The prevalence of damaged tails in New Zealand dairy cattle

Figures & data

Table 1. The number of enrolled farms and cows that were tail scored across nine regions of New Zealand to investigate the prevalence of tail damage on dairy farms.

Region	Number of farms scored	Number of cows scored (% of total animals)	Median herd size (IQR)
Bay of Plenty	20	8,553 (9.3)	420 (279–534)
Canterbury	25	17,750 (19)	650 (520–816)
Manawatū	20	6,507 (7.0)	291 (214–365)
Northland	20	7,050 (7.6)	284 (254–419)
Otago	20	12,092 (13)	570 (515–708)
Southland	25	15,673 (17)	599 (479–716)
Taranaki	25	5,865 (6.4)	236 (184–283)
Waikato	25	9,670 (10)	349 (210–525)
West Coast	20	9,188 (9.9)	429 (252–647)
Total	200	92,348	418 (248–608)

Table 2. Median, IQR and range of the prevalence of tail damage^a from 92,348 cows across 200 farms from nine regions in New Zealand.

Type of tail damage^b	Overall	Bay of Plenty	Canterbury	Manawatū	Northland	Otago	Southland	Taranaki	Waikato	West Coast
Deviated
Median	9.5	9.2	11.7	10.1	10.2	6.2	9.5	7.1	13.2	6.2
IQR	6.3–13.5	8.1–13.8	8.9–13.5	7.4–16.5	6.7–13.9	4.3–8.6	7.4–12.5	5.4–10.2	11.8–16.7	4.4–9.2
Range	0.9–40.3	2.0–20.0	5.3–20.0	1.9–30.1	0.9–22.9	2.3–14.7	4.7–26.4	2.8–20.0	6.1–40.3	0.9–22.8
Trauma
Median	0.9	0.4	0.7	0.4	0.0	4.4	4.9	0.9	0.9	0.6
IQR	0.3–2.8	0.0–0.5	0.4–1.4	0.3–1.0	0.0–0.1	2.6–6.7	3.3–5.2	0.3–2.8	0.7–1.1	0.1–1.1
Range	0.0–10.7	0.0–5.4	0.0–3.1	0.0–4.9	0.0–1.0	1.5–10.7	2.6–10.0	0.0–5.9	0.0–2.4	0.0–3.0
Shortened
Median	4.5	6.3	6.1	4.1	0.2	8.0	14.2	5.0	3.2	0.5
IQR	1.3–10.8	3.4–11.5	2.5–8.4)	2.7–12.3	0.0–0.6	5.1–25.1	5.2–25.7	1.3–20.7	2.7–7.4	0.3–1.5
Range	0.0–70.4	1.3–49.3	0.4–32.7	0.0–69.1	0.0–3.3	1.1–56.7	1.2–59.1	0.0–45.9	0.5–57.2	0.0–70.4
Any damage
Median	17.0	16.8	16.5	17.6	10.7	21.6	29.1	15.7	19.0	7.4
IQR	12.7–24.6	14.0–23.3	13.5–22.2	13.7–27.4	6.7–14.1	14.9–32.8	19.5–38.8	12.0–28.1	15.9–23.5	6.1–16.5
Range	1.7–73.7	3.3–54.2	10.0–35.2	6.3–70.1	1.7–22.9	9.9–63.4	12.8–65.4	6.0–57.3	9.4–62.0	3.1–73.7
Deviated + trauma
Median	11.5	11.5	11.8	11.1	10.4	10.6	13.3	10.8	13.9	6.8
IQR	7.8–15.0	8.9–14.6	9.6–13.9	8.8–16.6	6.7–13.9	8.0–14.3	11.7–17.2	6.3–12.1	12.7–18.6	4.9–10.0
Range	0.9–40.7	2.0–20.0	5.3–21.7	2.3–31.9	0.9–22.9	4.9–19.7	7.8–29.6	3.5–20.4	6.7–40.7	2.8–23.9

^a Defined using a modified version of the New Zealand Veterinary Association Industry Scoring System (Anonymous 2021a)

^b Lesions were recorded as deviated (i.e., non-linear deformity), shortened (tail appearing shorter than normal) or trauma (all other lesions). All lesions on a tail were recorded so a cow could have more than one lesion type and location, and/or multiple lesions of the same type

Figure 1. Boxplots summarising tail scoring data using a modified version of the New Zealand Veterinary Association Industry Scoring System (Anonymous 2021a) from 92,348 cows on 200 farms across 9 regions of New Zealand for the prevalence of deviated tail damage (non-linear deformity: top facet) and traumatic tail damage (all damage except deviation and shortening: bottom facet) by region and split by location of damage on the tail (Upper (blue/dark grey), middle (yellow/white) or lower (red/light grey) third of the tail). All lesions on a tail were recorded so a cow could have more than one lesion type and location, and/or multiple lesions of the same type. Each box represents the 25^th and 75^th percentile with the median marked by a horizontal line. Each whisker extends to 1.5 times the IQR and outliers outside this point are marked by solid grey dots. To view the figure in colour please see the online version.

Table 3. The proportion of cows (n = 92,348) from 200 farms across nine regions in New Zealand with deviated (non-linear deformity), tail shortening^a, or traumatic (all other lesions) tail damage^b for the lower, middle and upper third of the tail. The percentage of each lesion type at each position is shown in parentheses.

Position on tail	Proportion of animal (% of lesion)
	Deviated	Trauma	Shortened
Upper	0.001 (7)	0.0016 (9)	0.001 (1)
Middle	0.07 (66)	0.009 (51)	0.017 (17)
Lower	0.03 (31)	0.007 (41)	0.082 (82)

^a Shortened tails appeared shorter than normal and were classified according to the zone within which shortening had occurred.

^b Scored using a modified version of the New Zealand Veterinary Association Industry Scoring System (Anonymous 2021a). All lesions on a tail were recorded so a cow could have more than one lesion type and location, and/or multiple lesions of the same type.

Table 4. The required number of animals to sample to achieve the stated level of precision^a.

Number sampled	Precision (%)
40	10.0
44	9.5
49	9.0
55	8.5
62	8.0
70	7.5
80	7.0
93	6.5
109	6.0
130	5.5
157	5.0
194	4.5
245	4.0
320	3.5
435	3.0

^a Based on Wald confidence limits with 95% confidence; (Vallejo et al. 2013) for estimating the prevalence of herd level tail damage when the median prevalence of damage = 11.5%, α = 0.05, and the population is assumed to be infinite.

Table 5. Bootstrap sampling distribution for different sampling scenarios (front of herd, back of herd and randomly throughout the herd) compared to the herd-level prevalence of tail damage estimated from 92,348 cows across 200 farms and 9 regions of New Zealand.

Number sampled	Sampling scenario	2.5th percentile (%)^a	50th percentile (%)^b	97.5th percentile (%)^c	95% width^d
40
	Random sample of herd	−9.00	−0.26	10.89	19.89
	Sample front of herd	−10.81	0.30	19.88	30.69
	Sample last of herd	−11.49	−0.98	18.99	30.48
70
	Random sample of herd	−7.19	−0.24	8.01	15.20
	Sample front of herd	−9.34	0.42	14.40	23.74
	Sample last of herd	−9.80	0.00	13.65	23.45
157
	Random sample of herd	−4.96	−0.07	5.24	10.20
	Sample front of herd	−6.54	−0.30	9.40	15.94
	Sample last of herd	−6.52	−0.04	7.84	14.36
194
	Random sample of herd	−4.34	−0.06	4.63	8.97
	Sample front of herd	−5.84	−0.14	7.64	13.48
	Sample last of herd	−6.03	−0.07	6.87	12.90
245
	Random sample of herd	−3.94	−0.03	4.19	8.13
	Sample front of herd	−5.33	−0.03	5.87	11.20
	Sample last of herd	−5.59	−0.13	5.68	11.27
320
	Random sample of herd	−3.41	−0.04	3.63	7.04
	Sample front of herd	−4.48	−0.10	4.81	9.29
	Sample last of herd	−4.89	−0.03	4.80	9.69
435
	Random sample of herd	−2.98	−0.02	3.17	6.15
	Sample front of herd	−3.48	−0.09	4.00	7.48
	Sample last of herd	−4.07	−0.04	3.43	7.50

^a 2.5% of all differences between prevalence estimated using sampling scenario and whole herd assessment are more negative than this figure (e.g. for a sample size of 40 where the bootstrap sampling was used on the last 40 cows in the milking order, sample prevalence was > 11.49% lower than whole herd prevalence in 2.5% of bootstrapped samples across all 44 herds).

^b Median difference between prevalence estimated using sampling scenario and whole herd assessment (sample prevalence – whole herd prevalence).

^c 2.5% of all differences between prevalence estimated using sampling scenario and whole herd assessment are more positive than this figure (e.g. for a sample size of 40 where the bootstrap sampling was used on the last 40 cows in the milking order, sample prevalence was > 18.99% higher than whole herd prevalence in 2.5% of bootstrapped samples across all 44 herds).

^d 97.5th percentile – 2.5th percentile. As 50th percentile for all sample sizes was ∼0, this width is equal to ∼2* the precision for the sampling scenario.

*Anonymous. NZVA Standardised Tail Scoring System. https://nzva.org.nz/assets/Policies-Guidelines-Resources/tail_scoring.pdf (accessed 25 January 2024). New Zealand Veterinary Association, Wellington, NZ, 2021a

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Vallejo A, Muniesa A, Ferreira C, de Blas I. New method to estimate the sample size for calculation of a proportion assuming binomial distribution. Research in Veterinary Science 95, 405–9, 2013. https://doi.org/10.1016/j.rvsc.2013.04.005

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