaughterhouse.
The data collection from undocked finishing pigs has been described in detail by Valros et al. (
Pictures and live observations were used to train the researchers to harmonize the scorings before the actual data collection at the slaughterhouse line. The scoring point was situated after singeing, whipping, bung drilling, and chest opening. Altogether six researchers, two at a time, were responsible for the scorings, which took about 7–8 s per tail due to slaughterhouse line speed. One of the two main scorers was present during all scoring sessions. The scorers were standing on a platform high enough for them to palpate and measure each tail easily. One researcher measured the tail of the carcass with a 50 cm long ruler and assessed the possible tail lesion while the other recorded the observations. With the carcasses hanging upside down, the end of the ruler was placed on the dorsal side of the tail and firmly pushed toward the base of the tail. The tail was then manually extended against the ruler. During scoring, the observers consulted each other actively in case of questionable scorings.
The scoring system used included elements from the systems developed by The FareWellDock-consortium (
Tail scoring system used at the slaughter line after scalding of the carcass and the mean percentage and standard deviation of one delivery group of finishing pigs from 84 herds (10,517 carcasses) according to their tail lesion scores and tail length in centimeters.
Intact | The tail is fully intact, the end is rounded, and slightly flattened | 48.1% (19.3) | 30.4 (2.7) |
Healed | The tail is clearly shortened; the tail end is scarred, of abnormal shape or too thick to be intact. The skin is totally healed (no scab, wound, or missing tissue) | 37.3% (13.9) | 26.4 (5.1) |
Minor acute wound | The tail has missing tissue, which has not yet fully healed; uneven “dents” in the skin; or a part of the tail is missing. Wound is >0 cm but <2 cm in diameter or length | 12.4% (9.0) | 28.9 (4.3) |
Major acute wound | The tail has missing tissue, which has not yet fully healed; uneven “dents” in the skin; or a part of the tail is missing. Wound is ≥2 cm in diameter or length | 2.3% (2.1) | 24.2 (6.0) |
Data concerning the finishing pigs in 84 herds were collected from the national health classification register for pig farms in Finland, Sikava (
Detailed information of the health classification system can be found at
In this study, we included observations about pig health, behavior and use of enrichment for the pigs recorded by the veterinarian during the herd health visit according to the scoring system acquired by Sikava (
Summary of the data collected by the herd health veterinarians in finishing units of 84 herds during routine Sikava herd health visits.
1. Percentage of pigs with bitten tails | None or single pigs | Some, 1–5% of the pigs | Several, 6–10% of the pigs | Plenty, >10% of the pigs |
2. Disease symptoms (arthritis, claw injury, leg problem other than arthritis, coughing, sneezing, diarrhea, skin injury or infection, abscesses, central nervous system symptoms, runts, and hernia) | None or single pigs | Some, 1–5% of the pigs | Several, 6–10% of the pigs | Plenty, >10% of the pigs |
3. Evaluation of the percentage of intact tails (=a tail with full length and curled up. If a tail has signs of healed or acute TB and the tail is shortened/damaged/stuck between legs, it is not intact). | Intact >95% of the pigs | Intact >80% of the pigs | Intact >70% of the pigs | Intact <70% of the pigs |
1 = Good | 2 = Satisfactory | 3 = Poor | ||
1. Explorative behavior to given material. Behavior of standing animals if they are not eating, drinking defecating or urinating. The behavior should be directed toward enrichment material, not toward pen structures or pen mates. | >70% of pigs explore enrichment | 40–70% of pigs explore enrichment | <40% of pigs explore enrichment | |
2. Reaction of the pigs to the examiner, evaluated after examiner was first walking from one end of the corridor to another. The examiner did not enter the pen. | Pigs approach the examiner within few minutes | Only some pigs dare to approach the examiner | Pigs do not approach the examiner, are afraid, stay in the back of the pen | |
Use of materials as environmental enrichment, the material used was recorded (Toy, straw, sawdust, wood, paper, peat, hay, wood chips, other) | 0 = Not used | 1 = Yes, used | ||
Inter-visit mortality | % of finishing pigs dead or euthanized after the previous visit |
The slaughterhouse continuously collects the following information on parameters for follow up of production quality and saves this data in Sikava database: annual mortality, annual percentage of carcasses with total carcass condemnation, and annual percentage of carcasses with partial carcass condemnation. The herd owners and health care veterinarians can see these parameters and use them as long-term animal health and welfare estimates for the farms and follow-up of production quality. In this project, we refer them as production parameters. They were available for 79 herds of this study for the period from July 2018 to June 2019.
All statistical analyses were performed using IBM SPSS statistics version 25. The unit of interest was the herd.
At first, the data were checked (
Continuous variables were assessed for normality visually and using the Shapiro–Wilk test. The correlation between the percentages of different tail scorings at the slaughterhouse was calculated with Pearson correlation. Differences between farms within different tail lesion percentage class, based on data collected by the veterinarian during the heard health visit (tail lesions below 1 vs. 1–10%) in the tail scoring at the slaughterhouse was evaluated using separate
Finally, based on the univariate test results four different multivariable linear regression models were built for the different outcomes using a manual backward elimination model building strategy. Variables were excluded one by one based on non-significant
Correlations of the production parameters (annual mortality, annual total, and partial carcass condemnations) and the four different tail outcomes in the slaughterhouse (intact tails, healed tails, tails with minor wounds, and tails with major wounds) were tested separately with Pearson correlations (total and partial carcass condemnations) and Spearman rank correlation (annual mortality, which was non-normally distributed).
Out of the 84 herds in this study, 69 (82.1%) were finishing units growing feeder pigs from a weight of ~30 kg until slaughter and 15 (17.9%) were farrow-to-finish herds. The production type did not affect the prevalence of the different tail scorings at the slaughterhouse (
On average, the mean percentage of fully intact tails at the slaughterhouse was 48.1% (see
Correlation of percentages of herd-level tail evaluations from 84 Finnish herds.
Intact | −0.858 |
−0.706 |
−0.539 |
Healed | 0.258 |
0.270 |
|
With minor wounds | 0.522 |
Frequency distributions of percentages of tail classifications in 84 herds:
Study herds (
During the one herd health visit, the herd veterinarians recorded TLs in 21 (25%) herds in none or single animals. In addition, 58 (69%), 5 (6.0%), and 0 herds were given a score of 1 (1–5% of the pigs), 2 (6–10% of the pigs), or 3 (>10% of the pigs), respectively. Later in the analyses, the herds were divided in the following two groups: 21 herds with no or single animals with bitten tails and 63 herds with TL in 1–10% of the pigs.
The average percentage of undocked tails of finishing pigs per herd (
The veterinarians scored the percentage of intact tails in finishers during the herd health visit as follows: in 43 herds (51.2%) > 95% of the tails were intact, in 23 herds (27.4%) > 80% of the tails were intact, in 16 herds (19.0%) > 70% of the tails were intact, and one herd (1.2%) had ≤ 70% intact tails.
The average percentage of undocked tails of finishing pigs per herd (
Descriptive herd data (84 herds) that were used in statistical analyses are shown in
Information recorded by veterinarian during one herd health visit on the use of different materials used as environmental enrichment in 84 study herds growing finishing pigs.
Toy | 16 (19.0%) | 68 (81.0%) |
Straw | 21 (25.0%) | 63 (75.0%) |
Sawdust | 27 (32.1%) | 57 (67.8%) |
Wood | 56 (66.7%) | 28 (33.3%) |
Paper | 58 (69.0%) | 26 (31.0%) |
Peat | 64 (76.1%) | 20 (23.8%) |
Hay | 65 (77.4%) | 19 (22.6%) |
Wood chips | 83 (98.8%) | 1 (1.2%) |
Other | 82 (97.6%) | 2 (2.4%) |
The presence of different symptoms in the finishing pigs (number and percentage of herds out of 84) recorded by herd veterinarians during one herd health visit.
Arthritis | 10 (11.9%) | 68 (81.0%) | 6 (7.1%) | 0 |
Claw injury | 68 (81.0%) | 16 (19.0%) | 0 | 0 |
Leg problem other than arthritis | 40 (47.6%) | 44 (52.4%) | 0 | 0 |
Coughing | 73 (86.9%) | 8 (9.5%) | 3 (3.6%) | 0 |
Sneezing | 77 (91.7%) | 7 (8.3%) | 0 | 0 |
Diarrhea | 66 (78.6%) | 18 (21.4%) | 0 | 0 |
Skin injury or infection | 44 (52.4%) | 40 (47.6%) | 0 | 0 |
Abscesses | 50 (59.5%) | 34 (40.5%) | 0 | 0 |
Central nervous system symptoms | 79 (94.0%) | 5 (6.0%) | 0 | 0 |
Runts | 36 (42.8%) | 48 (57.1%) | 0 | 0 |
Hernia | 10 (11.9%) | 71 (84.5%) | 3 (3.6%) | 0 |
The final regression model for percentage of intact tails (
Percentage of undocked, intact tails of finishing pigs evaluated at the slaughterhouse. The pigs originated from 84 herds, where the herd veterinarian collected the data during one herd health visit. The results are shown separately for herds using wood as enrichment and having leg problems other than arthritis present in the herd during the herd visit (interaction in the regression model). Different letters represent statistical difference: ab
The final regression model for healed tails (
The final regression model for percentage of tails with major acute wounds (
Percentage of undocked, tails with major acute wounds evaluated at slaughterhouse. The finishing pigs originated from 84 herds, where the herd veterinarian collected the data during one herd health visit. The results are shown separately for herds using wood as enrichment and according to explorative behavior of standing animals if they were not eating, drinking, defecating, or urinating (interaction), as evaluated by a veterinarian during the herd health visit. The behavior was directed toward enrichment material and not toward pen structures or pen mates. Different letters represent statistical difference: ef
The production parameters (long-term animal health and welfare estimates of the herds) revealed an average annual mortality of 1.9% (sd = 1.88), an annual total carcass condemnation of 0.27% (0.17), and an annual partial carcass condemnation of 6.0%.
The percentage of intact tails in the slaughterhouse data tended to correlate negatively with annual total carcass condemnations (
Our study revealed that the prevalence of four different tail scores (intact, healed, minor wounds, and major wounds) in the herds varied considerably and herds commonly had different combinations of tail scorings evaluated at the slaughterhouse. Further, the correlations between the occurrence of healed and acute tail lesions were rather weak. Therefore, against our hypothesis, it is not possible to directly estimate the TL score at the slaughterhouse by recording only one type of pigtail score (such as major acute wounds of the tail at the slaughterhouse). As recorded by a veterinarian during one herd health visit, the tail score recorded at the slaughterhouse was only moderately related to the on-farm TB level. We further observed some herd-level factors and long-term indicators of herd health (one parameter, leg problems other than arthritis) and welfare status (production quality) that were associated with TL scores at the slaughterhouse, indicating that slaughterhouse tail scoring might be indicative about the overall welfare status of the farm. In particular, the tendency of the association between the using of wood as enrichment and tail scorings is interesting.
The fact that there was a great variation in the tail lesion profile (i.e., the distribution of different types of damage within different herds,
The scoring at the slaughterhouse was performed by the researchers and was much more detailed than the one performed by veterinarians in the herds. However, as shown in
Healed lesions are problematic from both an animal welfare and economical perspective. A healed tail has been bitten at some point and caused pain and stress in the pigs. No information is available about the time needed for the tail to heal after being bitten. The wound caused by tail docking heals in 4 to 8 weeks (
Meat inspection data could be better used in herd health and welfare planning at the farm level (
Nearly half of the tails at the slaughterhouse were scored as intact, which is a very low figure. However, after dividing the tails into those without wounds (intact 48.1% and healed 37.3%, altogether ~85%) and those with wounds (minor 12.4% and major acute wounds 2.3%, altogether ~15%), the results seem to be in the same range with the results from other studies (
We showed that the results of different tail lesions at the slaughterhouse are associated with some herd-level parameters, such as use of enrichment. EFSA (
Sickness has been considered as a risk factor for TB (
It is difficult to find results about the possible association between mortality and TLs. Moinard et al. (
Our study further shows that it is possible to grow undocked pigs with only a small percentage of pigs with serious tail wounds at the slaughterhouse. In almost 20% of the herds (
This study has some limitations. It was not possible to evaluate the same pigs in the herd and at the slaughterhouse. However, we believe that the risk factors and situation in the herds are quite constant except for occasional TB outbreaks. The fact that piggeries usually empty their finishing units in 3–4 deliveries may have caused selection of certain types of pigs in our slaughterhouse data of 1 week. For example, the last delivery group of the pigs in one room may include those that have grown slower than the ones that were sent to slaughterhouse in the first delivery group. Due to these two factors, we may not have identified all real associations between the risk factors in the herd and the tail scoring results at slaughterhouse. However, we believe that the ones that have been identified are correct. The herd visits were performed by several different veterinarians, which also caused variation in the evaluation. However, this variation is likely mitigated by common educational background (veterinary studies and Sikava course).
Our results show that by recording only one type of tail condition such as tails with major acute wounds at the slaughterhouse, it is not possible to estimate the total tail lesion situation in herds before slaughter. Herds seem to have varying combinations of percentages of tails that were intact, healed, with minor acute wounds, and with major acute wounds. Each of these provide different information about the situation on the farm. Tail lesion scoring at the slaughterhouse appears to be a more precise measure than that performed on-farm as part of a herd health visit. Tail condition as measured at the slaughterhouse shows potential to estimate the long-term welfare level on the farm. This is related to management, such as the use of manipulable objects, and maybe also to some health parameters on the farm.
The data of the slaughtered pigs are owned by the producers. Those interested in the datasets should contact Anna Valros (
Ethical review and approval was not required for the animal study because the data was collected firstly from database where veterinarians had stored their herd health evaluations and secondly in the slaughterhouse after stunning and bleeding. Written informed consent for participation was not obtained from the owners because the data from the database was anonymous.
AV was responsible for the data analysis. All authors contributed to the study design, data collection, interpretation of the results, preparation of the manuscript, participated in writing of the manuscript, and gave their approval for the final manuscript.
EV and JV are employees of the slaughterhouse company. The University of Helsinki was responsible for data analysis and scientific publication throughout the study. The company involvement did not have any effect on the study design, data collection, interpretation of results, or the writing of the manuscript. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
The authors acknowledge Riitta Pietilä and Johanna Daka for assistance in data collection at the slaughterhouse. The authors also acknowledge the abattoir personnel for their assistance during the data collection.