Bovine Infectious Diseases
One of the most discouraging problems in cow-calf operations is abortions. The cow or heifer got bred, conceived and is carrying the calf and BANG! You’ve got nothing! At least if the calf was born and developed scours or pneumonia you would have a chance to treat and save the calf. But with an abortion, you’ve lost a year’s production with that cow.
What causes abortions? For the most part abortions are caused by infectious agents–viruses, bacteria, and protozoa. In California, selenium deficiency is also a common cause of late term abortions. The common bugs are Bovine Virus Diarrhea virus (BVD), Infectious Bovine Rhinotracheitis virus (IBR, rednose), Foothill Abortion, Leptospirosis, and Neospora. One bug we can’t forget is Brucella abortus (Brucellosis).
How many abortions are too many? It is common in nature to have 1% abortions in a herd of cattle and these commonly occur just before the anticipated calving season or early in the calving season. When the number exceeds this level it is time to act.
What if I have too many abortions? The first abortion that occurs is usually not a cause for concern; but if a second one occurs don’t hesitate to call your veterinarian. The California state diagnostic laboratory (California Animal Health & Food Safety [CAHFS] laboratory system) does an excellent job of finding out the cause of abortions at a very reasonable price. Your veterinarian will submit
samples (often the entire fetus) to the lab. If there is a delay in getting the fetus to the lab–refrigerate it, do not freeze it. When you get a diagnosis back you and your veterinarian will know what steps to take or what to fine-tune in your current prevention program.
What should I be doing to prevent abortions? There are a number of things that must be done to prevent each type of abortion and these are briefly listed below. The main thing to do is to consult with your veterinarian well ahead of time to be sure you are doing all those things that are critical to your operation.
Viral Abortions–BVD and IBR
These are viruses that can be spread on equipment and clothing, as well as by contact with infected animals. Be sure to vaccinate all replacement heifers with a modified live virus vaccine (usually a 4-way IBR, PI3, BVD, BRSV vaccine) at some point prior to breeding. Afterwards, give yearly boosters with the killed virus vaccines (any time before the third trimester of pregnancy [before they are 6 months pregnant]) or use the modified live vaccines when they are open, just
before turning in the bulls. Most MLV vaccines are not approved for use in pregnant cattle. If you have any questions regarding virus vaccines, contact your veterinarian.
This is a group of bacteria transmitted via the urine of infected animals contaminating feed and water. It can be spread by many species of animals, such as dogs, rats, and wildlife. Infection usually causes late term abortions (6-9 months). Most veterinarians recommend annual or twice-annual vaccinations with multivalent vaccines, such as 5-way (L. pomona, L. hardjo, L. grippotyphosa,
L. canicola, L. icterohemorrhagia) or GHP (3-way) can usually prevent abortions. It is best to vaccinate when turning the bulls in or before the cows are 5 months pregnant.
This disease is almost eradicated from cattle in the U.S. Almost, but not quite! Veterinarians and your state animal health officials highly recommend you continue to vaccinate all your replacement heifers against Brucellosis (Bang’s vaccination) at or near weaning.
This is a bacterial disease that is carried by the Parajuello tick and causes late term abortions. This disease costs California cattle producers an estimated 13-18 million dollars annually. There has been great progress made by UC researchers in the past few years; however, there is no vaccine currently available. When susceptible cattle are bitten by the tick during the first to seventh month of
pregnancy they can abort in 90 to 120 days. The best prevention is to expose cows and heifers to the tick inhabited areas when they are open or greater than 7 months pregnant and to keep them away from these areas when they are bred from 1-7 months. Contact your veterinarian or livestock advisor if you are unsure where the ticks might be on your ranch. Also, if you anticipate bringing pregnant
cattle (1-7 months pregnant) into a high risk Foothill Abortion area contact your veterinarian ahead of time.
A protozoon carried by dogs and transmitted to cows through the feces, then transferred on to fetus through the placenta. Also, the agent can be transmitted from the cow to the calf. Usually causes abortions at 4-6 months of pregnancy. This is a very common cause of abortion in dairy cattle, much less common in beef cattle. Restrict access of dogs (potential carriers) to stored feed and feeding areas. If the disease is diagnosed in an aborted calf and its dam is found to be
seropositive for the disease, considering culling the cow and any female offspring. Also, testing of the cows in the herd can be used in a test and cull program to help eliminate the agent from a closed herd. Consult with your veterinarian about the various options if this disease is a problem in your herd.
This trace mineral deficiency causes white muscle disease, weight loss, diarrhea, infertility, retained placenta and decreased immune function. When selenium deficiency causes abortions it is usually in the last trimester. The fetus develops white muscle disease before it is born and dies–thus the abortion. Prevention is best accomplished by use of the new selenium boluses that last for one year or feeding of a loose salt mineral mix containing 120 parts per million at one ounce per head per day. Consult your veterinarian if you are unsure if your herd is selenium deficient. He or she can do blood tests to determine the selenium
status of your herd.
John Maas, DVM, MS
UCD VET VIEWS
CALIFORNIA CATTLEMAN, SEPTEMBER 2001
More Information about Causes of Abortion
Bovine Trichomonosis: Essential Facts and Testing
What is bovine trichomonosis?
Bovine trichomonosis (a.k.a. trichomoniasis) is an important cause of economic loss in cattle operations that use natural service. Surveys in California beef cattle operations have shown that more than 15 percent of herds had at least one infected bull.
This disease is caused by a protozoan organism called Tritrichomonas foetus. This organism lives in the folds of the bull's penis and internal sheath. In cows this organism colonizes the vagina, cervix, uterus and oviducts.
How does it get transmitted?
Trichomonosis is a venereal disease of cattle. It is transmitted from cow to cow by a bull or, in rare cases, by contaminated semen or insemination equipment or nonhygienic artificial insemination (AI) procedures.
How does it affect cattle?
The most common signs in an infected herd are:
• Early abortion (too early to find an aborted fetus).
• Repeated breeding resulting in long breeding seasons.
• A wide range of gestational ages at pregnancy check.
• Pyometra (pus-filled uterus) in about five percent of cows.
• In first-time infected herds, it is common to end with a 50 to 70 percent calf crop strung out over three to eight months.
• Bulls show no clinical signs.
• Cows can commonly clear the infection within a few months, however, infection in bulls over 4 years of age is usually permanent and is the main source of transmission from one breeding season to another.
How can you test your herd for infection?
Testing for Tritrichomonas foetus is usually done on breeding bulls by performing a scraping of the penis and prepuce in order to obtain a preputial (internal sheath) fluid sample, and inoculating the sample into special culture media. If one bull is found positive, you should assume that the whole herd is exposed.
Studies of positive bulls have shown that this culture method will miss about 10 to 20 percent of infected bulls if the test is performed only once. So, if no infected bull is found on the basis of one culture of all the bulls in the herd, then we can be 80 to 90 percent sure that the herd is "clean."
How can you treat infected herds?
The disease is self-limiting in cows, as opposed to bulls, that will be permanently infected. After several heat cycles, most cows and heifers clear the infection, but this may take months.
There is a vaccine available for Tritrichomonas foetus (Trichguard or Trichguard Plus [Ft. Dodge]). The vaccine helps cows/heifers to clear the infection in a matter of weeks (vs. months in unvaccinated cows). In most cases, it does not prevent infection.
No vaccine efficacy has been shown in bulls.
There is no approved treatment for infected bulls.
How can you prevent the disease in your herd?
• Use young, fertile bulls or artificial insemination (AI).
• Culture new bulls at breeding soundness exam time.
• Keep a closed herd and test any animal that you buy.
How can you control the disease in your herd?
If one of your bulls is positive for trichomonosis, it is recommended to cull all bulls and vaccinate all females twice, one month apart. The best option to control trichomonosis is to use artificial insemination. If you want to keep your bulls, you can vaccinate all females annually, but it would be better to cull all bulls and open cows before next season.
An alternative, if you don't want to cull all bulls, is to sample them at least three times at weekly intervals. With three negative tests, we will be 99 percent confident that a bull is negative. Given the sensitivity of the culture diagnostic test, the table below will give you an idea of the confidence you should have in a "negative" bull, depending on how many times he is tested.
How sure can you be that your bulls are clean after a negative test result? The new “real-time” qPCR test is 99% sensitive, meaning that only one test is necessary to be certain a bull is clean.
Regulations regarding Trichomoniasis: (Effective October 5, 2007)
1. Positive Trichomonosis cases must be reported to CDFA within two days of diagnosis.
2. All Trichomonosis tests are official tests; animals require official identification and samples must be evaluated in approved laboratories.
3. Confirmation of positive test results by PCR may be requested – but is not required.
4. CDFA will investigate cases, notify owners of potentially exposed cattle, and quarantine bulls in affected and exposed herds.
5. Bulls from affected herds require three negative tests at least seven but not more than 28 days apart, to move anywhere except slaughter.
6. Bulls from exposed herds require one negative test before movement.
7. Bulls 18 months of age and older sold at public saleyards in California require a negative Trichomonosis test within 60 days before sale or be consigned as slaughter only.
8. Public auction yards must post a notice in a prominent place stating, “All bulls 18 months of age and older must have a negative trichomonosis test or be consigned as slaughter only.”
9. Bulls18 months of age and older entering California require a negative test within 60 days unless entering for slaughter, semen collection or exhibition (not commingling with other cattle).
10. Pasture-to-pasture bulls require a negative test within 12 months.
John Maas, DVM, MS