A study of some factors influencing fertility and sterility in the bull

by Herbert Lester Gilman

To summarize the work already done, most investigators have considered the bull as merely a mechanical carrier of Bact. abortum infection, though all are more or less suspicious of his ability to become an active spreader. Schroeder, however, states that the organisms are eliminated with the semen, but infection of the female occurs secondarily through the digestive tract by contamination of the food with the semen. Other investigators bring out fundamental points demonstrating the importance of other organisms than the Bang bacillus and call attention to the need of a more thorough study of the anatomy, physiology, and pathology of the male genital tract.

Any study of the genital organs must of necessity rest fundamentally upon a thorough knowledge of the anatomy and physiology of those parts. Too few of us have stopped to consider these questions thoroughly, with the result that our ideas on the problem are more or less vague. It is much easier to understand why abnormal spermatozoa occur so frequently, or changes take place in the semen with death or weakening of the germinal elements, if we realize or stop to consider the highly differential process of spermatogenesis, and the various structures which contribute to the formation of the semen. We must come to realize that each part of the genital tract is essential to the normal functioning of the whole, and that the genital tract and reproduction are in turn dependent upon the proper functioning of the entire body.

Walker (20) emphasizes the importance of a thorough knowledge of physiology in stating, “Although the subject of sterility has attracted the attention of the medical profession; and although much has been written on its causes and treatment, it cannot be claimed that the practical results obtained up to the present time are satisfactory, or that when consulted for sterility, the medical man of today can hold out to his patient much more hope of successful treatment than the medical man of fifty years ago. Our failure in this respect is in the main due to an ignorance of the physiology of reproduction.”

To bring out some of these points, the anatomy of the tract will be reviewed briefly, together with the physiology of reproduction, and the various factors which should be considered in a study of the problem.

Anatomy and Physiology

In origin and early development the ovary and testis are identical. The gonad and mesonephros or primitive kidney are developed from the urogenital fold. The gonad first forms as a medio-ventral thickening of the fold, which gradually expands until it becomes attached by a mere stalk. At first, the gland is made up merely of a superficial epithelial layer, and an inner epithelial mass, or epithelial nucleus. In the process of development, large primordial germ cells migrate from the entoderm of the future intestinal canal, and pass through the stalk to the gonad. In the case of the male gonad, seminiferous tubules are very difficult to make out in embryos smaller than 24 millimeters. Then they suddenly differentiate out as solid cords of germ cells, while the connective tissue grows in around them. These connective tissue sheaths unite at the center of the organ to form the anlage of the mediastinum testis. The testicular tubules unite and converge toward the hilus, there to meet the anlage of the rete. At the mesonephric end of the testis, the rete first appears as a collection of cells, differentiating out from the inner epithelial mass of the gonad. These cells gradually grow out to meet the collecting portions of the mesonephric tubules on the one hand, and the seminiferous tubules on the other. The rete is represented as cords of cells at first, which in forty millimeter embryos hollow out to form tubules.

The mesonephros, or primitive kidney, early starts to degenerate cranio-caudally,—the tubules becoming separated into a cranial and caudal group. The collecting and secretory parts of the cranial group separate, the collecting tubules growing out to meet the rete with which they unite to form the efferent ductules of the epididymis. The caudal group of tubules is vestigial and becomes the paradidymis. The mesonephric duct becomes the vas deferens, connecting as it does with the tubules of the epididymis, and emptying into the urethra at Müller’s tubercle or, as it later becomes, the colliculus seminalis.

The seminal vesicles arise as hollow saccules from the dorsal wall of the mesonephric duct just as it empties into the urethra. The prostate develops as an outgrowth of the dorsal urethra just posterior to Müller’s tubercle. The bulbo-urethral glands appear as solid, paired, epithelial outgrowths from the entoderm of the urogenital sinus.

Müller’s duct, at first a solid tube growing from the anterior part of the mesonephros, and ending at Müller’s tubercle, becomes a hollow tube, and in the female forms the entire genital tract except for the gonad and the lower part of the vagina. In the male, the anterior part remains as the vestigial appendix testis, and the posterior part, as the vagina masculina. Ellenberger states, however, that this embryonic structure is very seldom seen in the mature bull.

The Male Reproductive Organs include the penis and testes, together with the excretory passages which connect the testes with the urethral canal. These excretory ducts include the epididymis, vas deferens, and seminal vesicles. Posterior to their termination in the urethra, there are connected the ducts of the prostate gland and the bulbo-urethral or Cowper’s glands.