Developments in the Use of Penicillin for Controlling Mastitis

New Zealand Journal of Agriculture, Volume 79, Issue 2, 15 August 1949, Page 134

Developments in the Use of Penicillin for Controlling Mastitis

DURING the season just ended New Zealand dairy farmers for the first time have been able to obtain penicillin in suitable form and in adequate quantities for the treatment of all cases of mastitis, stated J. F. Filmer, Director of the Animal Research Division, Department of Agriculture, in a paper delivered at the Dairy Farmers’ Week at Massey Agricultural College recently. Two New Zealand firms have .put up penicillin cerate in the. now well-known collapsible tubes with nozzles which can be inserted into the teats. Because of temporary difficulties in tube manufacture, supplies were rather short during the first month or two of the season, but since then ample quantities have been available and penicillin has been used very widely by dairy farmers in the treatment of mastitis.

IT has been possible to obtain samples for bacteriological examination from only a small percentage of the cows treated, but R. W. Roach, Veterinary Research Officer, Ruakura Animal Research Station, has made some interesting observations. He was able to make before and after treatment bacteriological examination of 91 clinical quarters in 77 cows, all of which were infected with Streptococcus agalactiae. In 90 per cent, of the quarters there was a return to normal milk production; the germs were destroyed in 66 per cent, of quarters, but not in the other 24 per cent. The Herd Recording Department of the Dairy Board is collecting data concerning the effect of treatment from a number of herds for which mastitis data have been kept for some years, but there has not yet been time to analyse the results. The general reports have been very encouraging and complaints have been surprisingly few.

Negative Results Milk samples were examined from 167 quarters which were reported not to respond to penicillin treatment. Strangely, no harmful germs could be found in 91 of these samples, and no explanation can be offered to account for the failures in these cases. In 28 quarters germs were found which are not affected by penicillin. It has always been realised that mastitis caused by such - germs would not respond to penicillin, but fortunately only a small percentage of such cases occurs. In 33 quarters Str. agalactiae was found ana testing in the laboratory afforded no evidence that it had acquired any unusual resistance to penicillin.. Obviously, in these cases the penicillin had not made contact with the germs in sufficient concentration for a long enough period. This stresses the necessity for promptness and care in the administration of penicillin.

Faults in Treatment A few cases of faulty treatment have been reported. It cannot be overemphasised that the best results will be obtained only if treatment is begun as soon as any abnormality in the milk or the udder is detected. A delay of even one day may be quite serious. Carrying out the treatment carefully and thoroughly is equally important. The whole contents of the tube must be injected. Observations have shown that even when the greatest care is taken about 10 per cent, of the contents

is left in the tube, and the manufacturers allow for this. If care is not taken, a much larger proportion may be wasted and the dose will then be inadequate. If any of the contents of a tube are accidentaly lostfor example, through a cow kicking—another tubeful should be injected. A number of cases have been reported in which farmers have used only 1 tube. The temptation to do so is great when the quarter appears normal 24 hours later, and it must be admitted that some cases do clear up satisfactorily after treatment with only 1 tube; quite a few of these would probably have recovered without any treatment. However, the practice is extremely dangerous, as it is likely to lead to the development of resistant strains of organisms. The mechanism by which this occurs is quite simple: In any congregation of germs there will always be a few which are more resistant to penicillin than the others; if too small a dose of penicillin is given, or if treatment is stopped too soon, the more susceptible germs are killed, but the few more resistant ones survive and in the absence of competition they multiply rapidly.

Therefore, all cases should be treated early, a full course of 3 tubes should always be given, and the whole contents of 1 tube should be injected at each treatment.

Use of Larger Doses Recently some farmers have used tubes containing doses of 50,000 or 100,000 units of penicillin instead of the standard tube, which contains 25,000 units. In special cases veterinarians may advise the use of larger doses, and this advice should be followed, but in general no better results are obtained than with the standard dose, and the very much greater cost is not justified (275. 6d. per dozen for 100,000 units as against 13s. 6d. per dozen for 25,000 units). It must be emphasised that 1 dose of 100,000 units is not as effective as 3 doses of 25,000 units given at 24-hour intervals; in fact, if the latter treatment is not effective, generally it is better to give 1 or 2 more doses of the same size than to increase the size of the dose. Where the larger doses are used special precautions must be taken by suppliers to cheese factories. Penicillin is particularly active against cheese starters, and during the past season a few cases have been reported in which cheese quality was deleteriously affected by milk containing

penicillin. Where the standard dose of 25,000 units is used, this can be prevented by withholding milk from treated quarters from the start of treatment up to and including that taken at the second milking after treatment ceases. Where larger doses are used it is essential to exclude the milk up to and including that taken at the fourth milking after the last injection.

Treatment at Drying Off

Last year the suggestion was made that streptococcal mastitis might be reduced or perhaps eliminated by the treatment of all quarters of all cows at drying off.. A large-scale experiment conducted in collaboration with the New Zealand Dairy Board and a number of veterinarians has been completed, but there has not yet been time to collect and analyse results. However, some results are available from a smaller but more intensive experiment conducted by Roach. Fifty-five cows infected ■ with Str. agalactiae, but not showing obvious symptoms of mastitis, were treated with 1 tube of 25,000 units per quarter at or after drying off. Of these cows 84 per cent, calved free from infection and 73 per cent, remained free from infection for 3 months after calving. In 11 herds containing 616 cows in which all quarters had been treated with 1 tube of 25,000 units of penicillin at or after drying off, milk samples were examined bacteriologically after the subsequent calving. Three herds calved free from infection and the average incidence of infection in all herds was 4.8 per cent, of cows and 1.4 per cent, of quarters. The average incidence of infection in untreated herds is about 24 per cent, of cows.

Further observations are being made in a few herds at the end of this season. One tube of 25,000 units of penicillin is being injected into all quarters of all cows, the teats are being disinfected, and special attention is being paid to treatment of sore teats. This work is being done under direct veterinary supervision, and bacteriological examination will be made of samples from all quarters after calving. At present it is not possible to give an exact estimate of the effect of treatment at drying off on the incidence of obvious mastitis in the following season, but it seems certain that it will cause some reduction. Perhaps the best advice that can be given at this stage is along the following lines:— Carefully examine milk from all quarters of all cows with a strip cup just before they are dried off. Treat all obviously-affected quarters with 3 tubes of 25,000 units of penicillin, at 24-hour intervals, giving the last tube after the last milking. In badly-infected herds inject 1 tube of 25,000 units of penicillin into every quarter of every cow after the last milking.

Whether the increased factorycheques resulting from an unknown reduction in the incidence of mastitis would justify the expenditure of 4s. 6d. per cow can only be a subject of speculation. Farmers have been known to make much wilder speculations.