by Boehringer Ingelheim Animal Health Sr. Associate Director John M. Davidson, DVM, DABVP
American ranchers have been dealing with Tritrichomonas foetus or Trich since 1932. Interestingly, only in the past 10-15 years has this disease been getting the attention it deserves across the Gulf Coast. I say deserves because there is not another disease that carries the financial impact that Trich does for the cow-calf producer in the southern United States. There are certainly lots of opinions on this disease surrounding testing, management and prevention. Of significant concern to a lot of folks in the cattle industry is the variation in understanding and awareness of this disease. In my professional experience, I’ve seen several instances where this misunderstanding has actually worsened the problem of Trich on the ranch. In this article, I will attempt to help clarify some of these areas.
UNDERSTANDING THE DISEASE
The bull is the long-term carrier of the organism without ill effects or visible lesions. As reported in 1941, we used to think that older bulls carried more trich in structures known as ‘crypts’ located on the surface of the penis. Recent research from Auburn University has proven the crypt theory to be a myth. There are no structures that resemble crypts and no structural differences between young or older bulls. The take away is that all breeding bulls should be tested, regardless of age.
In female cattle, the organism is introduced during breeding yet does not impair conception. The presence of the organism in the uterus results in severe uterine inflammation (metritis) which usually, but not always, results in fetal death or abortion generally around 60-90 days of pregnancy. This gives rise to the extended time period between observed heats. In a small percentage of the infected cattle, a uterine infection or pyometra develops. This infection can be detected by your veterinarian via rectal palpation or ultrasound and confirmed with a testing procedure similar to that of the bulls. Of great concern to me is the often over-simplified notion that sexual rest of the exposed females always results in spontaneous clearance of the infection. It should be emphasized that a low percentage of the exposed cow population will maintain a persistent infection, which means the cow carries the infection through pregnancy into the next breeding and re-infects the bulls. Though the estimated frequency is low (less than 1 percent), it requires consideration of the female carrier state for management decisions when Trich is diagnosed in the herd.
A key factor in the profitability of the cow-calf operation is weaning a high percentage of uniform healthy, heavy calves while keeping inputs reduced to an acceptable level. According to University of Florida’s Owen Rae, DVM, net income from the cow-calf operation can be defined as:
[(# of calves weaned X weight of calves weaned) X price per pound] – maintenance cost per cow/calf
Bovine trichomoniasis affects most, if not all, components of the equation. Reduced pregnancy rates and the variable distribution of the live-born calves over the calving period are the most obvious. The increased testing, culling and prevention costs decrease the overall net per exposed female. The impact to the cow-calf producer’s profitability based on simulated models was significant. Dr. Rae’s disease model predicted a reduction of 14 to 50 percent in annual calf crop, a prolonged breeding season, a reduction of 5 to 12 percent in the suckling or growing period, a reduction of 4 to 10 percent in pounds of marketable calf crop at weaning, a reduction of 4 to 10 percent in monetary return per calf born, and a substantial reduction of 5 to 35 percent in the return per cow confined with a fertile bull. Prevalence in this model varied from 20-40 percent (one to two infected bulls out of five total breeding bulls). Income from calves sold was reduced by $24,551. This was strictly related to decreased number of calves as a result of trichomoniasis in the herd. This value does not include losses for culled cows, bulls, testing and prevention strategies. When those additional factors are included, the financial impact is even more significant. The use of excessive numbers of bulls, i.e. over mating, favors a higher incidence of infection in cows due to multiple services at estrus, or heat.
There are no legally available drugs to treat affected cattle in the U.S. Infected cattle must be sent to slaughter.
Over the years, various methods of sample collection have been performed by veterinarians. Currently, most veterinarians rely on preputial scrapings as the collection method of choice. Once the sample is collected, it is then inoculated into the culture and transport media (In Pouch TF). The quality of the sample is highly dependent on the skill and experience of the collector. The sensitivity of the test is affected by the field conditions (i.e. low number of organisms collected when sampled) and handling conditions (i.e. temperature and transit time to laboratory). Samples can be tested by culture, DNA – based on the polymerase chain reaction – or both. Due to the limitations of the culture method, I am no longer recommending this test at this time. The sensitivity of the available tests vary (influenced by collection techniques, field conditions, and sample handling) and are reported in a range from 75 to 93 percent, depending on the type of tests performed. This illustrates the point that, though veterinarians are dealing with the best test we have available, we know that it is not 100 percent effective at detecting an infected bull. Research out of the University of Nebraska indicates that a minimum of three properly performed tests are required to identify all the infected bulls on a premise. Pooling of samples at a ratio of 5:1 is now an option for testing at the Texas A&M Veterinary Medical Diagnostic Laboratory in College Station, Texas. Pooling lowers the average cost per bull without sacrificing diagnostic sensitivity. Working with your veterinarian to determine your herd’s risk factors and potential for infection will help determine the timing, type and number of tests to be performed.
Once the diagnosis of trichomoniasis is made in a beef herd, the timely and accurate identification of the diseased bull(s) begins. It is a common misconception that young bulls cannot get infected with Trich. This is simply not true. An Australian study in 1976 demonstrated the ability of a known Trich-infected three-year-old Hereford bull to infect 19 of 20 virgin Hereford heifers after a single service over a two-week period.
Ranches that practice high levels of biosecurity, keep excellent records, and monitor reproduction rates are not as likely to be severely impacted by bovine trichomoniasis.
In 1947, a leading expert on Bovine Trichomoniasis, Dr. Bartlett, proposed two basic principles of control of trichomoniasis in cattle: 1) keep from breeding susceptible cows to infected bulls, and 2) keep from breeding susceptible bulls to infected cows. Knowing the status of all bulls pre- and post-breeding is still the best form of herd surveillance. Verification of pregnancy rates after breeding is another key to ensuring the herd is not affected by a venereal pathogen like T. foetus. The following list of management techniques will reduce the potential impact of bovine trichomoniasis in a cattle herd:
- Biosecurity: Keep fences in good repair, and make note of any contact with breeding stock from neighboring herds.
- Breeding season: Shortened breeding season (i.e. 90 day) should be used. If the breeding season is extended or year-round, the disease will be more difficult to control and to identify animals carrying the organism.
- Replacement bulls should always be virgins. Never lease or borrow a non-virgin bull. Period.
- Test ALL bulls four to six weeks prior to breeding season, along with a properly performed breeding soundness exam, and two to three weeks after breeding season. Keep excellent bull-pasture breeding records. Do not move bulls to another pasture without a negative Trich test.
- Palpate cattle after breeding season.
- Cull or separate open cows at pregnancy check time as well as those that abort or have a noticeable discharge. Check the aborted fetus and any discharge for T. foetus.
- Purchase only virgin replacement females from known, reputable sources.
- Vaccinate: Early vaccine studies showed favorable outcomes when heifers were challenged with large numbers of T. foetus organisms. In fact, a 1992 study 1 showed an increase in calving rates from 31 to 63 percent in challenged heifers. A commercial vaccine (TrichGuard® – Boehringer Ingelheim Vetmedica, Inc.) containing inactivated T. foetus is available for use to reduce the shedding associated with T. foetus. Recently, a 2017 study 2 from Auburn University demonstrated that TrichGuard® vaccinated heifers had a significant increase (50 percent versus 20 percent) in calves born when compared to non-vaccinated controls. When the real-world economics are applied to these results, the results are impressive. A key point when using the vaccine is to follow the label. Initially, two doses are required, each given two to four weeks apart, 30 days prior to the breeding season. The timing of administration and number of doses administered are critical to proper timing of immunity and exposure. Also, control other reproductive diseases like Lepto, Vibrio (campylobacteriosis), infectious bovine rhinotracheitis, bovine viral diarrhea, and brucellosis with an appropriate vaccination program.
- Artificial insemination can reduce the spread of bovine trichomoniasis.
Trichomoniasis can have significant impacts in the reproductive performance of a beef cattle operation. An awareness of the impact that the carrier animals can have on a beef operation is the first step to developing a sound T. foetus control or prevention program. When biosecurity, surveillance, herd health, and record keeping come together in a well-managed system, the beef cattle rancher can feel rest assured that the silent profit taker is not at work on their ranch.
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- Will vaccination prevent infection? No. The trich organism is introduced at breeding and its transmission cannot be prevented by vaccination. The only way to ensure no bull transmission is to utilize artificial insemination from bulls collected in CSS-certified facilities.
- Do I need to follow the vaccine label for best results? Yes. Same is true for any biological used in livestock.
- Should I vaccinate my cattle for Trich? Vaccine protocols for cow-calf producers should be built around risk and not tradition. If you ranch in a Trich endemic area such as the Texas Gulf Coast, then you are at an increased risk of having trich introduced into your herd. The vaccine has been shown in numerous studies to increase the number of live calves born in exposed females.
Kvasnicka WG, Hanks D, Huang JC, et al. Clinical evaluation of the efficacy of inoculating cattle with a vaccine containing Tritrichomonas foetus. Am J Vet Res 1992; 53:2023-27.
Edmondson MA, Joiner KS, Spencer JA, et al. Impact of a killed Tritrichomonas foetus vaccine on clearance of the organism and subsequent fertility of heifers following experimental inoculation. Therio 2017; 90:245-251.