BLACKLEG AND ITS CONTROL.

New Zealand Journal of Agriculture, Volume XIII, Issue 2, 21 August 1916, Page 121

BLACKLEG AND ITS CONTROL.

C. J. REAKES, D.V.Sc., M.R.C.V.S., Director of the Live-stock Division

Blackleg, often termed “black-quarter” or quarter-ill,” is, practically speaking, a disease of cattle alone, though it is said that sheep and horses have very rarely been known to be affected. No cases among these animals have, however, been met with in this country. The disease, fortunately, is present only in limited areas of New Zealand, but the mere fact of its limited distribution renders it necessary to take all possible precautions to prevent its further spread, and at the same time to keep it under control in the already affected localities. This can be done effectively at but slight cost and with but little inconvenience to farmers, provided they co-operate with and assist the departmental officers in carrying out the necessary measures. The affected areas are

(1.) The Taranaki District, where the disease has existed for several years, but now, thanks to the yearly inoculation of calves rendered necessary by the operation of the Blackleg Regulations, causes practically ■no loss. This inoculation has become a part of the annual routine of farmers in ’ the district, and is carried out with little or no inconvenience to them, and at no monetary cost.

. (2.) Portions of the Auckland District, where regulations similar to those in force in Taranaki come into full operation during the present season. •

NATURE OF THE DISEASE.

Blackleg may be described as a form of blood-poisoning, caused by a specific organism, without whose presence the disease cannot exist. . The' germs of the disease can- retain their vitality, in the soil for a long period of time, and it is usually' through grazing on land infected with these germs that animals, contract the disease. Save in rare instances,. only young' cattle are susceptible, and it is very unusual to find one under three months or over eighteen months old affected. Further, it is the best - conditioned animals which suffer, particularly those which are making flesh rapidly. Calves while in. poor condition ' are in some way non-susceptible so much so that direct experimental inoculation with virulent virus may fail to produce any sign of the disease in them. The first symptoms appear in from two to five days after infection has taken place, occasionally earlier.

HOW BLACKLEG WAS INTRODUCED INTO NEW ZEALAND.

There is good reason to believe that the use of non-sterilized imported bone manure in years past is responsible for blackleg gaining a foothold in this country. In Taranaki,. so long ago as 1889, isolated cases were found in a small area where this fertilizer had been used, and for several years no cases outside this area were noted. Then the disease began to spread rapidly, and it became necessary to take proper measures to get it under control. These measures have proved remarkably satisfactory and effective. In the Auckland affected areas no doubt the same original cause has operated, and there is reason to believe that isolated cases, not recognized at the time as being blackleg, occurred several years ago in the Waikato. Certainly there is no evidence to show that the disease spread to there from Taranaki —in fact, the distance between the two districts and the time necessarily occupied by cattle travelling between them would practically preclude the possibility of this, seeing that calves ■ infected when leaving Taranaki would be dead long before they ' could get anywhere near the Waikato. Imported bone manure is no longer able to cause trouble through this disease, as its sterilization before shipment has been compulsory since 1905, and the effectiveness of the sterilizing process is ensured by it ■ being carried out under the direct supervision of Inspectors appointed by the New Zealand Government.

SPREAD OF THE DISEASE. The principal methods by which the disease is spread may be summarized as follows :

(1.) Movement of young stock- from farm to farm, either through saleyards or direct. Striking instances. have lately occurred in the Auckland District, where the disease has been introduced to previously clean farms through the medium of calves bought in ' the saleyard. '

(2.) Failure to properly bury or otherwise completely destroy the carcases of young cattle dead from blackleg. This not only infects the soil where .the carcase lies, but allow . dogs and hawks, by feeding upon 'the carcase, to spread the infection. They do not themselves become affected, but they act as carriers.. '.

SYMPTOMS.

The most 1 characteristic symptom is an extensive swelling of- one fore or one hind quarter, combined with very definite symptoms of ill health, the animal being dull, feverish, and off feed, with loss of

cud. At times the swelling may appear at other parts of the body than a fore or hind quarter; the neck, breast, loin, or flank may exhibit it. The skin of the swollen part is tense, and on passing the hand over it with a light pressure a peculiar crackling is noted, this being due to the tissues beneath being distended with gas. Before the swelling becomes established lameness is noted, and indications of sickness make their appearance. Death occurs quickly in from two to three days from the appearance of the earliest symptoms, and often even earlier. It may be noted that, if the swollen part were cut into, the tissues under the skin would be found to contain a quantity of dark, soft, brownish-red material, while the muscles beneath are very dark-coloured, in places almost black. T -

PREVENTIVE MEASURES

In affected areas any calf showing lameness should be at once isolated and carefully watched. Medicinal treatment, from a curative point of view, is of little or no value, and the one effective measure is prevention. A calf dead from blackleg, or suspected to have died from the disease, should never be skinned, but should with the least possible delay be deeply buried, or burned, with the skin intact. This will lessen the risk of infection of the surrounding soil. At the' time of death a little blood, which is very infective, may come away from the nostrils or the anus. A good fire should be burned over the spot where death occurred, and this, if done properly, will ensure safety so far as infection of the soil is concerned.

Apart from these precautionary and preventive measures necessary to be carried out by the farmer, a thoroughly effective means of preventing the occurrence of the disease lies in the inoculation of young cattle with a properly prepared vaccine. This has proved most valuable in Taranaki, and now that it has become necessary to enforce vaccination in the Auckland District there can be no doubt but that it will be equally effective there. The vaccine is prepared at the Wallaceville Veterinary Laboratory, and the work of vaccination. is carried out by trained departmental officers, all vaccinated calves being at the same time branded, on the neck with the letter “ S.” This is done entirely free'of charge, and all that is asked of the farmer is that he brings his calves to a convenient centre for vaccination. Due notice is always given by advertisement and otherwise, so that as little' inconvenience as possible is caused. The hearty co-operation and assistance of farmers in these measures is looked ’ forward to with confidence.'.

BLACKLEG REGULATIONS.

The following is a summary of the regulations under the Stock Act for the control of blackleg:—

Infected areas are divided into two classes, according to the extent to which they are infected. These are designated by the letters “A ” and “B ” respectively (the boundaries in the Taranaki and Auckland Districts being duly declared by Gazette notice): — (1.) “ Young cattle ” means cattle between the ages of fourteen days and eighteen months. • , .

(2.) Removal of any young cattle from an infected area “ A” or “ B ” is prohibited unless such removal is authorized and takes place in accordance with the regulations. ' . Vaccination of Cattle on certain Lands.

(3.) If the Inspector of Stock is satisfied that blackleg exists on any land wherever situated, or that any land is likely to become infected with blackleg, he may cause the owner to muster all his cattle for inspection and vaccination.

Removal of Young Cattle from an Infected' Area A.’

(4.) Any owner desirous of removing from an infected area “ A ” any young cattle that have not already been vaccinated, or that have been vaccinated more than twenty-one days prior to the date of their proposed removal, must not less than fourteen days and not more than twenty-one days before such removal is intended apply to the Inspector of Stock for the district for a permit to remove the said cattle. Within a reasonable time after the receipt of such application the Inspector will vaccinate such cattle at a time and place as may be arranged. On the expiration of seven days after such vaccination the Inspector may, if satisfied, grant a permit for the removal of the said cattle. (5.) Any owner desiring to remove from an infected area “A” any young cattle that have been vaccinated within twenty-one days next preceding the date of their proposed removal must apply to the Inspector of Stock for the district for permission to remove such cattle. , (6.) Notwithstanding the foregoing, young cattle may be sent for immediate slaughter to a public abattoir or meat-export slaughterhouse from an infected area “ A,” subject to the following conditions: Every owner must apply to and obtain from the Inspector of Stock for the district a permit to remove such cattle to a specified public abattoir or meatexport slaughterhouse. No permit will be granted in respect to young cattle from a place on which a case of blackleg has occurred during the' six months immediately preceding the date of their proposed removal. ■

Sale oj Young Cattle within an Injected Area A.”

(y.) No young cattle shall be sold or offered for sale in a public saleyard without having first been vaccinated and branded at least seven days previously in the manner provided for in the regulations. (a.) If it is desired to sell in a public saleyard any young cattle that have not been vaccinated, the owner shall make application within the prescribed period to the Inspector of Stock for the district for such vaccination and branding to be carried out.

(6.) If any young cattle that have not been vaccinated and branded in accordance with paragraph 7 above are found in any yard or on any land or other places where stock are offered for sale, they shall be deemed to be offered for sale in a public saleyard, and the owner of such young cattle shall be deemed to have committed a breach of these regulations, unless such cattle have been brought into such yard or upon such land by order of the Inspector for the purpose of being vaccinated. • ’

Removal of Young Cattle from an Infected Area “ B.

(8.) Owners desirous of removing young cattle from an infected area “ B ” must within the prescribed period first make application to and obtain from the Inspector of Stock for the district a permit to do so. Before granting such permit the Inspector of Stock may, if he considers it desirable or necessary, vaccinate such young cattle, also all other young cattle on the same farm. (It is anticipated that the action will only be necessary in a small proportion of cases.)

. General. (9.) Permits issued for the removal of young cattle must be produced for perusal on demand. ' (10.) Whenever any stock dies or is found dead in an infected area the owner shall, unless otherwise ordered by the Inspector, at once cause the carcase to be destroyed in accordance with the regulations. , . (11.) The maximum penalty for a breach of the regulations is £2OO.

For further information, particulars of boundaries of infected areas, &c., application should be made to the local Inspector of Stock.