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Early Treatment of Experimental Subclinical Mastitis Found Advantageous

Dairy Pipeline: January 1999

Gerald M. (Jerry) Jones
Extension Dairy Scientist, Milk Quality and Milking Management
Virginia Tech
(540) 231-4764

Scientists at the Institute for Animal Health in Compton, Newbury, Berks, England, selected 24 mid to late lactation cows, free of mastitis in the current lactation, examined foremilk at each milking, measured Somatic Cell Counts on quarter milk samples, and measured electrical conductivity with a manual meter. One quarter of each cow was infused with Streptococcus uberis microorganisms (a common source of environmental mastitis) and cows were monitored for 10 days. When the cow had a positive conductivity, she was either: (1) treated with intramammary antibiotic (early group), (2) treated by oxytocin injection intramuscular at label recommendations for no more than 6 milkings and immediately after the milking unit was removed after which the milking unit was reattached to collect additional strippings milk (oxytocin group), or (3) left untreated until clinical signs occurred and then treated with antibiotic (normal group). Four cows showed clinical mastitis at the same milking as conductivity changed and received intramammary antibiotic immediately (clinical group). The normal, clinical, and oxytocin groups received three doses at 24 hr intervals and continued treatment until foremilk was free of clots. The early group received one dose for 6 consecutive milkings. Bacteriological cures were determined on foremilk samples taken at both 14 and 21 days after last treatment. The 4 clinical cases were cured clinically but required 10 days and only three were bacteriological cures. Clinical signs were observed 1-3 days after the change in milk conductivity in 19 cows. In the early group, five cows were treated but none became clinical. All infections were eliminated by the six doses of antibiotics. SCC remained low (averaging 1,585,000), required only 9 days to return to less than 400,000, and antibiotic was cleared from the milk by 13 days. Eight infections were detected in the oxytocin group. Two cases showed no clinical mastitis and both infections were eliminated. The other six infections became clinical and required 7 doses of antibiotic over 7 days. It took longer for SCC (approximately 9 million at time of treatment) in this group to return to less than 400,000 (15 days) than the normal group (12.5 days) which received antibiotic treatment after clinical signs were detected. In summary, cows in the early group were detected and treated when the infections were less severe. Milk yield in the early group was depressed 13% at detection while depression was 31% at the time clinical signs were observed. The SCC and yield returned to levels similar to those occurring pre-infection for all treatment groups. All cows treated early remained free of disease, but all cows left untreated developed disease. Early intervention following infection resulted in less antibiotic being required to eliminate infection, the disease was prevented from developing, the effects on SCC and yield were less severe, and the cow and milk quality recovered sooner. These results were achieved using double the label recommendations and an increased frequency. This was extra-label drug use which needs confirmation by other studies, especially natural occurring infections, but it looks promising.

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