May 3, 1920.] Agricultural Gazette of N.S.W. 341 



By the Introduction of Diseased Stock 



First, and most important of all, comes the introduction of diseased 

 stock on to a farm. It might be thought that this could easily be prevented, 

 but such is not the case. Every infectious disease has what is known as a 

 period of incubation — that is to say, a more or less definite time elapses in 

 each disease from the entry of the organism into the body till the appearance 

 of the first symptoms indicating that the animal is diseased — and it may 

 happen that stock are purchased and moved on to a farm in that 

 period. Ayain, there are in many diseases acute and chronic forms, and 

 animals affected chronically may often show very little sign of disease, 

 especially if the conditions under which they are living are good as regards 

 feed and general hygiene ; later, when adverse conditions occur, the disease 

 may again become active. In one or two diseases the e.x:istence of "carriers " 

 (that is, animals which are affected and infectious to others but which at no 

 time show^ signs of disease) is more than probable. Further, it is not usual 

 for the farmer to know sufficient; of these diseased conditions to be able to 

 say that animals are affected or not, and owing, therefore, to one factor or 

 another a diseased animal slips in. In passing, it may be mentioned that such 

 animals are more often obtained through buying in open saleyards than when 

 purchasing direct from the owner or breeder. The complaints which are more 

 particularly introduced in themanner now under consideration are tuberculosis, 

 contagious abortion, contagious mammitis, swine fever, and swine plague. The 

 first three are chronic diseases, although acute cases of contagious mammitis, 

 terminating rapidly in death or serious incapacity, are not uncommon ; the 

 last two are usually introduced in the incubative stage, but chronic cases may 

 also occur. An animal in the early stages of actinomycosis might also escape 

 notice, and it is of course possible for an animal in the incubative stages 

 of any of the diseases mentioned to be purchased, though in some (such as 

 anthrax and blackleg) it is very unlikely. 



When purchasing horses, particularly young animals, strangles may very 

 readily be introduced ; in fact, if anything like large number's of young- 

 animals are bought and kept together it is very probable that strangles will 

 appear sooner or later. So much is this the case that various methods of 

 vaccination have been used in remount camps and other collecting places, 

 but with no striking measure of success. The farmer buying one or two 

 animals only, however, does not run such risks, especially if he is buying 

 animals over 5 years old. Influenza is still less likely to be introduced ; in 

 any case, the lapse of a week or little more without the animal showing signs 

 of illness will generally mean that the owner is safe with regard to, these 

 diseases. From this it will be seen that if newly-purchased horses are kept 

 apart for a fortnight from those already on the farm, they can then be 

 placed with the others without much fear of ill results, providing they are 

 still in good health. 



Thus it is evident that in this country the introduction of infectious 

 diseases on to a farm by horses is relatively small, but when we come to 

 consider the same question in regard to cattle, a very different state of affairs 



