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.