THE DEVELOPMENT OF THE TESTES AND SCROTUM 

 OF RAM, BULL, AND BOAR 



By Ralph W. Phillips, Instructor in Animal Husbandry, 

 and Frederick N. Andrews, Graduate Assistant in Animal Husbandry 



INTRODUCTION 



A thorough understanding of the rate of development of the testes, the age at 

 which spermatozoa are first produced, and the factors which affect the develop- 

 ment of the testes and scrotum is essential as a basis for recommendations for 

 tre management and feeding of young males. Little definite information is 

 available concerning these problems, and the experiments herein reported were 

 designed to help supply this lack. 



Research in recent years has shown that the testes of most mammals must 

 be maintained at a temperature considerably lower than that of the body cavity 

 if they are to develop and function normally. The temperature in the scrotum 

 is considerably lower than the body cavity temperature and is maintained at a 

 fairly constant level by the activity of the tunica dartos, a muscular tissue 

 which lies just under the skin of the scrotum. This muscle reacts very quickly 

 to any temperature change, acting very much like a thermostat, drawing the 

 testes close to the body in cold weather, allowing them to be at a maximum 

 distance from the body in hot weather, and at intermediate temperatures con- 

 stantly lengthening and shortening as the temperature in the scrotum varies. 1 

 Since the tunica dartos muscle is essential to normal functioning of the testes, 

 a knowledge of how this muscle develops and the relationship between its 

 development and that of the testes becomes of interest and value. 



Studies of the following phases of these problems are reported here: 



(1) The normal development of the testes of the ram, bull, and boar. 



(2) The effect of low nutrition upon the development of testes in the boar. 



(3) The normal development of the tunica dartos in the ram, bull, and boar. 



(4) Factors which affect or control the development of the tunica dartos. 



DEVELOPMENT OF THE TESTES 



Ram 



A series of fourteen rams (Southdowns and Shropshires) was castrated at 

 ages varying from 21 to 189 days. Blocks of tissue were taken, fixed, sectioned, 

 and stained for histological study. 



At 21 days of age the seminiferous tubules contained only a single, irregular 

 row of cells on the basement membranes, the lumina being filled with an opaque 

 mass and an occasional free cell. At 42 days the row of cells had become more 

 regular and the material filling the lumina showed signs of breaking up. Little 

 change occurred from this time until 63 days when a few primary spermatocytes 

 had appeared. At 84 days an increase in primary spermatocytes was noted, a 

 further increase was noted at 105 days, and at 126 days some secondary sper- 

 matocytes were present and the lumina were clear in most of the tubules. 

 Spermatozoa had appeared at 147 days of age. 





'Phillips, R. W., and McKenzie, F. W. The thermoregulatory function and mechanism of the 

 scrotum. Mo. Agr. Kxpt. Sta. Research Bui. 217. 1934. 



