PATTERNS OF INTRAMAMMARY INFECTION AND CLINICAL MASTITIS OVER A 5-YEAR PERIOD IN A CLOSELY MONITORED HERD APPLYING MASTITIS CONTROL MEASURES

The udder health of a research herd of between 160 and 220 Friesian co ws run on st commercial basis has been monitored closely, including de tailed bacteriological study, over 5 years. The fire point mastitis co ntrol plan had been in use for several years prior to this study and w as continued with minor alterations to the management of the plan, mor e detailed bacteriological monitoring and increased encouragement to a pply it. It has proved possible to make a substantial improvement in t he udder health of the herd. The percentage of infected cows fell from 21.9 to 12.0 and the percentage of infected quarters from 7.3 to 3.3. The main benefit has been a drastic reduction in the rate of clinical and subclinical mastitis caused by coagulase-positive staphylococci. However the total incidence of clinical mastitis did not change substa ntially; averaging around 30 cases/100 cows per year. This was largely because environmental mastitis organisms were responsible for 65% of all clinical cases. The results showed marked differences in the patte rns of infection due to the environmental mastitis pathogens, Gram-neg ative bacteria and aesculin-hydrolysing streptococci, suggesting diffe rent mechanisms of invasion of the gland.