Milk quality and mastitis in Jimma, Ethiopia – Risk factors and constraints

Tadele Tolsa

Mastitis remains an economically important disease in the dairy industry worldwide. The general aims of this thesis are to investigate milk production, quality and consumption and to study the prevalence of mastitis and associated risk factors at herd, cow and quarter level in Jimma, Ethiopia.

Milk production, marketing, quality, consumption and its associated constraints in Jimma were investigated in four studies. First, 47 dairy farmers and 44 milk retailers were interviewed to gain a better understanding of dairy farming and marketing, and the associated constraints. Second, bulk milk samples (n = 188) were collected for four consecutive weeks to investigate milk quality (Total Bacterial Counts (TBC), Coliform Counts (CC), Somatic Cell Counts (SCC), and antimicrobial residues). Bulk milk samples from 32 farms, 46 milk retailers and the three local milk collection centers were collected to determine the presence of oxacillin susceptible and oxacillin resistant Staphylococcus aureus isolates. Finally, 208 adult inhabitants were interviewed to gain more insight into milk consumption and concerns of consumers.

The average dairy farm, which consisted of five lactating cows, produced 43 liters of milk per day and was owned by literate adults. Milk was sold to retailers (71 per cent) and directly to customers (25 per cent) without any quality control, whereas 4 per cent was self-con

sumed. The median TBC, CC and SCC were 122,500 CFU/mL, 1005 CFU/mL and 609,500 cells/mL, respectively.

Antimicrobial residues were detected in 20 per cent of all milk samples. Staphylococcus aureus was isolated from 12 (38 per cent), 13 (33 per cent), and two out of three of the milk samples originating from the dairy farms, the milk retailers, and the milk collection centers, respectively. Seven (26 per cent) of the isolates were resistant to oxacillin suggesting the presence of Methicillin Resistant Staphylococcus aureus or MRSA (Lee, 2003).

Most consumers are concerned about adulteration and milk-borne diseases, but not about the presence of antimicrobial residues. Educated consumers (secondary school or higher) were more likely to boil milk for own consumption and to be concerned about the presence of antimicrobial residues in milk. They were also more likely than poorly educated consumers to be concerned about milk-borne diseases and, as a result, were willing to pay more for milk with proven quality.

The prevalence of subclinical mastitis and associated risk factors at the herd, cow and quarter level were studied in smallholder dairy farms in Jimma, Ethiopia. Forty-two herds were visited, a questionnaire was conducted, and 635 quarters belonging to 176 lactating cows were screened to detect the presence of subclinical mastitis using the California Mastitis Test. Sixty-two per cent of the cows and 51 per cent of the quarters had subclinical mastitis. Quarters from cows in a later stage of lactation (>180 days in milk) and quarters from cows with a tick-infested udder had higher odds of subclinical mastitis, as reflected by the California Mastitis Test.

A cross-sectional study on clinical mastitis, intramammary infection and blind quarters was conducted. Risk factors at the herd, cow, and quarter level for clinical mastitis and (pathogen-specific) intramammary infection were studied using multilevel modeling and factors associated with quarters being blind were also investigated. Eleven per cent of the cows and 4 per cent of the quarters had clinical mastitis, whereas 85 per cent of the cows and 51 per cent of the quarters were infected. Most of the cows had one or more blind quarter(s), whereas 6 per cent of the quarters were blind. Non-aureus staphylococci were the most frequently isolated pathogens from the clinical mastitis cases and causing most of the intramammary infections. The odds of clinical mastitis were lower in herds where heifers were purchased in the last year, old cows (>4 y) and quarters not showing teat injury. The odds of intramammary infection caused by any pathogen was higher in herds not practicing teat drying before milking, late lactation cows (> 180 days in milk), cows with high body condition score (>3)], right quarters (opposed to left quarter position) and quarters showing teat injury. Quarters of cows in herds with bucket-fed calf feeding (opposed to suckling) had higher odds of intramammary infection caused by Staphylococcus aureus. Except for body condition score, intramammary infection caused by non-aureus staphylococci was associated with the same risk factors as intramammary infection caused by any pathogen. Risk factors for quarters being blind include no access to feed and water immediately after milking, higher parity and tick infestation.


Tadele Tolosa (PhD) holds his first degree in DVM and second degree in Master’s of Tropical Veterinary Medicine from Addis Ababa University, Ethiopia. He also holds a PhD in veterinary science from Ghent University in November 2016. His PhD research is entitled: Mastitis and Milk Quality in Jimma, Ethiopia.

His work takes an interdisciplinary perspective that aims to better understand the nature of animal and public health. He has been awarded research funds from a variety of sources, including Belgium University, the Ethiopian Sciences and Technology Commission, the Ethiopian Agricultural Research Institute, the Centre for disease prevention and control (CDC), and Jimma University.

He has established an ambulatory clinic and is the head of mastitis and milk quality laboratory at Jimma University, Ethiopia. In March 2017, he was appointed as the head of school of Veterinary Medicine at Jimma University.