Stephen Hughes BVSc, DACT, MMedVet(Gyn)
Cell no: 082 894 3568
Trichomoniasis is a true venereal disease of cattle caused by the extracellular, flagellated protozoan Tritrichomonas foetus. Infected bulls efficiently transmit the organism to a female during coitus despite the fact they are asymptomatic carriers of T. foetus (Rae & Crews 2006). Infected females may develop vaginitis, cervicitis, or endometritis and can exhibit infertility, embryonic death, abortion, foetal maceration or pyometra (Lovelady 2013). Trichomoniasis seriously impairs the reproductive efficiency of natural service beef operations imposing a costly impact on the cattle industry (Rae 1989).
The major economic losses associated with T. foetus are due to:
1) reduced calf crop due to early embryonic loss or abortion, 2) reduced weaning weight due to delayed conception, and 3) culling and replacement of infected cattle (Edmondson 2013).
The aim of this article is to provide the veterinarian with a framework of control measures that will assist in managing a commercial beef herd infected with T. foetus. The focus is on a “herd approach” and the treatment of the individual bull is not discussed.
Once T. foetus has been confirmed in a commercial beef herd, usually after testing the breeding bulls, a combination of control measures will be required in order to “clean up” a specific herd. These control measures may include:
1. Test and cull all positive bulls. Positive bulls should be sold for slaughter only. This requires accurate identification of positive bulls, which comes at a cost with respect to time, effort and fees (see below*). The safest and often more practical approach when one or more bulls have tested T. foetus positive is to assume that all bulls within a herd are positive. Then, based on this assumption, it can be more cost effective for the producer to slaughter out all the breeding bulls and to replace them with young/virgin bulls from the reliable source. These new bulls needn’t be of high genetic value (i.e. no higher than that of the female herd) as these bulls will be slaughtered after the next breeding season and this process is continued until the herd is negative. This may take 2 to 3 years, after which, bulls with higher genetic value may be bought and retained in the herd for a few years.
*Recommendations regarding the accurate identification of a positive bull in an infected herd:
Positive bulls are more accurately identified when samples are tested in parallel, performing cultures and confirming with PCR on a single sample (Cobo et al. 2007). To optimise sampling technique and test accuracy, the recommendation is to submit three samples at one week intervals for parallel testing. A bull should not be considered negative until three negative test results have been achieved (Lovelady 2013).
2. After pregnancy check open cows and heifers should be culled. If there are too many open cows for culling to be economically feasible, then these animals should at least be separated into a high-risk herd. Ideally, continue to keep the pregnant animals segregated from the rest of the herd through the next breeding season (Kimsey 1986). Another option is to separate the herd into a low-risk group (≥ 5 months pregnant) and a high-risk group (< 5 months pregnant and open animals). Once the calving season is complete, all animals without a calf-at-foot are retained in the high-risk group or slaughtered if possible.
3. Decrease the number of bulls per breeding unit. The higher the bull number per breeding unit is, the greater the risk that a venereal disease will establish itself within the herd. Single-sire herds offer the lowest exposure potential. However, single-sire units may not always be practical (Lovelady 2013).
4. Reducing the average age of the bull herd is a important step. Bulls that are > 5 years of age have an increased risk of developing carrier status and maintaining the disease within the herd (Lovelady 2013).
5. Only purchase bulls from herds known to be free of T. foetus. All purchased bulls must pass a breeding soundness evaluation and have a least one negative T. foetus culture before being allowed into the herd. The test should be performed after two weeks of sexual rest. Ideally, three negative test results at weekly intervals would be obtained.
6. Reduce the breeding season to 70 to 90 days. A long breeding season not only allows propagation of T. foetus, but may also hide production losses due to reduced weaning weights because of delayed conception (Kvasnicka 1999). Pregnancy exams should be performed 45-60 days after the breeding season.
7. Utilise artificial insemination when possible (Peter 1997). The development of synchronisation programmes that facilitate large scale fixed-time insemination programmes in beef herds has made this a feasible option.
8. Consider culture of all pyometras diagnosed in cows or heifers during pregnancy examinations. Submit all aborted foetuses and placental tissue to a diagnostic laboratory, to rule out other causes of reproductive wastage(Lovelady 2013).
9. Vaccinate all breeding age females against trichomoniasis. Vaccination does not offer complete protection, but it does reduce the duration of infection therefore mitigating the reproductive wastage caused by T. foetus (Lovelady 2013).
10. The single measure of testing bulls and prohibiting introduction of positive bulls is not necessary sufficient to prevent T. foetus infection in a herd. Additional methods of prevention include (Lovelady 2013): i. Avoid grazing cattle on public lands to reduce exposure through coitus with other T. foetus infected animals; ii. Control animal movement into a herd by maintaining good fences; iii. Purchase virgin bulls and heifers as replacements. Buying older bulls and cows as replacements greatly increases the chance of purchasing a T. foetus infected animal; iv. Maintain as young a bull battery as possible. Older bulls are much more likely to be chronically infected with T. foetus; v. Breed purchased cows and heifers in a separate herd. Cull all the cows and heifers that are not pregnant after the breeding season.
Cobo ER, Favetto PH, Lane VM, et al: Sensitivity and specificity of culture and PCR of smegma samples of bulls experimentally infected with Tritrichomonas foetus. Theriogenology. 2007; 68: 853-860.
Edmondson MA: Managing bovine trichomoniasis in the female. Proceedings of the Society for Theriogenology 2013 Annual Conference, p 225-230, Aug. 7-10, 2013, Louisville, KY, USA
Kimsey PB: Bovine trichomoniasis. In: Morrow DA, editor. Current therapy in theriogenology. 2nd ed. Philadelphia: W.B. Saunders; 1986. p.275-279.
Kvasnicka WG, Hall MR, Hanks DR: Bovine trichomoniasis. In: Howard JL, editor. Current veterinary therapy 4: food animal practice. Philadelphia: W.B. Saunders; 1999. p.420-425.
Lovelady AS: Trichomoniasis in the bull: a review. Proceedings of the Society for Theriogenology 2013 Annual Conference, p 231-236, Aug. 7-10, 2013, Louisville, KY, USA
Peter D: Bovine venereal diseases. In: Youngquist RS, editor. Current therapy in large animal theriogenology. Philadelphia: W.B. Saunders; 1997. p.355-363.
Rae DO: Impact of trichomoniasis on the cow-calf producer’s profitability. J Am Vet Med Assoc. 1989; 194: 771-775.
Rae DO, Crews JE: Tritrichomonas foetus. Vet Clin North Am Food Anim Pract 2006; 22: 595-611.