162 PHYSIOLOGY OF FARM ANIMALS [CH. 



Castration and the Internal Testicular Secretion. The practice 

 of castration or the removal of the testes has been carried out upon 

 the domestic animals for economic purposes from the earliest times 

 onwards. It is generally believed that the flesh of cattle, sheep, and 

 pigs is much improved therebj^ and that the animals fatten faster 

 and more readily, but whether this effect is due directly to the 

 removal of testicular inflvience upon the metabolism, or whether 

 it is an indirect result of the greater lethargy and absence of 

 excitement displayed by de-sexed animals is still an open question. 

 Castration is practised on horses to make it possible for them to 

 work in association with mares ; moreover, geldings are in a general 

 way more manageable and less excitable than entire animals. 



It is usual to castrate colts or yearlings in the summer following 

 birth. Calves are operated on at an age of six to twelve weeks. 

 Lambs are castrated at any age between three weeks and three 

 months; and young boars are 'cut' preferably when from six to 

 eight weeks old. 



The general effect of castration in all animals is to prevent the 

 development of the secondar}^ male characters, that is, of those 

 characters which while correlated with the sex in question are not 

 directly concerned with the reproductive processes. But this 

 effect is usually only brought about provided that castration is 

 performed prior to puberty or the age when sexual maturity is 

 reached. Thus in man, early castration arrests the enlargement 

 of the larynx and the consequent deei^ening of the voice; it like- 

 wise prevents the growth of hair on the face and the other parts 

 of the body which are usually provided with hair in the adiilt, and 

 consequent^ it produces a general apj)earance of femininity which 

 is in reality a condition in which certain of the male characters 

 are absent rather than one in which female characters have been 

 acquired. In animals the effects are similar. For example, in those 

 breeds of sheep which are horned in the male but hornless in the 

 female (Herdwicks, Merinos, etc.) castration arrests the develop- 

 ment of the horns, and it is noteworthy that this happens at what- 

 ever stage of growth the operation is performed, the horns ceasing 

 to grow forthwith. It is clear therefore that the testicular stimulus 

 is necessary not only for the initiation of horn growth but also for 

 its continuance. In other breeds of sheep in which both sexes are 

 horned (e.g Dorset Horns, Scottish Black-faced and Lonks) the 

 wethers have horns which are finer and less massive than those of 



