A comparison of inflammation models in weaner pigs

Inflammation models are used to compare the effectiveness of anti-inflammatory agents. Subcutaneous injections of turpentine have been used in the past to cause an acute phase response in pigs (Lampreave et al. 1994; Eckersall et al. 1996). It has been suggested that some vaccines may be used as models for inflammation due to the sickness-like behaviour they elicit (Fangman et al. 2011), but there have been no controlled studies to investigate this claim. In this study it was hypothesised that the administration of Improvac^® and Neovac^® would provide an inflammation response similar to the administration of turpentine.

This trial involved 24, 7-week-old male Landrace x Large White weaner pigs (n = 6/treatment). Pigs were housed in pens of four (one per treatment group). Inflammation was induced by a single subcutaneous injection behind the right ear with one of the following: physiological saline (2 mL, 0.9%), Improvac^® (2 mL; Zoetis, Sandton, South Africa), Neovac^® (2 mL; Zoetis, Rhodes, NSW, Australia), or pure turpentine (0.2 mL/kg) on d 1. Inflammation was assessed by measuring haptoglobin and C-reactive protein (CRP) concentrations in blood collected on d 0, 2 and 4 after injection using Tridelta^® Phase™ Range assays. Infrared eye temperatures (IET) were collected from images taken daily (d 0 – d 4) 45 cm from the left eye and eye temperature determined by dot point analysis. Tear staining areas were measured from photographs taken daily of the left eye and analysed using the freeware Image-J software (NIH; Rockville, MD, USA). Haptoglobin, CRP and IET data were analysed using a linear mixed model (LMM) (Genstat, 17^th Edition; UK). Tear staining data were log transformed and analysed using LMM.

The administration of turpentine, Improvac^® and Neovac^® resulted in increases in haptoglobin (P < 0.001) and CRP concentrations (P < 0.001) relative to saline controls. Turpentine-treated weaner pigs had higher eye temperatures compared to all other treatment groups (P < 0.05). Pigs administered Neovac^® had lower amounts of tear staining than pigs administered Improvac^® or turpentine (P < 0.05) (Table 1).

Table 1.  Haptoglobin and CRP concentrations, IET and tear staining area after a subcutaneous injection of either saline, Improvac^®, Neovac^® or turpentine. Values are mean ± SE

The increases in haptoglobin and CRP concentrations indicated that the subcutaneous administration of Improvac^®, Neovac^® and turpentine caused an inflammatory response in weaner pigs. Pigs administered turpentine showed a severe behavioural pain response (data not shown), and so this is not recommended for future work. Pigs treated with Improvac^® showed an acute phase response similar to turpentine, without the associated pain, which indicates that this model may be suitable for testing the efficacy of analgesic/anti-inflammatory drugs.