The correlation between TBC and CC (r = 0.5) in this study corroborated previous studies that reported a moderate to high correlation [ 13, 15, 56, 69]. This indicates that TBC could be used as a single microbiological hygienic indicator for total aerobic bacteria present in raw milk [ 15]. Sargeant JM, Schukken YH, Leslie KE. Ontario bulk milk somatic cell count reduction program: progress and outlook. J Dairy Sci. 1998;81:1545–54. Lingathurai S, Vellathurai P. Bacteriological quality and safety of raw cow milk in Madurai (South India). Bangladesh J Sci Ind Res. 2013;48:109–14. Martin NH, Trmcic A, Hsieh T-H, Boor KJ, Wiedmann M. The evolving role of coliforms as indicators of unhygienic processing conditions in dairy foods. Front Microbiol. 2016;7(1549):1–8. https://doi.org/10.3389/fmicb.2016.01549.

Lakew M, Tolosa T, Tigre W. Prevalence and major bacterial causes of bovine mastitis in Asella, South Eastern Ethiopia. Trop Anim Health Prod. 2009;41:1525–30. Fig 5: There is little sense in treating an older cow with chronic Staph aureus and a persistently high cell count Antibiotics Murphy SC, Martin NH, Barbano DM, Wiedmann M. Influence of raw milk quality on processed dairy products: How do raw milk quality test results relate to product quality and yield ? J Dairy Sci. 2016;99:1–22. Aqua (H₂O’s Fancy Name), Prunus Amygdalus Dulcis (Sweet Almond) Oil, Cetearyl Alcohol (Plant-Based Emulsifying Wax), Olea Europaea (Olive) Fruit Oil, Aloe Barbadensis Leaf Juice (Aloe Vera), Stearic Acid (Plant-Based Emulsifier), Polysorbate 60 (Food Grade Emulsifier), Oryza Sativa (Rice) Bran Oil, Tocopherol (Natural Vitamin E), Piroctone Olamine (Olamine Salt), Allantoin, P Anisic Acid (Natural Preservative), Coco Caprylate (Coconut-Based Conditioner), Guar Hydroxypropyltrimonium Chloride (Guar Gum), Hydrolyzed Milk Protein (For Skin Elasticity), Fragrance (Phthalate Free - Oatmeal), Humulus Lupulus (Hops) Extract. The quality of milk produced at the farm level depends on farm management practices, and hygienic milk production at the farm level is a key factor for protecting milk from microbial contamination and safeguarding consumers from milk-borne health risks [ 4]. The initial microbial load of raw milk at farm level determines the quality of products across the dairy chain [ 5]. For example, if the initial bacterial load is high, further heat treatments may not sufficiently eliminate them [ 6]. At the farm level, microbial contamination of bulk milk occurs via 3 main sources: bacterial contamination from the external surface of the udder and teats, from the surface of the milking equipment, and from mastitis organisms from within the udder [ 7].

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Staphylococcus aureus is a major cause of bovine mastitis [ 20], resulting in large economic losses due to reduced milk production and quality [ 21]. S. aureus is frequently isolated from cows with mastitis [ 22, 23, 24, 25] and bulk milk [ 26, 27, 28] in Ethiopia. The presence of S. aureus in bulk milk samples indicates that infected cows are present in a herd [ 9]. The public health concern due to staphylococcal food poisoning is potentially serious in Ethiopia due to widespread raw milk consumption habits [ 29, 30, 31]. S. aureus produces enterotoxins that cause food poisoning when ingested in contaminated food. Milk and milk products are frequently implicated in staphylococcal food poisoning [ 32]. Kelly PT, O’Sullivan K, Berry DP, More SJ, Meaney WJ, O’Callaghan EJ, O’Brien B. Farm management factors associated with bulk tank total bacterial count in Irish dairy herds during 2006/07. Ir Vet J. 2006;62:36–42. Oikonomou G, Bicalho ML, Meira E, Rossi RE, Foditsch C, Machado VS, Teixeira AGV, Santisteban C, Schukken YH, Bicalho RC. Microbiota of cow’s milk; distinguishing healthy, sub-clinically and clinically diseased quarters. PLoS ONE. 2014;9:e85904. Intramammary drugs tend to be best for single quarter mild mastitis, while systemic treatment is better for more severe cases or multiple quarter infection. Nacul HZ, Revoredo‑Giha C. Food safety and the informal milk supply chain in Kenya. Agric Food Secur. 2022;11(8):1–14. https://doi.org/10.1186/s40066-021-00349-y.

Metzger S, Hernandez L, Skarlupka J, Suen G, Walker T, Ruegg P. Influence of sampling technique and bedding type on the milk microbiota: results of a pilot study. J Dairy Sci. 2018;101:6346–56. Mhone TA, Matope G, Saidi PT. Aerobic bacterial, coliform, Escherichia coli and Staphylococcus aureus counts of raw and processed milk from selected smallholder dairy farms of Zimbabwe. Int J Food Microbiol. 2011;151:223–8. Isaac P, Bohl LP, Breser ML, Orellano MS, Conesa A, Ferrero MA, Porporatto C. Commensal coagulase-negative Staphylococcus from the udder of healthy cows inhibits biofilm formation of mastitis-related pathogens. Vet Microbiol. 2017;207:259–66.

Mastitis is characterized by mild or severe pathological changes in udder tissue, increased somatic cells count (SCC) and abnormal milk quality ( 4). Dairy cow mastitis is the most expensive infectious disease in dairy cow breeding worldwide. In terms of the impact on animal husbandry in the United States alone, the annual losses caused by the decline of milk production and quality, the soaring cost of veterinary treatment and the increasing cost of farm management are as high as billions of dollars ( 5). Cow mastitis is usually divided into clinical mastitis and subclinical mastitis according to the visible changes of udder and milk ( 6), and there are 137 kinds of pathogenic bacteria in dairy cow mastitis ( 7, 8), and Staphylococcus aureus, Escherichia coli, Streptococcus are the most common pathogens that cause mastitis ( 9, 10). Chambers JV. The microbiology of Milk and Milk products. In: Robinson RK, editor. Dairy microbiology handbook. 3rd ed. New York: John Wiley & Sons, Inc; 2002. p. 39–90. ISO 6888-3:2004. Microbiology of food and animal feeding stuffs — horizontal method for the enumeration of coagulase-positive staphylococci (Staphylococcus aureus and other species) — part 3: detection and MPN technique for low numbers. Geneva: International Organization for Standardization; 2004. Lima SF, Teixeira AG, Lima FS, Ganda EK, Higgins CH, Oikonomou G, Bicalho RC. The bovine colostrum microbiome and its association with clinical mastitis. J Dairy Sci. 2017;100:3031–42. Fig 1: Stripping milk onto a dark surface before milking the cow is a simple and effective method of early mastitis detection Examining the udder

Moossavi S, Azad MB. Origins of human milk microbiota: new evidence and arising questions. Gut Microbes. 2020;12:1667722.

Heikkilä A-M, Liski E, Pyörälä S, Taponen S. Pathogen-specific production losses in bovine mastitis. J Dairy Sci. 2018;101:9493–504. Jayarao BM, Donaldson SC, Straley BA, Sawant AA, Hegde NV, Brown JL. A survey of foodborne pathogens in bulk tank Milk and raw Milk consumption among farm families in Pennsylvania. J Dairy Sci. 2006;89:2451–8. The samples were labelled with the farm code, sample type and date of collection with a permanent marker and transported to Asella Regional Veterinary Laboratory using an icebox for bacteriological analysis. The samples were stored at 4 °C and cultured the next morning (within 15–20 hours). Informed consent was obtained from each dairy farmer before sampling, and they were asked to rule out whether their cows had been given antibiotic treatment recently. Questionnaire survey TBC was enumerated on plate count agar (HiMedia Ltd., Mumbai, India) according to ISO 4833:2003 [ 41], while CC was counted on violet red bile agar (HiMedia Ltd., Mumbai, India) according to ISO 4832:2006 [ 42] using the pour plate method in both cases. One hundred microliters of serially diluted milk was aseptically withdrawn from each dilution using a micropipette and plated using 15–20 ml plate count agar and violet red bile agar, which were kept at 47 °C in a water bath. After thorough mixing by rotating, the plated samples were allowed to solidify and incubated aerobically at 30 °C for 48–72 hrs and 24 hrs for TBC and CC, respectively.

Callahan BJ, McMurdie PJ, Rosen MJ, Han AW, Johnson AJA, Holmes SP. DADA2: high-resolution sample inference from Illumina amplicon data. Nat Methods. 2016;13:581–3. Naing YW, Wai SS, Lin TN, Thu WP, Htun LL, Bawm S, Myaing TT. Bacterial content and associated risk factors influencing the quality of bulk tank milk collected from dairy cattle farms in Mandalay region. Food Sci Nutr. 2019;7:1063–71. Team RC. R: a language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. 2020. O, Solbu H, Refsdal A, Roalkvam T, Filseth O, Minsaas A. Results and evaluation of thirty years of health recordings in the Norwegian dairy cattle population. J Dairy Sci. 2007;90:4483–97.Amentie T, Eshetu M, Mekasha Y, Kebede A. Milk postharvest handling practices across the supply chain in eastern Ethiopia. J Adv Vet Anim Res. 2016;3:112–26. Tarekgne E, Skeie S, Rudi K, Skjerdal T, Narvhus JA. Staphylococcus aureus and other Staphylococcus species in milk and milk products from Tigray region, Northern Ethiopia. Afr J Food Sci. 2015;9:567–76.