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Perry encourages caution when using modified live vaccines in breeding cattle

by Wyoming Livestock Roundup

Breeding cattle can experience embryonic losses and low conception rates early in the breeding season if modified live vaccinations are used prior to breeding. 

George Perry of South Dakota State University tells producers, “Don’t use a modified live vaccine around breeding season. I don’t think there is anyone out there who would disagree with that given the known negatives.”

Perry shares several studies showing how cattle receiving the vaccine can have lower conception rates, particularly during the beginning of the breeding season when producers are artificially inseminating them. 

“We think the vaccine gets into the large dominant follicle and disrupts the corpus luteum,” he explains. “We also think it can hang around for an extended period of time, affecting the smaller follicles.”

Disease challenges

Which vaccines to give breeding cattle is one of the most important decisions a producer can make. 

“The fertility level of the herd is critical,” Perry says. “One of the biggest things that can impact reproductive efficiency, and the fertility level of the herd is affected by reproductive diseases.”

Producers worry about diseases like Infectious Bovine Rhinotracheitis (IBR), Bovine Viral Diarrhea (BVD), trichomoniasis, leptospirosis, vibriosis and neosporosis. 

“They worry about  fetal infection and pregnancy loss. But, IBR and BVD can also impact ovarian dysfunction and the estrus dysfunction cycle. It impacts the fetus and the ability of the cow to conceive,” he explains. “BVD is a family of viruses with reproductive symptoms that are very wide, depending upon when they are exposed to it.” 

“We worry about BVD for many reasons. It can cause early embryonic death, low conception rates, persistently infected calves, calves with birth defects and congenitally infected calves,” he adds.

IBR is actually a herpes virus that can be latent in the body for years, Perry says. 

“Studies show it can be brought back from latency with enough stress. As producers, we need to think about these things and how it impacts reproduction. IBR causes symptoms like late-term abortions and problems like respiratory, ocular and vaginitis,” he notes.

Vaccine options

Producers control these diseases by vaccinating their breeding cattle with inactivated or modified live vaccines. 

Typically, the vaccinations are combinations of IBR and BVD with vibrio and leptospirosis. By label instructions, they are typically given at least 30 days before the start of the breeding season. 

“The modified live vaccine has better cell mediated immunity, so it needs a booster less often. However, there are safety concerns with handling it,” he says. 

Killed or inactivated vaccines are safer for producers to give and work by impacting the antibody mediated immunity. It can be used in pregnant and open animals and calves without any problems, Perry relates. 

However, it needs more frequent boosters.


In a study released in 2017, heifers were given either a modified live or saline vaccination at weaning. They received a booster prior to breeding. 

Of the group vaccinated with the modified live, half received another modified live vaccination prior to breeding and the other half was vaccinated with the inactivated vaccine. The third group that received saline at weaning received a saline booster before breeding.

After breeding as two-year-olds, they were exposed to BVD and IBR. The scientists wanted to see if the vaccines would hold up and protect the fetus from being aborted, Perry explains. 

In the group of heifers that received two rounds of modified live vaccine, three of 23 aborted. In 17 percent of the calves, they were able to isolate the IBR or BVD virus.

Of the heifers that were vaccinated with the modified live at weaning but switched to a chemically altered inactivated vaccine, one out of 22 aborted, and they couldn’t isolate the IBR or BVD virus in any of them, Perry shares.

In the control group that received saline, 100 percent had either disease or both. 

“Over 70 percent aborted,” Perry explains. “That study showed us the inactive and modified vaccines performed similarly, with less than 10 percent aborting.” 

“So is there a benefit to modified vaccines for fetal protection? The idea of timing is important when we think about what could be affecting follicular growth and luteal function,” he says. 

Take home point

“I think modified live vaccinations have their place,” Perry continues. “It sets animals up and primes their immune system, but when we move to the reproduction phase, it can have adverse effects. All the studies show mounting evidence of this.”

“Preconditioning these animals is critical. They need that first exposure, so we recommend a modified live vaccine at weaning and then switching to an inactivated vaccine at breeding. That way it primes both sides of the immune system,” Perry states. 

“Then an annual booster of the inactive vaccine will provide the cattle with good immunity, if they are set up right,” he adds.

As a final word of caution, Perry tells producers they should consult with their veterinarian before changing their vaccination protocol. 

“Everyone’s circumstances are different. Some may not have the same virus load as others depending on how isolated or commingled the cattle are,” he notes.

Gayle Smith is a correspondent for the Wyoming Livestock Roundup. Send comments on this article to

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