From the May/June issue: Vigilance, timely testing and management can prevent losses from trichomoniasis.
As breeding season gets underway in spring-calving beef herds, veterinarians and producers need to be aware of the risk of introducing trichomoniasis, or trich, into their herds. And in addition to managing for disease prevention, they need to comply with state regulations regarding trich testing and, in some cases, navigate additional complexity related to variation in testing standards and requirements from one state to the next.
In April 2014, National Institute for Animal Agriculture (NIAA) and the U.S. Animal Health Association (USAHA) hosted a joint forum on trich, focused on creating more harmonization among state regulations to facilitate disease control while allowing efficient movement of cattle between and within states.
Leading into the forum, Jeff D. Ondrak DVM, MS, from the University of Nebraska’s Great Plains Veterinary Educational Center, provided some background on the disease.
Trich is caused by a sexually transmitted protozoa, Tritrichomonas foetus, which causes pregnancy loss or abortion in the cow, prolonged calving intervals and high open rates in infected herds. Infected bulls show no clinical signs and can quickly spread the disease to a high percentage of females in a herd.
Ondrak says that in females the infection leads to inflammation but does not interfere with conception. Infection rates in females exposed to a carrier bull can exceed 40 percent, and early embryonic deaths and abortions typically occur 50 to 80 days after breeding. Usually, cows clear the infection after two to five months and return to normal fertility, but occasionally, cows can become asymptomatic carriers. Research indicates these cases are rare, Ondrak says, but when they do occur they can infect bulls and spread the disease within a herd. Open females that are marketed and introduced to new herds potentially can spread the disease.
Ondrak stresses that prevention, through biosecurity, is critical in dealing with this disease, and testing plays a key role in identifying carrier animals. With the assistance of their veterinarians, producers should isolate and test any non-virgin bull introduced to a herd, introduce only virgin or pregnant replacement females, and monitor fences and any potential exposure to neighboring bulls. In herds with risk of exposure, such as from the neighbor’s bulls, surveillance testing is prudent. Practices such as using artificial insemination exclusively and maintaining a closed herd can minimize risk but are not practical for many producers.
Diagnosis in bulls requires a preputial scrape of wash, 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. Dan Givens, DVM, PhD, from Auburn University, 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.
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.
Vaccination is an option in high-risk herds, and currently, there is one vaccine, TrichGuard, licensed to help prevent trich 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 T. foetus prior to breeding. The researchers then tested the heifers regularly through 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 trich out of their herds, but in case of exposure, vaccination could provide a 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.
When a third or more of a rancher’s cows turn up open, which can happen when trich infects a herd, the rancher obviously takes a significant economic loss. But due to the sporadic nature of the disease, quantifying losses the disease causes across a region or across the country presents a challenge.
Texas A&M University economist David Anderson, PhD,worked with university veterinarians to develop a set of assumptions and calculate the annual losses across the Texas cow-calf sector attributable to trich. He estimates that 20 percent of the 150,000 beef herds in Texas have some degree of trich infection in any year. Based on research, he used an average calving rate of 85 percent for the 80 percent of herds that do not have trich and a 73 percent calving rate for herds that do have it.
For this model, he based the estimates on a 90-day calving season. When cows are exposed to trich from bulls during breeding, they often conceive but lose the fetus 50 to 80 days into gestation. Over time, cows typically clear the infection and return to near-normal fertility in two to five months. So, with a 90-day breeding season, trich-infected cows probably will be open at the end of breeding. A longer breeding season could increase calving rate, but late calves would be much lighter at weaning, also resulting in financial losses.
Based on Anderson’s assumptions, trich could be reducing annual calf production in Texas by 2.5 percent, or 96,000 calves. Using 2013 averages, the lost revenue for those calves would be $95 million. At the finishing level, the lost value for those 96,000 missing calves is another $156 million.
He also applied his model to an actual ranch using historical data from Texas A&M’s Agriculture and Food Policy Center. Anderson selected a 335-cow operation and examined the impact of a 73 percent calving rate versus 85 percent. The model shows the loss of 40 calves at a 73 percent calving rate would result in a reduction of $44,000 in net farm revenue, and because the farm would have invested in maintaining the cows and all other associated costs, that loss represents an 81 percent reduction in net farm revenue, which clearly would not be sustainable for the business over time.
Seeking harmony on trich standards
At the trich forum, much of the discussion centered on standardizing testing protocols and state regulations for testing cattle shipped between or within states. Currently, 22 states have some regulations regarding testing cattle for trich, but variation in those regulations can complicate cattle marketing, particularly for seedstock producers who sell bulls to customers in multiple states. In some cases, transport of purchased bulls can be delayed by several days while the seller arranges for appropriate testing based on the bulls’ destinations.
Forum participants discussed opportunities for more uniform standards in several areas.
Age for testing
Some states specify that imported bulls over 12 months of age must be tested; others specify older than 24 months. Some participants maintained that older bulls could be verified as virgins and shipped safely without testing. Others argued that more advanced age increases the likelihood a bull has had contact with females, either intentionally or unintentionally.
Duration of test
Some states have required bulls to be shipped within 30 days of testing; others allow up to a 60-day window from the test to the shipping date. There was general agreement among participants that 60 days provides greater flexibility for the seller and can achieve program goals, provided the bulls have no contact with females during that time.
Type of test
Diagnostic laboratories have, in recent years, increasingly shifted toward the PCR test rather than the culture method. ThermoFisher Scientific (formerly Life Technologies Corp.) recently announced the availability of the VetMAX-Gold Trich Detection Kit, the only USDA-licensed, real-time PCR test to detect T. foetus. The kit includes a positive control to help minimize errors during sample processing. Tiffany Bergner, DVM, with the Colorado Department of Agriculture, says her lab currently uses a PCR test on about 90 percent of trich samples. There was general agreement, though, that states should not mandate a specific test and should keep options open for emerging technologies. Bergner, for example, says her lab is evaluating the new Xtreme Chain Reaction or XCR test from Fluoresentric, which can complete a trich test in 25 minutes, compared with about 90 minutes for real-time PCR, three hours for conventional PCR and five to six days for culture tests. Also, systems for on-farm testing likely will become available in the future, and regulations should allow for their adoption once accuracy is proven.
Sampling and shipping protocols
Ondrak notes that errors can occur at the pre-analytical phase, such as when samples are improperly collected, labeled or handled; at the analytical phase with technician errors or faulty equipment; and at the post-analytical phase, primarily through reporting errors. He notes, though, that reports from human medicine indicate up to 90 percent of diagnostic test errors occur in the pre- and post-analytical phases of testing.
T. foetus samples need to be stored and shipped within a temperature range of about 60° F to 98° F, according to diagnosticians presenting at the conference. The label on the Biomed TF Transit Tube specifies a narrower temperature range of 18° C to 25° C (64° F to 77° F).
Specifications for how soon the samples should be shipped vary between states and individual laboratories, and different labs have different tolerances for samples contaminated with blood or other foreign material, or samples in expired transit pouches or tubes. Texas A&M veterinarian Tom Hairgrove says that Texas labs will analyze marginal samples but only for diagnostic purposes and not to meet regulatory requirements. In Colorado, Bergner says labs had to “put their foot down” and notify veterinarians and producers they would no longer accept expired pouches or tubes. Bergner also says her lab prefers veterinary clinics send samples directly to the lab for incubation rather than incubating and freezing them. Some other states and labs are comfortable with frozen samples.
Most participants seemed to agree that some variation between laboratory protocols and policies is understandable and acceptable, based on differences in their facilities, staffing and other factors.
Pooled versus individual samples
Currently, 11 states of 22 with trich regulations allow laboratories to pool samples from up to five bulls for a single PCR test. If the laboratory finds a positive result in a pooled sample, they can go back and test individual samples to identify the infected bull. This reduces the cost of the PCR test to the producer but with a small decline in accuracy. Representatives from ThermoFisher Scientific outlined a recent study, published in the Journal of Veterinary Diagnostic Investigation, comparing the sensitivity of pooling trich samples with individual samples. The study, led by Lee Effinger from the Oregon State Department of Agriculture, involved five feeder diagnostic labs in different states, with the Kansas State Veterinary Diagnostic Laboratory serving as the central study lab and analyzing the same samples. The researchers found pooling at 1:5 missed 4 percent of T. foetus-positive samples, and 1:3 pooling missed 3.5 percent of positive samples.
Several forum participants maintained that pooled testing encourages more producers to test more bulls, a benefit that overshadows the small decline in accuracy. Some favored individual testing, arguing the potential cost of an infected bull slipping through the system justifies investing in the most accurate method available.
While testing and regulatory efforts currently focus on bulls, participants generally agreed the industry will need to develop strategies and educate producers to reduce the risk of purchased females spreading trich.
See this article and features on organic dairy production, the precautionary principle, vitamin A deficiencies, electrolyte therapy and a new approach to bovine veterinary practice in our May/June issue.