410 Growth and Development of Breeds and Crosses of Pigs 



to show (61) that pigs are particularly susceptible to in-breeding and 

 consequently respond readily to an out-cross. The application of this 

 principle has been made in Denmark where two pure breeds are kept for 

 the purpose of crossing to produce the commercial pigs. 



The reciprocal cross — Berksliire-Large Wliite — is interesting because 

 where the Berkshire sow is used the off.spring at the earher ages appear 

 to be smaller than the reciprocal cross although they eventually reach 

 the same size. Loudon (62) states that the way of stock improvement is best 

 if the females are large and the males of smaller size ; the female is then 

 able to nourish the young better. It may be that Berkshires are not 

 particularly good mothers and that pigs suckled by them do not grow 

 so fast at first, but it is more probable that it is a case of sex linked 

 inheritance of early maturity. Tliis appears to be a case similar to that 

 of the Aberdeen- Angus-Shorthorn cross in cattle (63) where early maturity 

 seems to be inherited througli the male rather than the female. Berkshire 

 crosses with both Tainworths and Lincolnshire Curly Coated seem to be- 

 have in the same way ; although no difference is seen when early maturity 

 comes in from both sides such as in the Berkshire-Middle White cross. 



Table XIV shows the rate of maturity of the crosses as a percentage 

 of the weight at 11 months old and from it the facts mentioned above 

 will be clearly seen. It will also be noticed that the general tendency 

 seems to be not only for cross-breeding to increase the actual weight but 

 also for it to increase the rate of maturity in Uve weight. Punnett and 

 Bailey (64) found in rabbits that crossing distinct breeds may in some 

 cases lead to early maturity in the first cro.ss. 



The comparative carcase weights of cross-bred pigs at different ages 

 have been calculated by correcting for age and are shown in Table XV, 

 as with the pure breeds the hve weights are much below those of the 

 Uve classes more particularly at the older ages. 



Table XVI shows the proportions of the carcase, pluck and alimentary 

 canal etc. to live weight in cross-bred pigs and when comparison is 

 made with the pure breeds in Table VII it will be seen that, on the 

 whole, there is a tendency for early maturity in carcase weight to be 

 improved by cross-breeding when an early maturing is crossed with a 

 late maturing breed (Berkshire-Large Black) or even when two late 

 maturing ones (Large White-Large Black) are crossed together. When, 

 however, two early maturing breeds (Middle White-Berkshire) are 

 crossed no improvement in this respect is evident. The number on 

 which these conclusions are based is small however, and they are at the 

 best only tentative ones. 



