532 GENETICS IN RELATION TO AGRICULTURE 



Shorthorn or Hereford cattle, the hybrids partook most of the characters 

 of the Northern breed, save for the slight hump and greater development 

 of dewlap and sheath, which are characteristic of the zebu. This ob- 

 servation is borne out by the zebu-Hereford hybrid shown in Fig. 206. 

 With respect to market features, the hybrids appear to be held in high 

 regard in regions where the cross has been made in great numbers. In 

 Tunisia and Brazil at least butchers prefer them and are willing to pay 

 a premium to get them. 



With regard to resistance to disease the zebu appears to transmit 

 most of its qualities, at least in some degree, to the F t offspring. They 

 are resistant to foot-and-mouth disease, anthrax, and splenetic fever. 

 They withstand the heat of tropical climates, and the insect pests which 

 thrive in such places. According to several notes they are not infested 

 by ticks, but this lack of infestation does not appear to be associated 

 with any definite immunity to Texas fever itself. On the contrary one 

 note states explicitly that both the pure-bred zebu and the Fi hybrids 

 are susceptible to infection with the Texas fever protozoon, but their 

 high resistance to the disease keeps it from becoming as serious with 

 them as with Northern cattle. 



Apparently both male and female hybrids are fertile, in which respect 

 they appear to differ from most other species hybrids among the Bovidse, 

 the females of which are commonly fertile while the males are sterile. 

 There is evidence of Mendelian inheritance when specific characters are 

 considered, but coupling and physiological relations appear to exert a 

 considerable influence on the segregation and expression of characters. 

 Evidence of this comes from the fact that so many of the F 2 hybrids so 

 closely approach to an expression of the sum total of characters of either 

 the zebu or the Northern breed as to be. indistinguishable from them. 

 In Brazil free interbreeding in hybrid herds apparently leads to a pre- 

 dominance of zebu charaeters in a very few generations, perhaps on 

 account of the greater prolificacy of the zebu. The increased size and 

 vigor of the FI is not maintained, and constancy of blended characters 

 has apparently not been attained in any case. Tick resistance at least 

 appears to be carried over to subsequent generations, although unfor- 

 fortunately the records are not satisfactory. 



From a practical standpoint, therefore, it appears that the zebu might 

 be used as a means of combating tick fever in the Southern cattle district. 

 Whether the method would prove desirable in view of the perfection 

 attained by other methods of ridding pastures of ticks is, however, ques- 

 tionable. If utilized, however, it appears that the method should be 

 that of continually mating zebu bulls with range cows. In this fashion 

 it is possible to secure animals free from disease and at the same time of 

 very superior market qualities. This would necessitate a practice like 



