The diagnosis of chronic streptococcus mastitis : reaction, chlorine, methylene blue and Hotis tests, and microscopic examination

Abstract

(1) An account is given of the abnormal conditions which may be encountered in the bovine udder and its secretion in chronic streptococcus mastitis. It is pointed out that, on account of these different manifestations of the disease, it is not possible for any single test to reveal the condition in all its forms. (2) The results obtained by the application of the alkalinity, chlorine, methyleneblue and Hotis tests and by microscopic examination are detailed. (3) For the estimation of the alkalinity of milk the British Drug Houses' Universal Indicator was compared with brom-thymol-blue in 123 samples and revealed 39.1 per cent. of infected samples as against 25 per cent. shown by brom-thymol-blue. (4) Chlorine determination was compared with alkalinity in 837 samples and detected a larger number of abnormal quarters, but its value as a test for mastitis is nullified by a tendency to show a large percentage of false positives on account of its sensitiveness to physiological as well as pathological factors. (5) The methylene blue reduction test was applied to composite samples from 32 infected and 15 clean cows. The reduction time was under 8 hours in 24 (75 per cent.) infected udders and in 1 (6.7 per cent.) streptococcus free udder. (6) Although reduction time is greatly reduced by mastitis streptococci, the reduction test cannot be regarded as specific for mastitis since reduction is also brought about by organisms other than mastitis streptococci. (7) There appears to be no correlation in streptococcus free milk between the reduction time and the chlorine content, alkalinity and sediment. (8) The Hotis test was applied to 269 individual quarter samples from 69 animals. It gives a high percentage of false positives and reliance can only be placed on its results if these are substantiated by microscopic examination of smears prepared from the milk after incubation. (9) A review of the literature dealing with microscopic examination of milk for the detection of mastitis streptococci is given. (10) The technique for preparing smears for microscopic examination is described. (11) It is concluded that microscopic examination of smears from fresh milk is unreliable while that of smears taken after centrifuging fresh milk is of limited value. On the other hand, smears prepared from 267 samples after incubation overnight detected 93.6 per cent. positives as against 88.8 per cent. revealed by cultural methods. (12) The lack of agreement between cultural and microscopic examinations in a small percentage of cases is attributed to the absence of infection in the particular sample in which the test concerned apparently failed. (13) In an examination of over 1,000 milk smears from quarters known to be free from mastitis streptococci long chain streptococci were detected in only one case. These, however, were not the same morphologically as mastitis streptococci. (14) The cell content of the milk as revealed in the smears provides a usefu1 indication of the extent of the changes in the quarter and in the milk. (15) For the detection of mastitis streptococci microscopic examination of smears made from milk that has been incubated overnight at 37°C. is just as reliable as cultural methods. It requires less time, labour and equipment and can easily be adapted to testing under field conditions.