lowed by eat-h kind of host is greatly reduced. This simple 

 procedure often causes (|uite startling results and may, by it- 

 self, be sufficient to prevent actual disease. Thus, on heavily 

 infected horse pastures, sheep may remove 100,000 eggs per 

 head daily. 



Hay often has the effect of mechanically removing a large 

 number of infective larvae from a pasture. 



Actual removal of the turf and re-so«ing to permanent pas- 

 ture may be and has been used in extreme cases. But this can 

 only be recommended when heavily infested but very valuable 

 land is concerned or where the tu:f may be sold for urban 

 purposes. 



3. Avoidance of Infection of the Host and Prevention 

 of Ingress of the Parasite 



(a) General Hygiene — This is of the utmost importance. 

 Many horses are confined to stables throughout the year and 

 when they are kept clean and permanent litter avoided, the 

 worm infections are at a decidedly low level. Ordinary methods 

 of cleanliness alone can be of great value. This indeed is 

 one of the basic principles underlying the very successful Mc- 

 Lean County Sanitation System for controlling Ascarids in 

 pigs; in its essentials, this system simply requires cleanliness 

 of sow and breeding places and avoidance of exposure of the 

 young animals to infection. 



(b) Disinfection — Small quantities of faeces, overlooked in 

 general cleaning of stables are important sources of infection. 

 These may be sterilized by very hot water or steam. The gen- 

 eral bactericidal disinfectants are not very good for this jiur- 

 pose, the least ineffective being 3 percent lye and .l percent 

 lysol. These are of value both for horse and sheep strongyles, 

 but require an hour's contact to destroy them. They are prac- 

 tically useless against A.scarids and related worms, however. 

 Lye in its usually applied strength (about 1 percent) is quite 

 useless iis a disinfectant for any kind of worm, although it is 

 useful in freeing parasite eggs from dirt and making them 

 more readily available to the destructive action of other agents. 



(c) Permanent Pastures — There is no doubt that permanent 

 pastures form the greatest single danger to stock and that 

 Maurice Hall's dictum "Permanent pastures perpetuate para- 

 sites'' is still of the utmost importance. The pastures con- 

 centrate eggs and larvae, and improved pasture culture, by in- 

 creasing the stock-carrying capacity, still further increases 

 the danger. At present there is no effective method of pre- 

 venting infection on them. 



It was once believed that temporary pastures, plowed in and 

 re-sown would overcome this difficulty, but recent work has 

 shown that heavy infections of sheep may result from such a 

 practice. The eggs and larvae plowed in are protected from 

 sun, heavy rain and drought and many emerge with the new 

 grass. 



So far attempts at altering the pasture flora to produce an 

 environment less suitable for development, or a type of grass 

 less suitable for migration of the worms and so less likely to 

 cause an infection, have been comparatively ineffective but are 

 still being tested. Taylor finds that larvae climb higher on 

 clover than on grass and that such fertilizers as basic slag, 

 by encouraging clover growth, increase parasitism. On tlie 

 other hand, sainfoin carries only 5.50 larvae per pound, under 

 conditions where grass carries 1,1)00, probably because of the 

 relatively slight contact with the ground which the large sain- 

 foin plant makes. 



Manuring a pasture by nitrates encourages rapid growth of 

 grass and may lead to a reduction in larvae per pound of grass 

 and so produce a smaller intake. However, a dense growth of 

 grass provides favourable cover for parasites and infection is 

 proportional to density of cover; sparse growth permits natural 

 agencies to reach them. 



(d) notations. Rotation of permanent pasture when this is 

 possible, is of value but it postulates a large amount of pasture 

 land and much fencing as the animals have to be moved on 

 before the eggs they have passed give rise to infective larvae 

 (5 to 7 days) and kept away from the "used" land until all 

 larvae are dead; this period varies with the parasite con- 

 cerned, the soil and the climate and no general rules are yet 

 possible. The cleanest land should always be reserved for grow- 

 ing stock which is more susceptible to worm disease than older 

 stock. 



However, a certain amount of rotation of stock may be prac- 

 ticed. Not only may horses follow ruminants, but cattle may, 

 to some extent, follow sheep and old animals follow young 

 ones. Under these circumstances, a shorter fallow period is 

 possible as subsequent animals eat many of the larval parasites 

 of their predecessors. 



It is often practicable to graze lambs on clean pasture and 

 follow them by old sheep which have some degree of resist- 



ance to gastro intestinal nematodes. In choosing a rotation 

 such as this (or such as cattle following sheep) care must be 

 taken to know which parasites are concerned as only some may 

 thus be treated. The simultaneous grazing of several kinds of 

 animals (such as horses and sheep) is only an extension and 

 improvement of this method. 



(e) Bare Lots — The use of bare lots for young stock has 

 much to recommend it. There is no grass for them to eat and 

 conditions for development of worms are highly unfavourable, 

 iloreover, as the animals must be watered from troughs the 

 danger of infection is further decreased. 



This method has enabled lambs to be raised in districts where 

 worm infections are so high as to kill a large percentage of ani- 

 mals raised on pasture. 



Partial bare lots in pig pastures, in lands where the kidney 

 worm is prevalent, are of assistance in controlling this parasite 

 also. Faeces also are concentrated, making their removal or 

 treatment easier. 



(f ) Fencing — Fencing is of value in dividing pastures for ro- 

 tation, or to ensure uniform grazing and to avoid overgrazing 

 of certain parts. Temporary fencing (as in folding) so ar- 

 ranged to allow lambs (but not ewes) to reach new pastures 

 in a progressive system of feeding, is also of value, but entails 

 a certain amoui\t of labour, as the fences must be moved weekly. 

 In this case the lambs, if they are not weaned, have the run 

 of the pasture ahead as well as the one in which the ewes are 

 kept, or, if they are weaned, the one ahead only. The very 

 greatest care must be taken to prevent the lambs gaining ac- 

 cess to old ground already grazed by the ewes and from which 

 they have been moved on. If this is not done a heavy infec- 

 tion is extremely probable. 



(g) Limitation of Numbers — Limitation of numbers is really 

 an attempt to return to nature from artificial conditions of 

 modern farming. It is the rational method with permanent 

 pastures where over-stocking has such disastrous results. A 

 reduction of .50 percent in numbers on a pasture means a much 

 greater reduction than that in parasites. It also spreads out 

 the rate of intake of parasites and allows resistance to de- 

 velop. Moreover, overstocking decreases the food yield of the 

 pasture and encourages closer grazing and a higher worm in- 

 take. The poorness of the food supply decreases body resist- 

 ance and so encourages parasitic disease. 



(h) Night Housing — Night housing is often valuable as most 

 strongyle larvae are able to climb on to grass but do so only 

 when it is damp, retreating towards the soil as it dries. Heavy 

 dews are very suitable for this upward migration and the simple 

 procedure of keeping stock — especially young stock — off the pas- 

 ture until the dew has evaporated, has frequently made all the 

 difference between health and disease. Husk in cattle is often 

 caused by early grazing and night housing is particularly use- 

 ful with that disease. 



(i) Saised Troughs — Feed racks, raised troughs and clean 

 water — especially in connection with bare lots and permanent 

 pastures which are heavily stocked — is valuable in reducing 

 intake of parasites. It is of value also in stables where 

 the floors are often heavily contaminated with infective larvae 

 and it is especially valuable for young stock. 



(j) Silage and Folding — The use of silage helps to reduce 

 numbers of larvae taken in by the host, and the temjierature 

 generated in its preparation may destroy some larvae and shor- 

 ten the life of others; in general, silage does not carry the 

 heavy infections that grass does. 



Folding on green crops, with the aid of hurdles, is also of 

 value, provided the same ground is not used too often for 

 this purpose. The animals must be moved every 6 days or so 

 and the young must have first choice — even going one fold ahead 

 of the adults — and must not under any circumstances be per- 

 mitted to enter old, used folds. 



Eotational grazing (e.g., nitrogenous stimulation of grass 

 which is grazed on successive fields) may cause a heavy infec- 

 tion but generally increases resistance to disease. 



The penning of stock on arable ground is more dangerous 

 than the free ranging of stock on permanent pastures as they 

 tramp faeces into the ground and so improve the chances of 

 the parasites developing; under these conditions sandy soil 

 is probably more dangerous than clay. 



Food cabinets, as recently developed, afford a method for 

 the quick growing of green crops under circumstances which 

 preclude any infection at all. The animals, if housed on con- 

 crete and kept clean, need never acquire aii.v intestinal para- 

 sites at all with this system. The food cabinets permit of 

 the growing of "grass" in a week from seed without the aid 

 of soil. This is done by using perforated trays of certain 

 grains (notably barley, wheat and maize) in a constant tem- 

 perature cabinet and exposing them to the action of moisture 

 and artificial fertilizer daily. By a suitable rotation a constant 



306 



