I BULLETIN 36, PUERTO RICO EXPERIMENT STATION 
A not hti- limiting factor in the more humid areas during the rainy 
season is the torrential showers, which have a decidedly cleansing 
action in washing down and carrying oil' the source of infection, such 
as the eggs ana larvae of parasites. This infective material is 
either washed into streams and destroyed or is deposited on the more 
level lowlands. The abundant moisture which remains after the 
ii of heavy rains is very favorable for parasites and usually it 
i- during this time that the heaviest infestations are obtained. 
( )n the basis <>f variation in rainfall and differences in topography, 
Puerto Rico may he divided into three parts— the wet coastal plains 
of the north, east, and west; the Avy southern coastal plain: and the 
central mountain area subject to torrential rainfall. The [sabela 
district on the northern coast and the island of Vieques are other dry 
area-, -mailer hut similar to the southern coast. 
In general, livestock of the wet coastal plains suffer more from 
worm parasites than those of the other areas. The abundant mois- 
ture and the more level lands which tend to retain moisture are more 
favorable for the development of parasites. The southern coast 
area is the most favorable for raising cattle. The dry season with 
its destructive influence on parasites, and the rich limestone soils are 
very favorable, especially for young growing animals. This area 
appears to be especially suited as a breeding area for improved 
dairy cattle. However, the light and variable rains characteristic of 
the wet season in this area are favorable for several species of round- 
worms, and preventive measures and treatment are necessary. Seri- 
ous infestations with roundworms among calves of this area have 
been especially noticeable during and following the unusual heavy 
rains of 1933. 
The mountain areas where suitable grasses are grown are favor- 
able for raising livestock, even though the rainfall may be very 
abundant. Hillsides or mountain slopes carry less infestation than 
bottom lands because they benefit by the cleansing action of the rain 
and the following run-off, as well as b}' holding less moisture. The 
benefit of the natural advantages, however, is often lost by allowing 
the young stock access to the stream beds and low areas. 
As these differences in the climate and topography result in con- 
siderable variation in the prevalence of parasites and also some 
variation in the parasitic fauna, the methods used in control of 
parasites must vary somewhat in different parts of the island and 
at different time- of the year. 
RELATION OF PARASITES TO LIVESTOCK IMPROVEMENT IN PUERTO RICO 
Stockmen and both Insular and Federal Government agencies have 
imported livestock of the improved breeds in order to develop better 
and higher producing animals. New importations and the progeny 
of those already introduced are replacing the native animals. The 
higher producing animals are very susceptible to parasites and para- 
sitic diseases. The recommendations in regard to control of para- 
sites are directed especially toward the animals of the improved 
breeds because of their rapidly increasing numbers, higher value, 
and need for better care and management. The same methods. 
however, can be used to advantage with the native stock. 
