420 Growth and Development of Breeds and Crosses of Pigs 



is contrary to what occurs in sheep where variability in phick increases 

 with Age but it should be remembered that with pigs the pluck includes 

 the caul fat and that this in sheep decreases in variability with age. The 

 variability in the proportion of alimentary canal etc. undergoes the same 

 changes as the carcase. 



The alimentary canal has the greatest coefficient of variability, the 

 pluck (including caul fat) comes next and the carcase has least. The 

 causes underlying the variation in carcase percentage at any one age 

 are probably mainly due to differences in fatness, early maturity and the 

 amount of food contained in the alimentary canal; other factors however 

 play a part. Sanborn (7i) and Henry (72) found that a ration low in protein 

 affected the proportions of the body, and their results have been confirmed 

 by Enmiett el al. (73). Hart and McCollum(74) have shown that a diet of 

 maize alone reduced the rate of growth in pigs considerabh^ while 

 Jackson and Stewart (75) have shown that rats subjected to periods of 

 deficiency in diet were subnormal as regards skeletal and nmscular 

 development, while the viscera were above normal in weight. ElUot, 

 Crichton and Orr(7n) found that in pigs with rickets the head was 

 abnormally large and Henseler(7()) found that by controlling the nutrition 

 of pigs he could not only affect the hve weight but also the proportions 

 of the body. 



Correlation. In order to determine the effect of weight, independent 

 of age, on the proportions of the body and also the correlation existing 

 between the proportions of the different parts of the body Table XXI has 

 been prepared. This table shows that, independent of age, a liigh live 

 weight is correlated with a large percentage of carcase and a small 

 percentage of pluck and alimentary canal, etc.; that is within a breed 

 the heavier a pig is for its age the higher will be the proportion of carcase 

 to hve weight. This fact is consistently confirmed by the various groupings 

 made. The remainder of the table shows that the proportions of the 

 carcase vary inversely as the proportions of the pluck and aUmentary 

 canal, this appearing as the result of every grouping. 



Similar results were obtained experimentally by Henseler(76) who 

 took two pigs from the same litter, one was well fed and the other starved ; 

 both were killed at 9 months old. The starved one weighed 58 lbs. and 

 the well fed one 279 lbs., the former having a carcase percentage of 

 73 per cent., while the latter killed at 87 per cent. 



The main cause of the increased carcase percentage with age is the 

 development of muscle and fat rather than great alterations in the size 

 of the other organs of the body. 



