PRINCIPLES OF LIVESTOCK BREEDING. 



45 



to produce lambs out of season. Under some circumstances dairy 

 cows can well be bred to bulls of the beef breeds in order to produce 

 calves which can be fattened profitably. In some cases it may even 

 be worth while to develop races within two breeds specially designed 

 to be complementary to each other in crosses. The danger in any 

 system of crossbreeding is that the very excellence of the first genera- 

 tion will tempt the breeder to use them as breeding stock. The 

 additional vigor due to crossing decreases after the first generation 

 and uniformity of type is lost at once. 



IMPROVEMENT. 



There is a certain antagonism between control over heredity and 

 radical improvement. Perfect control over heredity implies the 

 absence of all variation among the progeny of a mating. A useful 

 new type is most likely to be found where there is a maximum of 

 variation. Thus the pioneer breeder must make wide crosses. The 

 first generation may be expected to be about intermediate between 



- )*M^&^Z' : ^M$^ ik ; Bk>M: 



Fig. 11. — A group of Corriedale rams. This breed originated in Australia in the crossing of Lincoln or 

 Leicester rams with Merino ewes. It has been developed into a true type by years of close breeding 

 and selection. 



the parents and as uniform as the uncrossed parental lines. The 

 second generation, however, will in general show distinctly more 

 variability. The ancestral characteristics will be found in every 

 compatible combination and in all degrees of development if enough 

 young are produced. Characteristics may be found which appear 

 wholly new. If a promising new type is formed it remains to fix it 

 by careful selection and close breeding. 



There will doubtless always be room for the production of new 

 types and from time to time even new breeds. But this work of 

 radical improvement is not likely to occupy more than a few of the 

 most ambitious breeders. Others will have such superior stock that 

 they can do no better than conserve it by close breeding, making such 

 slow improvement by selection as the limited variability of the stock 

 permits. With a larger number, periods of close breeding must be 

 interrupted by periods in which new blood is infused into the stock, 

 a certain amount of uniformity being sacrificed to obtain renewed 



