Background: Tail biting is a common problem in swine production. Tail biting not only causes economic losses for pork producers, but also results in major negative implications for welfare of pigs. Currently, the common method to prevent tail biting is tail docking. While tail docking reduces incidence of tail biting, it does not eliminate the problem completely. Because tail docking is a painful procedure for pigs, it is under scrutiny because of animal welfare concerns. In this project, we quantified the impact of tail docking and tail biting on the welfare and performance of pigs to evaluate the need for tail docking.

Objectives were to: 1. compare incidence of tail biting among pigs with docked tails vs. intact tails; 2. investigate the development of tail biting behavior to predict outbreaks of tail biting; 3. evaluate the impact of tail biting on welfare and performance of victimized pigs and tail biters.

Procedures: The project was conducted at the University of Minnesota West Central Research and Outreach Center in Morris, MN. Pigs (Yorkshire × Landrace × Duroc) in the control group were tail docked after birth, and pigs in the treatment group were left with intact tails. Pigs (n = 352) without any sign of tail damage were weaned into a confinement nursery barn and housed in 44 pens of 8 pigs each, with 20 pens housing pigs of the docked group and 24 pens housing pigs with intact tails. Pigs remained in the nursery barn for 5 weeks. At 9 weeks of age, 240 pigs with no tail lesions were moved to a confinement grower-finisher barn and housed in 8 pens (4 pens of docked pigs and 4 pens of pigs with intact tails) of 30 pigs each, where they remained for 16 weeks until they reached market weight (average weight = 278 lb). Pigs were weighed at birth, when entering and exiting the nursery barn, every 4 weeks in the growing-finishing barn, and at the conclusion of the study. Feed intake was recorded on a pen basis during both the nursery and growing-finishing periods. To accomplish objective 1, all pigs were assessed for tail damage at entry to the nursery barn, 2 weeks thereafter, and when exiting the nursery barn, and then at 3 days, 1 week, 2 weeks, 5 weeks, 8 weeks, 10 weeks, and 16 weeks after entering the growing-finishing barn. Each pig was given a score of 0 to 4 depending on tail damage: score 0 = no damage; score 1 = healed lesions without visible blood; score 2 = open wounds without signs of infection; score 3 = open wounds with signs of infection, or partial loss of the tail without signs of infection; score 4 = partial or total loss of the tail with signs of infection. Pigs in pens with outbreaks of tail biting were scored for tail damage daily starting on the day that the first pig with a tail score of 2 emerged. Since tail biting may be associated with ear biting and body sucking which can cause skin lesions, lesion scores on the ears and the body were assessed at the same time that tail scores were assessed during the growing-finishing period. Incidence and reasons for morbidity and mortality were recorded throughout the study. To achieve objective 2, behaviors of all pigs were video-recorded twice weekly for 13 weeks when pigs were 10 to 22 weeks of age. Our hypothesis to predict outbreaks of tail biting was that pigs will increase their activity levels before the outbreak. To test the hypothesis, 3 hours (one hour each in the morning, noon, and afternoon) of video recording on each recording day were analyzed for optical flow which measures movement of pigs in each pen. Meanwhile, behaviors of interest (tail biting, ear-biting, pig-directed behavior, eating, drinking, standing/walking, and lying) were analyzed through scan sampling of video-recordings at 5 min intervals. In addition, live observations were conducted for 2 hours per week for 4 weeks when pigs were 17 to 21 weeks of age to record areas where tail biting occurred in a pen. To accomplish objective 3, tail biters, victimized pigs, and non-victimized pigs were defined during the growing-finishing period. Tail biters were identified through live observations 2 hours per day for two days, starting immediately after the first victimized pig emerged in a pen. Pigs identified to be biting tails of other pigs repetitively or obsessively were classified as tail biters. Pigs that had tail score 3 or 4 were classified as victimized pigs. Pigs that were neither tail biters nor victimized pigs were considered non-victimized pigs. Blood samples were collected from tail biters, victimized pigs, and non-victimized pigs from the same pen that housed victimized pigs for analysis of total serum protein, Ig-G, and substance P (pain indicator) concentrations. When pigs reached market weight, carcass weight was recorded at the packing plant for all pigs that were harvested. Incidence of subjective carcass trim loss was recorded.
Objective 1: Tail docking reduced incidence and severity of tail damage in both nursery and growing-finishing pigs. During the nursery period, 2% of pigs with docked tails vs. 41% of pigs with intact tails had skin lesions (score 1 or greater) on their tails. None of the docked pigs were scored 2 or greater for their tail lesion, but 7% of undocked pigs were scored 3 or greater, suggesting that undocked pigs suffered from more severe tail damage than docked pigs. During the growing-finishing period, 48% of pigs with docked tails and 89% of pigs with intact tails had skin lesions on their tails at some time point, with 5% of docked pigs and 30% of undocked pigs scoring 3 or greater. Tail docking did not affect weight gain or feed intake of pigs that survived to market. However, compared to pigs with docked tails, pigs with intact tails had higher morbidity. During the growing-finishing period, 5% of docked pigs and 21% of undocked pigs were removed for tail damage or tail biting. As a result, more pigs with docked tails (97% vs. 90%) were harvested without carcass trim loss at the packing plant than pigs with intact tails.
Objective 2: During the growing-finishing period, tail docking reduced tail biting behavior. Pigs with docked tails spent less time tail biting (0.08% vs. 0.33% of observation time; P = 0.01) compared to pigs with intact tails. Outbreaks of tail biting started in pigs with intact tails when they were 11 weeks of age, which was 6 weeks earlier than pigs with docked tails. Pigs with intact tails decreased time spent lying and increased time spent standing/walking 3 days before and during the first outbreak of tail biting, which may be used for prediction of tail biting outbreaks among these pigs. Compared to pigs with docked tails, pigs with intact tails had greater average optical flow, indicating higher activity levels. In addition, optical flow measures of pigs with intact tails changed according to outbreaks of tail biting. Average optical flow of intact pigs was increased during the 1st outbreak of tail biting compared to periods without outbreak. Results of the current study suggest that optical flow analysis might be a promising tool for monitoring activity levels of pigs and predicting outbreaks of tail biting among pigs with intact tails. Results from live observations indicate that tail biting events occurred most at the area near the pen perimeter (37% for docked pigs and 42% for undocked pigs), followed by the feeder area (37% for docked pigs and 26% for undocked pigs), and least at the drinker area (10% for both docked and undocked pigs). Previous studies have shown that tail biting may be alleviated by enriching the environment suggesting that a follow-up study should be conducted placing enrichment devices in locations where tail biting occurs most, such as near pen perimeters and feeders.
Objective 3: Victimized pigs gained less weight between 17 and 21 weeks of age during which tail biting prevailed in this study. More victimized pig carcasses (7% vs. 1%) were trimmed for abscesses or other imperfections at the packing plant, resulting in a lower dressing percentage (74.5% vs. 76.3%; P < 0.05) compared with carcasses from non-victimizedpigs. There was no difference in birth weight, weaning weight, market weight, or overall weight gain during the finishing period among tail biters, victimized pigs and non-victimized pigs. Compared to victimized pigs and non-victimized pigs, tail biters had lower total serum protein (P = 0.01) and Ig-G (P = 0.01) concentrations suggesting that tail biters may suffer from compromised immune functions. For victimized pigs, total serum protein and Ig-G concentrations were elevated 5 days after tail damage suggesting that bitten tails can cause inflammation which in turn may lead to carcass abscesses. No differences in Substance P concentrations were detected among victimized pigs, tail biters, and non-victimized pigs. It is not clear whether tail damage did not cause much pain in the current study or Substance P was not sensitive enough to detect pain in tail-bitten pigs.
Conclusions: Tail docking is an effective tool for preventing tail biting in pigs raised in confinement housing systems in the U.S. Without tail docking, pigs in our study experienced tail damage more frequently and more severely, resulting in increased morbidity rate. While tail damage did not affect overall weight gain or market weight of pigs that survived, pigs with tail damage were more likely subject to carcass trim loss and reduced dressing percentage compared to pigs without tail damage. Pigs with intact tails displayed more tail biting behavior than pigs with docked tails. Pigs with intact tails started outbreaks of tail biting at a younger age compared to pigs with docked tails. Pigs with intact tails increased their activity levels 3 days before and during the first outbreak of tail biting. Optical flow technology can detect activity levels of pigs, and might be a promising tool for prediction of outbreaks of tail biting in pigs with intact tails. Victimized pigs with damaged tails experienced inflammation which may lead to carcass abscesses and trim loss. Tail biters had lower Ig-G and serum protein concentrations, suggesting that they may suffer from compromised immune functions which in turn might predispose them to tail biting. Tail biting events occurred most frequently at areas of pen perimeters and near the feeder where enrichment devices to alleviate tail biting could be placed.
Key words: behavior, pain, performance, pigs, skin lesion, tail biting.
Contact details: Yuzhi Li,; office: 320-589-1711