Skip to main content
ARS Home » Midwest Area » West Lafayette, Indiana » Livestock Behavior Research » Research » Publications at this Location » Publication #311266

Title: Tear staining in pigs: a potential tool for welfare assessment on commercial farms

item TELKANRANTA, HELENA - University Of Helsinki
item Marchant, Jeremy
item VALROS, ANNA - University Of Helsinki

Submitted to: Animal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/11/2015
Publication Date: 8/26/2015
Citation: Telkanranta, H., Marchant Forde, J.N., Valros, A.E. 2015. Tear staining in pigs: a potential tool for welfare assessment on commercial farms. Animal. doi:10.1017/S175173111500172X.

Interpretive Summary: In stressful situations for rodents, it appears that the Harderian gland beside the eye is activated and a red-brown, iron-containing substance is secreted, resulting in a red-brown tear stain. We have noticed a similar staining pattern in pigs and have shown that the stain size is related to stressors such as isolation, aggression and lack of environmental enrichment. We have also shown a relationship with sympathetic nervous activity. Thus, tear staining may be a useful, non-invasive and relatively easy to measure indicator of a pig's welfare on farm. We measured the tear staining of pigs, using a simple 0-5 numerical, descriptive scale on three different farms and including a range of pigs of different ages. The pigs were part of another study investigating the use of various environmental enrichment objects on tail and ear biting. We found that tear-stain scores correlated with tail- and ear-damage scores, so that those pigs with larger amounts of damage also had larger tear stain scores. We also found that pigs with lots of enrichment had lower tear stain scores and that pigs with higher tear stain scores were slower to approach novel objects. These results confirm that tear staining does appear to be related to the amount of stress, from a variety of sources, that the pig is encountering, and that tear staining has promising potential as a low-cost, easy-to-use welfare indicator for the assessment of pigs on commercial farms.

Technical Abstract: Tear staining or chromodacryorrhea refers to a dark stain below the inner corner of the eye, caused by porphyrin-pigmented secretion from the Harderian gland. It been shown to be a consistent indicator of stress in rats, and recently it has been shown to correlate with social stress and a barren environment in pigs. The current study was to our knowledge the first to test it on commercial pig farms as a potential welfare indicator. The study was carried out on three commercial farms in Finland, in connection to a larger study on the effects of different types of manipulable objects on tail and ear biting and other behavioural parameters. Farm A was a fattening farm, on which 780 pigs were studied in 73 pens; Farm B had a fattening unit, in which 656 pigs were studied in 44 pens, and a farrowing unit, in which 29 sows and their litters totalling 303 piglets were studied. On Farm C, 167 breeder gilts were studied in 24 pens. Data collection included individual-level scoring of tear staining and, for the fattening pigs and breeder gilts, tail and ear damage; behavioural observations on video recordings of Farms A and C to quantify the frequency of object exploration and pre-rest behaviours; and a novel object test for the piglets and a novel person test for the fattening pigs on Farm B and the breeder gilts on Farm C. On Farm A, tear staining were found to correlate with tail damage scores (n = 780, rs = 0.14, P < 0.001) and ear damage scores (n = 780, rs = 0.16, P < 0.001). On Farm B, tear staining of the left eye correlated with tail damage (n = 656, rs = 0.12, P < 0.01) and that of the right eye correlated with ear damage (n = 656, rs = 0.10, P < 0.01). On Farm A, tear-staining scores were lower in the treatment with three object types as compared to controls (mean scores 3.3 and 3.9 respectively, n = 31, F29 = 4.2, P < 0.05). In the suckling piglets on Farm B, tear staining correlated with the latency to approach a novel object (n = 29, rp = 0.41, P < 0.05). It was concluded that as tear staining has promising potential as a low-cost, easy-to-use welfare indicator for commercial pig farming. Further research is needed on the mechanisms of tear staining.