56 DISEASES OF CATTLE, SHEEP, GOATS, ETC. 



that the smaller streams and ponds have a like effect. It is common 

 practice to dig out a pond to receive the surface water from buildings 

 and yards, to dam ravines and creeks, to catch the water from tile 

 drains and springs for water for hogs. In such cases it follows that 

 they receive only surface water. It is apparent then, that the first 

 step to be taken in the prevention of hog cholera, is the securing of a 

 wholesome water supply. 



All animals are more or less subject to parasitic diseases, and the 

 intestinal tract, owing to its relation to the food and water consumed, 

 becomes the favorite seat of attack. Countless numbers of germs, 

 eggs, larvae, etc., enter with the food, but only a small part are in a 

 proper state of development when they enter or they do not find 

 suitable conditions for continuing life and therefore perish. Water 

 plays a more important part as a carrier of parasites than does the 

 food. 



The life cycle of the parasites that affect animals, nearly always 

 includes a stage of development outside of the body. Some parasites 

 are passed out of the body as eggs. These hatch and after under- 

 going greater or less change, they may be prepared to again inhabit 

 another animal. Some pass out, as larvae, and after a certain time 

 may infect an animal if taken in the stomach. A few require an 

 intermediate host, as the liver-fluke, which infects the snail, and most 

 tapeworms must usually pass one period of their existence in a differ- 

 ent species of animal before they can again cause disease in another 

 animal. Altogether the number of parasites which again find their 

 way into another host, represent a very small per cent of the eggs 

 produced. The eggs and larvae of all these parasites contain a great 

 deal of water and are easily killed by drying. Moisture is a necessary 

 factor in their existence outside of the body, and hence it is that they 

 are found in large numbers in surface water and are ingested (taken 

 up) with it. Bacteria can stand drying better than parasites, but 

 must have water in which to multiply. It follows then, that fewer 

 parasitic diseases of stock will occur upon high pasture land when 

 well water is furnished, than upon bottom land where they must de- 

 pend upon a natural supply. 



Among the most destructive parasitic diseases with which we 

 have to contend, is the twisted stomach worm of sheep (Strongylus 

 contortus) . It is found especially on low lands along creek bottoms 

 and around ponds. It affects sheep of all ages but is particularly 

 fatal to lambs. In seasons of excessive rainfall it may occur upon 

 any pasture, but in ordinary seasons it causes little damage except 

 upon the low pastures. The eggs and embryos are passed from the 

 sheep and fall with the droppings upon the pasture, and may be 

 washed into the streams or ponds from which the sheep drink. Mois- 

 ture is necessary for their existence outside of the body, and the dryer 

 the pasture, the less the opportunity for conveying the parasite from 

 one sheep to another. In seasons of heavy rainfall, when the grass 

 is kept constantly wet, the danger may be mitigated to a certain ex- 

 tent by changing the sheep from one pasture to another every other 

 day. 



