The owner of a healthy herd should be very careful about buying in hogs for feeding or breeding purposes, and, in the Western states especially, all public stock yards and stock cars must be regarded as possible sources of spread. Hogs coming into the herd for breeding purposes, if by rail, should be shipped in other than stock cars, and should not be unloaded so as to go through stock yards. All new hogs coming on to a farm where the disease has not appeared, should be kept carefully apart from the herd for from two to three weeks after arrival. The disease may thus have time to develop, if the animals have been infected before shipment or en route. It is decidedly worth while to be careful about clean feeding, for it seems probable that this is a common method by which infection enters the body. This being the case, troughs and feeding floors should be frequently disinfected with steam, boiling water, or a very dilute corrosive sublimate solution (1:1,000 dissolved in water), with the troughs subsequently rinsed out with plain water. Or the troughs and feeding floors may be disinfected with any of the coal tar disinfectants if they are used in sufficient strength. These are not poisonous in any probable quantity which hogs would get.
A Disastrous Experience.
—The farmer should be especially careful about buying hogs out of stock yards. Some years ago a certain Minnesota farmer purchased a lot of feeders from Sioux City and took them home to his farm. In about two weeks his hogs commenced dying. A little later hogs previously on the farm began dying. In a little while he was losing hogs at the rate of 25 a day, losing a total of about 200. This loss of 200 hogs was scarcely a drop in the bucket—too small for consideration in comparison with the loss which this outbreak cost the state, for, with some others coming into the state from Iowa and Nebraska, this outbreak cost the state, as carefully estimated, about $1,250,000 during that one year. As soon as the Minnesota farmer here referred to realized that he had cholera and was liable to lose a large portion of his herd, he shipped out a lot of fat hogs ready for market. These were yarded for a time in the public stock yards of his town, and one of them died while waiting for shipment. This hog was left for a day or so in the yard. Later a carload of feeding hogs was shipped in from a point in South Dakota, where they had never had hog cholera. These South Dakota hogs were unloaded into the yards where the fat hog had died some time before, and were sold out from there by auction.
It was a very interesting study to follow the resulting outbreaks; but a very serious matter for the owner and for that entire portion of the state. Practically every farmer who bought hogs at this sale, and very many of those who walked around the yards looking at the hogs, but without buying, had hog cholera on their farms in a very uniform period after the sale. Surely the moral of this tale is so self-evident as to need no further suggestion.
Cleaning Up.
—Troughs and feeding floors, at least, and, if practicable, the hog house also, should be kept clean and frequently disinfected during an outbreak. When the outbreak appears to be over, the owner must decide as to just what he will do in the way of disinfection and cleaning up, or whether he will stay out of the hog business for a year and allow the infection to die out. This is, of course, without regard for the possibility of putting in vaccinated and immune hogs. Feeding troughs and feeding floors and the hog house in general, may be disinfected if of reasonably good construction, by a thorough cleaning and then by one of the methods suggested under prevention. If the sick hogs have been kept in an old straw shed or in an old hog house that is about ready to fall down anyway, by all means the best method of disinfection is by burning. Without disinfection or burning the owner cannot be safe in putting in susceptible hogs within much less than a year after the last hog died or recovered. The slow old chronic cases that go dragging around at the end of an outbreak should usually be killed and safely buried, for it is rarely profitable to put such hogs in shape for market. It might possibly be worth while to hold such a one over and nurse them along, in case of valuable brood sows, for hogs having recovered from cholera are usually immune for life.
Brood sows which have had the disease and recovered usually give something more than natural immunity to their offspring. But the degree of immunity so conferred is so variable in degree and uncertain otherwise that it cannot be depended upon as a routine method of establishing immune herds. Yards may be practically disinfected by plowing or by burning off a good layer of straw.
Hog Cholera Vaccination.
—Generally stated, this vaccine consists of two parts: (a) Blood serum from the body of a specially immunized hog; and (b) virulent blood serum from the body of a hog about to die from cholera. The general theory upon which this double vaccine is used is that of giving the animal an infectious disease and at the same time a treatment which enables the animal to resist the infection. When the hog is through with it he is in exactly the same condition as though he had gone through a natural exposure and recovered.