Abstract
The assay procedure for N-acetyl-β-D-glucosaminidase (NAGase) was considered to be the most reliable, simple, and rapid enzymatic method for estimating the severity of mammary tissue damage. This study was carried out to assess the relationship of NAGase enzyme activity, California mastitis test score (CMTS) and somatic cell counts (SCC) in milk and the influence of breed, parity and age of the cow on NAGase activity. The results showed that prevalence of sub-clinical mastitis (SCM) was 74.5% (41/55) in the population of cows tested. The isolated pathogens were Staphylococcus spp. (34%, 14/41), Escherichia coli (34%, 14/41) and Streptococcus spp. (32%, 13/41). The SCC showed a significant (p<0.05) positive correlation with the activity of NAGase (R2= 0.796) and CMTS (R2= 0.709). A significant correlation was observed between the NAGase activity and SCC in SCM positive milk, where the correlation was stronger (R2= 0.748) in the former than in the latter. The parity (R2= 0.843) and age (R2= 0.758) of the cow also showed a significant (p<0.05) positive correlation with enzyme activity. The mean SCC and enzyme activity of different crossbreds of the study population did not show a significant correlation, but mean values of SCC and enzyme activity were higher when an animal was phenotypically more related to European breeds (779– 1848 x103 SCC/ml;0.64 -0.89 μmole/min/ml) than tropical breeds (427–534x103 SCC/ml; 0.26-0.43 μmole/min/ml). It could be concluded that, the prevalence of SCM in crossbred cows in North-Western Province of Sri Lanka is considerably high. The determination of NAGase enzyme activity in milk could be used as a method for early detection of SCM more accurately than CMTS and SCC.
Highlights
Sub-clinical mastitis (SCM) adversely affects milk production, milk quality and herd health (Schultz et al, 1978)
The results of both California Mastitis Test (CMT) and microbiological analysis showed that the prevalence of SCM of the study sample of crossbred cows was 74.5% (41/55)
According to Kitchen et al (1978) the enzyme NAGase is released from both white blood cells and epithelial cells, and its concentration and activity are low in healthy quarters (Pyorala et al, 2011) and increase with SCM condition
Summary
Sub-clinical mastitis (SCM) adversely affects milk production, milk quality and herd health (Schultz et al, 1978). The milk quality is affected due to the enzymes secreted from bacteria and the enzymes released into milk through the damaged epithelium of mammary tissues. These enzymes decrease the quality of raw milk and reduce the keeping quality of processed milk products (Barbano et al, 1991). This study was carried out with an aim of finding the relationship of SCC, CMTS and NAGase activity tests that are used to determine subclinical mastitis, and of selecting the most suitable method for early detection of SCM in crossbred cows
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