Inability of the female or male to reproduce. Insidious but great losses are directly due to failure to breed on the part of otherwise promising animals. The immediate loss to the individual owner of livestock is not so apparent as with certain specific diseases, but it is infinitely greater than the loss accruing from any other single specific or non-specific disease. This loss is made up by the keep of the barren animals, the absence of offspring, reduction of the milk supply, and interference with breeding programmes. (See also CALVING INTERVAL.)
The most common and important causes of infertility can be grouped for convenience under the following headings.
1. Feeding and Condition
Under-feeding is a common cause of infertility in heifers. The diet must include adequate protein of good quality and sufficient vitamins, especially vitamin A, plus essential trace elements including copper and iodine.
Excessive fat in cows, heifers or bulls may lead to infertility problems or to inability on the part of the male to accomplish coitus. (See also FATTY LIVER SYNDROME.)
In cows, temporary infertility may apparently be closely associated with the feeding at about the time of service. Cows losing weight are likely to be affected, especially if fed on poor-quality hay or silage. With ad lib feeding systems, heifers and more timid cows may not be receiving enough roughage. Kale is sometimes responsible.
In ewes, infertility and fetal death are always serious in many hill areas, the result — to quote Dr John Stamp — ‘of keeping pregnant sheep under conditions of near-starvation during the winter months when weather conditions are atrocious’. (See DIET; FLUSHING OF EWES; STILLBORN PIGS; REPRODUCTION; VITAMINS; KALE; SELENIUM.)
2. Environment and Management
A sudden change of environment, close confinement in dark quarters (formerly the lot of many a bull), and lack of exercise may all predispose to, or produce, infertility. Abnormal segregation of the sexes and the use of vasectomised males (for purposes of detecting oestrus) are other factors. A low level of nutrition may cause a quiescent or dormant state on the part of the ovaries. At the same time there are seasonal cycles of sexual activity, and a ‘failure to breed’ during the winter months may be natural enough, even if the farmer regards it as infertility. This ‘winter infertility’, as it is often called, may be influenced by temperature, length of daylight, lack of pasture oestrogens, underfeeding, etc. At this season, heifers often have inactive ovaries, while in cows irregular and ‘silent’ heats give low conception rates.
Infertility may result from the oestrogenic effects of red clover in the UK, as well as from subterranean clovers in Australia.
In outdoor pig herds, ‘summer infertility’ is common, partly due to seasonal loss of fertility in the boars.
The most frequent reason for poor fertility is poor management. In cows, poor oestrus detection or timing, or bad technique if artificial insemination is used, are common. Similar problems occur in pigs. In cattle and, particularly, pigs, when natural service is used, all matings must be seen and at least 2 undertaken within the heat period. In sheep, fertility problems often follow when too few rams are used, or those which are too young or unproven.
3. Diseases of the Genital Organs in the Female
While there is a very long list of such diseases, their overall importance in causing infertility is much less than that of management problems such as poor oestrus detection.
Inflammation or other disease of the ovaries: ovaritis; the non-maturation of Graafian follicles, from any cause, and the presence in the ovary of cysts (which often form from a corpus luteum), are causes of infertility; another is blocked Fallopian tubes.
Persistent corpora lutea: as a true clinical condition, these are not very common. Where they do exist, the animals may have a uterine infection. The persistence of the corpus luteum prevents the ripening of the Graafian follicle, so the animal does not display oestrus and is not mated. (See under OVARIES, DISEASES OF; HORMONES; HORMONE THERAPY.)
Inflammation of the uterine mucous membrane: a large number of cases of infertility can be ascribed to infection of the uterus (metritis) or the oviduct by organisms. (For a list of the infections which cause infertility, see under ABORTION. For infections causing infertility in the mare, see under EQUINE GENITAL INFECTIONS.)
When the condition is mild, following a previous calving, it may disappear spontaneously, but in many instances it persists and becomes chronic. Associated with inflammation of the mucous membrane of the uterus or oviduct is often a persistent corpus luteum in the ovary. Carelessness during parturition, the use of unclean instruments or appliances, decomposition of retained membranes, and other similar factors, also bring about infection of the uterus. Brucellosis though not necessarily itself a cause of sterility, by lowering the vital resistance of the uterus, favours infection by a multitude of other organisms which normally may be non-pathogenic. The details of uterine infection, including salpingitis (inflammation of the oviduct), in the causation of sterility, are highly technical, but, generally speaking, it may be said that the presence of organisms in the uterus, or the presence of the products of their activity, either kills the spermatozoa, or renders the locality unsuitable for anchorage of thefertilised ovum (or ova), with the result thatit perishes.
Abnormalities of the cervix may prevent conception — mechanically when the lumen is occluded or plugged by mucus of a thick tenacious nature; and pathologically when there is acute inflammation of the mucous membrane of the cervix, or even of the whole uterus. Scirrhous cervix — where much fibrous tissue is laid down in the cervix — when very advanced may cause sterility, but by itself is not usually of great importance. It is much more serious as a hindrance to parturition (see, for example, ‘RINGWOMB’ of the ewe).
Cysts and fibrous bands in the os are seldom sufficiently extensive to occlude the passage through the cervical canal. Occlusion may, however, occur as the result of swelling and congestion of the mucous membrane, due to infection and inflammation. In such cases the sperms are unable to penetrate into the uterus, and fertilisation does not occur. This may also be the result of acidity (and thickened mucus) following a mild infection, and sometimes syringing the vagina a short time before service with a weak alkaline solution (e.g. 5 per cent potassium bicarbonate ) proves successful. (See ‘WHITES’; ‘EPIVAG’.)
Tumours — either malignant or benign.
Specific disease, such as tuberculosis in cattle, or in mares. Contagious equine uretritis. (See VULVOVAGINITIS.)
4. Hereditary Abnormalities in the Female (see FREEMARTIN).
Hypoplasia of the ovaries of cows may occur as an inherited condition in the female. It may involve 1 or both ovaries, causing either infertility or complete sterility. The uterus, also, may be hypoplastic. (See also under GENETICS.)
Endocrine failure: heredity may be involved.
‘White heifer disease’ (see under this heading).
It has been estimated that up to 10 per cent of female pigs are sterile. Group studies have shown that 25 to 50 per cent of infertile gilts had abnormalities of the genital tract sufficient to cause sterility, and two-thirds of these were regarded as hereditary.
5. Disease of the Genital Organs in the Male
Orchitis, or inflammation of the testicle, and epididymitis, inflammation of the epididymis, due to injury from kicks, or to infection from external wounds, or from specific infection, such as brucellosis or trichomoniasis in the bull. (See TESTICLE, DISEASES OF; VENEREAL DISEASES.)
Tumours of the testicles may destroy the tubules or prevent spermatogenesis, and on the penis, or in connection with the prepuce, may act as purely mechanical agents, which prevent coitus by the male.
Adhesions between penis and prepuce, the result of acute or chronic balanitis, though rare, may cause mechanical inability to protrude the penis and fertilise the female. (See also under PENIS.)
Inflammation in the secondary sexual glands — i.e. in prostate, seminal vesicles, or other glands — may occlude the vasa deferentia or ejaculatory ducts, and cause inability to pass semen, while in other cases the semen may be so altered as to cause death of the sperms in the female passages.
Affection of the prepuce, such as balanitis, and injuries accompanied by laceration or severe bruising, may cause temporary sterility, but when recovery occurs fertility returns. (See also under PENIS.)
6. Hereditary Abnormalities in the Male
Cryptorchidism, in which 1 or both testes do not descend into the scrotum, is a well-known cause of infertility in the male. When 1 testis properly descends, and is fully developed, conception may follow service, and a sire suffering from this disability has upon some occasions been regularly used in a flock or herd; but when the rig animal has both organs retained, although sexual desire may be emphatic, service is usually unsuccessful. The condition unfits a male animal for use as a breeding sire, since there is evidence that it is a hereditary unsoundness. (See HORMONE THERAPY.)
Hypoplasia or under-development of the male sex organs, particularly of the testis, is an important cause of sterility. It may involve both testicles or only 1.
Endocrine failure may arise as a result of an inherited predisposition. In bulls this may occur in later life, rendering them sterile after they have produced a number of progeny which, in their turn, may perpetuate this form of infertility.
Hermaphrodism, or hermaphroditism, in which an animal possesses both male and female organs, but is without a full complement of either, is usually, but not always, associated with sterility. (See also GENETICS; INTERSEX.)
7. Physical or Psychical Inability or Disturbance
Under this heading are grouped a number of conditions which are difficult to classify elsewhere. Some occur in the male, some in the female, and some are common to both sexes.
Incompatibility between the blood of sire and dam may be responsible for some cases of abortion in cattle, etc. (See HAEMOLYTIC DISEASE.)
Old age: when an animal reaches a certain age, reproduction becomes impossible. The periods of oestrus cease. Breeding ceases earlier in the female than in the male.
Discrepancies in size between male and female may result in failure to breed. The penis may be too short or too large; the vagina may be too long or too small; the female may not have the strength to carry a heavy male; or the male may not be tall enough to reach the female.
Injuries to the back, hips, hind legs, or feet of the male, and sometimes to the same regions of the female, may be severe enough to prevent successful coitus. Progressive spinal arthritis is a common condition in bulls. (See also BREEDING OF ANIMALS; REPRODUCTION; EMBRYOLOGY; UTERUS, DISEASES OF; HORMONE THERAPY; GENETICS; VENEREAL DISEASES; ANOESTRUS; ABORTION; MUMMIFICATION.)