59
52
inspection in the proportion of tuberculous milk is likely to be associated with a noticeable diminution in the extent to which human infection occurs from that source. But it is possible that the results of such a policy would prove disappointing. We have evidence which suggests that the rural parts of the West Riding, where routine veterinary inspection is energetically carried out, are no more free from bovine tuberculosis than the rural parts of Kent, where there is no routine inspection.
134. An advantage of veterinary inspection over some methods of improving the milk supply is that it benefits the health of the country as well as that of the town population. We look forward to the day when eradication of tuberculosis will provide a complete With a vigorous safeguard to the milk supply in rural areas. campaign the interval need not be too long. But until that time, clinical inspection, especially in herds from which milk is sold directly by the producer, should reduce the extent of infection of milk consumed by the public.
135. The second advantage sometimes claimed for more frequent veterinary inspection, is that it reduces the incidence of disease by removing infectious cows from herds where they may do considerable damage. But cows in the early stages of tuberculosis, before clinical symptoms appear, may spread infection as readily as those removable under the tuberculosis order, and as they are much more numerous, the strict administration of the order, though it might have some, would be unlikely to have an important, effect in this respect. Witnesses before us have generally confirmed this conclusion.
136. The prompt elimination of diseased cows is not the only We have already advantage of routine veterinary inspection. indicated the part which day-to-day management and hygienic precaution play in the prevention of disease. A veterinary officer making periodical examinations of dairy herds would be well placed both for observing the effects of different plans of management upon the health of cattle, and for giving advice directed towards their improvement. Farmers are often unaware of the presence of disease in their herds. It is an essential preliminary to the reduction of disease that their attention should be directed towards its existence. Routine veterinary inspection, carried out with a sympathetic under- standing of the farmers' point of view, would not only do this, but would also play a most important part in creating among farmers an atmosphere favourable to eradication schemes such as we discuss further on.
V. METHODS OF ERADICATION.
(a) Bovine tuberculosis.
137. The total eradication of bovine tuberculosis from all herds is generally agreed to be the only complete solution of the problem of tuberculous milk. It should also, to some extent, reduce the
59
farmer's costs in producing milk, so offsetting some of the costs incurred in eradication, especially if this is economically carried out. But any such scheme must take account of conditions peculiar to Great Britain. In the first place, the incidence of tuberculosis among our cattle is so high that the wholesale slaughter of infected animals (as in the United States and Canada) is out of the question. Not only would its immediate cost be prohibitive, but it would also seriously contract the supply of milk. Further, the continual move- ment of dairy cattle, not only between farms, but also between districts, adds very materially to the difficulties of freeing herds from tuberculosis and of keeping them free afterwards.
138. It is not enough to secure that all infected animals have once been removed from a herd; steps must also be taken to ensure that no infected animals are subsequently introduced into the herd. Nor is it enough to secure that all animals introduced themselves come from disease-free herds and do not, at the time, react positively to the tuberculin test. For there is always the risk that they may have incurred infection in transit. As the presence of infection in its early stages is not disclosed by the tuberculin test, the fact that they pass this test is no guarantee that they will not subse- quently develop disease. This risk of reinfection has an important bearing on the question of eradication of tuberculosis in this country. It is sometimes held that it would be sufficient to take the important step towards eradication of encouraging individual farmers to free their own herds from tuberculosis. In this way it is hoped that a gradually increasing number of disease-free herds would be created. But the difficulties that exist, and would continue to exist, in preventing the reintroduction of disease in herds which depend even in part on recruitment from outside for the maintenance of their numbers, seriously limit the usefulness of such a policy.
139. Self-supporting herds, indeed, may be cleared of tuber- culosis by the method first proposed by Professor Bang in Denmark, or by some modification of it. According to this, calves are reared in isolation on pasteurised milk. At maturity they pass into a separate herd, which ultimately entirely replaces the old infected herd. The period of building a free herd may be shortened by dividing the original herd into two sections, reactor and non- reactors to the tuberculin test.
140.
But most herds are not self-supporting, and some special provision must be adopted to deal with them. The first of the possible ways of doing so would be to eliminate flying herds (i.e., those entirely or mainly maintained by buying-in cows to replace those dropping out) by obliging all farmers to rear enough calves of their own to maintain the strength of their herds. In existing circumstances we unfortunately cannot advocate such a policy, as it would run counter to the present organisation of the industry. Though there are large numbers of herds, already self-supporting
60
No comments yet.
Private notes are available after approval.