Good progress has been made during the past two decades in improving the diagnostic methods for detecting the various types of bovine infertility. Nevertheless, the sterility worker is still frequently confronted with cows and heifers belonging to a category variously designated as "repeat breeders", "problem cows'', "slow breeders'', "hard-to-settle" cows, etc. Vanderplassche (1957) who refers to the condition as "Symptomlose Unfruchtbarkeit", with some justification states that this "Sterilitat sine materia" is one about which we know nothing or very little.
Reproductive failure due to physiological or functional derangement of ovarian activity is known to be an important cause of poor breeding performance in bovines, and may be present to such a degree as to constitute a herd problem.
Most forms of this physiological infertility are manifested by objective symptoms, notably cyclic irregularities, which attract attention and render diagnosis of the
actual type relatively easy. Ovulatory failure, however, is an exception to this rule since it usually presents no visible evidence suggestive of an ovarian aberration.
Even palpation of the ovaries per rectum generally fails to reveal the abnormality unless such an examination is carried out a day or two after the animal was known to have been in oestrus.
This type of infertility frequently presents the most puzzling problems to both the owner and the sterility worker, since the oestrous cycle generally runs a normal course, except when the more advanced stage of cystic degeneration has been reached.
Notwithstanding this apparent regularity of the cycle and the absence of evident pathology or infection in any part of the genital tract, the fertility of the affected
animal is subnormal.
By virtue of its abstruse nature ovulatory failure has not been subjected to intensive research in the past, and information on its prevalence and significance is scanty. Roberts (1957), for instance, states that delayed ovulation has not been
studied sufficiently to ascertain its importance, and that it probably does not occur very frequently.
Successful fertilization of the ovum is conditioned by a close co-ordination between the time of insemination or coitus and the time of ovulation, and by the viability of the sperm in the female genitalia. The cow is unique in that ovulation normally occurs only six to fourteen hours after the cessation of oestrus, and since the fertilizing capacity of sperm is lost after a sojourn of 24 to 48 hours in the female genitalia, any undue delay in ovulation will prevent conception, especially if the cow is bred during the early stages of oestrus.
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