Annual Report for 1911 of Royal Veterinary College. 355 



that the summer and auXumn of l^tlO were also characterised 

 by a heavy rainfall, and thus for a period of a whole year the 

 climatic conditions were eminently favourable for the life of 

 the young worms. Probably during the whole or the greater 

 part of this period the stomachs of sheep at grass were 

 gradually becoming more and more infested with worms, and 

 eventually these became sufficiently numerous to cause serious 

 effects. In this connection it must be remembered that at 

 all times these worms are of nearly constant occurrence in 

 apparently healthy sheep of all ages, but only in small num- 

 bers. Given favourable conditions, therefore, the seeds of 

 serious mischief are constantly present in practically every 

 flock, and when an outbreak occurs one does not need to search 

 for an outside source to explain it. 



The losses during the past year were most severe among 

 ewes, and in many cases only the ewes were aflrected, although 

 the lambs were running with them. The escape of the lambs 

 in these cases was no doubt due to the fact that the drought had 

 already set in before the disease became serious among the 

 ewes, and this, in spite of the enormous number of eggs voided 

 \>y the ewes, saved the lambs from infection by interfering with 

 the development of the young worms. 



Coming next to the question of prevention, it must 

 be observed that the losses of the past year were not an 

 inevitable result of the preceding mild and humid season. 

 The al)solute eradication of stomach worms from a flock 

 caia scarcely be considered practicable in the conditions of 

 sheep-breeding in this country, but the prevention of serious 

 losses is possible even in the seasons which are most 

 favourable for the life of the parasites. The two things 

 which have to be avoided with that object are (1) over- 

 stocking with sheep, and (2) continuous grazing of the 

 same pastures with sheep for long periods. An outbreak of 

 parasitic gastritis can be determined at will by grazing a field 

 exclusively with sheep for several years. In reply to this it 

 may be said that the statement is contradicted by the experience 

 in connection with sheep-farming on hill and mountain land, 

 which has often been grazed continuously and exclusively by 

 sheep v.'ithout any sensible losses from parasitic gastritis. The 

 objection, however, does not apply, for on poor land the area 

 of groun'J y/iv sheep is large, and the pollution of the ground 

 with excrement is proportionally less, with the result that the 

 opportunities for worms to be taken in by sheep are reduced. 

 On the other hand, wlien comparatively good pasture is made 

 lo carry the largest possible number of sheep, and any of these 

 sheep are infested with stomach worms, the chances that 

 young parasites will be taken in with the grass are very great. 



