Prevalence and associated bacteria of mastitis in goats in northeastern Ethiopia

Abstract

Mastitis is a multifactorial disease that affects mammalian health, productivity, and public health. However, it remains considerably understudied in goats compared to cattle in Ethiopia. A cross-sectional study was conducted in selected districts of Northeastern of Amhara region between September 2024 and May 2025. The study aimed to determine the prevalence of mastitis in goats, identify the causative bacteria, and assess the associated risk factors. The detection of mastitis in goats was performed using a physical examination and the California mastitis test. Bacterial isolation and identification were performed according to established standard protocols. Statistical analysis was conducted using Stata 17 software. Among the 397 lactating goats examined, the overall mastitis prevalence at the goat level was 24.74%, comprising 2.52% clinical mastitis (CM) and 22.22% subclinical mastitis (SCM). At the udder halves level, the prevalence was 16.60%, with 1.39% CM and 15.21% SCM. Multivariable logistic regression analysis showed significant associations between goat mastitis and several factors: lactation stage (OR = 1.92; 95% CI: 1.89–6.30), district (OR = 3.47; 95% CI: 1.01–3.65), parity (OR = 2.73; 95% CI: 1.11–6.67), and previous history of mastitis (OR = 13.6; 95% CI: 4.64–40.15), all with p-values less than 0.05. Staphylococcus, E. coli, Enterococcus, and Klebsiella were identified in CM and SCM suspected cases at prevalence of 39.83%, 10.17%, 4.5%, and 2.4%, respectively. This study identified mastitis as significant production challenge-affecting goats in the study area. The findings revealed a considerable disease burden and a wide variety of bacteria, which indicates the importance of routine monitoring and the implementation of effective prevention and control measures.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-026-05348-4.

Introduction

The domestic goat is among the earliest domesticated livestock species and is recognized as the third-largest contributor to global milk production, often referred to as the "cow of the poor.” [80]. In Ethiopia, goat production plays a vital role in rural livelihood, especially in areas with limited infrastructure and arid climates prone to frequent droughts [64].

In 2021, Ethiopia's goat population surpassed 52 million [76]. However, despite this large population, the economic contribution of goat milk remains low relative to its potential, highlighting gaps in understanding and management factors that hinder productivity. Several factors contribute to this low productivity, including the widespread occurrence of diseases that result in production losses, high mortality, stunted growth, reduced fertility, and weight loss. Moreover, in East Africa, including Ethiopia, goat productivity is further constrained by inadequate feed, restricted access to veterinary services, and poor management practices [16, 64]).

Mastitis, a major global dairy production challenge, causes mammary gland damage, disrupts milk yield, and leads to substantial financial losses. Mastitis is classified into clinical (CM) and subclinical forms (SCM), with CM showing visible signs and milk abnormalities, whereas SCM remains hidden but causes significant, often underestimated economic losses.

Mastitis pathogens originate from infected animals and are transmitted via milking practices or unsanitary environmental conditions, including contaminated soil, manure, and bedding. Among these pathogens, Staphylococcus species are the predominant cause of mastitis in goats and other animals. Specifically, Staphylococcus aureus (S. aureus) is primarily linked to CM, whereas non-aureus staphylococci and mammaliicocci (NASM) are responsible for SCM [22].

Mastitis severely impacts dairy production by reducing milk yield and quality, increasing veterinary costs, and causing early culling, especially in cases of CM and contagious agalactia. SCM occurs more frequently and leads to significant hidden losses, emphasizing the need for effective vaccination.

A comprehensive dairy animal health and production management program includes several critical components, among which regular mastitis screening is particularly essential. Mastitis can be diagnosed through various methods such as the California Mastitis Test (CMT), somatic cell count (SCC), bacterial culture, and assessments of milk appearance and odor, as well as pathological and histological analyses. Additional, though less commonly used, diagnostic approaches include the Whiteside Test (WST), biosensors, and electrical conductivity measurements [80].

Recent advancements in artificial intelligence (AI) have introduced innovative diagnostic possibilities. AI algorithms integrated with smart sensors and imaging devices can enhance diagnostic accuracy by analyzing big data and enabling 3D anatomical visualization. These technologies also support continuous monitoring and tracking of vital infection indicators and animal behavior. Nevertheless, issues related to data quality, technical complexity, ethical concerns, and regulatory oversight challenge the adoption of AI in veterinary diagnostics [33].

In parallel, advances in immunization technologies are reshaping mastitis control strategies. Emerging mRNA vaccines can trigger rapid immune responses and offer broader protection against diverse pathogens . Similarly, nanovaccines provide significant advantages by improving antigen stability, enhancing immune responses, and ensuring targeted delivery to specific immune cells [57].

Mastitis has an enormous effect on goat milk production, quality, and public health in rural Ethiopian households; however, research coverage remains scarce compared to cattle. A meta-analysis of 12 out of 13 studies on goat-level mastitis prevalence indicated that individual study estimates ranged from 13 to 45% [48, 77], with a random-effects pooled prevalence of 26.0% (95% CI: 20–33%) (Related file Fig. 1).

Fig. 1.

Geographical map of Waghimra Zone showing study districts in northeastern Ethiopia

Staphylococcus, Streptococcus, Escherichia coli (E. coli), Micrococcus, and Corynebacterium were the most commonly identified bacteria. Eleven of thirteen studies identified and reported different species of staphylococci species. Furthermore, studies on this topic in Ethiopia have been conducted disproportionately in one region, Oromia (10 out of 13); there is no attempt in the Amhara region, despite the fact that the region is the third largest with a goat population [23]. Specifically, 80–98% of farmers in the Waghimra Zone of the Amhara region raise goats primarily for milk production but are unaware of mastitis-related losses and public health risks and never implement preventive and control measures [7]. This is a significant setback in milk production and mastitis intervention, emphasizing the importance of shifting research priorities, given that goats are the foundation of families’ economic stability in that area.

Mastitis in goats poses significant public health concerns due to the potential transmission of zoonotic pathogens through contaminated milk. Bacteria commonly associated with mastitis can enter the human food chain when raw or improperly handled milk is consumed. In rural Ethiopian settings, where goat milk is widely consumed fresh and awareness of mastitis is low, the risk of foodborne illness is high. Mastitis not only reduces milk quality by increasing bacterial load and altering nutrient composition but also raises concerns regarding antimicrobial-resistant strains, further threatening consumer safety [80].

Priority milking hygiene is essential for preventing mastitis in goats by reducing bacterial load and somatic cell counts. Forestripping (evacuation of first jets) removes milk rich in bacteria and somatic cells before full milking, while pre‑ and post‑milking teat disinfection lowers microbial contamination and protects against new infections. Proper milking machine maintenance prevents equipment‑related contamination and teat injury. Using individual towels, effective disinfectants, and adequate drying further improves milk hygiene. Collectively, these practices form an evidence‑based approach to mastitis control in goats [52, 82]. Overall, mastitis is one of the biggest constraints on animal welfare and public health, necessitating extensive research, monitoring, and regulations. Therefore, with this background in mind, this study was initiated to achieve the objectives (1), to estimate the prevalence of mastitis in goats and associated risk factors and to isolate and identify bacteria from mastitic milk samples.

Materials and methods

Description of the study areas

The study was conducted in three districts of the Waghimra Zone, Amhara Regional State, Ethiopia. Farmers in these districts have a long-standing tradition of raising goats. Due to the significant goat populations and established practices in milk production and utilization, Abergelle, Sekota, and Ziquala districts were purposively selected (Fig. 1). The Abergelle district had topographies of a lowland agroclimate, with elevations between 1,150 and 2,100 m above sea level. About 80% of the arable land suffers from moisture deficiency and is susceptible to soil erosion. The primary rainy period starts in late June or early July and typically lasts from a few days to a month, although in rare instances, it may extend for up to two months [79]. The villages selected for the study were Bertarf, Saziba, and Kassayard. The Ziquala district shares a similar agroclimate with Abergelle; however, it is known for cultivating drought-resistant sorghum and lowland pulse crops. Bilaku, Gitaw, and Alqozu were selected as villages for the district. The Sekota district features a midland agroclimate, characterized by an average annual rainfall of 774.3 mm and an elevation ranging from 2000 to 2300 m above sea level.

Study population characteristics

Lactating Abergelle breed goats were regarded as the study population. The Abergelle goat, mainly habituated in the Wag-Himra lowlands and along the Tekeze River in Tigray and East Gondar, is a breed valued for meat and milk production [1].

Goats were grouped by age, parity, udder characteristics (including circumference and length), and history of mastitis exposure. Although the optimal time for mastitis screening is during peak lactation [58], goats were also classified based on lactation stages to assess its association with mastitis. The age of the sampled goat was determined based on the owner’s recall with dental examination and categorized as < 2, 3–4, or > 4 years [62]. Similarly, the stage of lactation was classified as early (1st month), mid (2nd month), or late (≥ 3rd month) [62]. The parity of the goats was likewise grouped into < 2, 3–4, or > 4 kids [17, 65]. Udder circumference was measured at its widest point and categorized as < 27 cm, 28–37 cm, or > 37 cm. Udder length was measured from the top of the hind middle section to the lower end and classified as < 12 cm, 13–17 cm, or > 17 cm. The characteristics of the study population are presented in Related file Table 1.

Table 1.

CMT scoring, interpretation, and reaction description

CMT Score	Interpretation	Description
0	Negative	No precipitation
Trace	Negative	A slight precipitate which tends to disappear with continued movement of the paddle
+ 1	Positive	Mild reaction, a distinct precipitate but not forming a gel
+ 2	Strong positive	Moderate reaction, the mixture thickens immediately with some gel formation
+ 3	Very Strong positive	Strong reaction, a distinct gel that adheres to the bottom of the paddle formed

(Source: [18])

Study design

A cross-sectional study was conducted from September 2024 to May 2025 to estimate the prevalence and identify potential risk factors associated with mastitis in goats.

Sampling approaches and sample size determination

A multistage top-down sampling approach was employed, utilizing simple random sampling at the lowest level. Three districts were selected purposefully based on factors such as logistics, accessibility, and the availability of Abergelle goats. Subsequently, two villages were randomly chosen from each district for the mastitis field-screening program. The sample size for estimating the prevalence of mastitis in lactating goats was calculated using the formula [78]: 

where N is the sample size, Z is the desired confidence level, P is the expected mastitis prevalence, and D is the margin of error. Assuming a 95% confidence level, 5% margin of error, and 50% expected prevalence, a minimum sample of 384 lactating goats was required. To ensure adequate statistical power and account for potential sample losses, 397 goats (794 udder halves) were ultimately sampled.

Data collection

Lactating goat observational examination

A field mastitis examination was scheduled for late November 2024, the peak kidding season for Abergelle goats (personal observation). The goats’ udders, teats, and milk were carefully examined for visible abnormalities. The mammary gland mastitis examinations included checks for udder asymmetry, swelling, abscesses, ticks, cracks, dryness, roughness, color changes, cuts, keratosis, injury, teat blindness, and function loss. Each udder halves was palpated for firmness, hardness, heat, and pain. The milk was examined for viscosity, clots, pus, blood, and textural changes. CM was defined as an udder with visible inflammation indicators, mentioned above, and abnormal milk [18]. A goat’s udder halves with some or all of these visible clinical signs was regarded as CM positive, so a veterinarian collected a 5 ml milk sample for bacteriological analysis.

Milk sampling and screening test

Milk samples from apparently healthy goat udders were screened for SCM. Before sampling, teats were cleaned using cotton balls moistened with 70% alcohol, and the first two to three streams of milk were discarded to minimize contamination. Afterwards, about 3 mL of milk from each goat’s udder was squirted onto a paddle and mixed with equal parts of CMT reagent. After 10 s, the reaction was evaluated subjectively based on gel thickness and graded as 0, trace, and + 1 to + 3 [18, 39]. A reaction showing no precipitation or only a slight precipitate that disappears when the paddle is moving was considered mastitis-free. Reactions ranging from mild precipitate to a strong, distinct gel adhering to the bottom of the paddle were considered positive, with scores from + 1 to + 3.

The cow CMT reagent was used, as no validated goat-specific CMT reagent is currently available. However, the CMT test is influenced by both infectious and non-infectious factors and is therefore not considered a definitive diagnostic tool for mastitis, requiring further confirmatory testing. In this study, all clinical and subclinical mastitis cases identified by gross observation and CMT were further analyzed through bacterial isolation and identification. A veterinarian collected 5 mL of milk from each udder half with a grade of ≥ + 1 [18], labeled it, and transported in a cool box to the SDARC veterinary microbiology lab for analysis. Table 1 summarizes the intensity of CMT milk complex formation and its corresponding interpretations.

Bacterial isolation and identification procedures

Microbiological analysis was performed on milk samples that tested positive for mastitis based on physical and CMT examinations. Media and broth preparations adhere to manufacturer guidelines and standard protocols [61]. Peptone water broth (PW) was prepared for initial microbial cultivation to recover low and stressed bacteria. The next day, the PW broth was vortexed, and a loopful of suspension was plated on selective and differential media. Plates with ≥ 1 colonies of the target bacteria along the streaked line after 48 h were considered positive. Any mixed cultures were subcultured to produce pure colonies [39]. The size, shape, texture, and color of bacterial colonies were examined, and Gram staining and other biochemical tests were performed [61].

Mannitol salt agar (MSA) (Himedia, India) was used to selectively identify Staphylococcus and other salt-tolerant gram-positive bacteria. A loopful of PW broth suspension was spread on MSA, and incubated at 37 °C for 24 h [46, 84]. Gram staining was then performed, and Gram-positive cocci colonies were subjected to KOH and other biochemical tests such as catalase, urease, oxidase, methyl red and citrate tests. Staphylococcus, Micrococcus, and Enterococcus were identified based on their biochemical reactions.

MacConkey agar (Himedia, India) was used to selectively isolate and differentiate gram-negative bacteria based on growth and lactose fermentation abilities. Several biochemical tests, including the triple sugar iron (TSI) test, citrate test, motility test, indole test, MR test, urease test, and catalase test, were used. Gram-negative bacteria were identified as per described in literatures [5, 40].

Statistical analysis

All data collected was curated and cleaned in Microsoft Excel (Microsoft Office, 2016). STATA Version 17 (StataCorp, Texas, USA) software was used in the statistical analysis. Descriptive statistical analysis summarized data using frequency, and percentages. Pairwise correlation was first performed to assess the presence/absence of multicollinearity (Related file Table 2). Univariable logistic regression models were fitted for each pair of independent and dependent covariates initially. Then, variables with P < 0.25 were refitted to multivariable logistic regression modeling. The associations between independent and outcome variables were reported in crude and adjusted odds ratios, with statistical significance considered at P < 0.05.

Table 2.

General description of udder health status of goats at the animal and udder half levels

Health Status		Goat							Udder halves
		Examined	Bilateral	(%)	Unilateral	(%)	Subtotal	(%)	Examined	Positive	(%)
Abnormalities	CM	397	1	0.25	9	2.27	10	2.52	794	11	1.39
	SCM	395	30	7.59	58	14.61	88	22.28	776	118	15.21
	Blind Teat	397	1	0.25	5	1.26	6	1.51	794	7	0.88

Result

Prevalence of mastitis in goats

Table 2 presents the distribution of mammary gland health abnormalities at both the goat and udder-halves (UH) level. Among the 397 goats examined, 26.25% showed mammary gland abnormalities, which included 10 cases of CM (one bilateral) and 6 cases of blind teats (one bilateral). Upon physical examinations, common clinical findings include swelling, pain, hardened and increased viscosity, or decreased and abnormal milk color.

Among the 395 goats tested for SCM, after excluding one goat with bilateral CM and another with a bilateral blind teat, 22.28% (98out of 395) tested SCM positive. Of these, 7.59% had bilateral SCM, while 14.61% exhibited unilateral SCM. Consequently, the overall goat-level prevalence of mastitis, including both CM and SCM, was 24.8%.

Of the 794 udder halves examined, CM was detected in 1.39%, and 0.88% had blind teats. Consequently, only 776 apparently healthy udder halves were screened for subclinical mastitis (SCM), of which 15.21% tested positive.

Subgroup prevalence of mastitis at goat level

Table 3 summarizes the goat-level subgroup prevalence of CM and SC. Goats with a prior history of mastitis showed higher CM prevalence than those without previous exposure (8.7% vs. 2.48%). CM prevalence was higher in the Abergelle district compared with Sekota. Higher CM occurrence was observed during mid- (4.62%) and late-lactation (3.05%) stages. Additionally, goats with parity 1–2 exhibited lower CM prevalence than those with parity greater than three.

Table 3.

Subgroup prevalence of CM and SCM by risk factors at the goat level

Variable	Category	CM		SCM
		N	N + (%)	N	N + (%)
District	Abergelle	103	5(4.85)	103	36(34.95)
	Sekota	199	5(2.51)	197	29(14.72)
	Ziquala	95	0(0)	95	23(24.21)
Age	< 3 years	97	1(1.03)	97	16(16.49)
	3–4 years	176	6(3.41)	175	48(27.43)
	> 4 years	124	3(2.43)	123	24(19.51)
Lactation stage	< 30 days	275	5(1.82)	274	56(20.44)
	30–60 days	65	3(4.62)	64	23(35.94)
	> 60 days	57	2(3.51)	57	9(15.94)
Parity	1–2 kids	125	1(0.8)	125	20(16)
	3–4 kids	151	6(3.97)	150	40(26.67)
	> 4 kids	121	3(2.48)	120	28(23.33)
Mastitis history	No	374	8(2.14)	372	73(19.62)
	Yes	23	2(8.7)	23	15(65.22)
	< 27 cm	47	0(0)	47	11(23.40)
Udder circumference	28–37 cm	298	8(2.75)	296	58(19.59)
	> 37 cm	52	2(4)	52	19(36.54)
	< 12 cm	28	2(7.14)	27	5(18.24)
Udder length	13–17 cm	292	6(2.05)	291	65(22.34)
	> 17 cm	77	2(2.6)	77	18(23.38)

N = goats examined; N + = goats found with mastitis

The Abergelle district had the highest goat-level SCM prevalence (34.95%), followed by Ziquala (24.21%) and Sekota (14.72%). Subclinical mastitis was more common in goats in mid-lactation, aged 3–4 years, and with parity of 3–4 kids. Goats with a history of previous mastitis, as well as those with larger udder circumference and longer udder length, also exhibited higher SCM prevalence.

Subgroup prevalence of mastitis at udder half level

The udder-half-level prevalence of CM was 1.4 percent. Higher CM prevalence was observed with larger udder circumference (2.59%) and shorter udder length (2.55%). For SCM, Abergelle district showed the highest udder-half prevalence (34.95%), followed by Ziquala (24.21%) and Sekota (14.72%). Udder halves from goats in mid-lactation, aged 3–4 years, and with middle parity exhibited the highest SCM prevalence within their respective categories. Additionally, previously exposed udder halves showed higher SCM prevalence (Table 4).

Table 4.

Subgroup prevalence of CM and SCM by risk factors at udder half level

Variable	Category		CM		SCM
		N	N + (%)	N	N + (%)
District	Abergelle	206	5 (2.43)	201	N(23.38)
	Sekota	392	6(1.53)	385	41(10.65)
	Ziquala	190	0(0)	190	29(15.26)
Age	< 3 years	194	1(0.52)	193	22(11.4)
	3–4 years	352	6(1.7)	341	61(17.89)
	> 4 years	248	4(1.61)	242	35(14.46)
Lactation stage	Early	550	5(0.91)	540	75(13.89)
	Mid	130	4(3.08)	95	30(31.58)
	Late	114	2(1.75)	98	13(13.27)
Parity	1–2 kids	250	1(0.4)	249	24(9.64)
	3–4 kids	302	6(1.99)	291	52(17.87)
	> 4 kids	242	4(1.65)	236	42(17.8)
Udder circumference	< 27 cm	6	0(0)	6	2(33.3)
	28–37 cm	232	6(2.59)	223	37(16.59)
	> 27 cm	556	5(0.9)	547	79(14.44)
Udder length	< 12 cm	196	5(2.55)	189	35(18.52)
	13–17 cm	440	4(0.91)	435	58(13.33)
	> 17 cm	152	2(1.32)	152	25(16.45)
Total		788	11(1.4)	776	118(15.21)

Association between risk factors and mastitis at goat level

Udder length and udder circumference were found to exhibit multicollinearity (r = 0.6) and were therefore excluded from logistic regression analysis (Supplementary file Appendix 2). The multivariable logistic regression analysis indicated that previous mastitis exposure, district, lactation stage, and parity were significant risk factors for mastitis. Briefly, the Abergelle district had significantly higher odds of goat-level mastitis prevalence compared to the reference Sekota district (P < 0.001), and goats with a history of mastitis were 13.6 times more likely to test positive to mastitis (P < 0.001) than those without such a history. Furthermore, goats at parity 3 or 4 were 2.73 times more likely to test positive for mastitis compared to those at parity 2 or lower, and goats in the second lactation stage (30–60 days) were more likely to have mastitis than those in the first lactation stage (Table 5).

Table 5.

Univariate and multivariable logistic regression analysis of risk factors associated with mastitis goats at goat level

Variable	Category	COR	P value	LCI	UCI	AOR	P value	95% LCI	95%UCI
District	Sekota	Ref				Ref
	Abergelle	2.94	< 0.001	1.71	5.06	3.47	< 0.001	1.89	6.38
	Ziquala	1.54	< 0.15	0.85	2.85	1.39	< 0.34	0.71	2.74
Lactation stages	Early	Ref				Ref
	Mid	2.18	< 0.008	1.23	3.88	1.92	< 0.04	1.01	3.65
	Late	0.74	< 0.431	0.35	1.56	0.88	< 0.75	0.39	1.98
Parity	1–2 kids	Ref				Ref
	3–4 kids	2.06	< 0.016	1.14	3.69	2.73	< 0.028	1.11	6.67
	> 4 kids	1.71	< 0.092	0.92	3.18	2.11	< 0.18	0.7	6.41
Mastitis history	No	Ref				Ref
	Yes	9.44	< 0.001	3.4	26.2	13.6	< 0.001	4.64	40.15

COR Crude odds ratio, LCI Lower confidence interval, UCI Upper confidence interval

Association between risk factors and mastitis at goat level

The odds of udder half mastitis occurrence in the Abergelle district were 3.47 times greater than in the Sekota district and 1.92 times greater in middle-lactating goats. Goats with parity 3–4 had 2.73 times greater odds of udder half mastitis occurrence than goats with < 3 parity (Table 6).

Table 6.

Univariable and multivariable logistic regression analysis of risk factors associated with the prevalence of mastitis at udder half level

Variable	Category	COR	P value	LCI	UCI	AOR	P value	95% LCI	95%UCI
District	Sekota	Ref				Ref
	Abergelle	3.61	< 0.00	1.93	6.76	3.47	< 0.00	1.89	6.38
	Ziquala	1.72	< 0.12	0.87	3.42	1.39	< 0.34	0.71	2.74
Lactation stages	Early	Ref				Ref
	Mid	1.87	< 0.06	0.97	3.58	1.92	< 0.048	1.01	3.65
	Late	0.91	< 0.828	0.39	2	0.88	< 0.757	0.39	1.98
Parity	1–2 kids	Ref				Ref
	3–4 kids	2.42	< 0.035	1.08	5.96	2.73	< 0.028	1.11	6.67
	> 4 kids	1.97	< 0.232	0.65	6.01	2.11	< 0.186	0.7	6.41

Isolated and identified bacteria

The bacteriological analysis of mastitic milk samples indicated critical findings. 118 out of 129 samples (91.47%) exhibited bacterial growth. Among these, 72 (61.02%) had a unique bacterial colony and 42 (35.59%) had a mixed colony. About 88 (55.0%) isolates were gram positive and 72 (45.0%) were gram negative. Staphylococcus spp. was the most prevalent (47 isolates, 39.83% of the total isolates), followed by E. coli (12, 10.17%), Enterococcus spp. (5, 4.24%), and Micrococcus and Klebsiella (3 each, 2.54%). Staphylococcus and E. coli (n = 1), Staphylococcus and Enterococcus (n = 1), and E. coli and Enterococcus (n = 1) were identified from mixed colonies. All CM samples were culture positive, of which 5 (45.45%) were positive for Staphylococcus spp., 3 (27.27%) for E. coli, and 2 (18.18%) for Enterococcus spp., and one CM case was associated with other non-identified pathogen (Table 7).

Table 7.

Bacterial isolates identified in CM and SCM samples and their prevalence

Category	Bacteria identified	Sample	CM	SCM	Total	Prevalence (%)	LCI	UCI
Growth	Sample	129	11	107	118	91.47	86.65	96.29
	Staphylococcus	118	5	42	47	39.83	28.13	44.73
	E. coli	118	3	9	12	10.17	4.88	15.28
Isolates	Klebsiella	118	0	3	3	2.54	0.27	4.93
	Micrococcus	118	0	3	3	2.54	0.27	4.93
	Enterococcus	118	2	3	5	4.24	0.55	7.21
	Staph. + E. coli	118	2	2	4	3.39	0.11	6.09

Discussion

The field investigation of mastitis in goats resulted in various intramammary abnormalities, such as teat blockages, cracks, and inflammation indicators, with a goat-level mastitis prevalence of 24.8%. This prevalence was consistent with some reports in Ethiopia: 24% [17] and 33.33% [18], but lower than 45.05% [48]. Comparable findings in African countries include 19.45% in Algeria [68] and 17.80% in Botswana [47], but higher than a report in Kenya [32]. This prevalence was also comparable with the meta-synthesized estimate from Ethiopian studies, as illustrated in Related file Fig. 1.

The prevalence observed in this study, however, was significantly lower than several reports in Europe exceeding 80% [50, 55] and Indonesia [67, 83]. Conversely, lower prevalence (< 5% has been documented in some Asian nations [20, 36, 37], the Czech Republic [34], and the USA [11, 19].

The prevalence of CM was below the ≤ 5% threshold but was higher in goats with previous exposure to the disease. In Ethiopia, CM prevalence has been reported as 2.0% [17], 4.3% [43], and 4.4% [48], which is comparable to the findings of this study but lower than the 10.0% reported by Balemi et al. [18]. This finding also aligns with some African reports, including 3.0% [6] and 3.55% [26] in Algeria and 2.91% in Nigeria [14], while being slightly higher than the 1.88% reported in Kenya [40]. Other comparable reports were identified in South Asian countries, including Bangladesh (4.54% [36],) and Indonesia (1.82% [73]), as well as in Brazil (2.78% [38]).

The prevalence of SCM also remained below the ≤ 30% threshold. This is consistent with some Ethiopian reports, including 20.6% by Abera et al. [2], 23.0% by Badaso et al. [17], and 26.0% by Balemi et al. [18]. However, the SCM prevalence observed in this study was higher than the 12.0% reported by Megersa et al. [43], 13.27% by Mohammed [45], 13.0% by Teshome et al. [77], and 18.0% by Gebrewahid et al. [27]. Comparatively, lower prevalences of SCM were reported at 1.0% by Alemu and Abraha [8], 33.0% by Amenu et al. [10], and 42.0% by Abriham et al. [3] in Ethiopia. This SCM prevalence was also lower than some reports in Kenya [32, 51] and Algeria [26, 74].

This finding contrasts with studies reporting SCM prevalence exceeding 50% in Asian countries, such as Indonesia [83] and Saudi Arabia [9]. Similarly, higher prevalence has been reported in several European countries, including Greece [28, 53], Romania [50], and Poland [18, 55]. In contrast, some studies have reported SCM prevalence below 10% in Brazil [4], the Czech Republic [34], the USA [11], Italy [75], and the Netherlands [25].

Subclinical mastitis significantly reduces milk yield, and in this study, it was 10 times more prevalent than CM in both the goat and udder halves. Koop et al. [35] found that SCM from major pathogens resulted in a daily milk loss of 0.13 kg during early lactation and 0.29 kg during later stages. Gelasakis et al. [28] found that SCM reduced daily milk yield by 5.3%, with NAS accounting for 9.7% and gram-negative bacteria for 15%. The economic impact of SCM in the study area may have significant implications. About 75% of the economic impact of SCM [40] is attributed to the unnoticed decline in milk production. Untreated SCM can spread to healthy animals, posing a higher risk if not detected and controlled early. In addition, untreated SCM can damage the mammary gland tissue progressively, leading to CM. Only 20–60% of SCM cases can resolve without intervention,the remaining 40% either progress to CM or persist as SCM [40].

In Ethiopia, awareness of subclinical mastitis among herders remains low due to multiple constraints, including high illiteracy levels and the fact that goats are largely managed by resource-poor farmers. This limited awareness, combined with the productivity and economic consequences of the disease and the public health risks associated with the community’s tradition of consuming raw milk, may have profound implications.

Several factors contribute to the variation in SCM prevalence across reports, such as management practices, production systems, milking practices, equipment use, and diagnostic test accuracy. Factors like the breed, age, lactation stage, litter size, milk yield, and parity in goats can affect the prevalence of mastitis. For instance, the Abergelle goat breed, known for its small size, udder, low milk production, and ability to withstand harsh conditions, has a lower mastitis prevalence compared to the high-yielding Begait breed, as reported in a study in the Tigray region by Gebrewahid et al. [27].

This study found that parity was strongly associated with mastitis, a result in line with previous research [17, 36, 65]. The odds of developing mastitis were 2.7 times higher for goats with parities 3–4 and twice that for parity > 4 compared to the reference, parity 1–2. Later parities, which often involve increased chances of exposure to infections, have recurrence of mastitis in later kidding cycles. As the number of kidding increases, the openings of the teats tend to dilate, making them more susceptible to microbial entry and subsequent infections. According to Pratap et al. [56], SCM is most prevalent at the fourth parity, whereas CM peaks at the second parity.

This study also revealed that lactation stages were statistically associated with mastitis occurrence. The odds of mastitis was higher in the mid and late lactation stages than in the early lactation stages. As lactation advances, the cells indicating mastitis increase steadily, while milk production decreases [54]. Puggioni et al. [58] suggested screening goats for mastitis during peak lactation to enhance intramammary infection detection accuracy. Hristov et al. [29] also found that 41.67% of SCM cases from early lactation continued into late lactation, raising the odds of infection in subsequent stages. According to Koop et al. [36], late lactation and low milk yield were associated with higher odds of latent mastitis.

Mastitis prevalence in goats is significantly associated with a history of mastitis exposure. According to Megersa et al. [43], those with prior mastitis are twice as likely to develop mastitis as those without a history of the condition. Poor hygienic conditions can exacerbate this situation, as supported by Aqib et al. [15], and Qazi et al. [59].

The other factor influencing mastitis prevalence reporting is associated with diagnostic approaches used. The reliability of commonly used diagnostic tests, such as somatic cell count (SCC) and CMT for detection of SCM in goats, is questionable because healthy goats often have somatic cell levels that exceed the normal range established for cows [70, 81]. In goat milk, neutrophil levels range from 45 to 75%, while in cow milk, the range is 2% to 20%. Consequently, there is no universally accepted single cutoff point for SCC to detect mastitis in goats, resulting in disparities in regulatory standards and scholarly references [80].

Although CMT is the most widely used test, inexpensive, simple to perform, and requires no prior experience or advanced training from farmers, its low specificity for diagnosing IMI in goats remains a major limitation. The CMT test can only detect 80% of IMI cases if milk somatic cells exceed 7 × 10 cells/ml or 62%, if somatic cells exceed 5 × 10 cells/ml [80]. Increasing the CMT cutoff for declaring a positive result resulted in a trade-off in diagnostic performance, with reduced sensitivity and negative predictive value but improved specificity and positive predictive value [42]. Another important limitation of the California Mastitis Test (CMT) is that score interpretation is subjective. CMT readings depend on the examiner’s understanding and experience in interpreting the degree of gel formation in the milk–reagent complex. Consequently, variation in personnel expertise can lead to misclassification, thereby reducing the overall validity and reliability of CMT result interpretation.

Milk samples suspected of mastitis have revealed a wide range of bacterial pathogens across different studies. In the present research, Staphylococcus was the most common bacterium identified, consistent with Ethiopian findings reported by Badaso et al. [17], Amenu et al. [10], Mustefa et al. [48], and Hussen et al. [30]. Similar patterns were observed in other African studies, such as Kabui et al. [32], who found that Staphylococcus accounted for 42% of isolates in mastitic goats in Kenya. Findings from other regions likewise identified Staphylococcus as the predominant pathogen in mastitic milk, including reports by Gabli et al. [26], Qolbaini et al. [60], and Yoksa et al. [85]. In contrast, studies such as Scaccabarozzi et al. [66], Andrade et al. [12], Urbanska et al. [18], and Tvarožková et al. [81] documented different dominant bacterial profiles.

Staphylococcus was the most common bacteria in CM, consistent with RiPolveiro et al. [63], who reported that it was the predominant isolate of CM cases in Brazil. Other studies have indicated that S. aureus is responsible for both CM and gangrenous mastitis [25, 41]. Zhao et al. [86] found that NAS was the most common cause of SCM (59.52%) in China.

The high prevalence of Staphylococcus has significant implications for animal welfare, productivity, and public health, as the bacterium is transmitted from infected animals through improper milking procedures, the use of unclean equipment, or poor udder hygiene [13, 21, 39]. Limited knowledge and poor mastitis-related practices among herders further heighten the risk of transmission, especially given the public health concern associated with the widespread consumption of raw milk in the study area. The observed higher prevalence of bilateral mastitis may also reflect gaps in herders’ awareness and milking hygiene, facilitating the continued spread of Staphylococcus. The high prevalence of staphylococcal bacteria observed in this study highlights the need for future investigations focusing on species-level identification and antimicrobial susceptibility profiling to strengthen mastitis control and prevention efforts.

The prevalence of E. coli, the second most dominant bacterium identified in this study, was consistent with previous Ethiopian reports [17, 27, 48]. Similar findings were observed in other African countries, including Botswana (8.6% [47],) and Kenya (9.1% [39]). Compared to studies from other regions, the prevalence was comparable to China (11.4%, [86]), higher than reported in Brazil (2.4%; [38]), India (1.2% [44],), and Greece (< 1% [28],), but notably lower than in Pakistan (84.4%, [31]) and Kenya (34.2%; [49]).

The relatively low prevalence of E. coli in this study could be attributed to the study areas being lowland regions with limited moisture. As a result, this condition is thought to reduce environmental contamination and bacterial growth, thereby decreasing the risk of mastitis. As moisture levels increase, bedding material may splash onto the mammary gland, increasing the risk of mastitis from coliforms and other environmental pathogens [66].

In this study, other bacterial isolates included Enterococcus, Micrococcus, and Klebsiella. Alemu and Abraha (2017) isolated Micrococcus from goats with mastitis in Ethiopia, whereas Danmallam and Pimenov [24], and Mahlangu et al. [39] isolated those bacteria in Nigeria and Kenya, respectively. Specifically, Klebsiella was reported as one of the most common isolates in mastitic goats in Kenya (Okoko and Maina, 2020; [39]). In Europe, Enterococcus has been isolated from mastitic goats in Italy [71], Norway [69], and Poland [18]. Similarly, Lima et al. [38] reported Enterococcus in Brazil from mastitis in goats.

Enterococcus, Micrococcus, Klebsiella, E. coli, and streptococcal and staphylococcal species are often associated with an environmental origin. Poor-quality litter, contaminated watering points, and inadequate housing sanitation create conditions for goats to pick up these bacteria to udder. Unhygienic milking practices, lack of teat disinfection, muddy or wet bedding, abrasive fences or floors, excessive teat massage, under-milking, and improper milking machine pressure predispose these bacteria to cause opportunistic mastitis, often termed environmental mastitis [80]. These pathogens readily contaminate the udder and teat skin, causing intramammary infections, particularly during wet or unhygienic seasons and in districts with weaker husbandry practices.

Prevention and control of environmental mastitis involve maintaining clean, dry, and well-ventilated housing with proper bedding and drainage, ensuring udder and teat hygiene before milking, and monitoring animal comfort and milking practices. Regular record-keeping and prompt culture of clinical cases help detect and manage outbreaks early [72].

Overall, the high prevalence of mastitis and the presence of abundant zoonotic bacterial pathogens highlight the need for comprehensive mastitis prevention and control programs in goats within the dryland study areas. A key priority is to raise awareness among herders regarding mastitis and its welfare, production, economic, and public health consequences. Prevention and control strategies, such as practicing hygienic milking, maintaining clean bedding, cleaning feeding and watering areas, culling chronic or non-responsive cases, early detection and isolation of infected animals, and implementing dry-period treatment, should be effectively communicated and delivered to herders to improve herd health and reduce disease burden.

Limitation of the study

The unavailability of a validated goat-specific CMT reagent and the subjective nature of CMT milk–reagent complex scoring may introduce errors in the accurate detection of IMI. In addition, inaccuracies in farmers’ recall of the ages and parities of the examined goats may inevitably lead to errors in risk assessment. Of the 118 bacterial isolates, only Staphylococcus, E. coli, Micrococcus, Enterococcus, and Klebsiella were identified. Furthermore, except for E. coli, the identified bacteria were not further differentiated to the species level due to material and logistical constraints. Moreover, another limitation of this study was the absence of molecular typing of the identified bacteria and assessment of their antimicrobial resistance patterns.

Conclusion and recommendations

This study investigated that mastitis was an important production constraint in goats in the study area. The prevalence of mastitis in field tests and pathogen isolation and identification indicated an alarming burden of both. Subclinical mastitis was found ten times greater than CM. Besides, the occurrence of mastitis was statistically associated with some demographic risk factors such as district, animal’s age, parity, lactation stage and previous exposure to mastitis. This study also investigated Staphylococcus spp. was the most abundant bacteria, followed by E. coli and Enterococcus spp. The relatively high prevalence of mastitis indicates that it requires regular monitoring and the implementation of effective prevention and control strategies. Furthermore, regular mastitis screening and training for farmers on zoonotic, economic, and epidemiological impacts and modes of transmission should be designed and implemented. Moreover, further investigations to assess the bacterial load, especially Staphylococcus spp., at the animal and equipment levels and in ready-to-eat or semi-processed milk products should be undertaken to better understand potential sources of infection and public health risks.

Authors’ contributions

**AT**: conception, methodology, investigation, data collection, formal analysis, draft writing, and reviewing; **HT**: conceptualization, supervision, draft writing, and reviewing; **BT**: conceptualization, supervision, draft writing, and reviewing; **YT**: Data collection, investigation, draft writing, and reviewing;

Funding

This work was supported by the Amhara Agricultural Research Institute [S/LRD/AH/14/2023], Ethiopia.

Data availability

Data will be available upon responsible request to the corresponding author.

Declarations

Ethics approval and consent to participate

The non-invasive field animal experiments were conducted in strict accordance with the ARRIVE guidelines and complied with the U.K. Animals (Scientific Procedures) Act, 1986. The study was approved by the Sekota Dryland Agricultural Research Center Animal Health Research Review Committee (SDARC-AHRRC/23/05/2023). Verbal informed consent was obtained from goat owners prior to physical examination of the animals and collection of milk samples.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.