Managing Bovine Trichomoniasis - Avoiding An Emerging
Disease
During the summer of 1994, a number of bulls in northeastern
and southern Alberta were examined and found to be infected
with Tritrichomonas foetus. The isolation of the parasite
has been associated with an open cow rate of 11% - 84% in infected
herds.
Trichomoniasis is a venereal disease of cattle which results
in infertility by causing early embryonic death, abortion, and
uterine infections (pyometra) in infected cows The parasite,
tritrihomonas foetus, which causes the disease, lives
within the reproductive tract of the bull and cow. Although
the organism has been recognized as a cause of reproductive
problems in North America since the late 1800’s, a number
of cow/calf producers in Western Canada have recently become
aware of this insidious disease.
The parasite is spread from infected bulls to susceptible cows
or from infected cows to susceptible bulls during breeding.
In bulls, the organism resides on the penis and in the prepuce
(sheath). Trichomoniasis produces no signs of clinical disease
in the bull and does not affect semen quality Infected bulls
are simply carriers of the organism. Cows infected with Tritrichomonas
foetus during breeding will usually conceive normally. The
most common result of infection in the cow is early embryonic
death. This fetal wastage often occurs during the first 60 days
of gestation but abortions can occur throughout pregnancy. Cows
can harbor the organism for a variable length of time after
becoming infected and thus become a source of infection for
susceptible bulls in the breeding field.
Most cows will develop natural immunity, conceive and carry
a calf to term after 3 to 5 heat cycles following embryonic
loss. This immunity is short lived and the cows may become re-infected
with Tritrichomonas foetus in the next breeding season.
A small percentage of cows can carry theorganixm throughout
gestation and for up to 9 weeks post-partum. These ‘carrier
cows’ represent a potential problem when instituting various
control programs.
The diagnosis of trichomoniasis is usually made after an unacceptable
number of cows are found open by pregnancy examination. Veterinarians
diagnose trichomoniasis by culturing the organism from the sheath
of infected bulls. Bulls should be sexually rested for at least
2 weeks before attempting to culture them. Unfortunately, the
culturing technique to identify infected bulls is not 100% accurate.
Approximately 15% of infected bulls will be missed if only one
attempt to culture the organism is made. To decrease the chance
of missing infected bulls, it is recommended that bulls be tested
3 times, approximately 1 week apart.
There is now a vaccine available through your veterinarian.
It can help control the spread of trichomoniasis if used in
conjunction with other recommended control measures. It should
be emphasized that vaccination alone should not be considered
sufficient in controlling this disease. In addition to vaccination,
there are 2 useful principles to help in the management and
control of trichomoniasis:
- Use only clean (non-infected) bulls;
- Ensure these bulls are not exposed to infected (carrier)
cows.
Once trichomoniasis has been identified in a herd, producers
are encouraged to test all bulls 3 times and cull the positive
ones. Where trichomoniasis is a distinct possibility in a group
of cows, the breeding season should be kept short. This will
make it easier to spot the cows that have lost a pregnancy and
are recycling at a pregnancy examination. It is important to
cull every open cow and heifer in order to eliminate potential
carrier cows from the herd. Managers of community pastures should
be encouraged to only take cows with calves at foot into their
breeding field. Cows that have calved successfully have a low
probability of carrying the infection, and thus the bulls in
that field are unlikely to be contaminated.
While trichomoniasis is a relatively old disease in North America,
it is new to Western Canadian cattle producers. Don’t underestimate
it! This disease can reduce herd pregnancy rates to devastating
levels. As a rule, those producers who control breeding season,
consistently cull open and late calving cows, add few pregnant
‘outside’ cows to their herd, and keep their bull
battery young, have a low risk of seeing this disease. The risks
rise significantly, however, when cows from many farms are pastured
and bred together.
Text adapted from an original article written by
Dr. John Campbel, Professor
Western College of Veterinary Medicine.
