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

by Herbert Lester Gilman

The spermatozoa are the male procreative cells, and are characterized by the possession of a head containing the chromosomes necessary for fertilization, and a tail capable of propelling the organism on its way to meet the ovum. The length of the entire sperm, including the head, is seventy-five to eighty microns. The head is nine and five-tenths microns long, and five and five-tenths microns wide. It may be divided into two principal parts, the head and tail. The head, for the larger part, is made up of the nucleus, and may be differentiated by staining reactions into a darker staining posterior part, an anterior lighter part, and often a still lighter area between the two. On the anterior part is a sharpened edge, the acrosome, which serves to perforate the ovum. The whole is surrounded by a very definite limiting membrane which often becomes obscured under abnormal conditions. The tail may be divided into three parts: connecting piece, principal part, and terminal filament. The connecting piece, the essential motile apparatus, is the thickest and strongest part, and joins the tail proper to the head. It consists of the central axial filament, a spiral filament around this, and an outer mitochondrial covering. Anteriorly it is limited by the anterior portion of the posterior chromosome, and posteriorly by the annular chromosome. The anterior chromosome is directly connected with the head, there appearing a light break here at the neck where separation frequently occurs. This neck serves as a joint for the motion. The axial filament, therefore, does not reach the head, but extends back from the anterior part of the posterior chromosome. The principal part consists merely of the axial filament, and a thin outer covering, while the end piece is quite thin and is made up solely of the uncovered axial filament. The finer structures are seen only when special staining reactions are used, and then only when the sperms are obtained directly from the testicle. The function of the sperms is of course primarily that of fertilization. Numerous observers have, however, thought that they might have some other definite, though unknown, use.

An editorial in the Journal of the American Medical Association (33) raises several important questions regarding this obscure phenomenon. The fact that an enormous number of spermatozoa are produced, and only one, or at most, a few perform the function of fertilization, raises the question as to what becomes of the remainder. It is stated: “Zoologists have found that in some of the invertebrates the spermatozoa invade the entire body of the female, and in some species they reach the ovum by penetrating the cuticle from outside and migrating to their goal. Studies on rodents show that the sperms invade the epithelium of the generative mucosa and underlying connective tissue. These tissues seemed to be stimulated to growth, suggesting that this may influence the uterine mucosa in its preparation for receiving and embedding the egg, and in forming the decidua.” It has been shown that the sperms contain a specific protein capable of producing antibodies in the blood plasma, by citing the fact that rabbits develop a distinct Aberhalden reaction for testicular proteins shortly after cohabitation. One very important observation showed that by immunizing female rabbits with sperms they were rendered sterile for some time, although after a few months they again became capable of impregnation. The question raised is: “... if the spermatozoa invade the female tissues and cause the formation of specific antibodies which are capable of preventing fertilization, may not such a process participate in the problem of sterility?” This very problem seems to be a factor in explaining why some couples who are not fertile to each other subsequently are both fertile when they cohabit with other individuals.

Motility: After clinical observation of the motility of the spermatozoa of the bull, I find that it differs little or none from the types as observed by Reynolds (34) in his work on human spermatozoa. His observations are so accurate and well described that they will be given in his words. “All normal motions appear to be consecutive phases. Initial motion, i. e., motion as seen in fresh semen under favorable conditions, consists of a lashing of the after part of the tail from side to side which is so rapid as to constitute vibration. It produces rapid forward motion in a practically straight line, the head, middle piece, and forward portion of the tail maintaining their position in the line of motion with practically no swaying from side to side. The action of the flagellum is so rapid that it is quite impossible to follow its individual movements. Spermatozoa swimming in this manner head against the current and usually cross the field of observation in about five seconds in the absence of currents or obstacles. This type of motion will be described throughout the paper as ‘progressive vibratile’ motion. Progressive vibratile motion is normally succeeded after a variable length of time by what I regard as the second phase of normal motion.

“The second normal motion differs from the first not only in its character but in markedly reduced speed. The tail movement alters to a long stroke from side to side and almost the whole length of the tail partakes in the stroke. This is, moreover, accompanied by swaying of the head and middle piece through an arc which is always considerable and may even equal ninety degrees. The general outline of the spermatozoa, from being practically straight with almost non-detectable sharp, quick, small arc vibration of the after-tail, has become an S in outline, with large, slow, plainly perceptible undulations traveling gradually backward throughout the length of the spermatozoon. Speed has been lost and direction seems to be more specifically determined by the surroundings. Individuals at this stage show a pronounced choice of direction and go up to objects in the medium, from which they later make off as though the movement were determined by tactile reaction to some extent. This type of motion has, therefore, been named ‘undulatory tactile’ in contradistinction to ‘progressive vibratile.’

“The third type of normal motion succeeds the second and consists in a tendency on the part of the spermatozoon to push itself against or into any small masses of cells, or sometimes other materials, which it may find in the neighborhood, bunting itself into any small cove that can be found, and maintaining a slight burrowing motion by a lashing tail movement of the vibratile type not unlike the movements of the caudal fin of a fish. The movement of the flagellum in this third type is unlike the second type in that it is vibratile rather than lashing, but is slower than the vibratile motion of the first type and less limited to the afterpart of the tail. These spermatozoa are apparently not caught in the debris or unable to move off. From time to time, they back out of such a cove and seek another mooring place.

“This ‘stationary hunting’ motion is less universal than the other two. Many individual spermatozoa fail to attain it. It seems probable that only the most vigorous individuals ever reach this stair”. It has not been encountered in unmixed semen or in any artificial mediums. It has been observed only when the spermatozoon is in the secretions of the female genital tract. It is most frequent when the spermatozoon is in contact with a nest of epithelial cells....

“The three types of normal motion are not only distinctive but are always consecutive, i. e., the second follows the first after a period which is apparently determined both by initial vitality and by the favorable or unfavorable character of the medium, while the third has been observed to occur only in individuals which have already developed the second. They apparently constitute a normal cycle.

“This cycle is open to the theoretical explanation that these types of motion are directly adapted to the function of the spermatozoon; thus, the progressive vibratile motion which is characteristic of the earliest period of its existence appears especially suitable for its prolonged journey through the cervix and uterus to the fundus and tube. This is supported by the fact that during this motion it always heads directly against any existing current, and that during this stage of its journey it must under natural conditions be continuously exposed to the faint outward ciliary currents of the mucous membrane of these passages.

“The undulatory tactile motion which succeeds the progressive vibratile would then be well adapted to the later stage in which the spermatozoon has reached the tube, where its success in conjugation is dependent on its finding the ovum rather than on further progress.

“The stationary bunting type of motion is that which would be demanded by the passage of the spermatozoon through the egg membrane which has been so often observed in the lower animals. This very plausible explanation is, however, necessarily theoretical and must always remain so, as the conditions which surround the specimen on the field of the microscope vary in so many respects from those in which it accomplishes conjugation in the course of nature; but the practical importance of the study of types of motion is not affected by their explanation.”