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

by Herbert Lester Gilman

Discussion

A complete discussion of those factors which have a bearing on reproduction and fertility in an animal, includes not only a thorough study of the genital tract, but an appreciative consideration of various extrinsic factors. The effect of environment has long been known to have a marked influence upon breeding, particularly with reference to animals in domestication. Diet, though long relegated to a minor phase of the question, has, within recent years, come to be a matter of prime importance with regard to its bearing upon the entire body metabolism. The endocrine organs preside over and regulate the growth and functioning of the genital organs from the earliest embryonic stage to the cessation of sexual life. Any derangement in one results in functional or organic changes in the other. In a given mating, we must take into consideration such factors as impediments to coitus, as well as those numerous agencies in the female which may interfere with the union of sperm and ovum, or with the successful implantation of the fertilized egg in the uterus, and its growth and development there till normal parturition takes place. Successful reproduction depends upon the mating of sexually sound females to equally sound males. Considering the various factors which govern reproduction, sexual soundness must necessarily depend, to a large extent, upon a good general condition of the entire body.

Environment: The effect of environment on fertility in the bull is no doubt a minor factor. Cases in which changes in environment affect fertility probably occur, however, particularly when fear and other psychic disturbances play a part. Marshall (29) states: “It would seem probable that failure to breed among animals in a strange environment is due not, as has been suggested, to any toxic influence on the organs of generation, but to the same causes as those which restrict breeding in a state of nature to certain particular seasons, and that the sexual instinct can only be called into play in response to certain stimuli,—the existence of which depends to a large extent upon appropriate seasonal and climatic changes.”

Diet: Under this heading we may include not only the effect of deficient food, but also constitutional disorders, as a result of which the organs of generation and those glands guarding their function receive insufficient nourishment. It is a well known fact, and long has been, that animals fail to breed when they are in a run down condition or when they are fed a deficient diet. Cary (35), quoting Hagner, states that the virility of the spermatozoa is often in direct proportion to the general physical condition of the patient.

Reynolds (34) emphasizes the fact that it is an established principle among animal breeders that a high protein diet in both sexes is essential to full fertility. “Oligospermia with deficient vitality of the spermatozoa is not infrequently found from constitutional disorders. It can easily be demonstrated in animals that both low diet and conditions of life that produce a nervous excitable state are attended by oligospermia.” Animals that are closely confined, those that are over-fat (show animals), as well as those fed a deficient ration very frequently fail to breed, but exercise and change of diet soon overcome the impotency.

Dutscher, Hart, Steenbock, and other biological chemists have done extensive work to show the essential importance of vitamines and minerals in the diet. Their results indicate that animals cannot thrive and breed normally when fed a diet composed solely of the products of one plant. There must be variety, and there must be not only a correct nutritive ratio, but the mineral and vitamine content must be present as well. Cows fed on the products of one plant often failed to breed, and if conception occurred, it invariably resulted in a premature birth, or the birth of weak and poorly nourished calves. The work of these authors is fundamental, and brings out many important points. Is it not probable that the deficient diet results in weakened tissues which are easier prey to the invasion of bacteria?

Macomber and Reynolds (39) experimented upon white rats to determine the effect of defective diet as a cause of sterility. They call attention to the confusion caused by the application of the term sterility to most, or all, infertile matings. They believe that failure of reproduction is, in fact, the result of decreased fertility rather than of actual sterility on the part of the two individuals concerned. “There are certainly a large number of infertile matings which are purely functional and due to physiologic alterations or local conditions. Such physiological alterations moreover coexist in the sterilities of pathologic origin and when unrecognized and consequently unremedied, undoubtedly explain a large proportion of the continued infertilities after operation.” Is it possible for a bull to be infertile to the cows in his herd that have been fed a deficient diet, and at the same time to breed well when mated to animals outside this herd? This is rather improbable in practice, but there is always the possibility of its occurrence. In the experimental work, white rats were used: one strain from the Wistar Institute with a fertility of about 65 per cent, and the other from a Dr. Castle’s strain with a fertility of about 90 per cent. The Wistar rats were fed in groups, each group receiving a diet deficient in a certain substance: calcium, protein, or fat soluble vitamine. To this group was added a diet deficient in both calcium and protein (war diet). These diets reduced the fertility of the groups from the original 65 per cent, to 55, 31, and 14 per cent respectively. It delayed the appearance of fertility in young rats raised on these diets, and lowered its degree in the mature animals. Most of these rats, however, though infertile to each other, bred promptly when mated to the Castle rats of known fertility. This demonstrates clearly that relative infertility of given matings does occur. One interesting feature of the work is the fact that in the matings on the single deficiency diets, four deliveries of macerated fetuses occurred and there were two more in eight deliveries from those reared on the war diet. No cases of this kind had previously occurred in this strain, which had been under observation for several years. Does this throw any light upon the cause of macerated fetuses in cattle? Microscopically the testes and ovaries of these infertile rats showed no observable changes, a fact which is of great importance to bear in mind.

Williams, in his book on disease of the genital organs, brings out quite clearly the relation of defective diet, overfeeding, and lack of exercise, to reproductive efficiency.

Novarro (40) observed that pigeons fed on a diet without vitamine B showed degeneration of the seminal epithelium, with hypertrophy and hyperplasia of the interstitial cells of the testis. Another author (Allen) showed that reduction in the quantity of water-soluble vitamine in the diet of rats resulted in total degeneration of all the germ cells, but it did not interfere with growth and development in other respects.

The observations of Williams (41), in a pure bred beef herd in Hawaii, clearly demonstrate the intimate correlation between poor fodder as the result of extreme drought, and the accentuation of, or increased susceptibility to, genital infections, as demonstrated by clinical findings. The genital disorders started soon after the onset of the drought, and immediately took a downward trend with the advent of the rainy season.

Judging by the work quoted, we will observe that deficient diet, though it does not always affect the general health, has a profound effect upon the genital organs of both sexes, associated with disturbances of spermatogenesis in the male. In most debilitated and weakened conditions of the male, spermatogenesis ceases or is markedly defective. We must, undoubtedly, explain this fact upon the ground of deficient nourishment to the reproductive organs or possibly the endocrines. The vitamines have been termed nuclear nourishers, and their absence probably results in nuclear deficiency.

Endocrines: Bell (42) emphasizes the fact that not only the structure but also the function of every part of the body is in close correlation with the rest. “This is essentially true of the ductless glands: the shadow of their influence is over all.” Further he states that when we remember that the individual exists to perpetuate the species, it is not difficult to realize that the metabolic factors concerned in reproduction are the same as those related to the individual metabolism. It follows, therefore, that the ductless glands which regulate the individual metabolism concern equally the reproductive. Brown (43), discussing the same subject brings out the generalization that the sympathetic, since it is the most primitive part of the nervous system, is closely associated with the endocrine system, a still more elemental means of communication in the body. Also since specialized reproductive cells appear before the nervous system, the organs of reproduction remain closely associated with the older chemical reactions now specialized in the endocrine glands. “The endocrine glands, the reproductive organs, and the sympathetic nervous system, therefore, remain as a basic tripod, and it is not likely that a disturbance will occur for long in one limb without affecting the other two.” The former author believes that the gonad keeps the other ductless glands informed of the needs of the genital tract, they in turn influencing the general metabolism. Jump (44) states: “We are therefore justified in believing that there is a correlation of function between these (endocrine) glands and that some cases of sterility are probably due to a derangement of this correlation.” Biedl (45) concludes: “There appears to be an intimate anatomical and physiological interrelationship between the different blood glands which is manifested clinically by the fact that the pathological disturbance of one gland is accompanied by symptoms pointing to the functional derangement of one or more of the others. Knowing, as we do, the many sided interactivity which subsists between the different internal secretory organs, it is readily conceivable that isolated diseases of single organs of this group are very much rarer than, at the first glance, they would appear to be. In the present state of our knowledge, the only course of investigation which is open to us is to start with the known results of the functional derangement of any organ, and, by following these up, to seek the primary link in the pathological chain.”

Most workers seem to agree that a special connection exists between the normal function of the adrenal cortex and the sexual organs. Tumors of the former are usually associated with sex abnormalities, and feeding young animals the gland substance seems to stimulate growth of the testes.

Many arguments have been brought forward to show that the prostate produces an internal secretion. It is a well known fact that this organ atrophies after castration, and enlarges as the sex life dwindles. As has been previously stated, Serrlach and Pares reached the conclusion that the gland produces an internal secretion which controls the testicular functions and regulates the process of ejaculation. Also they state that if the prostate is removed, spermatozoa are no longer produced in the testes, and that the secretory activity of the accessory genital gland ceases. The secretion is, at any rate, a stimulus to the internal secretion of the testis.

The thyroid bears a distinct biological relationship to the sexual glands. Removal of the gland results in imperfect development of the gonads, infantilism, and general torpor. Bell (42) believes that the association between the thyroid gland and the genitalia is as intimate as the relation of the pituitary to the genital functions.

Of all the endocrines, perhaps the anterior lobe of the hypophysis is in most intimate correlation with reproduction. Castration results in hypertrophy of this organ, while removal of the anterior lobe usually leads to death. In those cases in which death does not ensue, it results in genital atrophy, stunting, and reduction of sexual activity. In young animals, spermatogenesis ceases entirely even after partial extirpation of the anterior lobe. Biedl (45) states that “in disease of the hypophysis, derangement of sexual activity occurs very early in the course of the disease, shown in women by the cessation of menstruation, and in men by impotence.”

The thymus, as is well known, is quite intimately associated with the development of the genital organs. Its normal disappearance is always associated with the development of sexual maturity in the individual. Hewer (46) conducted experiments to ascertain the effect of thymus feeding on the activity of the reproductive organs in the rat. She concludes in part: “Male rats appear more susceptible to the influence of thymus feeding than female rats. With moderate doses of thymus, sexual maturity in the animals treated is delayed, a phenomenon which is attributed to delayed development of the testis. With large doses of thymus, in the male, the testis is structurally affected: in the young animal in the direction of retardation of development, in the mature animal in the direction of degeneration. This degeneration is confined to the testes. In the degenerating testis, cells of Sertoli appear to be absent: the spermatogonia are present, also dividing, and may lie free in the lumen of the tubule; spermatids, many with abnormal nuclei, are shed into the lumen in large numbers; spermatozoa are practically absent. In the later stages, only a few dividing spermatogonia appear among the debris of the other unrecognizable cells of the tubule. In the epididymis which itself is normal, when the testis is showing degeneration, very few spermatozoa appear, in the later stages none. Many spermatids are present in various stages, and some spermatocytes. Animals in the hyper-thymic condition appear to be sterile.”

The foregoing references will, I hope, serve to bring out the facts that environment and diet, together with the general body metabolism and the endocrines, have a more or less profound effect upon the development, growth, and functioning of the genital system. In the experiments it has been shown that sterility is not necessarily accompanied by any apparent microscopical changes in the gonads, or even at times in the general body health. Nor can we exclude impotency of the male entirely even when the spermatozoa are normal in shape, and motility. Carnett, and others (38), years ago stated: “Indeed, there is abundant clinical proof to the effect that systemic conditions which have no appreciable effect upon the motility or conformation of the spermatozoa materially interfere with reproductive power.” The entire complex genital system is inseparably linked up with the body as a whole, a fact which we must bear in mind at all times.

Impediments to coitus may be due to great difference in the size of the two mated individuals, psychic disturbances, or inability to protrude the penis. Williams (17) mentions several physical impediments, as deformity of the limbs or feet, sore feet, overloading of the rumen, obesity, fear of falling, and paralysis. Coitus may be somewhat delayed, or even not performed as the result of a severe inflammation with sensitiveness of the penis or prepuce. Occasionally tumors of the penis are encountered which may interfere with protrusion of the penis, or its entrance into the vagina. Not infrequently the penis is rendered incapable of protrusion as the result of inflammatory adhesions, tuberculosis of the preputial lymph glands, etc.

Excessive sexual use, within certain limits, probably has not, in itself, any material permanent effect upon the reproductive capacity. The frequency with which bulls used to excess break down sexually, is probably due to the devitalizing effect upon the tissues of the genital organs, this opening the way to bacterial invasion and other destructive influences. Over-use is probably not dangerous, unless continued over long periods, but at the same time it offers greater opportunity for infection to be introduced into the body from intercourse with large numbers of females. Lloyd-Jones and Hays (47) carried on very interesting experiments on the influence of excessive sexual activity of male rabbits on the properties of the semen. Their plan was to mate male rabbits in quick succession, and study the character of the semen on the first service, and every fifth service thereafter. The safe limit was twenty services in three hours. As would be expected, the volume of the semen, after the first few services, became gradually reduced in amount. “In rapidly successive services, the semen becomes less viscous and tends to lose its characteristic milky appearance until at the twentieth service, when the fluid is thin and watery.” It seemed as though there was a well marked reduction in the number of spermatozoa per cubic centimeter in the advanced services. Successive copulations also resulted in a marked decrease in the number of motile spermatozoa, together with a shorter duration of perceptible vitality. The certainty of producing impregnation at the same time became less and less. “This reduction in the per cent of effective matings when the male is sexually overworked is recognized by those engaged in animal breeding as one of the most noticeable and universal concomitants of heavy sexual service.”

In another paper, these same authors studied the effect of sexual excess upon the character of the offspring. In part, they conclude: “By no means thus far used has any inferiority of progeny from the heavy sexual service been discovered. They are fully equal if not superior to progeny from very light service of male.”

Infection is without doubt the greatest single factor capable of producing functional and anatomic changes resulting in varying degrees of impotency and sterility. The changes produced range from the addition of the toxic products of bacterial growth to the seminal fluid, to the complete destruction of the parenchymatous tissue of one or more of the contributing sexual glands. Anatomic changes are by no means essential to the production of lowered fertility. As has been previously stated, the work on veal calves indicates that the genital organs of young bulls are normally free from bacteria. Likewise in normal adult animals, the bacterial content of the genital organs is as a rule low or negative. It is possible that a certain flora is normal for the tract at sexual maturity, as in several other organs of the body, but under the strain of sexual excess, defective diet, or other weakening influences, these organisms may become pathogenic. Streptococci and staphylococci have at times been found in apparently normal parts of the body, and at other times they are found associated with severe pathological lesions in the genital tract. The degree of pathogenicity is of course difficult to determine, except as we find the bacteria associated with abnormal conditions. Carpenter (9), however, injected streptococci into the genital tracts of female calves and produced lesions resembling very closely those from which the organisms had been isolated in adult sterile animals. Personally, I am inclined to believe that the genital organs normally are free from bacteria, or if any are there they are better able to multiply under the strain of devitalization of the tissues. Bacterial invasion, however, does take place quite frequently, but the paths of entrance of the organisms are somewhat problematical. Hematogenous origin is always possible, though it is rather difficult to definitely implicate this mode of entrance. The urethra is perhaps the easiest and most common path for the entrance of bacteria, though even here it is not possible to make definite assertions. Contiguous spread of infection from neighboring structures is very probable in some cases, particularly in pelvic peritonitis. The bacteriological results hardly bear out the theory of Williams that the organisms lie dormant in the genitalia of the animals until the advent of sexual maturity, at which time they acquire pathogenic powers. On the other hand, his clinical observations seem to indicate that this may be possible. Calves suffering from “calf infections” frequently do harbor organisms in their genital organs, but whether or not they persist there till sexual maturity is a matter of conjecture. The most logical theory seems to be that animals from herds in which genital infections are very severe, or those that have had severe attacks of scours or pneumonia, are more susceptible to those infections, due to the early lowering of their vitality. One bull in the department herd certainly had a severe ordeal as a calf, but as a mature bull he was highly fertile. Moderate sexual use and proper sexual hygiene probably had much to do with this. In the bull, infection of some part of the genitals, during some period of life, is very constant, however, whether or not it is productive of observable changes in his breeding efficiency. The finding of the fine connective tissue strands and tufts on the serous surface of the tail of the epididymis of practically all bulls examined, both sterile and fertile, indicates past or present infection of the scrotal sac. The vesicles and tail of the epididymis are, as stated previously, the most commonly invaded tissues of the tract. The testes are less frequently involved.

While it is difficult to obtain irreproachable proof that the bull is a disseminator of genital infections, the findings of clinicians quite clearly indicate that this is true, and laboratory methods tend to support this assumption. Williams believes that not only may the bull infect the female with organisms which interfere with the given conception, but that he often implants there organisms which interfere with future pregnancies, and even with the life of the individual in some cases. The high abortion and sterility rate following the use of certain sires, and the appearance of characteristic infections after service to certain bulls, clearly indicate that in all probability the bull does eliminate with his semen those organisms which produce lesions in his genital organs, and are capable of infecting the female. W. L. Williams (48) cites the case of a pure bred herd in which breeding had progressed satisfactorily until heifers had grown to breeding age and a second bull was obtained. “Some cows of the old herd were also assigned to the young bull which had not previously been in service. The cows bred to the old herd bull continued to breed normally. The cows and heifer’s bred to the new bull conceived with difficulty or not at all. Those which conceived mostly aborted, and those which calved had metritis and retained fetal membranes. The two first cows in which pregnancy terminated died of metritis.” I have frequently had semen samples sent in from bulls that were not only failing to get cows with calf, but following each service the females showed a severe vaginitis. W. W. Williams worked in a herd in which service to certain bulls was in each case followed by a severe vaginitis and cervicitis, only to be followed later by a characteristic salpingitis.

Vaginal smears taken before and after service, in many instances, show that in all probability bacteria, especially the streptococci, were deposited there with the semen. These results have been obtained upon several occasions, at which time the vagina was usually douched prior to each service with sterile saline solution. Streptococci and other organisms have been isolated from the vaginal samples obtained by this method. In most cases, they were absent from samples taken before service. Extraneous contamination, and error, must be taken into consideration, but the results tend to bear out clinical observations that the bull is probably a disseminator of some infections associated with the genital organs of both sexes. At any rate, organisms have been isolated repeatedly from the genital organs of the bull, of the same biological character as those which are associated with sterility, abortion, and allied phenomena in the female. In the absence of obstruction in any part of the tract, there is nothing to hinder infection from gaining access to the seminal fluid, and being excreted during ejaculation.

Hopper (18) states: “A diseased bull may manifest non-fertility or decreased potency in different ways—by repeated service to apparently normal females without conception, by a high abortion rate in females that have been apparently normal, by characteristic infections following the use of any particular sire, or by abnormalities in the breeding tract noted by rectal or physical palpation.”

Admittedly, Bact. abortum has little affinity for the genitalia of the bull, though Schroeder states that the bull harbors the organisms in his seminal vesicles and that they are eliminated with the semen. Other authors have occasionally isolated the organism from the vesicles, testes, or both. Schroeder’s theory that infection of the female occurs indirectly by contamination of the fodder with the semen is probably rare in occurrence. The very limited number of cases in which investigators have demonstrated the presence of the organism in the male genital organs, and the apparent immunity of the bull to the bacterium as determined by the agglutination reaction, seem to indicate that he plays a small part in the spread of this type of infection in the herd. On the other hand, it would seem that he is at times intimately associated with the spread of certain other organisms that interfere seriously with herd reproductivity.

The diagnosis of infertility and sterility rests upon a thorough physical examination of the genital organs, together with a detailed study of the semen. The history of the animal and herd involved must also be very carefully inquired into, especially the part covering the result of every service by the sire in question. Besides this, we must always consider all factors which have a bearing upon the subject, remembering the physiology of each part, and the role it plays in reproduction. Bacteria gain entrance to many parts of the tract, where they multiply and probably add toxic products to the seminal fluid, altering its biological character and resulting in partial or total destruction of the secretory tissues. The testes, epididymes, vesicles, prostate, and other parts, each contribute their essential part to the semen, abnormalities of any one of which, as a rule, result in interferences with reproduction. If the vesicles are involved, we must bear in mind just what is the part played by their secretion, and what is the probable result if their essential elements are not added to the semen. In like manner, we must consider the prostate, whose secretion stimulates the vitality of the sperms, and adds fluid bulk to the semen. Extirpation of the vesicles or prostate alone results in lowered fertility, without altering the sexual desire, while removing both glands produces total sterility. Partial or total destruction of the parenchyma of either gland produces the same effect as extirpation, in that its function is altered or entirely absent.

The semen should be examined, not only for the number of spermatozoa and the percentage of those that are motile, but for the duration and type of motion. Normal semen, when first examined under the microscope, shows a field closely packed with highly motile spermatozoa. In every study of the semen, however, we must bear in mind the temperature and other conditions under which it has been kept since emission. On the other hand, semen from bulls of lowered fertility shows changes ranging from mild disturbances such as sluggish motility and a slight decrease in the number of sperms present, to aspermia, or total lack of motion. Normal semen, when compared with abnormal specimens, as a rule presents distinct differences, either in motility, staining properties, or structure of the spermatozoa. Impotent bulls, however, may show at times few or no observable changes in their genital organs. The only assumption here is that the condition probably is of endocrine origin, or is some functional disturbance. Of oligospermia Reynolds states: “Oligospermia, with normal motility and vitality, is not absolute sterility, but is of high importance because the percentage of destruction of spermatozoa during their passage through the genital canal of the female is so enormous that the possibility of impregnation by semen which starts out with a deficient number is always poor. When the genitals of the female partner are in a condition which is even moderately hostile to the spermatozoa, impregnation by such semen becomes so unlikely as to be not even a probability.”

Motility may be lacking in a small number, its absence may be observed in a large percentage, or even in all those in the field, as in necrospermia. On the other hand, the motility may be sluggish or of abnormal types in variable percentages. Sperms with sluggish motility are always low in vitality, and have weak powers of insemination, as the motion lasts but a comparatively short time. The vitality may be but moderately lowered, so that although the sperms are highly motile when ejaculated they soon lose their power of propulsion. The type of motion is likewise an indicator of lack of vitality. The “progressive vibratile” motion described by Reynolds should proceed to a high degree for a long period before the “undulatory tactile” or bunting types of motion appear. Early appearance of these two latter types indicates in most cases a marked lack of vitality of the elements. The motion should be vigorous and lasting, for, as stated by Reynolds, “nothing is more certain than that spermatozoa of merely moderate vitality seldom impregnate a female.”

The early precipitation out of the “Boettcherchen” crystals is very characteristic of oligospermia, and impotent semen. The theory here is that crystals do not precipitate out when a fluid is actively moving, but soon do so when the fluid is motionless. The sediment which normally makes up about two-thirds of the sample is usually decreased in abnormal samples. The semen itself should be observed for unusual viscosity or a thin watery condition. Clotting should occur readily after emission, but the clot soon liquefies to some extent, allowing the spermatozoa to become more active. This clotting is, of course, to protect the delicate sperms from the hostile secretions of the vagina.

The presence of immature and deformed types of sperms represents some disturbance of spermatogenesis, but it is difficult to explain the significance of these forms. They are seldom seen in normal samples, and undoubtedly none are capable of producing impregnation. In the case of minor abnormalities of staining reactions, the sperms are probably deficient in nuclear material or otherwise altered so that probably they are incapable of reaching and uniting with the ovum. When impregnation does occur in these cases, weak offspring undoubtedly result in many instances.

The work has by no means progressed to the point where one may, by an examination of the semen, determine the degree of impotency with great accuracy, or even whether the animal may be restored to sexual health by proper hygienic and therapeutic treatment. Relatively, the greater the changes in the semen and spermatozoa, the less the chances of impregnation. Infertility to any marked degree, is, however, usually accompanied by corresponding changes in the seminal fluid and its germinal elements.

Examination of the semen is, and probably always will be, simply an aid in reaching a diagnosis. While abnormalities of the semen and spermatozoa are associated with sterility or infertility, it is unwise to lay too much emphasis upon this method of diagnosis alone, especially with regard to the making of a definite prognosis. When large numbers of abnormal spermatozoa are present in the semen, we are safe in saying that the animal is, at the time, of lowered degree of fertility. One should be very cautious, however, in foretelling how long the condition will last, or if the animal may in time be restored to full fertility. Sterility, due to organic disturbances, probably seldom yields to treatment, but when it is due to functional disorders resulting from defective diet or lack of exercise, the condition is frequently remedied by overcoming the cause. Lack of exercise and overfeeding seem to be etiological factors in a fair percentage of cases.

Besides abnormalities of the male genital tract, we must always consider the numerous factors in the female that may kill or weaken the sperms. Impediments to successful coitus may be present in the form of vaginal constrictions, abnormally short or small vagina, or other deformities. Hostile exudates, mechanical obstructions, and other factors may interrupt the progress of the sperms at any point in the tract.

Although little is known definitely regarding disorders of the endocrines in the bull and their relation to reproduction, the work in human medicine and experimental researches upon laboratory animals warrant thoughtful consideration of these factors which are by no means insignificant. In the future, these glands will no doubt receive more and more attention in their relation to the genital organs and reproduction.