PREVALENCE OF CONTAGIOUS BOVINE MASTITIS PATHOGENS IN SAMPLES OF COLLECTED MILK
Authors: Zaritskyi R. V. , Zhuk Y. V. 
Published: May 2024

Dairy producers suffer significant economic losses due to various diseases of contagious and non-contagious etiology, among which inflammation of the mammary gland is one of the main ones. Mastitis is one of the most common diseases on dairy farms and causes significant economic losses associated with the cost of treating sick cows, reduced milk yield and quality of dairy products, and the risk of premature culling. The causative agents of mastitis are divided into two groups, among which the most important are contagious pathogens, including the five most important infectious agents: Staphylococcus aureus, Streptococcus agalactiae, Mycoplasma bovis, Streptococcus uberis, Streptococcus dysgalactiae, their habitat is sick animals and they are usually transmitted mainly from a healthy cow to a sick cow, especially through milking equipment, hands of machine milking operators, which in turn can lead to infection of the entire dairy herd. Therefore, establishing the prevalence of contagious mastitis pathogens is quite relevant today, it provides information on the possibility of creating rational and effective mastitis control programs on dairy farms, and also fills an important gap in veterinary medicine and farm management practice.

The aim of this study was to identify and establish the prevalence of contagious mastitis pathogens in tank milk samples using bacteriological and molecular genetic (PCR-RFLP) studies. Molecular genetic studies were performed by real-time polymerase chain reaction (RT-PCR). Nucleic acids were isolated using the KingFisher Purification System automatic isolation system using the MagMAX™ CORE Nucleic Acid Purification Kit (Thermo Fisher Scientific, USA). For the amplification reaction of the isolated nucleic acids, commercial VetMAX MastiType Micro4 Kit (Applied Biosystems™ by Thermo Fisher Scientific, USA) was used. The reaction was performed on a real-time PCR product detection system using a QuantStudio5 Real Time PCR System (Thermo Fisher Scientific, USA). Bacteriological studies of tank samples of cow milk were carried out according to generally accepted methods, the identification of bacterial cultures obtained on blood agar was carried out by MALDI-TOF using a VITEK®MS device (BioMérieux, France). The VITEK MS KB V3.2.0 US Version database was used to analyze the mass spectra.

The results of the study of contagious mastitis pathogens in tank milk samples by PCR-RF revealed that the most common are Streptococcus agalactiae 36% and Streptococcus uberis 35 %, Staphylococcus aureus occupies an intermediate position, accounting for 24 % of all isolates, Mycoplasma bovis, in turn, accounts for only 5% of isolates. When analyzing the data of the results of molecular genetic studies, it was found that the following associations of pathogens of contagious mastitis in tank milk samples were found Streptococcus uberis, Staphylococcus aureus, Streptococcus agalactiae – 29,8 %, Streptococcus agalactiae, Streptococcus uberis – 21,3 %, Streptococcus agalactiae, Staphylococcus aureus – 19,1 %, Streptococcus uberis, Staphylococcus aureus – 14,9 %, Streptococcus uberis, Staphylococcus aureus, Streptococcus agalactiae, Mycoplasma bovis and Streptococcus uberis, Mycoplasma bovis – 4,3 %, respectively. The associations of infectious agents Streptococcus uberis, Mycoplasma bovis, Streptococcus agalactiae; Mycoplasma bovis, Streptococcus agalactiae and Streptococcus uberis, Mycoplasma bovis, Staphylococcus aureus were found once each, which is 2,1 %.

The bacteriological examination of tank milk samples showed that the most commonly detected contagious pathogens were Streptococcus agalactiae – 55 % and Streptococcus uberis – 28 %, Staphylococcus aureus accounted for 11 % of isolates, and Streptococcus dysgalactiae was identified in only 6 % of tank milk samples. The following associations of pathogens of contagious mastitis were most often found in tank milk samples: Streptococcus agalactiae and Staphylococcus aureus – 35,7 %, Streptococcus uberis and Staphylococcus aureus – 28,6 %, Streptococcus uberis and Streptococcus agalactiae – 21,4 %. The associations of pathogens Streptococcus uberis, Staphylococcus aureus, Streptococcus agalactiae and Streptococcus uberis, Streptococcus dysgalactiae were found in tank samples only once, which is 7,1 % each.