Researchers at the University of Guelph, together with graduate student Kristi Bovey, are examining the behavioural and physiological effects of docked tail length and stocking density in the nursery barn. Tail docking is routinely performed in an effort to decrease tail biting behaviour. However, tail docking is not entirely effective in eliminating tail biting behaviour – studies show that up to two per cent of tail-docked pigs will show evidence of tail biting at market age. Tail biting is also associated with abscess and diseases such as vertebral osteomyelitis and arthritis, which decrease the value of the finished product.

The causes of tail biting are complex and multi-factorial. Factors include: gender, feed type (liquid or meal), bunk space, social factors, group size, stocking density, ventilation, lighting schedule and provision of environment without routing substrate or toys. Producer surveys have shown that tail length and stocking density are considered important factors in tail biting behaviour. Tail dock length may also play an important role in other production issues like rectal prolapses. Studies in lambs have shown that short tail docking results in the increased incidence of rectal prolapses due to the anal sphincter and perianal muscles.

The length of docked tails varies widely, as do the recommendations on how long a docked tail should be. UK authorities recommend leaving 2cm of tail after docking while the Canandian Code of Practice (1993) recommends removal of the last third of the tail.

Bovey et al. looked at tail-dock length in 1,022 pigs on commercial farms in Quebec from June through December in 2009. Each pig was assessed at two to three days of age and randomly assigned to two groups for tail length:

• Group 1 – long (4.5cm)
• Group 2 – short (1.2cm)

Both groups were then assigned to different stocking densities:

• Crowded – 0.15 square metres per pig
• Not crowded – 0.23 square metres per pig

Fifty-one pigs were removed from the trial for a variety of reasons. The remaining 960 pigs were randomly weighed and randomly assigned to identical nursery pens. The crowded pens contained 36 pigs and not-crowded pens held 24 pigs. Pigs were video taped to study their behaviour. Pigs were in the nursery pens for five weeks. At the end of the five weeks, pigs were weighed, scratch scored and the tail health assessed. The remaining pigs (880) were then assigned to an identical grower-finisher pen, with ten pigs to a pen. Pigs were weighed, scratch scored and tail health assessed every four weeks.

Results

Preliminary results show that tail-in-mouth and tail-biting behaviours were observed in the nursery, with over 50 per cent of the pigs having evidence of bitten tails when examined at eight weeks of age. By 12 weeks of age, 97.8 per cent of pigs had evidence of bitten tails. The greatest numbers of tail-bitten pigs in the nursery were seen in the crowded pigs, regardless of the length of the tail. However, pigs with long tails from either stocking density had the greatest degree of tail damage. Crowded pigs in the nursery also had the highest number of scratches.

Average daily gain (ADG) was highest in the not crowded pens, regardless of tail length. Short-tailed pigs in crowded pens had slightly higher losses at 2.70 per cent, while the highest mortality rate was recorded for long-tailed crowded pigs (3.47 per cent).

In the grower-finisher barn, average scratch scores were similar for the different groups. Long-tailed and crowded pigs had an increased rate of tail score when compared to the other groups. Five of the 44 pens of short tailed pens were classified as tail bitten (at least 10 per cent of pigs with a score of 2. Twenty-eight pens of long-tailed pigs were classified as tail bitten using the same definition.

Analyses of this research is ongoing. However, early results show that stocking density and tail length have some influence on tail biting.

April 2010