The dairy and beef industries of Australia are ultimately dependent upon good fertility of cattle, both as individual animals and as part of larger herds. The Australian herd numbers about 29m on 75,000 properties, with 1.7m of these as ‘milkers’ on 6,000 dairy farms, and ~8m cattle going through abattoirs (and another ~0.5m live exported cattle). Fertility itself can be divided into stages of successful ovulation, mating, fertilisation, implantation, gestation, parturition and rearing until weaning. A useful rule-of-thumb is that 65% of healthy cycling cows will conceive on 1st service, similarly for 2nd and a slight decline by 3rd so that after a 3 month joining period, 92-94% of beef cows and heifers ought to be pregnant 8-10 weeks after removal of bulls. The non-pregnant animals potentially are sub-fertile and ought to be culled as that may be at least partially heritable, as well as being removed to allow appropriate management and feeding etc of the pregnant animals. Infertility or sub-fertility in beef cattle is usually investigated as a herd problem, whereas in a dairy herd the focus may be on an individual animal. Diagnosis of infertility or sub-fertility, as in all other differential diagnoses, rests upon the pillars of clinical history, clinical signs and results of further testing. The differential diagnosis ought to be tailored to the local area and industry; with consideration of probabilities, possibilities, consequences, risks (to you the investigator, the farm staff, public etc; and other animals) based on history, experience, epidemiology, farm management, environmental factors etc, as the outcome of the investigation will lead to institution of treatment, control and/or prevention strategies. Laboratory testing can be undertaken to confirm or exclude particular differential diagnoses, and as such the tests have to be targeted and specific. It is possible to have more than one cause operative in a herd or an individual, and separate causes in different breeding groups on the same complex1. Veterinary laboratories such as the State Veterinary Diagnostic Laboratory have on-line manuals describing what samples to collect and what tests to request for particular diseases2, and veterinary pathologists are available to assist submitters select appropriate testing options. Details are available on costs, turn-around-times, test availabilities, out-sourcing, and instructions on how to package and despatch samples with accompanying submission forms. Appropriate interpretation of test results is important as that may indicate treatment and control options. However, it must be borne in mind that a small proportion of apparently healthy cows and heifers will suffer spontaneous foetal death and/or abortion: a useful guide is <2% in the first trimester, <2% in mid, and <1% in third; and limited studies indicate that some of these have chromosomal abnormalities, probably different incidences at different stages3.
A vaccine is available for the control of bovine vibriosis (bovine venereal campylobacteriosis due to Campylobacter fetus venerealis), however, many herds are not vaccinated, or ineffectively vaccinated. Transmission from an infected bull is common (>90%) to mated cows or heifers; many of those go on to develop infection (30-70%) and will have early embryo death resulting in extended return-to-service. Ultimately, local immunity develops and the cow/heifer successfully implants and carries foetus to term; but this will manifest as sub-fertility in a short mating season (25-50% pregnant after 3 months joining), or frequent return-to-service. Of those that successfully conceive, a few (<10%) will remain carriers of detectable infection through to parturition. After parturition some, but not all, of those will become effectively ‘cured’ and relatively immune to re-infection for a few years. Early foetal deaths are resorbed so there is little or nothing to observe except return-to-service; abortion of mid to late term foetuses is rare and characterised by mild foetal peritonitis and pleuritic, and oedema or mild focal mild haemorrhagic placentitis. In a herd situation with multiple bulls of which only one or some are infected, or only one infected cow acting as contagion-spreader, many animals may escape infection and identification of herd problem may be obscured. Diagnosis can be based on identification of the organisms by sampling bulls with either preputial wash or ‘tricamper’ scrapping, or by sampling cows and heifers: SVDL relies on culture with confirmation by PCR (instruction for media etc and sampling procedure available from SVDL)2. Culture of foetuses is possible, but rarely performed. Vaginal mucus samples can be collected from cows and heifers and tested for Campylobacter-specific IgA (contact SVDL for media etc and instructions on collection)2, this antibody is produced in infected animals but concentration fluctuates in individuals, and it fades away after some months, therefore testing is done on batches of 10 or more potentially infected animals and interpretation is as a batch, not as individuals within the group. There are no serological tests.
Bovine veneral trichomoniasis (Tritrichomonas foetus) is a notifiable disease in NSW. Infection closely resembles the clinical signs seen in vibriosis; that is, early foetal death and resorption with prolonged return to service, infertility etc; pyometra, macerated foetuses and abortion are rare. Bulls tend to be infected for life. There is no vaccine, and no immunological test. Diagnosis relies upon demonstration of the organism collected from bulls by preputial wash or ‘tricamper’; or from vaginal wash or ‘tricamper’ of cows or heifers2. The organisms are cultured in special media pouches, and if necessary confirmed by PCR. In the event of a herd diagnosis, the initial confirmatory testing will probably be conducted as part of notifiable endemic disease exclusion; however, testing associated with subsequent control and eradication will be under direction and at submitter’s (owner’s) expense.
Investigations of bovine abortion often do not result in a definitive diagnosis. This is in part due to the occurrence of spontaneous abortions for which there is no particular diagnosis; and in part due to incomplete or inadequate testing to arrive at a definitive diagnosis: bovine abortion due to Neospora caninum cannot be made on the grounds of seropositivity as many cows seropositive for neospora do not abort, and confident exclusion of neospora requires histological examination of at least 5 HE ‘full’ slides of foetal brain – cost usually prohibits this level of investigation; cattle aborting due to Leptospira pomona are often seronegative at the time of abortion and the organisms are fragile and readily disintegrate in transit so are not easily observed under dark-field examination, whereas cattle aborting from L.hardjo are usually strongly seropositive at the time (cattle are also seropositive as a result of vaccination, and post-infection high serological reactions fade to lower titres within a few months even if the cows are still shedding organisms). Data from Bairnsdale laboratory, Vic, showed that a reasonably high proportion (~60%) of abortion investigations did not yield a significant aetiology despite optimal sampling (foetus for necropsy, placenta, and maternal blood taken at the time), and detailed testing4. Investigation of an aborted foetus sent into SVDL can easily result in $5-800 of testing and although excluding many options, still not arrive at a satisfactory explanation. Archival data from SVDL (1995-2008) revealed that less than a third (902) of (2,587) bovine abortions investigated by us resulted in a diagnostic finding5 – this is consistent with other studies. However, exclusion of serious contagious diseases and metabolic disorders can be extremely important, and the benefits of a negative investigation result should not be under-estimated.