Speaking to veterinarians at a “Prevention Works” conference hosted by Boehringer Ingelheim Vetmedica Inc. last week, Dan Givens, DVM, PhD, from Auburn University, outlined the need for prevention in dealing with trichomoniasis, or “trich.”
Trichomoniasis is a sexually transmitted protozoan disease that causes pregnancy loss or abortion in the cow, prolonged calving intervals and high open rates in infected herds. An infected bull can quickly spread the disease to a high percentage of females in a herd. To reduce the risk of transmission, several states have adopted rules requiring documentation of trich testing for some classes of breeding cattle imported from other states. Twenty-five states, mostly in the West, have adopted cattle-import rules relating to trichomoniasis. Alabama, Georgia and Tennessee are the only Eastern states with such rules.
Givens says bulls typically are asymptomatic, and infections usually are transient, although some bulls and cows can develop chronic infections. In the cow herd, the most typical signs include an extended calving season and reduced calf crop, likely due to embryonic fetal loss. Some infected cows can have a mucoid discharge, endometritis or pyometra, and some late-term abortions occur.
There is no approved treatment for the disease.
Studies have shown the incidence of Trichomoniasis at 6 to7 percent of U.S. herds, with an annual economic impact of about $65 million due to reduced calf crops and lower calf weaning weights along with the cost of culling and replacing infected cows and bulls. Risk factors include herd size, with larger herds more likely than small herds to experience trich infections at some time. Natural breeding presents more risk than artificial insemination, and older bulls are more likely to carry the infection than young bulls.
Diagnosis in bulls requires a preputial wash or scrape, with samples tested either by cultures or polymerase chain reaction (PCR) testing. The culture method requires three samples taken one week apart to achieve adequate sensitivity. Givens says the first culture, if negative, provides about 80 percent sensitivity. A second test boosts the sensitivity to 96 percent and the third provides 99 percent. National bull studs require six tests to achieve near-100 percent sensitivity. Some state regulations specify either cultures or PCR testing for imported non-virgin bulls, and some require both tests.
Preventative strategies include using AI exclusively, importing only virgin bulls, testing older bulls and vaccination. Once the disease breaks out in a herd, culling infected animals is the primary response. If a producer does nothing in response to an outbreak, calving rates will improve in subsequent years as animals develop a degree of resistance, but will remain lower than normal.
Currently, there is just one vaccine, TrichGuard, licensed to help prevent trichomoniasis in cattle. The vaccine should be administered in two doses, two to four weeks apart, with the second dose four weeks prior to breeding.
Givens and Auburn researchers recently completed a study in which vaccinated and control heifers were intra-vaginally inoculated with Tritrichomonas foetus prior to breeding. The researchers then tested the heifers regularly though the gestation period. Due to the severity of the challenge, virtually all the heifers showed infection shortly after inoculation. Some vaccinated heifers cleared the infection quickly and some did not. Some cleared the infection early, but turned up positive later. The trial did not show large differences in rate of infection or time to clear infections between the two groups. Pregnancy and calving rates however, differed significantly.
Among the vaccinated heifers, 95 percent became pregnant compared with 70 percent of controls. Considerable fetal mortality occurred in both groups due to the severity of the challenge, but 50 percent of the vaccinated heifers delivered live calves compared with 20 percent of the control heifers.
Givens urges producers to do everything they can to keep trichomoniasis out of their herds, but in case of exposure, vaccination could provide a 30 percent larger calf crop based on the results of his study. In herds where managers have needed to cull in response to an outbreak, he recommends vaccinating all females the following year, and subsequently making vaccination decisions based on risk levels.