An observational study of farmer-reported clinical mastitis in New Zealand dairy ewes

Figures & data

Figure 1. Incidence (with 95% CI) of farmer-reported clinical mastitis on 20 dairy New Zealand sheep farms in the 2022–2023 season, (A) based on data collected during the study, and (B) based on estimates made by the farmer at the end of the season (there is no farmer-estimated clinical mastitis incidence for farm L because the number of cases was unknown). Asterisks indicate farms on which the first milking was delayed ≥ 10 days postpartum because lambs were reared on the ewe.

Figure 2. Timing, in relation to lambing, of farmer-reported clinical mastitis cases on 20 dairy sheep farms in the 2022–2023 season in New Zealand.

Table 1. Clinical features of farmer-reported clinical mastitis cases (n = 236) on 20 New Zealand dairy sheep farms in the 2022–2023 season.

Variable	Prevalence^a
Affected gland(s)
Both	11/143 (7.7%)
L	58/143 (41%)
R	74/143 (52%)
Clots observed in milk	55/94 (59%)
Gland was painful	41/92 (45%)
Gland was swollen	51/93 (55%)
Udder was uneven	68/96 (71%)
Lumps in gland	36/92 (39%)
Mastitis was gangrenous^b	6/93 (6.5%)
Ewe was depressed^c	24/92 (26%)
Ewe was pyrexic	19/76 (25%)

^a Denominators differ due to incomplete data collection on farm.

^b The gland was cold to the touch or sloughing.

^c The ewe was lethargic, inappetent, or unable to stand.

Table 2. Associations between the presence of pyrexia (rectal temperature $\ge$ 40.0°C) and depression (lethargy, inappetence, or inability to stand) with other clinical features of farmer-reported clinical mastitis cases on 20 New Zealand dairy sheep farms in the 2022–2023 season.

Variable	Presence of pyrexia		P-value^b	Presence of depression		P-value^b
	Pyrexic (n = 19)^a	Not pyrexic (n = 57)^a		Depressed (n = 24)^a	Not depressed (n = 68)^a
Clots observed in milk	12/19 (63%)	33/57 (58%)	0.423	18/24 (75%)	37/68 (54%)	0.947
Gland was painful	10/18 (56%)	23/56 (41%)	0.374	19/22 (86%)	22/68 (32%)	0.143
Gland was swollen	13/19 (68%)	28/56 (50%)	0.340	19/24 (79%)	32/67 (48%)	0.025
Udder was uneven	15/19 (79%)	37/56 (66%)	0.843	22/24 (92%)	42/67 (63%)	0.426
Lumps in gland	8/19 (42%)	22/55 (40%)	0.894	14/23 (61%)	22/67 (33%)	0.145
Mastitis was gangrenous^c	2/19 (11%)	3/56 (5.4%)	0.460	6/24 (25%)	0/67 (0%)	0.997
Ewe was depressed^d	12/19 (63%)	8/56 (14%)	0.010
Ewe was pyrexic				12/20 (60%)	7/55 (13%)	0.010

^a Denominators differ due to incomplete data collection on farm.

^b From separate logistic regression models for each variable with farm included as a fixed effect.

^c The gland was cold to the touch or sloughing.

^d The ewe was lethargic, inappetent, or unable to stand.

Table 3. Treatment protocols reported by farmers for clinical mastitis cases (n = 109) on 20 New Zealand dairy sheep farms in the 2022–2023 season.

Variable	Prevalence^a
Route
IM	52/91 (57%)
PO	2/91 (2.2%)
SC	37/91 (41%)
Site
Mouth	2/91 (2.2%)
Neck	38/91 (42%)
Rump	51/91 (56%)
Milk withholding period applied (days)^b
0	2/91 (2.2%)
3	50/91 (55%)
5 (twice daily milking) or 10 (once daily milking)	11/91 (12%)
30	1/91 (1.1%)
35	27/91 (30%)
Meat withholding period applied (days)
0	2/89 (2.2%)
7	2/89 (2.2%)
10	48/89 (54%)
14	11/89 (12%)
21	17/89 (19%)
30	1/89 (1.1%)
35	8/89 (9.0%)
Primary treatment^c
Immune support bolus	2/109 (1.8%)
Oxytetracycline injection	37/109 (34%)
Penethamate hydroiodide injection	14/109 (13%)
Procaine penicillin injection	1/109 (0.9%)
Tylosin injection	55/109 (50%)

^a Denominators differ due to incomplete data collection on farm.

^b Milking frequency = once a day or twice a day.

^c If more than one product was administered concurrently, and only one antibiotic was used, the antibiotic was deemed the primary treatment. If more than one antibiotic was administered in series (none were administered in parallel), the first antibiotic to be administered was deemed the primary treatment.

Table 4. Reported outcomes among ewes (n = 199) with cases of farmer-diagnosed clinical mastitis (n = 223) on 20 New Zealand dairy sheep farms in the 2022–2023 season.

Outcome	Prevalence
Culled: due to lasting mastitis problems	23/199 (12%)
Culled: due to non-mastitis problems	1/199 (0.5%)
Died: due to mastitis	4/199 (2.0%)
Dried off: full recovery with no lasting problems	13/199 (6.5%)
Dried off: recovered with lasting problems	2/199 (1.0%)
Euthanised	2/199 (1.0%)
Instantly dried off to be culled without treatment	63/199 (32%)
Other	21/199 (11%)
Put out with lambs (removed from milking flock)	4/199 (2.0%)
Still milking: full recovery with no lasting problems	17/199 (8.5%)
Still milking: recovered with lasting problems	49/199 (25%)

Table 5. Aetiology of farmer-diagnosed clinical mastitis cases (n = 160 glands from 135 cases on 16 farms) in a prospective study of clinical mastitis on 20 New Zealand dairy sheep farms in the 2022–2023 season.

Aetiology	Prevalence
No growth	75/160 (47%)
Streptococcus uberis	22/160 (14%)
Staphylococcus aureus	18/160 (11%)
Contaminated	9/160 (5.6%)
Unidentifiable	7/160 (4.4%)
Escherichia coli	5/160 (3.1%)
Staphylococcus simulans	5/160 (3.1%)
Staphylococcus warneri	4/160 (2.5%)
Staphylococcus chromogenes	3/160 (1.9%)
Staphylococcus haemolyticus	3/160 (1.9%)
Acinetobacter pseudowolffii and Streptococcus uberis	1/160 (0.6%)
Arthrobacter gandavensis	1/160 (0.6%)
Enterococcus faecalis	1/160 (0.6%)
Enterococcus villorum	1/160 (0.6%)
Klebsiella oxytoca	1/160 (0.6%)
Staphylococcus borealis	1/160 (0.6%)
Staphylococcus devriesei	1/160 (0.6%)
Staphylococcus haemolyticus and Staphylococcus warneri	1/160 (0.6%)
Streptococcus uberis and Enterobacter ludwigii	1/160 (0.6%)

Figure 3. Microbiological aetiology of farmer-reported clinical mastitis cases (n = 69), excluding contaminated, unidentifiable, and culture-negative (NG) samples, on 20 dairy sheep farms in the 2022–2023 season. The number above the bars represents the number of isolates for each farm. “Other” includes Escherichia coli, Arthrobacter gandavensis, Enterococcus faecalis, and Klebsiella oxytoca.