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

by Herbert Lester Gilman

Prostate: The bull possesses what Ellenberger calls a diffuse prostate. That is, there is no distinct glandular body as in man. It is composed principally of a glandular sheath around the urethral wall. Just posterior to the neck of the bladder, and in front of the urethral muscle, there is formed a slight dorsal transverse elevation, extending downward on the sides. This is what might be termed the body. The greater part of the gland is “disseminate” in form, being a sheath of glandular tissue embedded in the urethral wall. Dorsally it is about ten to twelve millimeters thick, and ventrally about two millimeters. The gland is a branched tubular structure, the interlobular tissue of which contains much unstriped muscle. The lobules are lined by a columnar type of epithelium. The ducts, about thirty to forty in number, open into the urethra in two rows posterior to the colliculus. The secretion is a thin, slightly turbid fluid, of a faintly alkaline reaction. Its function is to dilute the semen, stimulate the motility of the spermatozoa and nourish them.

Fish (28) believes that the activating property of the secretion is due to enzymes, because boiling deprives the fluid of its power to accelerate the motility of the spermatozoa. Serrlach and Pares, quoted by Marshall (29), working on dogs, have adduced evidence indicating that the prostate is an internal secretory gland which controls the testicular functions, and regulates the process of ejaculation. It is stated that if the prostate is removed, spermatozoa are no longer produced in the testis, and that the secretory activity of the accessory genital glands ceases. These changes, however, can be prevented by the administration of extracts of the prostate. The fact that the prostate elaborates a secretion having a definite relation to the testis, has been verified by other authors.

Cowper’s Glands (Bulbo-Urethral): These glands are paired, oval structures about one and one-half by two and one-half centimeters in size, situated on either side of the dorsal pelvic part of the urethra close to the ischial arch. They are deeply embedded, with the bulbus urethae, in the bulbo-cavernosus muscle, thereby being inaccessible to palpation. In general, they are of a well developed anastomosing tubular type. The connective tissue stroma is relatively thin, and thickens only in between the larger lobules, where one finds the larger collecting ducts. Each gland opens by a single duct. The epithelium is of the simple cuboidal type. Little is known of the function of its secretion, though Kingsbury (30) regards it in the light of a mating gland; that is, it lubricates the genital passages during coitus, as does its homologous structure in the female, Bartholin’s gland.

Ellenberger describes the urethra, slit ventrally, as presenting the following picture: “The colliculus seminalis distinctly appears as a process or offshoot of the crista urethralis of the Trigonium Vesicae. At the summit, and at the bottom of the two slits, open laterally the ducts of the vesicles, and medially the ductus deferens.... From the caudal slope of the colliculus go two distinct mucous membrane folds which run through the entire pelvic urethra, near together, somewhat diverging, and then coming together, so that they form an elongated, narrow oval. At their caudal union, the excretory ducts of the bulbo-urethral glands open side by side. At the point of departure of the folds from the colliculus, arises a niche-shaped opening, between both folds, and likewise lateral to each fold. In these niches open the ducts of the prostate. The openings of the disseminate prostate lie in rows as in the horse, but form not less than six rows. There is one row medial to each fold, and two lateral. Mullet mentions only the medial rows. These rows extend to the opening of the ducts of Cowper’s glands. The stratum glandulare (disseminate prostate) is very easy to recognize with the naked eye.”

Semen: The semen is the mixed product of the testicles, their excretory passages, and the accessory sexual glands, a fact which complicates its study considerably. The freshly ejaculated fluid is cloudy, tenacious, more or less coagulable, and is rich in albumen. It is weakly alkaline in reaction, and contains eighty to ninety per cent of water. Of the solid constituents, there is forty per cent of ash, of which three-fourths is calcium phosphate. Besides the spermatozoa, the semen frequently contains epithelial cells, leucocytes, concentric amyloid concretions, and lecithin bodies. When cold, the characteristic phosphoric acid salts are precipitated. The fluid content is the product of the tubules of the testicles, their excretory ducts, and the accessory sexual glands. The characteristic odor of the semen is supplied by a slimy nucleoalbumen “spermin” which forms the spermatic crystals, and is furnished by the prostatic secretion.

During ejaculation the spermatozoa and secretions added by the testicle and epididymis are probably carried to the ampulla by peristaltic muscular action, in the earlier stages of the orgasm. At the height of the orgasm, the ampulla is emptied into the posterior urethra in common with the secretion of the contracting vesicles, here to be admixed with the thin prostatic secretion. The entire mixture is then propelled, and ejaculation produced by strong muscular contractions of the entire urethra. As was stated before, the semen is the product of the testicles, the excretory ducts, and the accessory sexual glands. The testes furnish the essential germinal elements, the sperms, and some of the fluid content. Then is added the product of the epididymis, vas, and ampulla, which stimulates the spermatozoa to active motility, nourishes the organisms, and adds somewhat to the fluid bulk of the secretion.

Stigler (25) states: “During its sojourn in the epididymis, the properties of the spermatozoa are modified; the motility, ability to resist heat, and other properties are augmented, at least in the case of the guinea pig, rat, and mouse.” To the secretion is then added the product of the vesicles, which contributes markedly to its fluid content, nourishes the sperms, and supplies the ferment which induces clotting of the semen when ejaculated. This is very important because the clot formed in the vagina protects the delicate spermatozoa from the hostile acid vaginal secretion. The prostate likewise adds bulk and nourishing substances, besides stimulating the spermatozoa to fuller and more lasting motility. The addition of the spermin is perhaps unimportant. The function of the secretion of the Cowper’s glands, which is added at this time, is problematical. It does, however, have a diluting action on the semen. Perhaps its secretion is poured out prior to ejaculation so as to lubricate the canal and prepare the way for the semen.

Fish (28) has demonstrated by means of darkfield illumination, the presence of numerous minute particles or ultraparticles in this fluid. Their character and significance are matters of conjecture, but it would seem as though they were not identical with the “chylomicrons” or fat particles found in the blood by Gage. Perhaps further researches will reveal some intimate connection between the number present in a field, and the relative potency of the animal.

Each portion of the tract furnishes some essential element to the mixed product which is so remarkably adapted both as a vehicle for the ejaculation of the spermatozoa, and as a fluid in which their motility is initiated and maintained. Any derangement of one part is fraught with danger to the existence of viable spermatozoa, and the continuation of full fertility on the part of the animal. The physiology of each contributing gland must be borne in mind at all times. Walker (31) investigated the fertility of the semen of the dog, taken from various parts of the tract. His results were: (1) semen from the testicle and head of the epididymis showed no motility, (2) semen from the tail of the epididymis showed some motility in the more fluid contents of the preparations, (3) semen from the vas deferens appeared about the same, (4) a mixture of epididymis semen and prostatic secretion showed active motility, and (5) likewise in a mixture of epididymis semen, though only in those places where the fluids had become well mixed. My observations, however, differ in one respect with regard to the bull, as I have found full motility of the spermatozoa from the epididymis, but it is not so lasting as when augmented by the addition of the prostatic fluid. Boettcher (32) concludes: “that the secretion of the accessory male genital organs possesses a protective colloid, which (1) hinders the spermatozoid action of the vaginal secretion, at least until the sperms have time to reach the interior of the uterus which is an alkaline reaction, (2) that it makes the ejaculate more voluminous, so that by cohabitation, a very good part of the vagina becomes moistened, and the spermatozoa become distributed over the greater part of the vaginal mucosa. This distribution is rendered necessary because some of the fluid flows from the vagina following coitus. In this manner the opportunity is given for a part of the ejaculate containing the spermatozoa to be brought easier to the external os, and (3) it happens that because of its content of sodium chloride the life of the spermatozoa is stimulated and prolonged.” A fuller discussion of the essential physiology of the various parts of the tract on the semen content, and fertility, will be taken up later. The changes in biochemical content, reaction, and the result of the addition of bacterial products will also be more fully discussed.

Spermatozoa: The history of the discovery of spermatozoa is very interesting, and for that reason a brief outline will be given. The “semen threads” were first observed in the year 1667, by Ham, a student of Leeuwenhoek at Leyden. The discovery was announced, confirmed by findings in the dog and rabbit, and discussed by the latter author under the title: Observationes Anthonii L. de natis e semine genitali animaculis (Upon the formation of young from procreative material). The sperms were taken to be animals on account of their motility, and their significance remained questionable if not unknown. Spallanzani, quoted by Marshall (29), was the first to show that the filtered fluid was impotent, and that spermatozoa in the semen were essential to fertilization. Kolliker, in 1841, discovered that the sperms arise from the cells of the testis, and Barry in 1843, observed the conjugation of sperm and ovum in the rabbit. This led to a clear understanding of the function of these important germinal elements.