Prevalence of bovine mastitis and its associated risk factors under different production system in Borena district of South Wollo Zone, Amhara, Ethiopia

Abstract

The study was designed to determine the prevalence of bovine mastitis and its associated risk factors under different production systems in rural and peri-urban areas of Borena District, South Wollo Zone, Amhara Region, Ethiopia. A total of 180 households were interviewed using a semi-structured questionnaire concerning the different potential risk factors for mastitis prevalence, and 229 lactating cows were subjected to clinical examination and California Mastitis Test (CMT) screening to determine the prevalence of subclinical mastitis. The prevalence was determined in peri urban and mixed farming systems. The prevalence of mastitis was significantly higher in peri-urban production systems (87.0%) than in rural smallholder production systems (68.6%). The overall prevalence of bovine mastitis determined in the area was 73%, from which the subclinical mastitis accounts 55.5% and remaining 17.5% was clinical mastitis. Out of 916 examined quarters, 5.4% were clinically affected, 1.5% were blind, and 46.1% were CMT positive. In general, the prevalence of mastitis was high, with breed, stage of lactation, parity, and barn hygiene all playing significant roles. To overcome this problem, awareness creation among dairy cow owners on how to keep the udder clean, improving floor conditions through regular cleaning, and medical intervention are needed to improve mastitis prevention and control programs in the study areas.

Keywords:

• clinical mastitis
• risk factors
• subclinical mastitis
• revalence

PUBLIC INTEREST STATEMENT

Mastitis (inflammation of the mammary gland) is one of the most common diseases affecting dairy animals and is caused by pathogenic bacteria, viruses, fungi, and the toxins of these pathogens. The pathogens enter through the milk canal, interact with the mammary tissue or cells, and then multiply. It is the most expensive and damaging disease to the dairy sector because it causes enormous financial losses, jeopardizes the health and wellbeing of animals, and has a negative impact on both the quality and quantity of milk. The economic losses are mostly due to a reduction in milk output, but also to the culling of chronically infected cows, the expense of veterinary care, and negative effects on milk quality. Some causative agents of the disease are also hazardous for public health. Based on the severity, it can be either clinical or subclinical mastitis. Clinically diagnosed mastitis (CM) is defined by visual signs such as udder redness, swelling, heat, and pain, as well as milk clots and other macroscopic milk alterations; however, the subclinical form has no visible signs. There are several risk factors that cause the occurrence of mastitis, such as animal husbandry, hygienic milk production, tick infestation, teat lesions, history of mastitis, unhygienic equipment, etc. Therefore, this work has been developed to determine the prevalence of the disease and its risk factors. It will help farmers and livestock owners to raise awareness and control the disease in order to improve milk production, reduce economic losses and ensure animal welfare and consumer safety.

1. Introduction

Ethiopia has significant dairy development potential, due vast cattle population, and comparatively good environmental conditions for enhanced high-yielding animal breeds (Bereda et al., 2014). Ethiopia has approximately 65.34 million cattle, according to the livestock population census (CSA (Central Statistics Agency), 2021). According to the report of Feed the Future, the livestock industry contributes up to 40% of agricultural GDP, over 20% of total GDP, and 20% of national foreign exchange income (Management Entity, 2021), which shows that the dairy sector in Ethiopia has the potential to contribute to poverty alleviation, improved nutrition, and household income. However, the sector has not been fully exploited and promoted because of the absence of contemporary livestock farming and management, limited professional staff in dairy technology and marketing, poor distribution infrastructure, and a restricted dairy cows’ health program, the sector has not been adequately exploited and pushed in Ethiopia (Central Statistical Agency CSA, 2007).

A variety of dairy cattle diseases, including bovine tuberculosis, brucellosis, and mastitis, are caused by inefficient husbandry and management systems. Mastitis is one of the diseases that infect and harm the dairy cattle population, resulting in reduced milk production and quality, and increases the cost of treatment for dairy farmers (Moges et al., 2012). It is one of the serious diseases of dairy cows that involve interplay between management practices and infectious agents, having different causes, degrees of intensity and variations in duration and residual effects. Moreover, mastitis is an economically important and expensive disease of dairy production, and it is the major concern of the dairy industry worldwide (Lidet et al., 2013). Similarly, Kebede and Weldemariam (2015) revealed that mastitis was shown to be one of the most common diseases affecting dairy cows in Ethiopia. Several studies conducted in various parts of Ethiopia showed a higher and more varied prevalence of mastitis depending on the type of farm, animal breed, and management style. The prevalence of the disease ranges from 0.93% to 25.1% and 15% to 56% of clinical and subclinical mastitis, respectively (Belay et al., 2022; Deng & Asebe, 2015; Tesfaye et al., 2009; Zenebe et al., 2014). The highest prevalence of mastitis (74.7%) was reported by Zeryehun et al. (2013) from central Ethiopia, Addis Ababa.

While bovine mastitis has been a more prevalent and serious issue for farmers, it is still insufficiently investigated, and information relating to its distribution and risk factors is limited in some parts of Ethiopia (Nurye et al., 2021). The establishment of preventative and control methods for the disease in a specific area is in need depends on epidemiological studies on the prevalence, associated factors, and the microorganisms that cause the disease. According to the study area’s district livestock office, the disease is poorly understood, and there is limited information on its prevalence, magnitude, related risk factors, or associated economic loss in the Borena District of the South Wollo Zone. Furthermore, periodic assessments of animal health have had a significant impact on providing safe and high-quality products and meeting the continuous rise in demand for milk and milk products, as well as reducing its prevalence and effect. Therefore, the goal of this study was to determine the prevalence of mastitis, and its impact on milk quality in different production systems in the Borena District of Southern Wollo, Ethiopia,

2. MAterials and methods

2.1. Description of study area

The study was conducted in the Borena District which is located in the north-central highlands of Ethiopia. The area is found in the South Wollo administrative zone of Amhara Regional State and is found 577 northwest of Addis Ababa and 180 km west of Dessie. It lies between 10° 34’ N, to 10° 53’ N latitude and 38° 28’ E to 38° 19’ E longitude. Borena District covers a total area of 937 km². The elevation of Borena is found to be between 1500 and 3200 meters above sea level. The total annual rainfall of the area varies from 889 to 1500 mm per year. The area receives the highest rainfall during summer, which starts in June, and ends in September and the short rainy season in spring which consists of March, April, and May. The mean annual temperature of the region varies from 14°C to 19°C (Meteorological records of the woreda from 2008 to 2010).

2.2. Study design and study animal

A cross-sectional study design was used to estimate the prevalence of bovine mastitis and associated risk factors in the study area. The study animals were lactating smallholder dairy cows of different management conditions with different breeds, age groups, lactation stages and parity were examined as study population.

2.3. Study procedure and sampling method

The study area was selected purposively based on milk production potential and livestock population using data from livestock and fishery offices. A purposive sampling procedure was applied to select a sample Kebele considering the population of cows, accessibility, and security of the Kebeles. Thus, six Kebeles were selected based on the data gathered from the preliminary exploratory field visit along with the available secondary data. Smallholder farmers were also purposively selected based on the presence of lactating cows, high milk production, and husbandry practices. Then, a simple random sampling was used for each lactating cow. The sample size was determined based on the formula described in Thrusfield (2007). A total of 229 cows were taken for the CMT test, and a total of 180 households (30 from each Kebele) were selected and subjected to a semi-structured questionnaire.

2.4. Data collection

2.4.1. Physical observation of udder and cow

The udder was visually and physically examined for fibrosis, inflammatory swellings, visible injury, tick infestation, tissue atrophy, and swelling of supra mammary lymph nodes. The size and consistency of mammary quarters were examined for any abnormalities, such as swelling, firmness, or blindness. A semi-structured questionnaire was used to collect information about the previous health history of the mammary quarters and types of production system practiced as well as other data about risk factors (host and environmental risk factors) from the cow owners.

2.4.2. Sample collection

Standard milk-sampling techniques were employed for the collection of milk samples. The near teats were sampled first then the far to reduce contamination of the teat ends during the collection of samples. After discarding the first three milking streams, about 10 mL milk was put in a sterile sample cup.

2.4.3. California Mastitis Test (CMT)

The California Mastitis Test was performed for each quarter to diagnose the presence of subclinical mastitis. It was carried out based on the method described by Quinn et al. (2004). The first stripping of the milk was discarded, and a few streams of (fore)milk from each quarter were milked into four plastic dishes set on a paddle using the proper milking procedure. Then, an equal amount of commercial CMT reagent was poured into each cup containing the milk in the paddle cup with an equal amount of commercial reagent in each cup. A gentle circular motion was applied to the mixtures in a horizontal plane for 15 seconds. Then, depending on CMT, results were categorized based on the thickness of the gel formed by the CMT reagent and milk mixture and scored as 0 (negative), T (trace), 1 (weakly positive), 2 (distinct positive), and 3 (strongly positive) (ICAR Indian council of agricultural research, 2011).

2.5. Data analysis

The collected data was cleaned, categorized, and entered into the Microsoft Excel sheet. SPSS version 16 has been used for statistical analysis. The questionnaire and CMT data were both analyzed using the statistical software provided. The odds ratio was used to determine the association between different risk factors (host and environment) and the prevalence of mastitis. The level of confidence was set at 95% and a probability of P < 0.05 was considered statistically significant.

3. Results and discussion

3.1. Dairy production systems

A mix of farming and peri-urban production systems was identified in the study area. The crop-livestock production system is the major system practiced by 90% of the households. In crop-livestock production or mixed farming systems, farmers may use their cows for multipurpose, while the remaining 10% of the households reared dairy cattle for only milk production. In addition, 92.2% and 87.8% of the respondents practiced mixed farming production in highland and midland agro ecology, respectively. A mixed farming production system was practiced in the rural area of the district. Based on the survey result, cows were reared for milk production, as well as breeding to get oxen, and the main feed resource in this production system was free grazing, crop residue, and hay. However, the peri-urban production system is predominant in those Kebele near the district town and most of the owner’s rear improved dairy breed cows for milk production. The feed resources include purchased hay, crop residues, and supplements like fermentation byproducts of local beverages. Moreover, this production system is predominantly practiced in midland than in highland areas of the district. The majority of the animals kept in this production system received relatively better animal health services, such as vaccinations to overcome disease outbreaks and treatments in cases of disease incidence.

The prevalence of mastitis under different production systems was presented in Table 1. Mastitis was found to be more common in the peri-urban production system (87%) than in the mixed farming production system in the current study. Farmers’ management practices, environmental conditions and genetic differences in the animals were the main factors for the differences in the prevalence of mastitis in the different production systems. This result is in line with the reports of Tolosa Fulasa and Begna Deressa (2022). The result of the present study is in line with the report of Kebede and Weldemariam (2015), in Dire Dawa, Eastern Ethiopia. However, the finding of the present study is higher than the previous findings of other authors (about 48.6%) in different regions of Ethiopia (Abebe et al., 2016; Biffa et al., 2005; Mungube et al., 2005; Seid et al., 2015; Yemane et al., 2015). The highest prevalence observed in the peri-urban production system might be due to poor hygienic milking practices and cow houses, most of the respondents cleaned the milking barn weekly and more than a week, and the presence high yielding lactating cows.

Table 1. Prevalence of mastitis in function of production system

Variables	Number of animals examined	Positive, n (%)		Prevalence (%)	OR (P)
		Clinical	Sub-clinical
Production system
Mixed farming	175	28 (16.0)	92 (52.6)	68.6	6.38 (0.000)
Peri-urban	54	12 (22.2)	35 (64.8)	87.0
Total	229	40 (17.5)	127 (55.5)	73.0

n = number of animals, OR: Odds ratio.

3.2. Prevalence of mastitis

Mastitis was investigated in a total of 229 lactating cows from 180 households (Table 1). Based on clinical examination and the California mastitis test (CMT), cows were classified as having clinical or subclinical mastitis. Out of the total examined lactating cows, 17.5% had clinical mastitis, from the clinical positive cows, 12 (5.3%) were from peri-urban, and 28 (12.2%) were from rural (mixed farming), and 55.5% had subclinical mastitis, from those CMT (SCM) positive lactating cows, 35 (15.3%) were from peri-urban, and 92 (40.2%) were from rural (mixed farming). In the current study, the overall prevalence was 73%. This is comparable with the findings of Mekibib et al. (2010) and Zeryehun et al. (2013), who found that the overall cow-level prevalence of mastitis is 71% and 74.7%, respectively. Furthermore, the findings of this study are higher than the findings of Lidet et al. (2013); Megersa et al. (2012) and Salih et al. (2011), who reported prevalence rates ranging from 34.3% to 58.2% across the country. The higher prevalence in the current study might be attributed to poor hygienic and husbandry practices, as well as a lack of knowledge about the disease and its treatment.

The prevalence of clinical mastitis in this study is similar to the findings of Zeryehun et al. (2013) and Biffa et al. (2005), who observed a prevalence rate of 19.6% and 16.11% in central and southern Ethiopia, respectively. However, it was higher than those obtained by Belayneh et al. (2013); Megersa et al. (2012) and Mekonnen and Tesfaye (2010), who revealed prevalence rates of 3.9%, 3.3%, and 5.9% from distinct parts of the country, respectively.

The prevalence of subclinical mastitis observed in the current finding agrees with previous findings that reveal prevalence rates of 55.1%, 54.4%, and 56% in distinct parts of Ethiopia (Belayneh et al., 2013; Moges et al., 2012; Zeryehun et al., 2013). Besides, the finding of this study is higher than Moges et al. (2011), and Delelesse (2010), who reported a prevalence of 30.6% and 33.8%. The highest prevalence of subclinical mastitis (SCM) in this study might be due to poor sanitary and housing conditions, poor milking procedures such as suckling before milking only, lack of milking order, and dung smear, which can create an opportunity for the contagious type of mastitis.

The majority of mastitis cases in the present study were subclinical, which agrees with much of the prior research from various parts of Ethiopia (Abebe et al., 2016; Seid et al., 2015; Zenebe et al., 2014; Zeryehun et al., 2013). Farmers were able to quickly identify clinical mastitis due to the changes they noticed, even though they were unaware of the disease and its causes. Besides, farmers can effectively treat this condition traditionally by washing the teats with warm water or providing antibiotics by working with a veterinarian. However, subclinical mastitis has no visible symptoms and is difficult to detect by farmers, making it a critical issue for dairy producers. The high prevalence of sub-clinical mastitis might be due to poor milking hygiene, poor house hygiene, a lack of post-milking teat dipping, and the use of lubricant by contact labor, as well as a lack of order in milking cows of various ages (Belachew, 2016).

3.2.1. Prevalence of clinical and subclinical mastitis at the quarter level

The overall quarter-level prevalence of clinical mastitis in this study was 49 (5.4%), which was comparable with reports of Girma et al. (2012), Seid et al. (2015), and Belay et al. (2022), who obtained a prevalence of 8.03%, 6.6% and 7.94%, from, West Hararghe, Arsi and Gamo Zone Ethiopia, respectively, but higher than the finding of Kebede and Weldemariam (2015) from Eastern Ethiopia and Dabele et al. (2021) from West Shewa Zone, Oromia, Ethiopia. Blind quarters observed in the current finding were lower than the finding of Tekle and Berihe (2016) and Tezera and Aman Ali (2021). Teat blindness could be caused by a lack of awareness to detect the disease in its early stages using strip cups or other methods, as well as the lack of treatment for this disease in this area. Of the 902 functional quarters tested for subclinical mastitis, 46.01% were positive for the CMT test (Table 2). This is comparable with the findings of other studies: 45.68% by Amin et al. (2017), 54.75% by Dereje et al. (2018), and 39.4% by Tesfaye and Abera (2018); however, the result was higher than the findings of Alemu et al. (2013), Seid et al. (2015), Tekle and Berihe (2016), Lakew et al. (2019), Kumbe et al. (2020), Abebe et al. (2020) and Tezera and Aman Ali (2021) with prevalence rate of 24.3%, 30.7%, 18.23%, 29.04%, 21.48%, 29.4% and 26.84% respectively, from different parts of Ethiopia. In this study, the overall quarter-level prevalence of mastitis was 47.5% and it is comparable with another finding from Adigrat, Northern Ethiopia (Alemu et al., 2013), however, the result was lower than the previous findings reported from various parts of Ethiopia (Ararsa et al., 2014; Mekonnen & Tesfaye, 2010). On the other hand, the current finding was higher than Zelalem (2001) who has reported a 15.92% prevalence rate. This might be due to poor husbandry practice, use of dung smear, and suckling without washing which may create an opportunity to transfer the pathogenic agent from one quarter to the other quarter.

Table 2. Clinical, blind, and California mastitis test scores of each quarter of a lactating cow

	Quarters Examined, N	Mastitis positive, n (%)	Severity of the diseases				Prevalence (%)	Blind teats, n
			T	1	2	3
Left front	225	84 (37.3)	7	36	22	19	9.9	4
Left rear	224	125 (55.8)	16	58	28	23	6.5	5
Right front	227	91 (40.1)	23	38	26	21	9.7	2
Right rear	226	115 (50.8)	13	30	34	27	5.75	3
Total	902	415 (46,0)	59 (6.5%)	162 (18%)	110 (12.2%)	90 (10%)	46.01	14 (1.5%)

N = number of quarters, T = trace (T),

1 = weak positive (1), 2 = distinct positive (2), 3 = strong positive (3).

Compared to quarter-level prevalence left rear quarters were highly affected (55.8%) in comparison to the right rear quarters (50.8%). This might be because of the hindquarters’ high production capacity and the increased risk of fecal and environmental contamination. A similar result was reported from in and around Sebeta, Ethiopia (Sori et al., 2005) and Tekle and Berihe (2016) from Sidamo, Ethiopia.

Besides prevalence, the severity of subclinical mastitis in each quarter was recorded (Table 2). The severity of sub-clinical mastitis in this study found was 18%, 12.2%, 10%, and 6,5% of the quarters scored as weakly positive, distinct positive, strongly positive, and trace, respectively. Moreover, the quarter-level prevalence was higher in the peri-urban production system (68.9%) than in mixed farming (47.9%). This might be due to differences in milking practices, breed types, and hygienic practices in the area.

3.3. Risk Factors Related with Mastitis Prevalence

3.3.1. Previous history of mastitis prevalence

The relationship between mastitis prevalence and previous mastitis history, teat lesion, and gross milk quality in the study was illustrated in Table 3. Of a total of 229 lactating cows, 17 cows had a previous history of mastitis of which 76.5% were mastitis positive. Likewise, 31 cows had teat lesions, of which 91.3% of the cows were positive. According to the results of this study, cows with a lesion on their teats or udder had a high prevalence of mastitis. A similar observation was reported from eastern Ethiopia (Abdurahman, 2006; Kebede & Weldemariam, 2015). According to Mbuk et al. (2016), cows with lesions on their teats or udder had a 10.7-fold higher risk of developing mastitis than cows without teat lesions.

Table 3. Previous history and visual observation of mastitis prevalence

Variables	Animals examined	No of Positive animals	Prevalence (%)	OR (p-value)
Previous mastitis history
Yes	17	13	76.5
No	212	154	72.6	3.5 (0.547)
Teat lesion
Present	31	28	91.3
Absent	198	138	69.7	2.5 (0.328)
Gross milk quality
Watery	28	24	85.7
Blood tinged	19	19	100	3.1 (0.426)
Clot	7	7	100	0.7 (0.000)
Normal	175	117	66.9	0.58 (0.000)

OR: Odds ratio.

The current study suggests that gross milk quality could be used to predict the occurrence of mastitis. Gross milk quality observed in the survey work of this study were as follows: 28 cows had watery milk, 19 blood-tinged, 7 clots, and 125 normal milk, and 85.7% and 66.9% of the cows had watery and normal milk; however, all blood-tinged and clot milked cows were clinically as well as sub-clinically mastitis positive. This result revealed that a higher prevalence was observed in animals that have previous mastitis history, teat lesion, and poor gross milk quality. This might be due to a lack of awareness about the disease and its treatment as well as mastitis tests in the study area and poor hygienic practices in the cow house, milking bran, udder of the cow, as well as the absence of bedding materials.

3.3.2. Host and environmental-related risk factors

The prevalence of mastitis could be determined by different risk factors like the number of affected cows out of the total examined. In this study, two major risk factors were mainly considered, which are host (cow) related and environmental risk factors. Breed, calving date, and parity were considered as the major host-related risk factors, for the occurrence of mastitis, while a sequence of milking, housing condition, husbandry system, hygiene of udder and milkers were considered as the main environmental risk factors.

3.3.2.1. Host-related risk factor

In the current study, the breed of the cow had a significant influence on SCM prevalence compared to CM (Table 4). The prevalence of SCM mastitis was significantly higher in high-grade HF dairy animals (69.2%) than in crossbreeds (60.2%) and indigenous breeds (50.8%). This agrees with Moges et al. (2012) and Tilahun and Aylate (2015) who reported that breed had a major influence on the prevalence of mastitis. However, the result of the current study was lower than the previous works reported (Argaw & Tolosa, 2008; Kebede & Weldemariam, 2015) from various parts of Ethiopia. On the contrary, other findings state that there was no significant difference between crossbreds and indigenous zebu (Rahman et al., 2009). In the present study, higher prevalence was observed in high-grade Holstein Friesian dairy animals and their crossbreeds.This might be due to high yielding capacity with large pendulous udder which exposes the udder and teats to injury, and this injury acts as a potential source for microorganism through contact with the environment, which increases the possibility of quarter infection. In addition, the difference in immunity of the animals was different among breeds which also might be the cause of the high prevalence in high-grade HF dairy cows.

Table 4. Host (cow) related risk factor

Variables	Category levels	number of animals examined	Clinical mastitis positive	Subclinical mastitis positive	Overall prevalence (%)	OR(P-value)
Breed	Local breed	132	21 (15.9%)	67 (50.8%)	66.7
	Cross breed	84	17 (20.2%)	51 (60.7%)	80.9	2.9 (0.018)
	Exotic breed	13	2 (15.4%)	9 (69.2%)	84.6	1.3 (0.013)
Calving date
	1–60 days	64	13 (20.3%)	38 (59.4%)	79.7
	61–120 days	48	14 (19.2%)	18 (37.5%)	58.3	1.5 (0.459)
	>120 days	117	13 (11.1%)	71 (60.7%)	71.8	1.7 (0.017)
Parity
	1 calves	40	4 (10%)	10 (25.0%)	35.0
	2 calves	73	10 (13.7%)	39 (53.4%)	67.1	34.3 (.000)
	3 calves	54	13 (24.1%)	34 (63%)	87.0	8.1 (0.11)
	4 calves	23	5 (21.7%)	15 (65.2%)	89.9	3.5 (0.031)
	>4 calves	39	8 (20.5%)	29 (74.4%)	94.9	2.9 (0.210)

OR: Odds ratio.

According to the results of this study, there was a strong relationship between mastitis incidence, parity, and lactation stage (Table 4). In the current study, higher prevalence of clinical mastitis was observed in early lactation (20%) followed by mid-lactation, which is similar to the previous finding reported by Mekonnen and Tesfaye (2010). This is might be due to high milk production, absence of dry cow therapy, and increasing udder size which creates opportunities for contamination and physiological stress caused by heavy milk yield, however higher prevalence of sub-clinical mastitis was observed in late lactation, followed by early lactation and mid-lactation 60.7% 59.4% and 37.5%, respectively, this in line with (Belina et al., 2016; Mekonnen & Tesfaye, 2010; Mungube et al., 2005). On the contrary, a higher prevalence of sub-clinical mastitis was reported in the early stage of lactation in distinct parts of Ethiopia (Delelesse, 2010; Girma et al., 2012; Zenebe et al., 2014; Zeryehun et al., 2013). The highest prevalence of subclinical mastitis observed in late lactation might be related to the prolonged exposure time of milking, the presence of milk residue, or the lack of complete milking due to suckling only before milking practice in this stage of lactation, and dung smear of the teat and udder.

Parity was found to have a considerable influence on the prevalence of subclinical mastitis; which shows that the risk of subclinical mastitis increases with increasing parity. The increased prevalence of sub-clinical and clinical mastitis with parity observed in the current study is comparable with the previous reports (Haftu et al., 2012; Kerro Dego & Tareke, 2003; Kivaria et al., 2004; Mekibib et al., 2010). This might be due to the generally increased risk of infection with time, the prolonged period of infection, and parity was related to animal age, when animal age increases immune system would decrease these conditions and increase the prevalence of mastitis.

3.3.2.2. Housing and hygiene-related risk factors

According to the current study, most of the interviewed households share a house with their cows to protect them from theft, predators, and other environmental factors (Table 5). In the study district, most dairy farms use stone-type floors (92.2%), and 83.4% of the dairy animals had mastitis positive, but the prevalence rate was higher in concrete-floor dairy farms, which account for 73.3%. According to the survey results, 96.7% of farmers remove manure once daily. This is contradicted with the finding of Tekle and Berihe (2016) who obtained 98% of farmers in the Sidamo Zone, southern Ethiopia, remove manure weekly. In this study, mastitis was found to be more prevalent on concrete floor types. This might be due to a construction problem that was uncomfortable for the cows and created trauma and lesions on the udder and teat, which might predispose the udder and teats to microorganisms that are responsible for the occurrence of the disease. A similar result was reported by Kebede and Weldemariam (2015) in Dire Dawa, eastern Ethiopia. Moreover, concrete floor types were higher in the midland, which is nearer to the district town than the highland, but in the highland, the floor was clean every day. Most of the household did not practice proper manure removal in the milking house, and a higher prevalence was observed on this dairy farm. This might be due to the increased chance of contact with the manure on the floor, which facilitates the entrance of microorganisms into the teat canal and udder contamination. In addition, most farms in the study area perform feeding, milking, and bedding activities within the same barn, which also increases the incidence of contagious mastitis.

Table 5. Housing-related risk factors (HHRRF) for mastitis prevalence

HHRRF	Number of households (%)	No Examined animals	Positive n	Overall Percent (%)	OR (P-value
Floor-type
Concrete	14(7.8)	38	28(73.7)	12.3
Stone	166(92.2)	191	139(72.7)	60.7	2.9(0.333)
Manure removal
Once a day	174(96.7)	204	143(70.1)	62.5
More than a week	6(3.3)	25	24(96)	10.5	0.9(0.825)
Manure removal in the milking house (barn)
Yes	71(39.4)	108	62(57.4)	27.1

OR: Odds ratio.

Generally, the highest prevalence observed in this study might be due to the lack of proper manure removal, absence of bedding material, and uncomfortable or poor hygienic floor in the cow house and milking barn.

3.3.2.3. Milking practice risk factors

There was a statistical association between bovine mastitis and milking practice-related risk factors such as udder washing, calf-suckling and hand washing (Table 6). The entire household interviewed in the study area used hand milking, which increases mastitis incidence. Kivaria et al. (2004) reported that the stripping type of hand milking technique was the most commonly used method by most of the dairy farms (90%) in Tanzania and believed that this technique causes microscopic trauma to the teat epithelium. Similarly, Hameed et al. (2012) revealed a higher prevalence in animals milked with a folded thumb than in animals milked with a full hand method. This could be because the high pressure used during milking affects the sphincter muscle of the teat.

Table 6. Milking practice-related risk factors (MPRRF)

MPRRF	Number of households (%)	No animals examined	No Positive animals	Overall prevalence (%)	OR (P-value)
Udder washing
Yes	34(18.9)	60	45(75)	19.7
No	146 (81.1)	169	122(72.2)	53.3	2.5(0.320)
Calve suckling
Suckle after and before milking	112(62.2)	125	88(70)	38.4
Suckle before milking	68(37.8)	104	79(75)	34.5	2.1(0.545)
Hand washing
Yes	180(100)	229	167(73.2)	73
No	0	0	0	0	-

OR: Odds ratio.

In the present study, most of the respondents allowed the calves to suckle before milking without washing the udder and after milking (62.2%) due to two main reasons. The first reason was that most households believed that the calves could wash teats with their saliva, and the second fact was that most of the cows were aggressive and did not milk without their calves. Calf suckling is also used to facilitate milk letdown, which increases mastitis prevalence. According to risk factor analysis, mastitis was found to be more prevalent in animals that suckle their calves only before milking, accounting for approximately 75% of the prevalence. This is consistent with a previous study published by Hameed et al. (2012), who discovered the highest prevalence of mastitis in calf-suckling animals, most likely due to injury sustained while dragging away during suckle. The highest prevalence observed in short suckling before milking only might be due to a lack of complete milking and poor hygiene in the milking barn.

In general, the highest prevalence observed in this study might be due to the absence of udder washing, milking cows that had been suckled by calves without washing the udders or teats, absence of milking order, use of common water for more than one cow, and absence of handwashing between milking.

4. Conclusion

The current research showed that mastitis is indeed one of the health issues affecting lactating cows in the study area, with an overall prevalence of 73%. The prevalence of the disease was higher in peri-urban production system, and subclinical was the most generic form of with a prevalence rate of 55.5%. The analysis of potential risk factors revealed that there were significant associations between bovine mastitis and past mastitis history, breed, parity, milking barn hygiene, and milking practice. Moreover, the results show that risk factors (host and environmental) were significantly affecting the prevalence of mastitis, the prevalence of mastitis was significantly higher in high-grade HF dairy animals (69.2%), and hygienic condition of the house or milking barn and milking practices performed in the farms was significant effect on mastitis prevalence. Generally, the prevalence of mastitis was significantly higher in the study area due to poor milking hygiene, inadequate dairy sanitation, insufficient attention to udder health, and limited veterinary services. To reduce mastitis prevalence, farmers’ awareness of hygienic milking practices and other risk factors should be improved through animal-health extension services, and dairy cattle should be regularly screened for subclinical mastitis. Meanwhile, this research was focused only on the prevalence of mastitis and its risk factors; further study on the isolation of bacterial causative agents, bovine mastitis pathogens, and antimicrobial sensitivity testing should be carried out.

Acknowledgements

We are profoundly grateful to the Ministry of Education and Haramaya University for admitting me to this program and covering my research budget. The authors express their gratitude to the farmers included in the study for their participation during the study period. The authors extend their sincere appreciation to the editors who dedicated their time and expertise to enhance the quality of this article. The editors’ invaluable contributions have played a pivotal role in shaping this publication into its final form. The authors are truly grateful for the editors’ commitment to excellence and unwavering support throughout the editorial process.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Notes on contributors

Muhammed Nurye

Muhammed Nurye Gebeyehu is a lecturer at Oda Bultum University in Ethiopia. He earned his M.Sc. from Haramaya University in Dairy Science, and now he is a PhD student at Haramaya University. His research interests are in dairy science and technology, dairy chemistry and microbiology, dairy product development, dairy nutrition and CH4 emission.

Mitiku Eshetu

Mitiku Eshetu Guya is a professor of animal production and product technology at Haramaya University. His research interests are in dairy science and technology, livestock product technology, livestock production and management, and related areas.

Mekonnen Yirga

Mekonnen Yirga is an associate professor of animal production at Wollo University. His research interests are in animal nutrition, livestock product technology, livestock production and management, and related areas.