366 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [VI, IV

                                                DISCUSSION

In 1933, Minett, Stableforth and Edwards demonstrated the possibility of
assembling a herd of cows free from Str. agalactiæ infection. The initial incidence
of infection in the herd concerned (Herd B), which contained 49 cows, was 24.5
per cent, and in 1933 infection had been absent for about three-and-a-half years.
At the present date the herd is still free.

In 1933, control work was also proceeding in the six herds now being discussed.
It was hoped that by the use of similar measures it would be possible to eradicate
the disease from these herds or, at least, to reduce the number of new infections to
such a point that, with the normal disposal of animals as they got older, final
elimination would be in sight.

In Herd I our hopes have been realised, since it has now been free from infec-
tion for nearly three years. Herds A, C, J and K on the other hand have
continued to show new infections, although in all four herds the proportion has
steadily fallen whilst the size of the herds has increased. With Herds J and K a
number of circumstances have probably contributed to the failure to effect eradica-
tion. Thus, the intervals between herd tests had to be prolonged to about six
months, post-calving samples were not examined, and freshly drafted cows were
not examined at once, and, finally, it was impossible in some cases to remove
infected animals to the separate farm for some weeks or months.

With Herds A and C there were several factors which increased the difficulties
of control. Firstly, although the owners had prescribed strict precautionary
measures for preventing spread of disease, a large infected section had to be main-
tained in the same or neighbouring sheds. Although it is difficult to see how
the precautions taken could have been improved, the results, in conjunction with
those of Herd I, suggest that the procedure of keeping infected and non-infected
cows in the same or adjoining sheds is less satisfactory than the total removal
of infected cows. This accords with the view of Seelemann [1933], that unless
infected cows can be quickly evacuated, the removal of infection by suitable
treatment is in most cases a valuable and perhaps essential aid to eradication.
Secondly, in both herds the retention of Str. agalactiæ infected cows has helped
to keep up the size of the infected group. Thus, in Herd A, there has been a large
number of cases of clinically evident mastitis due to streptococci other than Str.
agalactiæ, apparently arising in a sporadic manner. The Str. agalactiæ infections,
on the other hand, were insignificant clinically, and it was not to be expected,
therefore, that the owner would evacuate these in preference to the more obviously
affected animals. In Herd C, it is to be noted that many infected cows were re-
tained much longer than they would have been under ordinary circumstances
to their high pedigree breeding value.

In Herds A and C the results at first appear to be disappointing. When
the data are analysed, however, the results are less discouraging than they appear,