Trichomoniasis (Trich) is a sexually transmitted disease of cattle caused by the protozoa Trichomonas foetus. This organism parasitizes in the sexual organs of cattle.
In South Africa it contributes to huge losses due to the infertility it causes in beef cattle. Artificial insemination can stop transmission.
- Abnormal oestrus cycles
- Resorption of embryos
- Early abortions (low incidence)
- Reduction in calf percentages over consecutive years
- Uterine inflammation/infections
- Cows not in calf for longer periods of time
- Lower calving percentages
- Calves with lower growth tempo. This is due to the fact that they are born later in the growth season resulting in a reduction in milk quality and volume available to the calf as the nutritional value of the veld deteriorates.
- Costs of replacing animals due to culling of positive cows.
- Uterine infections occur in 5-10 % animals in infected herds.
- Up to 35 % loss of income in a herd running with a positive bull.
- Carrier bulls – up to 40 % cows can be infected.
Risk factors that contribute to the presence of Trich in bulls:
- Older bulls (> 5yrs) – less resistant to this disease than younger bulls and are, therefore, shedders of higher amounts of organisms. Sheaths of penises of older bulls contain more and larger folds in the laminae that provide shelter and a suitable growth media for the parasites.
- Sexual rest increases shedding.
- Common grazing – no biosecurity between herds.
- Contact with other herds-fences not effective.
- All breeds are susceptible and might carry organisms for life.
- Transmits during natural breeding – amount of cows infected depends on stage that infected bull entered herd. If 90 % of herd was already pregnant when bull picked up infection or when new infected bull was introduced, fewer cows will be infected for this season. Rate of infection will increase progressively during subsequent breeding seasons.
- A negative bull can pick up infection from a cow that has just been covered by a positive bull, mechanically transmit the disease and becomes positive.
- Cows can get rid of the infection after a couple of heats (the assumption to date suggested 3 cycles = 63 days). This, however, has proven to be incorrect, as (i) not all cows are monitored to show heats, (ii) uterine infections will exceed this period and will shed organisms and infect bulls.
- Cows develop a partial immunity but bulls stay infected and don’t develop immunity.
- Lower calf percentage.
- Longer inter-calf period.
- Heifers don’t fall pregnant.
- Sporadic abortions.
- Abnormal oestrus cycles (>21 or <21 days).
- Uterine infection/inflammation post breeding.
Isolation of T . foetes
Mainly from bulls +/- 2 weeks post breeding season or just before following breeding season.
During the breeding season, or when bulls stay with cows all year round, lower organism shedding occurs (less organisms are shed in the bulls’ ejaculate or rub off in the vaginas of the cows it covers).
Numbers of organisms in a bull also fluctuate from one sample taking to the next. A bull can, therefore, present a false negative result during the first scraping. Veterinarians take 3 samples 1 week apart to ensure that > 95% of positive bulls will be diagnosed.
The test conducted on the sample is done by Onderstepoort Veterinary Institute. Genetic DNA test done is called the ‘Polymerase chain reaction test’(PCR) and has a 98% reliability.
Recent research has pointed out that in case of beef herds where it is expected to utilise 3 bulls /100 cows, and one of 3 bulls is positive, it is safe to assume that all 3 bulls are positive (the other two therefore tested false negative).
Two more scrapings are suggested one week apart.
- Treatment of bulls is unpractical (sheath washes, drenching and injections for a week), expensive as the bulls have to be isolated, retested (3 times 2 months post treatment) and are only then declared negative (this takes 3 months). Results here can’t be guaranteed. They can test positive again.
- Artificial insemination (AI) of cows. This, however, is expensive as synchronization of cows, artificial insemination specialists and semen and equipment are costly.
- Establish a new negative herd:
- Make sure fences are new or well serviced and intact. This ensures bio-security. Make sure neighbours’ bulls are not capable of crossing fences and that one’s own bulls stay on one’s own farm. Good fences make good neighbours.
- Keep heifers away from old breeding bulls and run them with new annually bought in young bulls = HERD 1.
- Rectally examine all breeding animals and separate :
- Animals > 5 months in calf = HERD 2.
- Animals < 5 months in calf = HERD 3.
- Open animals = HERD 4.
Keep bulls away from HERD 2 and HERD 3. Make sure these herds give birth and mark cows that calved. They are negative when they carried until full term.
- Open animals (HERD 4).Vaccinate with Trichguard: two doses four weeks apart, including open breeding heifers (HERD1) that have been with new bulls.Two months later: introduce young cheaper bulls to HERD 4 for two months and slaughter bulls; bulls used in heifers the previous season may be used providing that biosecurity has not been compromised.Rectally examine HERD 4 five months later and slaughter open cows.
- Make sure all breeding animals have calved after this procedure and slaughter all the others.
- Buy new certified clean fertile bulls at least every four years.
- Start breeding season and test bulls between breeding seasons; all year breeding seriously complicates and compromises the process of cleaning up a contaminated herd.
Dr. Johan Wessels