Mastitis, somatic cell count and milk quality: an overview

Mastitis is the economically most important disease in lactating cows and the prevalence under any management condition is considerably high. It causes economic losses due to reduction of both quantity and quality of milk. The groups of microorganisms causing mastitis are categorized as bacteria, fungi, mycoplasma and nocardia. Among the several cow side tests to trace intra-mammary infections (IMI) at early stage, i.e. sub-clinical mastitis (SCM), California Mastitis Test (CMT) is commonly used in which somatic cell count (SCC) is indirectly taken into account. The SCC of milk is an indicator of mammary infections because SCC positively correlates with the severity of infection. The SCC of >200,000 cells/ml is considered to be an indication of IMI. However, SCC in the milk can also vary with some other factors such as breed, age of the cow, stage of lactation, body condition score, etc. A few studies have shown that high SCC in milk affect the composition, organoleptic properties and keeping quality of raw milk and heat treated milk, yoghurts and cheese. One could argue that low SCC milk (sub-clinical mastitis) will not have a significant effect on product quality. But it should be emphasized that the natural infection occurs with various types of microorganisms that can precipitate product defects despite the low SCC. Also, attention must be paid to the bulk tank somatic cell count (BTSCC) rather than individual animal SCC. The quality of raw milk collected from different parts of the country is reported to be low with high bacteria counts mainly due to unhygienic milking and field practices. Milk quality directly influences the income of the small scale milk producers which inturn affects the sustainable dairy production. In Sri Lanka the majority of dairy farmers are small scale producers and they practice minimum milk hygiene practices compared to medium and large scale producers. Therefore, it is essential to make them aware of hygienic milking practices and implement milk quality based payments (MQBP) with added premium and penalties for the existing milk price, with the objective of encouraging clean milk production.