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. 2025 Jun 28;13(7):1512. doi: 10.3390/microorganisms13071512

Clinical Mastitis in Small Ruminants Referred to a Veterinary Teaching Hospital: 23 Cases

Gabriel Inácio Brito 1, Liz de Albuquerque Cerqueira 2, Simone Perecmanis 3, José Renato Junqueira Borges 1, Márcio Botelho de Castro 2, Antonio Carlos Lopes Câmara 1,*
Editors: Luisa Zanolli Moreno, Andrea Micke Moreno
PMCID: PMC12299385  PMID: 40732022

Abstract

Clinical mastitis in small ruminants is usually seen with an incidence of less than 5% and most cases, especially with hyperacute evolution, are not referred for hospital care. During the 5-year survey, 16 goats and 7 sheep, totaling 23 small ruminants, met the inclusion criteria with a definitive diagnosis of clinical mastitis. Clinical signs ranged greatly among cases, varying from septic state in hyperacute cases, and enlarged, pendulous udder associated with chronic pain and abnormal gait in chronic cases. Microbiological culture revealed a wide array of bacterial pathogens, including Staphylococcus aureus, Escherichia coli, Streptococcus spp., and Pasteurella spp. In vitro antimicrobial susceptibility profiles varied greatly among bacteria isolates, ranging from sensitive to all tested antimicrobials to a multi-resistant profile. Pathological features included hyperemia and dark red areas of necrosis in the skin, marked hyperemia of the affected gland at the cut surface, lactiferous ducts and gland cisterns filled by cloudy or suppurative fluid, abscesses, and hardness of the mammary gland parenchyma. This retrospective study highlights the multifactorial nature and clinical variability of mastitis in small ruminants, demonstrating its significant impact on animal health, welfare, and production.

Keywords: intramammary infection, goat, mastectomy, sheep, systemic disturbances

1. Introduction

Mastitis is considered one of the most important diseases affecting domestic animals and is caused by several etiologic agents. The disease is economically relevant for sheep and goat dairy farmers due to the drop in milk production, premature culling of the dams, treatment costs, reduced offspring performance, and adverse influences on the welfare of affected animals [1,2,3].

The most common form of mastitis in sheep and goats is subclinical mastitis, with a prevalence ranging from 5 to 30% and occasionally reaching 50% in some flocks [4]. Clinical mastitis in small ruminants is usually seen with an incidence of less than 5% and most often occurs during the first third of lactation [5]. Nevertheless, mastitis outbreaks of bacterial etiology may be a prominent health problem affecting dairy sheep farms in some countries [1,2]. Early detection of mastitis during the subclinical phase is crucial for preventing progression to acute or chronic stages, reducing animal losses and minimizing economic impact [6]. Therefore, preventive measures such as the California Mastitis Test, monitoring somatic cell counts in milk, and maintaining udder and milker hygiene to enable early detection is essential [7].

The term mastitis refers to the presence of an inflammatory process in the mammary gland; typically, a bacterial infection triggers an inflammatory reaction, resulting in the development of variable clinical signs. The clinical syndrome can follow a variable course, ranging from hyperacute to chronic. Depending on the clinical course, mastitis can be conventionally differentiated into hyperacute, presenting a serious udder inflammation accompanied by an evident systemic response; acute, when severe udder inflammation is present but there is no systemic involvement; and chronic, when there is no systemic involvement and only fibrous lesions, sometimes poorly detectable, are present [2,8]. However, classification can be challenging, as some cases of chronic mastitis may also present with systemic signs, such as chronic pain, progressive weight loss, and anemia [8].

Additionally, as the goat and sheep dairy industry continues to grow substantially each year, it is essential to investigate whether antimicrobial-resistant bacteria are present in the milk of clinically affected animals, which is essential for both human and animal medicine, as part of the One Health perspective [9]. Considering this scenario, the present study aimed to present epidemiological, clinical, laboratory, microbiological, and pathological features of clinical mastitis in 23 small ruminants referred to a Veterinary Teaching Hospital.

2. Materials and Methods

A 5-years retrospective survey (from January 2019 to December 2024) was conducted in the records of small ruminants referred to the Large Animal Veterinary Teaching Hospital, Universidade de Brasília, located in Brasília, Distrito Federal, Midwestern Brazil. The criteria for inclusion were a conclusive diagnosis based on a combination of epidemiological, clinical, laboratory, and/or pathological evaluations.

Epidemiological aspects encompassed species (goats or sheep), breed, and age. Clinical aspects (clinical evolution, results of physical examination, affected mammary gland, treatment, outcome, and sequelae) were extracted from veterinary reports documented in the medical records. Clinical mastitis cases were classified as hyperacute (1–48 h), acute (48 to 96 h), and chronic (>7 days) according to the duration of the disease.

After the initial clinical examination, blood samples were collected by jugular vein puncture for hematological and biochemical analysis. Pathological evaluation of tissue samples obtained by surgical excision (radical or unilateral mastectomy) was performed, and dead animals (spontaneous death or humanely euthanized) were submitted for necropsy. Tissues were fixed in 10% buffered formalin, routinely processed, paraffin-embedded, sectioned at 5 μm thick, and stained with hematoxylin and eosin (H&E) for evaluation under an optical microscope.

Milk samples were collected aseptically from the affected mammary gland during the initial physical examination and transported to the laboratory. Immediately after, the fresh samples were seeded on 8% ovine blood agar medium (Sigma-Aldrich, Darmstadt, Germany) and MacConkey agar (Neogen Corporation, São Paulo, Brazil) medium at 37 °C in aerobiosis for 24–72 h. Simultaneously, the same samples were subjected to microaerophiles (5% CO2) and anaerobic cultures on sheep blood agar and incubated at 37 °C for 120 h. Isolates were identified based on the standard bacteriological approaches, such as colony morphology, pyocyanin pigment production, Gram staining, growth at 44 °C, and biochemical tests: oxidase, catalase, nitrate reduction, indole, methyl red, Voges–Proskauer, citrate utilization, and glucose fermentation according to Quinn et al. [10].

Isolates were subjected to in vitro susceptibility testing (disk diffusion method), according to the Clinical Laboratory Standards Institute (CLSI guidelines [11]) using 12 antimicrobials belonging to eight groups, as follows: (1) aminoglycosides (gentamicin 10 μg), (2) beta-lactams (amoxicillin 10 μg; ampicillin 10 μg; penicillin 10 μg), (3) cephalosporins (ceftiofur 30 μg); (4) fluoroquinolones (enrofloxacin 5 μg, ciprofloxacin 5 μg, norfloxacin 5 μg), (5) macrolides (azithromycin 15 μg); (6) florfenicol 10 μg, (7) sulfonamides (sulfamethoxazole 25 μg), and (8) tetracyclines (tetracycline, 30 μg).

3. Results

During the 5-years survey, 16 goats and seven sheep, totaling 23 small ruminants, met the inclusion criteria with a definitive diagnosis of clinical mastitis. Epidemiological data and clinical aspects are summarized in Table 1. The age of the affected females ranged from 12 to 72 months (mean: 43 months). The duration of the disease on the farms until clinical evaluation ranged from 12 h to 5 months. According to this data, clinical mastitis was classified as hyperacute (n = 11), acute (n = 3), or chronic (n = 9) cases. In the former group, the most important clinical signs included depression, anorexia, tachycardia, ruminal and intestinal hypomotility, and mammary glands with dark-blueish discoloration. Manipulating the affected mammary gland during milking elicited pain and yielded pinkish to dark-reddish milk coloration with a fetid odor. Physical examination in acute cases revealed mild clinical signs, such as hyporexia and hyperthermia, and most mammary glands presented reddish skin and red-black discoloration areas (Figure 1A), asymmetry of the udder (Figure 1B), and were hot at the touch. The most important clinical signs in chronic cases included loss of body condition score, pale ocular mucous membranes, and alterations on the mammary glands consisting of hardened consistency (fibrosis), lumpy areas (abscesses), and milking with varying degrees of clots to purulent discharge. In some cases, the enlarged udder caused abnormal gait. Hospitalization days ranged from 1 to 87 days (mean: 22.3 days).

Table 1.

Epidemiological data and clinical aspects from 23 small ruminants (16 goats and 7 sheep) with clinical mastitis.

Case Specie Breed Age Rearing System Milking Method Clinical Evolution Affected Mammary Gland Type of Mastitis Treatment Hospitalization Days Outcome Sequelae
1 Goat Crossbred 4 y Intensive Manual 48 h Right Hyperacute Clinical 9 Discharged Rigid MG
2 Sheep Crossbred 4 y Extensive None 45 days Both Chronic Surgical 15 Discharged None
3 Goat Saanen 2 y Intensive Mechanical 24 h Both Hyperacute Clinical 2 Death -
4 Goat Saanen 1 y Intensive Mechanical 24 h Left Hyperacute Clinical 1 Death -
5 Goat Saanen NAD Intensive Mechanical 24 h Right Hyperacute Clinical 1 Death -
6 Sheep Crossbred 2 y Extensive None 37 days Both Chronic Clinical 4 Euthanasia -
7 Sheep Crossbred NAD Extensive None 8 days Both Chronic Clinical 4 Euthanasia -
8 Sheep Crossbred 3 y Extensive None 96 h Both Acute Surgical 60 Discharged None
9 Sheep Crossbred 2 y Extensive None 96 h Both Acute Clinical 38 Discharged Rigid MG
10 Goat Saanen 5 y Intensive Manual 153 days Both Chronic Surgical 58 Discharged None
11 Goat Saanen 4 y Intensive Mechanical 24 h Both Hyperacute Clinical 1 Death -
12 Goat Saanen 6 y Intensive Mechanical 12 h Right Hyperacute Clinical 8 Discharged None
13 Goat Saanen 3 y Intensive Mechanical 12 h Both Hyperacute Clinical 10 Discharged NAD
14 Sheep Crossbred 5 y Extensive None 61 days Both Chronic Surgical 22 Discharged None
15 Sheep Crossbred NAD Extensive None 158 days Left Chronic Clinical 69 Discharged Rigid MG
16 Goat Crossbred 5 y Intensive Mechanical 12 h Both Hyperacute Clinical 5 Discharged None
17 Goat Saanen 3 y Intensive Mechanical 48 h Left Hyperacute Clinical 7 Discharged NAD
18 Goat Saanen 3 y Intensive Mechanical 96 h Right Acute Clinical 7 Discharged None
19 Goat Saanen 5 y Intensive Mechanical 15 days Left Chronic Clinical 7 Discharged Rigid MG
20 Goat Crossbred 3 y Intensive Manual 24 h Right Hyperacute Clinical 7 Discharged Rigid MG
21 Goat Saanen 2 y Intensive Mechanical 36 h Right Hyperacute Surgical 30 Discharged None
22 Goat Saanen 5 y Intensive Manual 65 days Both Chronic Surgical 87 Discharged None
23 Goat Saanen 6 y Intensive Manual 45 days Both Chronic Surgical 62 Discharged None
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NAD: no available data. MG = mammary gland.

Figure 1.

Figure 1

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Clinical aspects of the affected mammary glands of small ruminants with mastitis. (A) Goat. Redness and red-black areas in the skin of the teat and udder. (B) Goat. Asymmetry of the udder due to unilateral enlargement of the left gland.

Laboratorial data (blood tests and biochemical analysis) are presented in Table 2. One doe (Case 5) died shortly after initial clinical examination, and blood samples were not collected. In most cases, does with hyperacute mastitis presented leucopenia (n = 5), leukocytosis by neutrophilia (n = 2), or just an inversion in the neutrophils–lymphocytes ratio (n = 2). Serum biochemistry revealed hypoproteinemia by hypoalbuminemia in most cases, whilst increased creatinine levels was present in two animals (Case 3 and 4). Leucocytosis by neutrophilia was also present in acute mastitis cases associated to hyperfibrinogenemia. The most relevant alterations in chronic cases consisted of anemia, hypoalbuminemia, and hyperglobulinemia. Only two animals presented hematological and biochemical values within the reference range [12,13].

Table 2.

Laboratory data from 23 small ruminants (16 goats and 7 sheep) with clinical mastitis.

Case Ht RBC Hb Leucocytes SEG Bands LYM MON EOS Fibrinogen STP Albumin Globulin Urea CR AST GGT
1 34 18.8 11.3 7500 4275 - 3075 150 - 400 7.6 2.37 5.23 27 1.2 47 45
2 19 4.68 6.1 9100 7280 91 1547 91 91 600 6.4 1.25 5.15 30 1.4 165 7
3 40 18.7 12.2 2650 53 - 2518 53 27 400 5.1 2 3.1 130 2.3 146 45
4 35 13.3 10.9 3100 558 - 2201 310 31 1000 5.5 2 4.5 74 3.2 162 61
5 # - - - - - - - - - - - - - - - - -
6 19 4.9 5.8 14,850 10,247 - 3119 149 1337 400 7.4 1.6 5.8 16 1.3 131 53
7 14 3.6 4 5200 3744 - 1300 156 - 400 5.2 1.3 3.9 30 1.1 172 84
8 29 8.1 9.1 15,100 11,300 - 3800 - - 600 7.4 NP NP NP NP NP NP
9 15 4.2 4.8 8700 5220 174 3306 - - 800 6.8 NP NP NP NP NP NP
10 17 8.8 5.7 13,050 9135 - 3132 653 131 400 10.7 1.7 9 23 1.5 47 -
11 24 11 6.1 8200 4592 - 2542 164 902 600 7.2 2.1 5.1 83 1.2 94 53
12 29 15.3 6.3 3050 702 - 2318 31 - 400 6.6 NP NP 24 1.4 110 61
13 31 11.9 9.5 1800 612 - 1044 - 36 400 6 3.5 2.5 13 1.4 71 50
14 25 5,65 8 11,600 6264 - 1160 696 3480 200 7 2.8 4.2 34 0.7 109 72
15 29 7.9 6.4 7150 4219 - 1716 429 787 400 7.2 NP NP 23 1.4 104 NP
16 22 10 7.1 13,210 10,701 133 2114 133 133 400 6.9 3.1 3.8 20 0.9 67 38
17 32 12.8 9 8650 6488 - 1990 173 - 1200 6.2 2.4 3.8 51 1.5 47 38
18 29 13.3 8.9 7000 3710 - 3080 140 70 400 6.4 2.9 3.5 23 1.3 89 30
19 20 12.3 7.2 8950 3849 - 4833 269 - 600 6 2.3 3.7 26 0.7 78 48
20 25 11.6 7.5 17,500 15,400 - 1925 - - 200 6.2 1.7 4.5 49 1.1 115 122
21 34 16 10.8 3100 341 2449 279 31 800 5.5 2 3.5 67 1.7 178 30
22 24 10.9 7.7 5000 1300 - 2750 200 250 400 8.7 2.7 6 46 1.1 110 NP
23 30 12.9 9.7 8650 5709 - 2422 260 260 400 6.2 2.4 3.8 30 1.5 157 NP
X ± SD Goats 28.4 ± 6.2 13.1 ± 2.9 8.6 ± 2 7427 ± 4548 4495 ± 4453 133 ± 0 2559 ± 824 216 ± 155 187 ± 266 533 ± 269 6.7 ± 1.4 2.3 ± 0.5 4.4 ± 1.6 45.7 ± 31.6 1.4 ± 0.6 101.2 ± 43.6 51.7 ± 24.3
X ± SD Sheep 21.4 ± 6.2 5.5 ± 1.9 6.3 ± 1.7 8123 ± 4783 5433 ± 3471 132.5 ± 58.6 1833 ± 1305 304.2 ± 255.2 1423 ± 1462 485.7 ± 195.1 6.7 ± 0.7 1.7 ± 0.7 4.7 ± 0.8 26.6 ± 7.1 1.18 ± 0.3 136.2 ± 31.2 54 ± 33.8
RF Goats * 19–38 8–18 8–14 4000–13,000 1200–7200 0–100 2000–9000 0–650 50–650 100–400 6.4–7 2.7–3.9 2.7–4.1 21.4–42.8 1–1.8 43–132 20–56
RF Sheep * 24–50 8–16 8–16 4000–12,000 700–6000 0–100 2000–9000 0–750 0–1000 100–500 6–7.9 2.4–3 3.5–5.7 17.12–42.8 1.2–1.9 68–90 20–52
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Ht: hematocrit (%); RBC: red blood cells (×106/μL); Hb: hemoglobin (g/dL); SEG: segmented neutrophils (/μL); LYM: lymphocytes (/μL); MON: monocytes (/μL); EOS: eosinophils (/μL); STP: serum total protein (g/dL); CR: creatinine (mg/dL); AST: aspartate amino-transferase (UI/L); GGT: gamaglutamil transferase (UI/L); NP: not performed. RF: Reference values. * Meyer & Harvey [12], Kaneko et al. [13]. # The doe died shortly after clinical evaluation, and blood samples were not collected. X = mean; SD = standard deviation.

Microbiological assays and in vitro antimicrobial susceptibility profiles of milk samples were performed in 13 small ruminants (10 goats and 3 sheep) with clinical mastitis (Table 3). In hyperacute cases (n = 8) presenting the most severe clinical disturbances, the isolated microorganisms included Escherichia coli (n = 2), Staphylococcus aureus (n = 2), Streptococcus sp. (n = 1), and Pasteurella sp. (n = 1), whilst two cases presented no bacterial growth. One case with acute evolution (Case 18) yielded S. aureus on both mammary glands, but the bacteria presented different susceptibility profiles. Chronic cases included Case 6, which offered a mixed bacterial growth (E. coli and S. aureus); Case 14, with one bacteria species affecting each mammary gland (E. coli on right and S. aureus on left mammary gland); and Cases 7 and 19 with no bacterial growth. In vitro antimicrobial susceptibility profiles varied greatly among bacteria isolates, ranging from sensitive to all tested antimicrobials (Case 4) to a multi-resistant profile (Case 21).

Table 3.

Microbiological assays and in vitro antimicrobial susceptibility profile of milk samples from 13 small ruminants (10 goats and 3 sheep) with clinical mastitis.

Case Affected MG Isolated Bacteria CEF SUL + TRIM AMOX ENR PEN GEN FLOR CIPRO AMP TET NOR AZI
1 Right No growth - - - - - - - - - - - -
3 Both Escherichia coli S S R R NP NP NP NP NP NP NP NP
4 Left Staphylococcus aureus S S S S S S S S S NP NP NP
6 Both S. aureus/E. coli NP NP NP NP NP NP NP NP NP NP NP NP
7 Both No growth - - - - - - - - - - - -
11 Both S. aureus S S R R R S NP I NP S NP NP
12 Right No growth - - - - - - - - - - - -
14 Right E. coli R R S NP NP NP NP NP S R S R
Left S. aureus S R S NP NP NP NP NP S I S S
16 Both Streptococcus sp. S S S S R S NP NP R S NP NP
18 Left S. aureus S R S R R S NP S S NP R NP
Right S. aureus R I S R R S NP S S NP I NP
19 Left No growth - - - - - - - - - - - -
20 Right Pasteurella sp. S S S NP R S NP NP S NP S R
21 Right E. coli R R I I R R NP S R R S R
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MG: mammary gland; CEF: ceftiofur; SUL + TRIM: sulfadiazine plus trimethoprim; AMOX: amoxicillin; ENR: enrofloxacin; PEN: penicillin; GEN: gentamicin; FLOR: florfenicol; CIPRO: ciprofloxacin; AMP: ampicillin; TET: tetracycline; NOR: norfloxacin; AZI: azithromycin; S: sensitive; R: resistant; I: intermediate; NP: not performed.

Of the 23 small ruminants with clinical mastitis, 17 (73.9%) received hospital discharge, and 6 (26.4%) died. Euthanasia was performed due to welfare issues and poor prognosis in two animals (Case 6 and 7), and spontaneous death occurred in four small ruminants (Case 3, 4, 5, and 11) despite intensive care. Therefore, pathological evaluation was performed on six dead small ruminants (four goats and two sheep) and also on seven incisional biopsy samples from radical (n = 6) and unilateral (n = 1) mastectomy cases.

Gross and pathological findings observed in affected sheep and goats were hallmarks for diagnosing mastitis in this study. Affected animals frequently showed hyperemia and dark red areas of necrosis in the skin (Figure 2A), marked hyperemia of the affected gland at the cut surface (Figure 2A), lactiferous ducts and gland cisterns filled by cloudy (Figure 2C) or suppurative fluid, abscesses (Figure 2D), and hardness of the mammary gland parenchyma. Microscopically, acute mastitis was characterized by remarkable hyperemia, hemorrhagic foci, alveolar epithelial degeneration, and inflammatory neutrophilic infiltration (Figure 3A), mainly within glandular alveoli (Figure 3B). Chronic cases showed abscesses in the mammary parenchyma, numerous foci of lymphocytic or lymphoplasmacytic inflammatory infiltrate within lobes (Figure 3C) and surrounding alveoli (Figure 3D), and scattered foci of fibrosis.

Figure 2.

Figure 2

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Gross pathological alterations in the mammary tissues of small ruminants with mastitis. (A) Goat. Hyperemia in the skin of the udder and a dark area of necrosis affecting the teat. (B) Goat. Marked hyperemia of the affected parenchyma. (C) Sheep. Lactiferous sinus filled with a white-cloudy inflammatory fluid. (D) Sheep. An abscess within the parenchyma close to the teat cistern.

Figure 3.

Figure 3

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Histological findings in the mammary tissues of small ruminants with mastitis. (A) Goat. Marked hyperemia of interstitial vessels in the mammary lobes and inflammatory infiltrate filling alveoli (H&E, bar = 250 μm). (B) Goat. Alveolar epithelial degeneration, necrosis, and numerous neutrophils fill alveoli (H&E, bar = 50 μm). (C) Sheep. Interstitial mononuclear inflammatory infiltrate within mammary lobes (H&E, bar = 100 μm). (D) Severe lymphocytic inflammatory infiltration surrounding mammary alveoli (H&E, bar = 25 μm).

4. Discussion

Mastitis is considered a multifactorial disease, implying the possible involvement of multiple risk factors, which include environmental factors, nutrition, viral infections, stage of lactation, lactation number, udder shape, teat conformation, milking technique, and equipment hygiene [14,15]. Herein, all cases in goats (n = 16) occurred in Saanen or crossbred does from milk flocks under intensive management submitted to manual or mechanical milking methods. In these cases, it is possible to hypothesize that poor management practices, such as the use of unsuitable milking machines and/or inadequate training of milkers in correct milking techniques, may lead to incomplete milk-out or overmilking [16]. These, along with poor udder conformation, may lead to excessive machine stripping, all of which are risk factors for teat damage and mastitis [15]. Regarding sheep, all ewes were crossbred hair sheep from semi-extensive meat production flocks with suckling lambs. Therefore, in sheep and goats, risk factors such as crowded conditions and decubitus during rumination and sleep increase the udder’s exposure to environmental microbial flora, which, in poor hygienic conditions, may increase the risk of exposure to environmental pathogens [2].

This study provides insight into clinical mastitis in small ruminants referred to a Veterinary Hospital, reiterating that the disease is life-threatening. The severe systemic disturbances observed, especially in hyperacute cases, result from the liberation of bacteria, pathogen-associated molecular patterns (PAMPs), and damage-associated molecular patterns (DAMPs) into the circulation during the septic state. The profound systemic inflammatory effects can lead to remote organ dysfunction and the development of multi-organ dysfunction syndrome (MODS). Typical organs involved in MODS include, but are not limited to, the heart, lungs, kidneys, and liver [17]. Additionally, disrupting the blood–milk barrier in cases of severe mastitis facilitates the passage of bacteria from milk into the bloodstream, thereby enhancing bacteremia [18]. Therefore, implementing protocols to decrease mastitis incidence may also be considered a welfare issue [14].

Clinical mastitis treatment includes broad-spectrum antibiotics, non-steroidal anti-inflammatory agents, palliative treatments (intravenous fluid therapy or oral hydration), and sometimes surgery (teat amputation, pudendal artery ligation, or mastectomy) [1,14,15,19]. Ideally, cultures should be obtained before the initiation of antimicrobial therapy [19], but in most instances, especially when dealing with hyperacute cases, treatment decisions have already been made before the results of antibiotic sensitivity testing become available [14,19]. In our study, four hyperacute cases that evolved to death presented antimicrobial resistance to the chosen antimicrobial when antibiotic sensitivity tests were available. Furthermore, a Saanen doe that presented a multidrug-resistant bacterial strain (Case 21) only improved with the association of an intermediate antibiotic in the sensitivity test (the only available for animal use) associated with unilateral mastectomy. These features underscore the need for aggressive treatment of hyperacute cases due to the risk of rapid deterioration, and that determining sensitivity patterns may help inform treatment decisions for future cases [13,18]. In two cases, severe damage to the mammary parenchyma caused by bacterial infection resulted in hardened mammary glands as a sequelae of clinical treatment, leading to decreased milk production and an increased future culling rate for the does and ewes [2,14,15,18].

Mastectomies were most commonly performed to resolve clinical signs associated with chronic mastitis and an enlarged, pendulous udder in the small ruminants in this study. Both conditions resulted in chronic pain and affected the quality of life, manifesting as abnormal gait, low feed intake, anemia, and weight loss, as previously reported [14,15,19,20]. After mastectomy, appetite, gait, and weight improved in all treated animals, with hospital discharges resulting in no sequelae. Despite this, the hospitalization period and surgery costs may limit mastectomies to high-value genetic animals or pet ruminants.

In this study, gross and microscopic findings were crucial in highlighting the severe suppurative inflammation, hyperemia, and hemorrhages in the mammary gland parenchyma of goats and sheep with acute mastitis, as previously described [8,20]. The majority of bacteria identified in the udders of affected animals are commonly associated with marked neutrophilic inflammation and tissue necrosis in small ruminants with mastitis [8]. As observed here, chronic mastitis is typically characterized by abscess formation, mononuclear interstitial inflammation, and fibrosis, often caused by the same pathogens in sheep and goats worldwide [8,19]. However, pathological investigations of mastitis in small ruminants remain limited, and further morphological characterization in relation to specific pathogens is still needed.

Microbiological assays in the present study revealed S. aureus affecting five goats and one ewe, resulting in 50% (6/12) of cultured milk samples testing positive. S. aureus is considered the most commonly identified cause of clinical mastitis in dairy does, and it is estimated that close to 50% of goat herds are infected with this organism [1,5,14,15], as observed herein. Additionally, a recent study in ewes highlights that, despite sampling after the regular post-milking cleaning of parlors and teatcups, staphylococci colonization still occurred [21]. The environmental group of pathogens was isolated in five cases, including pure cultures of E. coli obtained in two does with hyperacute mastitis. Although coliform mastitis appears to be much less common than other mastitis pathogens [15], accounting for between 1.4% and 14.2% of cases [4,7,19], it most often causes severe clinical disturbances. Other organisms that have been implicated include coagulase-negative staphylococci, Enterobacter spp., Pseudomonas spp., Trueperella pyogenes, Corynebacterium pseudotuberculosis, Listeria monocytogenes, Bacillus spp., mycoplasmas, and fungal organisms [2,3,4,5,14,15,19]. Over the last few decades, the year-by-year increase in antimicrobial resistance has become one of the most pressing global threats in both the animal and human health sectors [9,22,23]. Therefore, the microbiological isolation of multi-resistant bacterial strain raises concerns about the indiscriminate use of antibiotics in small ruminant practice, especially on milk-producing farms.

In four mastitis cases, microbiological culture resulted in no growth (Case 1, 7, 12, and 19). Since these were isolated mastitis cases in each flock, and three animals responded well to antimicrobial treatment, no further investigation was conducted to determine the etiological agent. Fortunately, Mycoplasma mastitis cases are uncommon in Brazil [24], and seems to be rare in our hospital routine, but since no molecular testing was performed herein, this possibility could not be dismissed. In contrast, a recent study showed that incurable mastitis in goats was associated to M. agalactiae infection in 59% of cases [23]. Thereby, the use of ancillary diagnostics tests, such as molecular techniques, are important to enhance diagnostic accuracy, characterize antimicrobial resistance and virulence genes of bacterial pathogens of clinical mastitis in livestock [25].

The main limitations of this study were the small sample size, lack of standardized microbiological protocols, the absence of statistical analysis, and limited examination of risk factors. Further studies are needed to address these shortcomings and produce more comprehensive and broadly applicable findings. Nevertheless, all findings reported herein are important data on clinical mastitis in small ruminants from real field conditions, since most cases, especially the hyperacute cases, are not referred for hospital care. Therefore, this retrospective study provides essential knowledge on clinical signs, laboratory and pathological features of this life-threatening condition.

5. Conclusions

This retrospective study highlights the multifactorial nature and clinical variability of mastitis in small ruminants, demonstrating its significant impact on animal health, welfare, and production. Clinical mastitis was classified as hyperacute, acute, or chronic, with substantial variation in disease progression and clinical presentation. Microbiological culture revealed a wide array of bacterial pathogens, including Staphylococcus aureus, Escherichia coli, Streptococcus spp., and Pasteurella spp. Several isolates showed resistance to multiple antimicrobials, reinforcing the importance of judicious antimicrobial use and susceptibility testing in treatment planning. Despite intensive care and surgical interventions, the mortality rate remained considerable, underscoring the disease’s severity and the challenges in managing advanced cases. These findings emphasize the need for early diagnosis, appropriate therapeutic strategies, and preventive measures to minimize the incidence and severity of clinical mastitis in small ruminants, especially within the growing dairy goat and sheep industries. Given the serious consequences of clinical mastitis in small ruminants, it is essential to regularly implement preventive measures on farms, such as the California Mastitis Test, monitoring somatic cell counts in milk, and maintaining udder and milker hygiene, to enable early detection during the subclinical phase.

Author Contributions

Conceptualization, G.I.B., L.d.A.C., A.C.L.C., and M.B.d.C.; Methodology and investigation, G.I.B., S.P., L.d.A.C., J.R.J.B., A.C.L.C., and M.B.d.C.; writing—original draft preparation, G.I.B., A.C.L.C., and M.B.d.C.; writing—review and editing, A.C.L.C. and M.B.d.C.; supervision, A.C.L.C. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

The small ruminants detailed in this study were referred as patients to the Large Animal Veterinary Teaching Hospital, Universidade de Brasília. The case management was not altered by the study and no ethical approval was obtained. The authors confirm that the study has followed the guidelines of the 1964 Declaration of Helsinki and its later amendments.

Informed Consent Statement

The animal’s owners signed a consent form to permit hospitalization and treatment. Additional consent was obtained for anonymized necropsy and post-mortem samples for research purposes.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

Funding Statement

The APC was funded by the Edital DPI/DPG/BCE Nº 01/2025 from Universidade de Brasília (Process Number: 23106.059941/2025-33).

Footnotes

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References

  • 1.Attili A.R., Preziuso S., Ngwa V.N., Cantalamessaa A., Moriconi M. Clinical evaluation of the use of enrofloxacin against Staphylococcus aureus clinical mastitis in sheep. Small Rum. Res. 2016;136:72–77. doi: 10.1016/j.smallrumres.2016.01.004. [DOI] [Google Scholar]
  • 2.Marogna G., Roselu S., Lollai S., Tola S., Leori G. Clinical findings in sheep farms affected by recurrent bacterial mastitis. Small Rum. Res. 2010;88:119–125. doi: 10.1016/j.smallrumres.2009.12.019. [DOI] [Google Scholar]
  • 3.Moura G.S., Mota R.A., Marques M.F.S., Abad A.C.A., Costa L.B.B.C., Souza F.N., Almeida V.M., Silva-Filho G.B., Bom H.A.S.C., Klaumann F., et al. Gangrenous mastitis in sheep caused by multidrug-resistant Staphylococcus haemolyticus. Pesq. Vet. Bras. 2020;40:947–954. doi: 10.1590/1678-5150-pvb-6658. [DOI] [Google Scholar]
  • 4.El-Zamkan M.A., Mohamed H.M.A. Antimicrobial resistance, virulence genes and biofilm formation in Enterococcus species isolated from milk of sheep and goat with subclinical mastitis. PLoS ONE. 2021;16:e0259584. doi: 10.1371/journal.pone.0259584. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 5.Cvetnić L., Samardžija M., Sukalić T., Lukačević D., Lolić M., Kompes G., Habrun B., Bagarić A., Cvetnić Z., Benić M. Mastitis pathogens in goats and sheep in the Republic of Croatia and their sensitivity to antimicrobials. Vet. Stanica. 2025;56:697–707. doi: 10.46419/vs.56.6.11. [DOI] [Google Scholar]
  • 6.Zafalon L.F., Santana R.C., Pilon L.E., Júnior G.A. Diagnosis of subclinical mastitis in Santa Inês and Morada Nova sheep in Southeastern Brazil. Trop. Anim. Health Prod. 2016;48:967–972. doi: 10.1007/s11250-016-1046-1. [DOI] [PubMed] [Google Scholar]
  • 7.Smistad M., Inglingstad R.A., Vatne M.K., Franklin F.V., Hansen B.H., Skeie S., Porcellato D. Somatic cell count in dairy goats II: Udder health monitoring at goat and herd level. BMC Vet. Res. 2025;21:157. doi: 10.1186/s12917-025-04556-8. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 8.Arteche-Villasol N., Fernández M., Gutiérrez-Exposito D., Pérez V. Pathology of the mammary gland in sheep and goats. J. Comp. Path. 2022;193:37–49. doi: 10.1016/j.jcpa.2022.02.007. [DOI] [PubMed] [Google Scholar]
  • 9.Garcia S.N., Osburn B.I., Cullor J. A one health perspective on dairy production and dairy food safety. One Health. 2019;7:100086. doi: 10.1016/j.onehlt.2019.100086. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 10.Quinn P.J., Markey B.K., Donnelly W.J., Leonard F.C., Fanning S., Maguire D., editors. Veterinary Microbiology and Microbial Disease. 2nd ed. John Wiley & Sons; Hoboken, NJ, USA: 2011. Laboratory diagnosis of bacterial disease; pp. 143–149. [Google Scholar]
  • 11.Clinical and Laboratory Standards Institute—CLSI . Performance Standards for Antimicrobial Disk and Dilution Susceptibility Test for Bacteria Isolated from Animals (CLSI VET 015) 5th ed. Clinical and Laboratory Standards Institute—CLSI; Wayne, PA, USA: 2020. [Google Scholar]
  • 12.Meyer D.J., Harvey J.W. Veterinary Laboratory Medicine: Interpretation and Diagnosis. 2nd ed. Saunders; Philadelphia, PA, USA: 2004. 351p [Google Scholar]
  • 13.Kaneko J.J., Harvey J., Bruss M., editors. Clinical Biochemistry of Domestic Animals. 6th ed. Academic Press; San Diego, CA, USA: 2008. 928p [Google Scholar]
  • 14.Smith M.C., Sherman D.M. Goat Medicine. 3rd ed. Wiley-Blackwell; Hoboken, NJ, USA: 2023. Mammary gland and milk production; pp. 728–780. [Google Scholar]
  • 15.Menzies P. Udder health for dairy goats. Vet. Clin. N. Am. Food Anim. Pract. 2021;37:149–174. doi: 10.1016/j.cvfa.2020.12.002. [DOI] [PubMed] [Google Scholar]
  • 16.Dzidic A., Rovai M., Poulet J.L., Leclerc M., Marnet P.G. Review: Milking routines and cluster detachment levels in small ruminants. Animal. 2019;13((Suppl. S1)):s86–s93. doi: 10.1017/S1751731118003488. [DOI] [PubMed] [Google Scholar]
  • 17.Osterbur K., Mann F.A., Kuroki K., Declue A. Multiple organ dysfunction syndrome in humans and animals. J. Vet. Intern. Med. 2014;28:1141–1151. doi: 10.1111/jvim.12364. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 18.Krebs I., Zhang Y., Wente N., Leimbach S., Kromker V. Bacteremia in severe mastitis of dairy cows. Microorganisms. 2023;11:1639. doi: 10.3390/microorganisms11071639. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 19.Plummer P.J., Brooks K.M.S., Edmondson M.A. Diseases of the mammary gland. In: Pugh D.G., Baird A.N., Edmonson M., Passler T., editors. Sheep, Goat and Cervid Medicine. 3rd ed. Elsevier; Philadelphia, PA, USA: 2021. pp. 385–404. [Google Scholar]
  • 20.Hermida J.A., Baird A.N., Hawkins J.F., Moore G.E. Mastectomy in 25 small ruminants (2002–2019) Vet. Surg. 2021;50:104–110. doi: 10.1111/vsu.13509. [DOI] [PubMed] [Google Scholar]
  • 21.Michael C.K., Lianou D.T., Vasileiou N.G.C., Tsilipounidaki K., Katsafadou A.I., Politis A.P., Kordalis N.G., Ioannidi K.S., Gougoulis D.A., Trikalinou C., et al. Association of staphylococcal populations on teatcups of milking parlours with vaccination against staphylococcal mastitis in sheep and goat farms. Pathogens. 2021;10:385. doi: 10.3390/pathogens10040385. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 22.Roșu R.-D., Morar A., Ban-Cucerzan A., Imre M., Sallam K.I., Maha A.-A.A., Abd-Elghany S.M., Popa S.A., Pătrînjan R.-T., Morar D., et al. The microbiological quality of raw ovine milk in the Banat region of romania with a focus on Escherichia coli and its pathogenic potential and antimicrobial resistance. Vet. Sci. 2024;11:562. doi: 10.3390/vetsci11110562. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 23.Zaitoun A.M.A., Khalifa F.A., Mokhtar A., Mazeed A.M., Yousef A.M.E. Conventional and molecular detection of the common etiologic agents of incurable mastitis of goats at various villages of South Egypt. J. Vet. Med. Res. 2025;32:47–54. doi: 10.21608/jvmr.2025.351941.1111. [DOI] [Google Scholar]
  • 24.Castilho-Júnior R.E., Almeida C.A.S., Santos V.M., Amorim A.T., Gaeta N.C., Souza I.R., Santos M.B., Campos G.B., Souza L.E.B., Cruz J.F., et al. Detecting Mollicutes by PCR in goats in southwestern Bahia, Brazil. Braz. J. Microbiol. 2021;52:1589–1595. doi: 10.1007/s42770-021-00517-z. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 25.Abboud Z., Galuppo L., Tolone M., Vitale M., Puleio R., Osman M., Loria G.R., Hamze M. Molecular characterization of antimicrobial resistance and virulence genes of bacterial pathogens from bovine and caprine mastitis in Northern Lebanon. Microorganisms. 2021;9:1148. doi: 10.3390/microorganisms9061148. [DOI] [PMC free article] [PubMed] [Google Scholar]

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