The Science of Tail Length in Sheep

As part of National Science Week, I thought I would re-look at the science that underpins the recommendations around docked tail length in Australian sheep.

Tail docking lambs is a long-standing practice used to reduce the life-long susceptibility of sheep to breech fly strike.

Six studies that investigated the most appropriate tail length for unmulesed Merino ewes were conducted in Australia during the 1930s and 1940s. These studies included more that 10,000 sheep on five properties in eastern Australia.

The studies demonstrated that docking long (at the fourth joint or to give a 9-10 cm long tail that extended just below the natural border of the bare area) gave better protection than docking short (tail tip not extending below the top of the vulva).

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Box and whiskers plot of fly strike rate and tail length

The strike rate in the three groups was statistically different F(2,32) = 4.54, p = 0.02.

The fly strike rate in the ewes docked long was 13 strikes per 100 sheep (95% confidence interval 6-20). In the sheep with short tails, the fly strike rate per 100 sheep was almost three times higher (38 strikes per 100 sheep, 95% confidence interval 21-55%). The difference was statistically significant (p = 0.015).

The fly strike rate of the ewes with medium length tails (5 cm long or tip opposite the vulva orifice) was in between that of the sheep docked long or short.

For those who prefer an odds ratio, the odds of a short-tailed ewe being struck compared to a long-tailed ewe ranged from 0.15 to 0.42. On average, the odds of a short tailed ewe being struck was three times that of a long tailed ewe being struck.

 
ewe_long_tail_tick.jpg

Long tail

  • Decreased risk of fly strike

  • Decreased risk of arthritis post-marking

  • Decreased risk of rectal prolapse especially if coughing from dust or pneumoniae

  • Decreased risk of skin cancer later in life

ewe_shor_tail_ticks.jpg

Short tail

  • Increased risk of fly strike

  • Increased risk of arthritis post-marking

  • Increased risk of rectal prolapse especially if coughing from dust or pneumoniae

  • Increased risk of skin cancer later in life

Joan Lloyd