8 BULLETIN 20, PORTO RICO EXPERIMENT STATION. 
certain feeds and may therefore have nothing to do with richness. 
Again, large dairy cattle are often preferred to small in the belief 
that they have possibilities of greater production on account of the 
larger amount of feed they consume. Too much stress should not be 
placed upon size. 
Only those factors which make for the success of the dairy cattle 
business should be given consideration in the selection of cattle. 
IMPROVING THE BREED. 
The fundamental principles involved in building up a dairy herd 
in Porto Rico are essentially the same as those obtaining in the 
Temperate Zone. Porto Rico has a splendid foundation stock 
adapted to local conditions upon which to build up a superior dairy 
industr} 7 . Cattle which do not naturally adapt themselves to climatic 
conditions can not be expected to attain their maximum of efficiency. 
By the importation of some of the best breeds of cattle, or by rigor- 
ous selection and careful crossing of the native cattle, the Porto 
Rican farmer should be able to develop after some years a race of 
cattle that will rank with or excel the improved breeds of the world. 
Effort to improve the breed should be confined to one particular 
type, rather than given to an indiscriminate mixing or crossing of 
two or more breeds. Like tends to produce like, and for this reason 
the stockman should endeavor to build up his stock by the intro- 
duction of improved animals. Probably the quickest way to build up 
a herd is (1) by the purchase of high-grade animals having the 
ability to transmit their characteristics to their offspring; (2) by 
systematic breeding and judicious feeding; (3) by eliminating all 
low-yielding females; (4) by improving the general average of the 
females by the purchase of males which will keep the strain pure 
and tend to increase the milk yield; and (5) by establishing im- 
proved breeds. A number of the Porto Rican crossbred animals show 
improved conformation and probably earlier maturity by reason of 
the cross (PI. II, Fig. 2). 
On account of the prevalence of the cattle tick, the stock raiser 
will do well to confine his purchase to the best native cows, regardless 
of whether they are native or graded stock, and import the very best 
bull that he can afford. The stockman is, however, justified in im- 
porting purebred cattle if he is prepared to meet the losses that 
occasionally occur in acclimating the stock, has a dipping tank in 
which to dip the cattle periodically, and provides a shelter from the 
sun and a plentiful supply of succulent grasses for the animals. 
THE CATTLE TICK (Margaropus annulatus). 
The cattle tick {Margaropus annulatus) is very abundant in Porto 
Rico and carries from one animal to another the disease commonly 
