Het effect van het behandelen van subklinische mastitis op de incidentie van klinische mastitis bij melkgevende koeien.
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Mastitis is known as one of the major diseases in Dutch dairy herds and causes great economic losses. Mastitis has a clinical and a subclinical appearance. The objective of this study was to investigate the effect and moment of treatment of subclinical mastitis (SCM) on the incidence of clinical mastitis during lactation. In this study, new cases of SCM were targeted. A new case of SCM was defined as > 150,000 cells/ml for heifers or a somatic cell count (SCC) > 250,000 cells/ml for older cows after two consecutive SCC below these thresholds. Milk samples of 2.784 cows with a new case of SCM were analyzed on SCC and bacteriological culture. All cows with positive milk samples on Staphylococcus spp., Streptococcus spp. or Escherichia coli were included in the field trial. The cows were randomly assigned intrammary treated with antibiotics or control. Untreated cows at the first elevated SCC with a second elevated SCC were again randomly assigned intrammary treatment if they were bacteriological positive. Information about the incidence of clinical mastitis was recorded for all cows. Differences in incidence of clinical mastitis were statistically evaluated using two-by-two tables and the Mantel-Haenszel-test. No significant differences were found in the incidence of clinical mastitis in treated or control cows at either the first or second elevated SCC. Differences in the incidence of clinical mastitis in cow factors, like parity and lactation stage, and pathogen factors, like SCC or pathogen identification, were also not significant. In conclusion, besides some well-known benefits of treating subclinical mastitis in lactating cows, there were no significant differences found in the incidence of clinical mastitis between treated and untreated cows.