CO129-562-12 Dysentry epidemic- recommendation to enforce compulsory pasteurization of milk 7-6-1937 - 17-8-1937 — Page 36

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in part, which might well be made entirely so, the fact that herds, and to some extent districts, are specialised for breeding and dairying respectively is economically so advantageous and so firmly established that the flying herd must be accepted as part of our system.

141. A second method that has been advocated is the progres- sive formation of disease-free areas, as has been done in both the United States of America and Canada. Eradication would be undertaken in contiguous farms, under compulsion where necessary, to form solid blocks of clean territory. Any movement of dairy cattle into such an area, unless under very stringent conditions, would be prohibited. It would be natural first to establish such areas in the cattle exporting districts, and to extend them gradually over the cattle importing districts.

142. The appeal to compulsion involved would give rise to acute difficulties. It would certainly create a demand for compen- sation on the part of farmers who were unwilling to free their herds on their own account. But it would be inequitable that those farmers who showed the least initiative in the matter of eradication should receive the most favourable treatment. Such a policy would also retard the progress of eradication. But, if compensation were granted to all farmers who undertook eradication the cost would be unduly high. Secondly, the setting up of special areas would necessarily be accompanied by regulation of the import of cattle into them. Even if the areas were selected with the greatest care, these regulations would entail a great deal of interference with the free flow of cattle, to the importance of which we have already drawn attention. Though for these reasons, we do not advocate the setting up of special areas to-day, the question will require to be considered further when most of the herds of the country have been freed from tuberculosis.

143. The third and last alternative involves neither compulsion nor undue restriction in the movement of cattle. Its aim is to prevent the infection of cattle from disease-free herds in transit by their strict segregation from all cattle other than from disease-free herds, by measures such as special markets (or sections of markets) and special precautions during transport. Similar precautions would be necessary to protect animals from infection when being exhibited at agricultural shows. The adoption of such measures would considerably increase the number of herds in which eradication would be feasible. The practical difficulties involved may be considerable; but they are not insuperable.

144. There are three ways in which the farmer may to-day reduce the incidence of tuberculosis among his cattle. First, he may slaughter tuberculous animals. Secondly, he may segregate them for the remainder of their lives. Thirdly, he may sell them to other herds. Slaughter is the most effective means of safeguarding the milk supply, but it is obviously not economical to sacrifice the milk

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of all cows that react to the test so long as good care is taken to prevent the sale of tuberculous milk. In view of the high rate of infection in this country the method of isolation, as well as that of slaughter, must be permitted under any scheme of eradication. The propriety of permitting the sale of reacting cattle in the open market has been called in question; but such sales do not increase the total amount of tuberculous milk sold at present, and they serve to reduce the number of tuberculous cows in the future. For though the sale of a reacting cow by A to B, and the sale of a clean cow to replace it by C to A leaves unaltered the total numbers of diseased and clean cows respectively, they advance eradication if carried through as a means of preserving the rest of A's herd from infection, so long as B's herd is already so heavily infected that it becomes no worse for the change. In fact, the sale of reacting cattle in the open market is probably a more effective method of progressive eradication than their isolation upon farms. It is also in many cases likely to be less expensive, for it does not involve the construction of temporary premises for their isolation. We are therefore strongly of the opinion that any official scheme of eradication should permit the sale of reacting animals.

145. To insist that known reactors should be declared as such on sale would obviously make eradication more expensive and might prejudice the success of any scheme. The objection to such sales has less weight if markets are set up devoted to the sale of tuberculosis- free cattle. Whoever then buys in the ordinary market does so with the knowledge that cattle bought there may be tuberculous. It would be unjust that one class of sellers in that market alone, namely, those who are taking part in an eradication scheme, should be forced to make a declaration which is likely to depress the value of the animals they are selling.

146. It is sometimes objected to schemes for eradication, that the advance of knowledge may soon make possible the immunisation of cattle against tuberculosis, and that if this were to occur a cheaper and more effective means of ridding this country of it would be available. In such circumstances, it is argued, it is improvident to encourage the expenditure of considerable sums of money on eradication. We do not share this view. We are aware that a high degree of resistance, amounting in some instances to complete immunity, to an experimental tuberculous infection can be conferred on the bovine animal by vaccination with the attenuated strain of bovine bacillus known as B.C.G. (Bacille Calmette-Guérin). This method of obtaining tubercle-free herds has, however, not yet been put to scientific proof under farm conditions in this country, and because it is essential that this should first be done, a long time must elapse before a decision can be reached on its efficacy and practica- bility in the field. On the practical side there are points in immunisation which have not perhaps been generally appreciated by the farming community. Immunity to tuberculosis produced by

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