Sexually Transmitted Diseases
Reproductive performance plays a fundamental role in the profitability of cattle herds, the main cause of economic loss as a result of infertility or subfertility being prolongation of the interval between calvings.
A great deal of research has been devoted to factors which may affect fertility (feeding, herd management, veterinary supervision, etc.), with the aim of reducing the proportion of cows culled because of infertility. The mean proportion may
range from 3 to 7% (Rollinson, 1955; Withers et al, 1959; Boyd et al, 1961), coupled with a figure of 1 to 5% for abortions. According to Erb et al. (1980), a survey of the incidence of relative infertility and reproductive disorders showed that 10-
30% of 2,960 lactations were affected, and 3-6% of the herd was culled for these reasons in a year.
As in many similar reports, this work (and a later report by the same authors published in 1981) classified the disorders by their clinical manifestations (ovarian cysts, endometritis, dystocia, placental retention, abortion, etc.) and not according
to the pathogenic agents responsible for them. Bretzlaff et al. (1982) investigated the occurrence of reproductive disorders after calving, and listed the microorganisms found in these situations. However, the list comprised only the common
bacteria which are occasionally pathogenic (Escherichia coli, Streptococcus, Corynebacterium, etc.) without indicating the involvement of specific pathogens responsible for the major diseases of the genital system.
Martinez (1983) studied reproduction in two large herds by means of weekly visits during two years, and found that 80% of animals were affected by reproductive disorders, among them puerperal endometritis at a frequency of 30-47% (and
linked to true anoestrus). Poor reproductive performance arose chiefly from events occurring after artificial insemination, such as anoestrus after insemination and failure to conceive. Other disorders responsible for reduced fertility were placental
retention, dystocia and ovarian disorders.
Such situations may give the impression that the major diseases of the genital system are no longer important, and it is true that many of them have been eradicated or at least brought under control by systematic vaccination, slaughter, restriction of movement, etc. The sporadic nature of those that remain does not lead to spectacular generalised occurrence, and their severe economic consequences are confined to limited outbreaks.
The disappearance (or reduced incidence) of the major diseases of reproduction has led to an improvement in fertility. However, this improvement has been matched by the growing importance of ordinary hygienic factors (bacteria which are
often non-specific) and management factors (supervision, overcrowding, increased productivity) in the aetiology of reproductive disorders (Uwland, 1984). These factors
alone are responsible to some extent for the aggravation and increasing importance of certain generalised diseases which may affect reproduction and are much commoner now than they used to be.
While it may be true to say that imbalance (or inadequacy) of physiological factors have assumed a more important role in reproductive disorders, and that such factors are more closely related to herd management than to infectious factors in
the narrow sense, it must not be forgotten that such imbalance permits the establishment of strains of micro-organisms of enhanced virulence (such as endometritis caused by Pseudomonas aeruginosa), and may favour the development of epidemics of diseases which currently occur only sporadically (infection with IBR/IPV virus and Chlamydia).
There is no merit in separating diseases transmitted venereally from other diseases of the genital system, because certain diseases (e.g. brucellosis) are transmitted only exceptionally at mating, and most female cattle are no longer at risk of infection
from natural service, this having been replaced by artificial insemination.
Therefore, particular importance should be attached now to diseases transmissible by semen.
We shall now examine the specific features of these infectious diseases in males and females, and the contamination of semen by bacteria which may prove pathogenic under particular circumstances. Disease hazards associated with embryo
transfer will be discussed, and finally ways of producing semen to diminish the risk of contamination with pathogens.
