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

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 has been shown to be a consistent indicator of stress in rats and 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 768 growing-finishing pigs were studied in 73 pens. Farm B had a fattening unit, in which 656 growing-finishing pigs were studied in 44 pens, and a farrowing unit, in which 29 sows and their litters totalling 303 piglets were studied in 29 pens. Farm C was a piglet-producing farm, on which 167 breeder gilts were studied in 24 pens. Data collection included individual-level scoring of tear staining; scoring of tail and ear damage in the growing-finishing pigs and breeder gilts; a novel object test for the piglets; and a novel person test for the growing-finishing pigs on Farm B and the breeder gilts on Farm C. On Farm A, tear staining was found to correlate with tail damage scores (n=768, rs=0.14, P<0.001) and ear damage scores (n=768, rs=0.16, P<0.001). In the growing-finishing pigs 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 sores were lower in the treatment with three different types of manipulable objects as compared with 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). Although correlations with tail and ear damage were low, it was concluded that tear staining has promising potential as a new, additional welfare indicator for commercial pig farming. Further research is needed on the mechanisms of tear staining.

Operationalizing Principle-Based Standards for Animal Welfare—Indicators for Climate Problems in Pig Houses

“…Ammonia is a gas that irritates the eyes and is present in high concentrations in pens with high pen fouling scores. These findings reconfirm that eye score is a good animal-based indicator, as described by Telkänranta et al [16]. …”

Evidence of Pain, Stress, and Fear of Humans During Tail Docking and the Next Four Weeks in Piglets (Sus scrofa domesticus)

“…We did not find any effect of docking on tear staining. Tear staining (or chromodacryorrhea) seems to be a promising tool to evaluate welfare of pigs at commercial large-scale level (15) or after strong stress [isolation: (36)]. In rats, the level of chromodacryorrhea is dependent on the level of stress, as there is more secretion after high stress (maintenance work taking several hours and involving several potential stressors such as transfer of cages into a different room, noise of power tools, a brief use of an electric drill within the unit) than after mild or low stress (e.g., visits by unfamiliar humans or fighting within a cage or having a dominated social status) (37).…”

Ocular Surface Disease in Rodents (Guinea Pigs, Mice, Rats, Chinchillas)

“…31 By a similar mechanism, the presence of chromodacryorrhea was even identified as a welfare indicator on commercial pig farms. 32 This finding may gain more attention in the laboratory animal sphere, where welfare is paramount. The presence of chromodacryorrhea should not be ignored, as it is not a normal finding.…”