Tear staining (TS) in the pig has been related to different stressors and may be a useful tool for assessing animal welfare on farm. The aim of the current study was to investigate TS across the finisher period and its possible relation to age, growth, sex and experimentally induced stressors. The study included 80 finisher pens divided between three batches. Within each batch, the pens either included pigs with docked or undocked tails, had straw provided (150 g/pig/day) or not and had a low (1.21 m2/pig, 11 pigs) or high stocking density (0.73 m2/pig, 18 pigs). Tear staining (scores 1 to 4; from smaller to larger tear stain area, respectively) and tail damage were scored on each individual pig three times per week over the 9-week study period, and the individual maximum TS score within each week was chosen for further analysis. Data were analysed using logistic regression separately for each of the four possible TS score levels. The TS scores 1 and 2 decreased with weeks into the study period and were negatively related to the average daily gain (ADG) of the pigs, whereas the TS score 4 increased with weeks into the study period and was positively related to ADG. None of the TS scores differed between females and castrated males, and neither straw provision nor lowering the stocking density affected the TS scores. However, the TS score 1 decreased the last week before an event of tail damage (at least one pig in the pen with a bleeding tail wound), whereas the TS score 4 increased. The results of the current study advocates for a relation between TS and the factors such as age, growth and stress in the pig, while no relation was found between TS and the environmental factors straw provision and lowered stocking density. The relations to age and growth are important to take into consideration if using TS as a welfare assessment measure in the pig in the future.
Keywords: animal welfare; development; slaughter pigs; stress; tail damage.