Veterinarians (left to right) Benjamin Newcomer, DVM, PhD, Paul H. Walz, DVM, MS, PhD and Dan Givens, DVM, PhD, research reproductive diseases and vaccination protocols in cattle at Auburn University. (Photo by Mitch Emmons, Auburn University)
Education and awareness, possibly augmented with government regulations, can help reduce losses from specific diseases in cattle herds. A few years ago, for example, outbreaks of trichomoniasis attracted attention and seemed to be trending upward. Increased awareness of the disease, its risk factors and control strategies, appears to have reversed that trend. Producer education, largely driven by veterinarians, improved understanding of how diagnostic testing and biosecurity can effectively prevent transmission of the disease, and veterinarians now report that new outbreaks appear to be declining.
However, the cyclical nature and stealthy behavior of some reproductive pathogens mean outbreaks still can occur, particularly if producers become complacent and cut back on preventative measures. Veterinarians can help protect their clients’ herds by paying attention to trends in the local area and within operations, watching for any decline in pregnancy or calving rates, says Auburn University Associate Dean of Academic Affairs M. Daniel Givens, DVM, PhD.
Tritrichomonas foetus is the pear-shaped flagellate protozoan that causes trichomoniasis, a venereal disease of cattle characterized by early fetal death and infertility, resulting in open cows and extended calving intervals. Control strategies should include biosecurity, testing, culling and vaccination. Testing focuses on bulls, and as there is no cure, infected bulls must be culled. Givens says trichomoniasis vaccination is not intended to control the pathogen, but to improve reproductive rates and reduce the economic impact of the pathogen in infected herds.
Trichomoniasis remains a cyclical but significant reproductive disease, Givens says. Regulations for testing bulls vary between states, but have helped build awareness among producers and apparently reduced the incidence of major outbreaks in most areas. Givens says most of the outbreaks he sees fall into two categories.
- Large herds with multi-sire units – By the time the disease causes a spike in open cows within a herd, the producer could be faced with culling and replacing an entire bull battery. Research has shown that vaccinating the cow herd can help reduce reproductive losses at this stage, but will not bring calving rates back to pre-infection levels.
- Bull sharing – Smaller operations sometimes lease bulls or share bulls with neighbors, and without regular testing, those bulls could be carrying the disease from one herd to another. Without accurate calving records, some of these producers might not recognize a subtle but costly decline in calving rates.
Iowa State University veterinarian Grant Dewell, DVM, PhD, also says outbreaks of trich seem to have declined as awareness has grown. The risk of transmission remains though, as the disease persists in some herds. Bull testing is effective, and remains the focus for regulatory activity, but actively infected cows also can spread the disease and Dewell sees marketing of open cows as a significant risk. Regulations do not prescribe testing in females, so producers who purchase females to add to their breeding herds could be unaware of the risk of an infected female passing the disease to a bull, which then could spread it among the herd. Years in which drought in some areas results in culling and cow movements to areas with more abundant forage can result in outbreaks. Producers who purchase open cows should keep them isolated, at least through the breeding season, to reduce the risk of introducing trichomoniasis to the herd.
Last year, Dewell and the team at ISU introduced a novel sampling method for detecting trichomoniasis in bulls. The method uses a sponge to collect a sample from the bull’s penis during a breeding soundness exam (BSE), rather than the traditional method involving preputial scraping with a pipette. Dewell says the method has gained acceptance in Iowa and elsewhere, particularly with veterinarians who lack experience with the scraping method. The ISU diagnostic lab, and some others, have become comfortable with processing the sponge samples.
Veterinarians can use the sponge method for internal screening and herd-health monitoring in client herds, Dewell says. For bulls marketed across state lines though, they might need to screen bulls using official sampling methods that conform to their state’s regulations.
Jeff Ondrak, DVM, MS, at Nebraska’s Great Plains Veterinary Educational Center, says the incidence of trichomoniasis outbreaks has declined noticeably in recent years as awareness grew. He knows of only one outbreak in Nebraska this year. The trend serves as a good example of how education and awareness can help address a disease problem. He cautions though, that trich incidence has fluctuated before, and with lower cattle values producers could become complacent in their testing and biosecurity efforts, possibly with costly consequences.
Ondrak says diagnostic labs can be a limiting factor in the sampling methods veterinarians use for trich or any other disease. Before making a change, veterinarians need to verify their lab can and will process the samples they provide.
Givens points out that anaplasmosis, not generally considered a reproductive disease, can lead to abortions in cattle. Disease incidence can vary widely between seasons and locations, but is relatively common across much of the central and southern United States.
Producers and veterinarians seem to be paying more attention to anaplasmosis lately due to the FDA’s revised veterinary feed directive (VFD) rules. Some medicated feeds containing chlortetracycline (CTC) are labeled for treatment of anaplasmosis, but they must be fed in accordance with the label and under direction of a veterinarian who fills the VFD order. This has ended some off-label applications producers might have used to control the disease in the past, meaning producers need to work with their veterinarians to initiate more preventative measures along with surveillance and strategic treatment.
Because of a slow, six-to eight-week incubation period, anaplasmosis often turns up in cattle herds around this time of year, as the disease emerges in herds exposed to ticks or other vectors during the summer.
However, Kansas State University veterinarian Hans Coetzee, BVSc, PhD , says outbreaks do not always follow conventional wisdom in terms of when, where and how infections occur. Coetzee presented the information during the recent American Association of Bovine Practitioners conference. In keeping with the conference theme of “What We Know that Isn’t So,” he set out to bust some common myths regarding anaplasmosis.
The pathogen causing anaplasmosis, Anaplasma marginale, is a rickettsiales bacteria that infects the red blood cells. Coetzee says the pathogen spread from Southern Africa to Europe, and was first recognized in the United States – in Kansas – in 1925. It now occurs in cattle in 48 states and causes an estimated $300 million per year in morbidity and mortality in cattle. There are no vaccines currently on the market, although one is in development, Coetzee says, and tetracyclines are the only approved treatments.
In the United States, the pathogen is endemic to the Southeast, but outbreaks increasingly occur in Kansas and across the Plains, Midwest and Mountain regions, he adds. Prevalence can vary widely from year-to-year and between herds. A recent study of samples submitted to diagnostic laboratories in Southern states indicates an overall prevalence rate around 16%. Coetzee notes though, that testing in Florida found some herds with 80% positive infection rates while other herds, even those in the same management system but on different pastures, tested 80% negative.
Ticks are an important carrier and vector for Anaplasma marginale, and insects such as biting flies and mosquitos can transfer the organism mechanically. Coetzee says though, that studies and field experience increasingly implicate needles as a common source of infection. In a K-State trial for example, researchers intentionally used the same needles, first on animals known to be infected then on healthy animals. About 60% of healthy animals exposed to the infected needles became infected with anaplasmosis. In a similar trial using needleless syringes, again alternating between injecting infected and non-infected animals, the infection rate in healthy animals was zero.
Coetzee also cites a case in which an 800-cow dairy experienced a 38% infection rate and 25% death loss after crews neglected to change needles while vaccinating cattle.
For diagnostics, Coetzee says a PCR test can detect the organism sooner after infection and provide fewer false-positive results compared with the competitive ELISA test, but the PCR test also comes at a higher price of around $35 per test. The K-State lab, he notes, provides a pooled test for groups of five cattle to reduce testing costs, particularly in low-prevalence areas.
For treating anaplasmosis with CTC, Coetzee reminds producers and veterinarians to make sure their feed formulations and treatment protocols adhere to approved label specifications. “Chemo-sterilization,” or total elimination of the pathogen from a herd, is not necessary and unrealistic in most cases. “You can live with a carrier herd,” he says, by using testing, targeted on-label treatment, vector control and injection biosecurity, particularly in endemic areas.
Besides some of the usual reproductive diseases such as BVD and IBR, Givens says Neospora caninum can cause abortions in beef herds and could be more common than many realize. This is a coccidian parasite, transmitted through oral ingestion of oocysts shed in canine feces. The parasite can pass from the dam to the fetus, and causes significant incidence of abortions in cattle in some regions, Givens says.
Without effective vaccines, the best control strategy is to minimize exposure of cattle, feedstuffs and water to domestic or wild canines. Givens suggests veterinarians can help clients assess their risk, identify potential problems and develop strategies for minimizing exposure of feeds and water to wild or domestic canines. When abortions occur with no known cause, collect samples for submission to your diagnostic lab for tests including Neospora caninum.
Givens described how reproductive diseases often can affect herds and damage profitability, sometimes without ranchers recognizing they have a problem. Unless they see late-term abortions, declines in calving rates often remain undiagnosed. Even when a cow aborts a fetus and the rancher collects samples, the causative agent is identified less than half of the time. Early embryonic losses or fetal deaths are more common, and while a wide variety of infectious and non-infectious factors can cause these losses, reproductive pathogens often play a role. In addition to those outlined above, Givens suggests watching for these reproductive pathogens:
Campylobacter fetus subspecies venerealis, or vibriosis: This is a bacterial disease with venereal transmission. It leads to infertility, embryonic and early fetal loss. Vaccines are available and effective in most cases, and the disease has been eradicated in some areas.
Histophilus somni: These Gram-negative, rod-shaped bacteria often occur as part of the normal flora in the cattle biome. In large concentrations, the bacteria can be pathogenic, and while it most often is associated with respiratory disease in feedyard cattle, it also can be associated with infertility in beef cows.
Brucella abortus: This Gram-negative intracellular bacteria causes brucellosis in cattle and also is zoonotic, with the human form often referred to as undulant fever. In cattle, brucellosis typically causes abortions during the second trimester of gestation. The national eradication program has mostly eliminated the disease from U.S. herds, although wildlife populations, such as bison in the Yellowstone region, can serve as reservoirs for the pathogen and pass it back to cattle herds.
Lepospirosis: Leptospirosis in cattle is generally caused by one of two types of the Leptospira hardjo bacteria -- Leptospira hardjo-bovis or Leptospira hardjo-prajitno. These bacteria infect the kidney and genital tract of cattle and are associated with abortions at all stages of gestation including early embryonic death. More than half of the abortions associated with leptospirosis occur during the third trimester. Vaccines are available and can be effective, but cross-protection against different Leptospira serovars appears to be limited.
Bovine herpesvirus 1: This viral pathogen is associated with infectious bovine rhinotracheitis (IBR) in cattle. It is transmitted through nasal and oral fluids and semen, and has a wide range of presentations including respiratory and reproductive disease. Latent infections occur with recrudescence when animals become stressed. Eradication is possible, Givens says, and vaccination plays a key role. Modified-live vaccines (MLV) can provide a faster response and longer duration, and can be safely administered to pregnant cows if the cows were previously vaccinated prior to breeding. Killed vaccines are safe to use in pregnant cows regardless of previous vaccination history.
Bovine viral diarrhea virus: BVDV causes some late-term abortions, but embryonic loss and low fertility are more economically significant impacts in cow-calf operations. Effective control strategies include biosecurity, diagnosis (especially detection of persistently infected (PI) cattle) and vaccination.
MLV Vaccines: All About Timing
Modified-live virus (MLV) vaccines can provide a high level of efficacy against diseases such as BVD and IBR caused by bovine herpesvirus-1 (BHV-1). Some producers remain concerned though, that MLV vaccines could present a safety risk if administered to nursing calves, to gestating cows or heifers, or to cows or heifers just prior to breeding, if those females were not previously vaccinated with a MLV vaccine.
Auburn University veterinarian Dan Givens, DVM, PhD, has conducted several studies on the efficacy and safety of MLV vaccines, and presented a review of findings at the 2017 American Association of Bovine Practitioners (AABP) conference. Higher efficacy comes with some risk, Givens says, but proper timing can keep those risks to a minimum and provide tradeoffs beneficial to many producers.
Givens notes that while no vaccine provides complete protection in all circumstances, recent studies using multivalent MLV vaccines have demonstrated consistent BVDV fetal protection rates in the range of 85 to 100% in randomized, controlled clinical trials. Similarly, multivalent MLV vaccines for BHV-1 have demonstrated consistent fetal protection rates in the range of 84 to 100% in randomized, controlled clinical trials.
In their review, Givens and Auburn colleague Benjamin W. Newcomer, DVM, PhD, evaluated results of trials using MLV vaccines at several stages. Their findings include:
- The risk of transmission of attenuated viruses from calves to pregnant dams resulting in reproductive loss appears to be relatively low, but producers can minimize that risk by employing vaccination protocols for stimulation of immunity in heifers prior to their first gestation.
- Annual revaccination of previously vaccinated pregnant cows with either an MLV vaccine or a killed vaccine facilitated protection against a rigorous viral challenge.
- Initial vaccination of pregnant heifers or cows may not cause undue harm in some previously exposed populations, but producers should avoid IM or SQ vaccination of naïve cattle during pregnancy. Prior MLV vaccination greatly reduces the risk of using MLV vaccines in pregnant females.
- The likelihood of causing harm with revaccination shortly before breeding is notably less than the risk from initial vaccination shortly before breeding. The authors recommend revaccination with MLV vaccines at no less than 30 days before breeding to facilitate optimal reproductive performance.
The authors conclude that MLV vaccines exhibit a low risk when administered to calves nursing unvaccinated pregnant cows. Similarly, risk of using MLV vaccines in pregnant females previously vaccinated with the same MLV vaccine is low but detectable. Notably, currently available MLV vaccines provide safe and critically effective protection when administered to developing heifers with the last dose administered at least 30 days prior to breeding. In summary the authors say, “proper timing of MLV vaccine administration can minimize the risk of undesirable side effects while maximizing vaccine efficacy to facilitate the control of disease due to BVDV and BHV-1.”