Over time, as we have selected for more fleece on a sheep, we have ended up with sheep that also have woollier tails. More wool on the tail (and around the breech) can lead to more of an accumulation of faecal matter (dags) and animals being more adversely affected by flystrike. This isn’t to say that animals with a shorter tail are necessarily flystrike-free, but they do have a lower chance of being affected. 

As the strong-wool market declines, we are seeing more farmers heading down the shedding and hair-type sheep routes. The hairy coat type found around the breech of barer-breech animals is difficult for faecal matter to stick to, reducing the ability to form dags. Even those that are keeping with strong wool are getting barer animals in their flock. The traditional Romney with ‘wool between the toes’ is a thing of the past, with plenty of more open-faced sheep in the industry. 

There are high correlations between bareness traits, with estimates being 70% phenotypically and 83% genetically for breech and belly scores. The correlations between breech cover and dag score are 14% phenotypically and 33% genetically, which are moderate (note that dag score is scored in the opposite direction to bareness, and these correlations are negative (Johnson et al. 2023)). 

By selecting for bareness of the breech and lower dag together, we will be able to produce sheep that are less prone to flystrike and less likely to need docking. If we can breed for shorter tails as well, there is potential to reduce the need for tail docking further.

The long and short of it

The majority of sheep found in New Zealand belong to the ‘long-tailed’ and ‘thin-tailed’ breeds (e.g. Romney, Merino and Down breeds), or their derivatives, while others belong to the ‘short-tailed’ breeds (e.g. Finnish Landrace and Gotland Pelt) and their derivatives. Texel and East Friesian sheep can be included in the ‘short-tailed’ sheep category. There are very few ‘fat-tailed’ sheep in New Zealand. Johnson et al. (2023) found that the heritability of tail length in New Zealand sheep is relatively high (68%), indicating that genetic progress can be made quite quickly in this trait. 

Tail length (actual length or visual score) and the length of bare skin under the tail (length only) can be recorded. In SIL, these data contribute to the Dual Purpose Bare Points index, in conjunction with dag score, bare breech score, bare belly score and weaning weight (with tail measures collected at docking, and bareness traits collected at or just after weaning). 

Heritabilities of bareness, dag and tail length

There is an indication that bareness scores have heritabilities in the 50-60% range, depending on the trait, and dag has a heritability of 33% (Johnson et al. 2023). Hodge et al. (2025) found that the heritability of objectively measured tail length (i.e. measured in centimetres) was 37% and was higher than a subjective tail length score (i.e. using a scale of 1-5) at 14%. 

While that difference in accuracy was significant, the authors concluded that assessing tail length subjectively with a visual score could lead to greater uptake in tail length recording in industry flocks, while more accurate objective measurement (i.e. measuring actual length) could be prioritised in resource flocks. 

Selecting for a combination of a shorter tail, less wool around the breech, and a lower dag score has the potential for a much lower maintenance sheep. However, at present, there is no tail length breeding value available through either SIL or Sheep Genetics. With more measurements being recorded and increased demand for an industry breeding value, it’s a case of watch this space. For interested breeders, our new neXtBV tool can generate within-flock breeding values for tail length in-house if desired. 

Taking advantage of variation to make genetic gain

Within the New Zealand sheep flock, there is a large amount of variation in breed composition, including those with short-tailed breed types, leading to plenty of variation in tail lengths. As we know, all you need to make genetic progress is variation and heritability, which are both abundant for this trait in the New Zealand sheep population. 

Therefore, measuring and genetically selecting for sheep with shorter tails will lead to reduced tail length across your flock. For those interested in labour-saving and welfare traits, incorporating genetics for bareness and lower dag into the breeding objective, along with reduced tail length, will accelerate your progress down the path towards a sheep that no longer needs docking.

References and further reading

Hodge, M.J., D.J. Brown and S.F. Walkom. 2025. ‘Genetic evaluation of tail length in Australian sheep’. Proceedings of the Association for the Advancement of Animal Breeding and Genetics 26: 407-410. https://www.aaabg.org/aaabghome/AAABG26papers/B%2051%20-%20Hodge%20250418%20Final.pdf.

Johnson, P.L., D.R. Scobie, K.G. Dodds, S-J.H. Powdrell, S.J. Rowe, and K.M. McRae. 2023. ‘Genetic parameter analysis of bareness of tail traits in New Zealand sheep’. Journal of Animal Science 101: 1-10. https://doi.org/10.1093/jas/skad161.

neXtgen Agri International Limited. 2025. ‘neXtBV: Designer breeding values’. neXtgen Agri Hub.  https://thehub.nextgenagri.com/c/nextsuite/designer-breeding-values.

neXtgen Agri International Limited. 2025. Visual appraisal guide. 28-29. https://www.nextgenagri.com/resources.

Scobie, D.R. and D. O’Connell. 2002. ‘Genetic reduction of tail length in New Zealand sheep’. Proceedings of the New Zealand Society of Animal Production 62: 195-198 https://www.nzsap.org/ym/ab02050.pdf.

In short: genetics of tail length in sheep

• Heritability: Research indicates that tail length is a highly heritable trait (up to 68% in New Zealand sheep), enabling breeders to achieve rapid genetic progress through targeted selection.
• Measurement methods: While objective measurement (in centimetres) yields higher accuracy, subjective visual scoring is a practical starting point for collecting tail length data in commercial flocks.
• Genetic variation: Within New Zealand and Australia, there is sufficient variation in the current sheep population for breeders to make effective genetic gain in tail length.‍
• Breeding values: Although industry evaluations for tail length are still evolving in both Australia and New Zealand, interested producers can use neXtgen Agri’s neXtBV tool to generate within-flock breeding values for tail length.

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Join the discussion

Head to the neXtgen Agri Hub to share your thoughts and questions about the genetics of tail length, breech cover and dag: https://thehub.nextgenagri.com/c/articles/the-genetics-of-tail-length-in-sheep.