The use of tear-staining as a non-invasive welfare indicator in pigs
During part of her MS research, Shelly DeBoer noticed that pigs housed with a lack of environmental control appeared to develop more red-brown facial staining around the eyes than pigs with more control. There is a small body of scientific literature on tear staining in rodents (chromodacryorrhoea – or ‘bloody tears’) and that this is as a result of Harderian glands secreting the iron-containing compound porphyrin, especially under conditions of stress. As a result of the observation, we have carried out a number of studies scoring tear staining in pigs, using both a 0-5 scoring scale and also taking photographs and measuring the area and circumference of the stain, and investigating whether they relate to other measures of stress.
So far, our studies have shown that tear staining increases in response to social isolation, increases with increasing sympathetic nervous activation and is greater in piglets with low social status.
Work in this area remains ongoing. Our methodology is also being tested by colleagues at the University of Helsinki, Finland, the University of Newcastle, UK, INRA, France and Charles Sturt University, Australia.
Some of these initial results are available here:
DeBoer, S.P.*, Garner, J.P., McCain, R.R., Lay Jr., D.C., Eicher, S.D., and Marchant-Forde, J.N.* (2015) An initial investigation into the effects of social isolation and enrichment on the welfare of laboratory pigs housed in the PigTurn System assessed using tear staining, behaviour, physiology and haematology. Animal Welfare 24:15-27. doi:10.7120/096277286.24.1.015
Telkanranta, H.*, Marchant-Forde, J.N. and Valros, A.E.* Tear staining in pigs: a potential tool for welfare assessment on commercial farms. Animal. doi:10.1017/S175173111500172X
Marchant-Forde, A.E.M. and Marchant-Forde, J.N. (2014) Social status and tear staining in nursery pigs. In. (Eds. X. Manteca, I. Estevez, R.H. Marin & X. Averos) Proceedings of 48th Congress of the International Society for Applied Ethology. Wageningen Academic Press, Wageningen, The Netherlands. P145T