It is critical that diagnostic information be utilized in the construction of the herd health program. The selection of vaccines to be used in a program and an individual producer’s cattle working schedules depends on the presence of a particular pathogen in the herd or geographical area and on the risk of introduction.² It is important to determine the category or period of reproductive loss since reproductive pathogens have a tendency to occur within specific stages of gestation. Classically these categories have been defined as early gestational, mid gestational, late gestational, and periparturient (Table 37.1). Determining when gestational losses occur is the first step in understanding the etiology of these losses and represents the starting point for building the vaccination program.

Utilizing diagnostic tools in cases of abortion can be very helpful and can be very frustrating due to diagnostic limitations and challenges. In cases of abortion an etiologic diagnosis is identified less than 50% of the time.³ However, several diagnostic advances, through conscious efforts by diagnostic laboratories, have been made to improve detection of certain pathogens.⁴ Even though an etiologic diagnosis can be challenging, infectious agents causing abortions can be identified. Table 37.2 highlights the multiple pathogens that have been associated with bovine abortions, the gestational period they normally affect, and common diagnostic procedures used to identify their presence.^2,5–9 Some pathogens are considered common reproductive agents and some are rarely identified. In addition, certain pathogens can be more prevalent in certain geographical areas.³

Diagnostic laboratories have different capabilities in handling an abortion case. As a practitioner, it is prudent to have a close working relationship with your laboratory. Diagnostician consultations are sometimes necessary to develop a systematic approach for abortions. Appropriate tissues and bodily fluids samples are more useful than others and comprehensive submissions are valuable.

Adequate information, including herd history, with complete submission to a diagnostic laboratory is the most important step to a definitive diagnosis.⁴ An abortion work-up can be costly and sometimes unrewarding. It is in the best interest to provide the diagnostic laboratory with the required information to minimize cost and maximize diagnostic success. Even though infectious agents comprise most of the reported etiology, practitioners, producers, and diagnosticians have to be aware that abortions are not limited to infectious agents.⁹ Noninfectious causes, such as environment, toxins, nutrition, and genetics, have to be considered as possible sources of reproductive failures.

Serologic sampling can be utilized in diagnostic work-ups for abortions but the results should always be interpreted with caution. Single serum samples have little to no value when diagnosing causes for abortions. It is difficult to differentiate the titer values based on vaccine and natural exposure to certain agents/antigens. However, a lack of titer in abortions may rule out certain causes.

Paired serum samples have also demonstrated limited value. Many of the bacterial and viral pathogens that cause abortion may infect the fetus or placenta long before the abortive event occurs. This lag time between infection and abortion may prevent the practitioner from detecting the rising or falling titers associated with the initial infection. This leads to the collection of two “convalescent” serum samples that will fail to detect the increase in antibody titer, if it indeed occurred. This is especially true when only affected females are sampled at the time when the abortion is noted. Overall, the time of seroconversion is dependent on the exposure of the agent and the amount of immunity established prior to the breeding and throughout gestation. Paired sera are much more useful when it is used as part of a complete diagnostic work-up that includes samples from the placenta, fetus, and fetal fluids.

Serologic profiling is one option to optimize the use of serologic testing. The basis of serologic profiling is analyzing titers from affected/aborted and nonaffected dams over the same time period.⁴ It is unclear how many samples are needed, but some suggest that the same number of affected and nonaffected animals, preferably at same stage of gestation and age, is adequate.⁵ In herds with chronic gestational losses serum may be collected and frozen from a statistically relevant number of cows for future testing as needed. These frozen samples may be collected as the females are processed prior to breeding and/or at the time of pregnancy examination. Then, as fetal loss is detected, banked serum samples can be submitted along with acute and convalescent samples to provide a clearer serologic picture of the affected animals and their normal cohorts. This should give a more complete picture of when seroconversion occurred and what pathogens were involved.

In some cases, all samples will have elevated titers due to endemic infections of specific agents. For example, in herds endemically infected with bovine viral diarrhea virus (BVDV), all animals may have seroconverted yet have no clinical evidence of etiologic diagnosis of abortions.¹⁰ On rare occasions, fetal/precolostral serology may be beneficial. Fetuses must be immunocompetent for specific agents (Toxoplasma gondii/Neospora caninum/BVDV/infectious bovine rhinotracheitis/Brucella) to produce serologic evidence in fetal fluids.^3,4,11 While serology may be valuable in certain circumstances, the interpretation of these results should be carefully assessed as it relates to the entire diagnostic work-up and clinical signs in the herd.

Designing herd vaccination protocols

While vaccines represent an important tool in protecting reproductive performance, they tend to be somewhat underutilized in beef herds (Table 37.3). When designing protocols to immunize the beef breeding herd against reproductive pathogens, there are several other important factors to consider. The potential at-risk level of the herd should be considered not only from the entry of potential pathogens, but also from the standpoint of the current disease level in the resident herd, different management groups on the ranch, breeding animal movement, and the potential side effects of the immunizing agents.² While complete protection against every pathogen in every individual is not realistic, the goal would be to minimize the number of susceptible animals in the population. This should prevent epidemic outbreaks of reproductive disease as well as the establishment of chronic endemic losses in the cow herd.