This article was originally published in the December 2015 issue of Drovers Cow/Calf.
If your goal is to produce more calves from a bigger cow herd, accidental introduction of reproductive diseases could defeat the purpose.
If you are one of many producers expanding your cow herd, especially if you import females from other sources, you can benefit by working with your veterinarian to build a strong disease-prevention program — including vaccinations, biosecurity and diagnostic testing.
Doug Ensley, a professional services veterinarian with Boehringer Ingelheim Vetmedica, Inc., says his territory ranges from Florida to the High Plains, so he sees a variety of disease challenges and management systems in different production environments. He says when cow-calf producers rebuild their herds, in many cases with purchased females, they run an inherent risk of introducing reproductive diseases such as trichomoniasis (trich), bovine viral diarrhea (BVD), leptospirosis or infectious bovine rhinotracheitis (IBR).
Open cows probably represent the highest risk for disease, particularly trich, but Ensley stresses that bred females also can introduce disease into herds. Most heifer-development operations incorporate good vaccination, testing and biosecurity practices, but he says veterinarians still should work with clients to minimize risk in importing females from any source.
BVD — Hold and test for PI
At the University of Nebraska’s Great Plains Veterinary Educational Center, veterinarian Jeff Ondrak says producers generally seem to be more aware of BVD and the role of persistently infected (PI) animals in spreading the disease. And while PI animals are uncommon, potential reproductive losses associated with a single carrier can be huge, with calving rates sometimes reduced by 50 percent or more.
Ondrak stresses the need for isolating new animals in a cow-calf operation, testing for BVD and vaccinating against the virus. He says isolation for imported females is one of the simplest but still underused strategies for preventing disease. South Dakota State University veterinarian Russ Daly agrees and adds that producers who purchase bred females should isolate them until they can test the calf. A female exposed to BVD during the critical time of gestation can clear the infection herself, producing a negative test, and yet be carrying a PI fetus. Just testing the dam could provide a false sense of security, he says, adding that BVD ear-notch tests are relatively easy and low-cost insurance against severe reproductive losses.
Trich-test bulls and take care with cows
Ondrak says females become infected by Trichomoniasis foetus by mating with an infected bull. Testing non-virgin bulls is the primary step in preventing introduction of trich to herds, but females also can carry the parasite. The clinical signs of infection in females are mild or unapparent and related to the stage of the infection, Ondrak says.
Initially the infection causes a vaginitis and endometritis which leads to a mild vaginal discharge. This discharge is typically mild enough that it is unlikely to be noticed by producers. The major outcome of infection is reproductive failure, with the parasite damaging the developing embryo, which typically dies and is expelled or reabsorbed at 50 to 80 days of gestation. Then the immune system clears the infection from the reproductive tract. Once the embryo has been eliminated the female will return to estrus.
Occasionally, though, females can retain the trich infection longer than usual, potentially infecting bulls at breeding time and leading to the disease spreading through the herd. Ondrak says estimates of reduced pregnancy rates for infected herds range from 20 to 40 percent, depending on the prevalence of infected bulls in the herd.
Daly notes that in 2005 in South Dakota, after some major trich outbreaks in the state, industry groups and livestock markets supported a moratorium on selling open females for breeding purposes. Since then, outbreaks declined significantly with just a few cases diagnosed in the past three years. Daly credits a comprehensive approach, with education, producer awareness and more bull testing for much of the decline, but he believes the moratorium also has contributed. This suggests producers in other states can benefit from avoiding introducing open females to their herds or taking strong precautions if they do import open females.
Testing for trich in females, especially weeks or months after exposure, is unreliable. Ensley says a common recommendation is to avoid purchasing bred females that are less than four months into gestation. In operations that purchase high-risk females without following those recommendations, it may be beneficial to vaccinate their cow herd with a trich vaccine to reduce the impact of the disease in their herd.
IBR — Vaccinate according to labels
IBR is best known as a virus associated with bovine respiratory disease, but it also causes abortions in cows. Daly says late-term abortions associated with IBR are not uncommon. The virus’ role in early embryonic loss is suspected but less known.
Vaccination can provide good protection against IBR in the cow herd, if producers follow appropriate protocols. Veterinarians can help clients determine the appropriate vaccines to use based on timing and animal history. Modified live vaccines (MLV), he says, are a great tool for stimulating both antibody-mediated and longer-term cell-mediated immunity. MLV products will generally produce broader immune response than killed vaccines.
However, Daly says MLV vaccines can have negative effects if given to naïve animals either at pre-breeding or during gestation. In females that have not received a previous IBR vaccine, using a MLV product too close to breeding can interfere with cycling, Daly says. Also, MLV vaccines should not be given to pregnant females unless they were previously vaccinated strictly according to label directions with the same MLV product. First exposure to the MLV product during pregnancy increases the risk of abortions.
Producers should, whenever possible, determine the history or likely vaccination status of any imported females, Daly says, and work with their veterinarians to design safe and effective vaccination protocols. If you import females without verifiable vaccination history, it is best to either use a MLV product only in open females well ahead of breeding or to use killed vaccines at pre-breeding or during pregnancy.
Vaccinate for leptospirosis
Ensley says cases of leptospirosis in cow herds tend to be sporadic, but the disease can lead to abortion rates of up to 30 percent when it occurs during the final third of pregnancy, and can contribute to the birth of weak calves.
In its acute form, signs of the bacterial disease can include toxic blood infections causing high fever, anemia, jaundice, labored breathing, mastitis, reduced milk flow, secretion of yellow, thickened, blood-contaminated milk, and abortion, according to information from Iowa State University. In its subacute form, there can be no clinical signs other than abortion and infertility.
The disease is spread by wildlife, with feral hogs a primary vector. Ensley says runoff from heavy rains this fall could increase risk of leptospirosis by concentrating the causative organisms, called leptospires, in ponds or other water sources. Vaccination is a key step in preventing the disease, and Ensley says two doses of vaccine per year can be appropriate in areas with high risk based on wildlife populations.
Across the spectrum of reproductive diseases that could affect cow-calf herds, Daly stresses the importance of obtaining a diagnosis whenever possible. Ranchers should work with their veterinarians to collect tissue samples from aborted or stillborn calves, submit them for diagnosis and work together to develop management strategies based on diagnostic tests. Do not treat an aborted fetus as normal or acceptable, but as a red flag and an opportunity to possibly prevent future losses.