Influence of magnesium on the behavioural disorder tail biting in pigs

Tail biting is a hazardous behavioural disorder occurring worldwide in pig industry. It is a sign of suffering of the animals and also leads to pain, damage and suffering as well as economic losses. Despite intensive research, the pathogenesis is still not understood, which makes secure prevention and intervention up to date impossible. Therefore, up to date, despite being forbidden by European law, most farmers need to perform tail docking with an exemption allowance, as otherwise tail biting will occur. However, this practice is widely criticized and has led to political penalties which puts a lot of pressure on pig farmers.

Therefore, understanding the causes of and preventing tail biting is of utmost importance. A recent study (Czycholl et al. 2023), focusing on the health status of tail biters, found 97% of the pigs to have a magnesium content in the blood below reference values. This is surprising, as magnesium should be sufficiently available in the basic feed. All pigs in that study were fed according to common guidelines and the participating farms achieved a high productivity. Magnesium is in general said to have a calming effect across species. For this reason, many advisory services also promote magnesium supplementation to prevent or cure tail biting. However, scientific evidence for this is lacking. A recent literature review (Bushby et al. 2021) summed up 16 studies on the effects of magnesium supplementation on the reduction of stress in pigs. Most studies were carried out on finishing pigs and evaluated the effectiveness of magnesium supplementation on transport stress and stress at the slaughterhouse.

However, tail biting (in undocked pigs) most often occurs in the rearing phase. Moreover, there is large incongruence on type, dosage, length and age class of supplementation. Thus, studies are needed to validate the effectiveness of magnesium supplementation and especially, more information is needed for farmers to implement it. Given the fact that in theory, magnesium supplementation in pig feed should not be necessary, the question arises whether a secondary deficit could play a substantial role in becoming a tail biter, i.e. in developing the behavioural disorder. Therefore, this study is designed as a controlled feeding trial under practical farm conditions in the rearing phase of pigs. Magnesium aspartate will be used, as Bushby et al. (2021) identified that supplement to have congruently positive effects on stress. However, there was no congruency on dosage, which is the reason why altogether five feeding groups with different dosages will be formed. The effectiveness of the magnesium supplementation in the different dosages will be analysed via regular blood checks. Moreover, the stress level of the pigs will be analysed by analyzing the cortisol content. Pigs will moreover be regularly evaluated for tail, ear and skin lesions.

The study is designed as controlled feeding trial under practical farm conditions. The experiment is carried out at a pig farm in Northern Germany, close to the border of Denmark. The farm works in a closed system DanBred genetics and has been involved in studies about management interactions for the prevention of tail biting with Kiel University since 2012. The farmer does not dock the tails of the pigs anymore. Male pigs are castrated under anesthesia in accordance with the German law. Of this farm, in the rearing barn, two compartments with five pens of 24 piglets each will be the experimental unit for two follow-up batches.

Each pen will be assigned randomly to: control (without magnesium supplementation), 5, 40, 1000 and 2000mg/kg feed magnesium aspartate supplementation. Altogether, in this way, in each group 96 pigs will be represented, totaling to 480 pigs in the trial. All pigs are individually tagged by eartags (for other purposes in relation to management) and will be individually marked with marking spray throughout the trial. Video observation of all pens over the whole rearing periods will be installed. Blood samples will be drawn directly after entering the rearing stable, in the middle (after three weeks into the trial) and at the end of the rearing period. These blood samples will be used on the one hand for analysing the magnesium content and on the other hand for analysing the cortisol content as stress marker. These analyses will be carried out at the University of Copenhagen, Department of Veterinary Clinical Sciences.

When the blood samples are drawn, the piglets will also be weighed individually. Every week, a trained observer will score each pig individually for tail, ear and skin lesions. If in one of the groups a tail biting outbreak occurs (> two tails with small or large injuries) and/or a specific pig has a conspicuously lower magnesium content in the blood than the average of its feeding group (a negative deviation of double standard deviation), retrospectively, the video material will be analysed with regard to received and performed tail in mouth behaviour in accordance to the ethogram used in Czycholl et al. 2023 for identification of tail biters.

Statistical analysis will be performed based on linear mixed models to allow a conclusion about the groups (different dosages) effects. Separate models will be created for the different parameters (magnesium content, in the blood, cortisol content in the blood (difference from basal cortisol to measurement value), tail lesion, ear lesions, skin lesions). If “biters” are identified, this will be added as effect. 

The project can be separated into four work packages, whereby each achievement of a work package poses a milestone to control that the goals of the project are actually reached.

The project period is planned for six months, starting in January 2024. The first month is allocated to arrangement of the practical settings (identification of participating piglets, planning of random group allocation, installation and technique checks of video observation) on the farm. The practical experiment will last for two consecutive rearing periods, i.e. two months. The last two months are reserved for statistical analysis and writing of a scientific publication.

Work package 1: Practical data collection

Work package 1 comprises the practical data collection on-farm with twice weekly monitoring of the pigs for tail, ear, skin lesions, individual weighing and the drawing of blood samples. Tail, ear and skin lesions are monitored according to standard validated protocols (Welfare Quality, German tail and ear assessment index). Directly after blood samples are drawn, these are cooled to 10°C and on the same day centrifuged and thereafter frozen at -21°C. Directly after the end of the practical data collection in the barn, these frozen blood samples are transferred to the Department of Veterinary Clinical Sciences where they are analysed for magnesium and cortisol content using the standard in house protocols. The end of the practical data collection including the laboratory work comprises the achievement of milestone 1 of the project, as therewith, all necessary data to answer the research questions has been collected.

Work package 2: Video observation

Work package 2 comprises the video observation. If at some point, a tail biting outbreak is identified, retrospectively, the time period from the last observation (without severe tail lesions) until the scoring of a potential tail biting outbreak is analysed in accordance to the ethogram described in Czycholl et al. (2023). However, as direct observation is not possible, randomly a half hour slot in the morning and afternoon activity period of the pigs is chosen to count the occurrences of tail-in-mouth behaviours and to identify potential tail biters. Moreover, retrospective video analysis will be carried out if in the blood work, animals with a particularly low magnesium content are discovered. In this case, three random days in the time period before the suspicious blood test are chosen and analysed in the 30 min frames in the activity phases of the animals and the tail in mouth behaviour of these animals will be compared to that of inconspicuous animals. The time frame work package 2 will take is impossible to plan beforehand, as it largely depends on the unforeseeable behaviour of the animals in the trial. Therefore, all video analysis will be carried out by student workers, the costs will be covered by the Department of the project leader (Department of Animal Welfare and Disease Control). If tail biting outbreaks are identified while the practical data collection is still running, the student workers will start with the respective data analysis right while the practical data collection is still running. Else, they will start as soon as the results from the blood work are retrieved. If no tail biting outbreak is identified, the video analysis will be skipped as no biters can then be identified. However, the research questions of the project can still be answered, only the effect of being a biter or not can not be included in the models. The completion of all necessary video observation poses the achievement of milestone 2.

Work package 3: Statistical analysis

Inferential statistical analysis will be carried out by linear mixed modelling using SAS, whereby separate models will be established for the different variables collected (tail, ear, skin lesions, magnesium level, cortisol, daily weight gain). The feeding groups and batch will be fixed effects, the individual pig a random effect. Further effects to be included (e.g. biting behaviour) will be considered in dependence on the outcomes of work packages 1 and 2. Models will be built stepwise, interactions will be tested and as quality of the model and goodness of fit will thereby be evaluated by Akaikes and Bayesian Information Criterions. Connections between the different variables collected will further be analysed by correlarion coefficients (coefficient dependent on the data distribution achieved) and potentially by regression analysis. The decision for the final models on which data will then finally be evaluated equals the achievement of milestone 3.

Work package 4: Dissemination of research results

The final work package builds on the former work packages. The main aim of the work package is the scientific publication that will be written, summing up and presenting the achieved results. This publication will be submitted to a scientific journal (most likely Porcine Health Management). However, in the bounds of this work package, the results will further be presented orally at least at one national and one international conference as well as one event specifically for farmers. Moreover, information about the results will be made available online – depending on the results in the form of concrete advise material. The described deliverables together are the final milestone 4 of the project.

Irena Czycholl: Irena has started in 2022 as Associate Professor for Animal Welfare and Behaviour at the University of Copenhagen. She is an educated veterinarian and has obtained her PhD about welfare assessment in pigs in 2015 at the University of Veterinary Medicine Hannover, Germany. Thereafter, she has worked as Postdoc at Kiel University (farm animal science) and focused on all relevant challenges in pig husbandry (e.g. group housing of sows, free farrowing, ban of castration without anesthetics, ban of tail docking, farm self-assessment etc.). From 2021-2022 she has worked for PIC as senior researcher for animal welfare and behaviour and supported the company in these areas. She recently published a study about the influence of the health status on tail biting in pigs, on which results will be built in the current proposal.

Peter Sandøe: Peter is Professor of Bioethics at the University of Copenhagen. He studied philosophy and also obtained his PhD in this field at Oxford University in 1988. Since 1990 a major part of his research has been within bioethics with particular emphasis on ethical issues related to animals, biotechnology, food production, and research practice. He has largely commited to interdisciplinary work combining perspectives from natural science, social science and philosophy. For the last 20 years he has collaborated with sociologists to study ethical issues and animal welfare challenges from an empirical perspective, originally mostly through qualitative studies, recently through mixed methods and surveys.

The results from this project will be made publicly available ultimo 2024 and remain online for at least five years.

With this project, we will be able to answer the following for research questions:

1. Does a feed supplementation with magnesium aspartate over the rearing period raise magnesium concentration in the blood? Does this magnesium supplementation
2. have stress reducing effects?
3. have an effect on tail and ear biting as well as social aggression and
4. on the performance?

This will answer the question, whether magnesium does play a role in the pathogenesis of the behavioural disorder tail biting in pigs. If magnesium does play a role in the development of tail biting, this project will yiel concrete advice to farmers. If magnesium is shown to not play a substantial role, this knowledge is equally important for the farmers, as then they have not to try it out (following e.g. anecdotal reports). In general, this study helps in understanding and therewith in the long term preventing the occurrence of tail biting which is of utmost importance for pig industry given especially the political ban of tail docking in Europe. The results of the project will result in a scientific publication and advisory material made available for farmers.

Results will be processed in a scientific publication (most likely to be handed in to the journal Porcine Health Management). Moreover, the results will be presented at the annual conference of the European Association for Animal Production/European Federation of Animal Sciences (EAAP), one of the largest European conferences in animal production with also a large outreach to industrial research and farmers. Moreover, results will be disseminated by a presentation at the annual Copenhagen Pig Seminar as well as via newsletters of the Center for Research in Pig Production and Health (CPH Health). If supplementation with magnesium aspartate is proven to be effective, concrete advises will be prepared for farmers which will be made available online at the CPH Pig homepage. Through the network of the project leader, results will further be disseminated to the German pig industry. Therewith, it can well be expected that this project will also build a bridge for closer cooperation of German and Danish pig industry (also via the involvement of funding of personal costs of a German postdoc via the German Academic Exchange Service).

This study contributes to the understanding of the pathogenesis of the behavioural disorder tail biting in pigs. The results are of interest to researchers trying to understand the phenomenon but especially also the farmers who are in need of effective prevention and intervention strategies, especially given the political ban of tail docking in Europe.

Moreover, Germany as important trading partner for the Danish pig industry is working intensely on a national total ban also of exemptions to tail docking which might become important for Danish farmers as German farmers will have to ask for pigs with long tails. If tail biting is better understood, it can possibly be prevented and therewith, also mortality of pigs will be reduced as well as the necessity for antibiotic treatment. Hence, this study contributes on the most to the aim of improvement of animal health and welfare, however, it also touches on improvement of sustainability, increasing of productivity and competitiveness as well as securing market access in the future.

Contribution to understanding (and preventing) the behavioural disorder tail biting in pigs with a direct potential for feasible practical implementation will help Danish farmers and Danish pig industry. This project moreover supports cooperation with German pig research as a German postdoc, supported by the German Academic Research Service, will be involved which offers the possibility to a large outreach of the project results also to the German pig research but, maybe even more importantly, to German pig industry and farmers.

The project team is comprised of an international project team and will be supported in this project by SEGES and will thus strengthen the Danish pig research network and likewise the Danish pig industry’s contacts, especially to the important trade partner Germany. Thus, this project builds on the Danish model of finding solutions by international and interdisciplinary cooperation.

Bushby, E.V., Dye, L. and Collins, L.M., (2021). Is magnesium supplementation an effective nutritional method to reduce stress in domestic pigs? A systematic review. Frontiers in Veterinary Science, 7, p.596205.

Czycholl, I., Büttner, K., Becker, D., Schwennen, C., Baumgärtner, W., Otten, W., Wendt, M., Puff, C. and Krieter, J. (2023). Are biters sick? Health status of tail biters in comparison to control pigs. Porcine Health Management, 9(1), pp.1-18.