Mastitis in sheep is mostly caused by Gram-positive bacteria
3. Most cases of clinical mastitis occur in the early stages of lactation and are reported to be caused mostly by S. aureus and Mannheimia haemolytica
8,9. Less than 5% of sheep incidences of mastitis often result in clinical mastitis
10. However, clinical mastitis is seen sporadically in sheep. Although rare, it can occur in the form of herd outbreaks. As the severity of the disease increases, clinical mastitis may transition from subacute to chronic. Clinical mastitis is straightforward to identify because it presents with physical symptoms such udder discolouration as well as easily observable clinical indicators. Clinical mastitis typically results in swollen, painful udder lobes. Affected ewes refuse to feed, are lethargic and often do not allow their lambs to suckle, resulting in reduced growth rates in suckling lambs. Milk from sheep infected with clinical mastitis has an unusual appearance and composition; it may be discolored, watery, or contain blood or serum
11-14.
Subclinical mastitis is one of the most serious diseases that cause economic losses in the mammary glands of goats and sheep worldwide. The disease is characterized by the development of intramammary infection without clinical symptoms28. Subclinical mastitis can be diagnosed through bacteriological tests or SCC in milk (neutrophil leukocytes and some epithelial cells)10,28.
It is stated that the prevalence of subclinical mastitis, which is quite common in small ruminants, varies between 6.5% and 40.2% (29, 30, 31). In a study conducted in Western Algeria, the prevalence of SCM among 150 goats was reported to be 20.7%32. In the Laghouat area, a higher prevalence of 46.6% was observed in 60 local goats33. In our study, 58.45% of subclinical mastitis cases were observed in 349 sheep according to the CMT score. The types of bacteria detected in subclinical mastitis milk and their isolation rates may vary depending on many factors such as milking techniques of animals, hygiene and sanitation methods applied, and growing conditions34,35. Ergene et al. 36 detected 27.3% bacterial growth in their study using 227 milk samples in Cyprus. Ergun et al. 37 found a lower rate of bacteriological growth (6.4%) in milk samples. Bergonier et al. 3 and Contreras et al. 8 found that the prevalence of subclinical mastitis ranged between 5% and 30%. In this study, bacterial growth was detected in 59.10% of the milk samples obtained from sheep.
Many researchers have claimed that CoNS is the most often identified bacteria in milk samples38-41. In sheep, CoNS are among the most commonly isolated bacterial species in subclinical mastitis, with a prevalence ranging from 25% to 90% at the herd level 3,9,15,41. Recent studies indicate the importance of CoNS as etiological agents of subclinical mastitis in sheep8,42. Zafalon et al. 41 found the frequency of CoNS in 56.8% of bacteriology positive samples. In the study conducted by Vasileiou et al. 34, CoNS was detected in 59.7% of subclinical ewes mastitis cases. Contrary to these studies, Gökhan and Gülaydın43 reported that they found 3% CoNS (S. simulans and S. epidermidis) in 103 milk samples. In this study, the most commonly isolated bacteria were CoNS with 58.33%.
The most frequently isolated bacterium after CoNS in subclinical mastitis is S. aureus16. Ergün et al. 37 reported that they found S. aureus at a rate of 3.1% in subclinical mastitis samples. Kern et al. 44 reported that S. aureus was detected in 5.5% of the isolated bacteria, while Zafalon et al. 41 identified it in 8.1% of bacteriology-positive milk samples. Tancin et al. 45 reported that they detected 3.33% S. aureus in a study conducted on 116 milk samples. Holko et al. 46 detected the incidence of S. aureus in 6.9% of milk samples. In this study, S. aureus was detected in 4.90% of 204 milk samples.
On the other hand, mycoplasmas are microorganisms that cause chronic infections that are difficult to eradicate, with complex unknown pathogenicity factors. Mycoplasma-induced mastitis continues to be a significant problem worldwide. Mycoplasma bovis is the most significant species in cattle, whereas its very close phylogenetic relative, M. agalactiae, causes very severe mastitis in small ruminants. Mycoplasma agalactiae is the main etiological agent of contagious agalactiae syndrome in sheep and goats and causes significant economic losses, especially as the infection lingers in milk for many years even after antibiotic treatment47-49. In their study, Göçmen et al. 50 found M. agalactiae positive in 9.14% of 339 samples. Similar to these results, in our study, M. agalactiae was detected as the second most isolated bacterial agent with a rate of 17.16%.
In their study conducted in Sharkia province of Egypt, Abdallah et al. 28 reported that the most common bacterial species isolated from sheep milk samples was E. coli (44.4%). In a study conducted by Ergün et al. 37 on sheep with mastitis, 2% of 1458 milk samples were reported to contain E. coli. In a study conducted on goats by Doğruer et al. 51, the E. coli rate was determined as 4.5%. In our study, E. coli (7.35%) was detected, similar to this study. The reason for this wide range of E. coli is that it is an environmental microorganism and is affected by factors such as poor ventilation, inadequate manure removal and general lack of cleanliness and sanitation on the farm.
As a result, it is seen that subclinical mastitis is an important health problem in Siirt province. In this study conducted on Hamdani ewes, 58.45% subclinical mastitis was reported. In the study on the isolation of the agent causing subclinical mastitis, it was determined that CoNS had the highest isolation rate. Following this, M. agalactiae, detected by molecular methods, was found to be in second place with 17.16%. In order to prevent and combat mastitis, it is thought that it would be beneficial to inform breeders in Siirt province about this issue and to provide the necessary incentives to ensure they pay attention to milking hygiene and have a healthier lactation period.
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