The frequency of tail damage amongst cows from a sample of New Zealand dairy farms participating in an animal welfare programme.

AIM

To explore factors associated with the frequency of tail damage in dairy cows on 29 New Zealand farms participating in an animal welfare monitoring programme.

MATERIALS AND METHODS

Herd-level tail score data were collected at the cow level and then summarised at the herd level as counts for each lactation over the period 1 June 2014 to 31 May 2018. A cow's tail was considered damaged if there was evidence of any injury that deformed the anatomical structure involving either bone or soft tissue and could include loss of use. There were four categories for tail scoring. Fracture or dislocation of tail bones was considered as a deviation (score 1). When the tail had been docked above the top of the cow's udder, this was considered as docked short tail (score 2). When there was evidence of soft tissue trauma (score 3) or bone damage but no fracture (score 4), this was recorded as damaged (other). Tails were scored for each whole dairy herd. Tail scoring was performed by trained veterinarians or veterinary technicians. The primary outcome variable was counts of deviated tails (DT). Other outcome variables were docked short, damaged (other), and total tail injuries (TTI) which was a summation of all tail injuries. The potential predictor variables were area, season, farm, region, replacement rate, and herd size. A mixed-effects negative binomial or Poisson regression was fitted to the count data.

RESULTS

A total of 29 farms contributed data for tail scoring, with 54,831 cows individually scored. The unadjusted regional prevalence of TTI ranged from 3.5% (64/1,835) in Taranaki in 2014-2015 to 28.7% (1,434/4,988) in Southland/Otago in 2017-2018. The unadjusted regional herd prevalence of DT ranged from 2.1% (280/6,862) in Taranaki (2014-2015) to 13.2% (4,627/30,165) in Southland/South Otago (2017-2018). The incident rate ratio (IRR) of DT in 2015-2016 was 1.74 (95% CI = 1.20-2.53; p = 0.003) times the incident rate for the reference group (2014-2015). The IRR for TTI in 2015-2016 was 1.70 (95% CI = 1.60-1.81; p = 0.001) times the incident rate for the reference group (2014-2015).

CONCLUSIONS AND CLINICAL RELEVANCE

This is the first quantitative study of the frequency of tail damage within New Zealand dairy farms and whilst variable between regions, it indicates that the frequency is increasing. Opportunities exist to better understand the causes of tail injuries and to improve animal welfare.