The routines in spring calving, typically done in rigorous winter weather, always create a physical demand on producers through late nights and pulling calves. But it’s during the post-calving stage that tougher mental exercise comes into play, specifically with vaccines.
Among the most important exercises: How should I be using modified live vaccines (MLVs) for cows and calves?
Dr. Lee Jones, DVM, and associate professor at University of Georgia College of Veterinary Medicine, told participants in last summer’s NCBA Cattleman’s College that the answers are never easy, and they depend on several factors that include logistics, vaccine labels, specific diseases and the maternal stage of the female. Overall, the goal is to protect not just one cow but all of them.
“What we’re really trying to do is protect cow herd fertility, both the individual as well as the herd,” Jones said. “So if an individual doesn’t respond to that vaccine, if her herdmates have responded to a vaccine, that’s a barrier around her to protect her from exposure that might break through my biosecurity program. It also is going to enhance colostrum quality, and that improves the passive immunity among calves.”
Calf vaccination – with the proper vaccine – increases herd resistance to calfhood diseases for marketed calves and those females you may wish to retain.
“The vaccine selection and timing in my cow herd really determines the vaccine options in my calves. If you go by the label, you know, there’s certain limitations, and I have to follow the label to include certain types of vaccines within our herd program.”
Fighting fertility culprits
Jones said that bovine viral diarrhea (BVD) and bovine herpes virus (BHV-1 or also IBR) are the key targets in a cow and calf vaccine program in the enhancement of fertility. Those pathogens wreak havoc on a herd in all stages of reproduction.
“BVD causes infertility, conception failure, abortion, a persistent infected [PI] calves. If that exposure occurs, you know, before like 4 to 4-and-a-half months [old] when the fetus develops its own immune system, then that calf is born with BVD and it becomes a source or a reservoir of BVD in the herd.”
Calves can be born with cerebral hypoplasia, congenital infection and defects, or blindness if infected, and BHV will also cause infertility and abortions in the last trimester.
Vaccine differences
Vaccines come in either a killed version or a modified live. The killed vaccine contains an inactivated virus that doesn’t replicate in an animal. That requires a proper dose, since all antigen exists in the syringe.
Killed vaccines also have an adjuvant to enhance immunity, and that requires a primary shot and booster dose. Many producers, Jones said, fail to follow up on that booster, meaning the cattle aren’t fully vaccinated for full immunity.
MLV is a live variant that replicates antigens in the animal. “It mimics a mild infection,” Jones said. “I can give a small amount of antigen [to] stimulate the immunity.”
That requires careful handling of the MLV so it isn’t deactivated.
Jones said MLVs “also stimulate a quicker, longer and stronger immunity than the killed virus and in one dose.”
Response in animals
But while killed vaccines require a second dose, the same can be said for MLVs in some animals. Producers commonly think a vaccine builds immunity in every animal with 100% efficacy every time. But not all animals respond equally.
Following label directions is one practice that can cover much of the herd. Another is the vaccine itself. Proper storage, transportation, handling and administration of the drug is critical. The animals also bring an array of differences in their health, whether they’re previously diseased, parasitized, stressed or malnourished.
Finally, people handling the vaccine – and the livestock – can reduce immune response in the animals by how they follow procedures and label instructions.
Fertility effects
This leads to the definition of “naïve cattle,” which Jones describes as cattle “who have not been vaccinated, exposed or who didn’t respond to the vaccine.” Jones explained that while an animal could be exposed to one pathogen like BVD, it could still be naïve to another like IBR unless vaccinated for it. When those females are naïve and haven’t developed immunity, the pathogens for IBR and BVD attack fertility. Jones outlined several studies showing how the use of modified live BHV-1 vaccines in naïve cows and heifers may lead to:
- Ovarian and luteal necrosis and inflammation
- Lower progesterone levels and luteal function
- Reduced conception
- Abnormal estrous cycles
- Abortion in late-trimester cows
- Reduced conception rate to A.I. in previously vaccinated cows
But Jones reaffirmed that MLVs are effective in controlling pathogens of BVD and IBR when they are administered properly. “If used incorrectly and farmers don’t quite understand or veterinarians made recommendations, then it actually can cause problems because vaccines are not totally benign.”
Abortion of calves
No question stirs more anxiety with the use of killed versus MLVs quite like the risk that some MLVs pose in heifers and cows. Through much of the ’90s and 2000s, reports showed greater efficacy of MLVs in cows; nursing calves, however, mostly avoided receiving MLVs, Jones recalled. Then an approval for the first MLV for use in pregnant cows was gained in 2003.
But studies cited by Jones that were done in the following years clearly identified higher risks and how to balance various forms of vaccines. Most important among them, Jones said, were those showing that a killed vaccine-only program isn’t protective enough against BVD.
The most promising study results – from Dr. Walls of Auburn University – to affirm MLV efficacy posed high challenges with PI calves to calves given killed vaccines. Recognizing the poor level of protection from BVD-PI in those cattle, Walls began using MLVs to start 5- to 7-month-old heifers, then did another MLV six months after that.
The heifers calved and were revaccinated in two groups: one receiving a combination killed vaccine, and another for the same MLV given previously. After the second year of calving, the same treatment occurred for rebreeding.
It was then the study identified that in the MLV-treated herd, three abortions occurred among 22 cows, and one PI calf was born. For the killed vaccine group, one calf aborted, but it was not positive for BVD nor IBR. The control group at that stage didn’t have a single normal calf born, Jones said.
Walls’ study showed a stronger immunity when heifers were given an MLV initially, given time to build immunity before conception and received two more killed vaccine treatments for the next two calves. “You can see that this practice of building immunity on the modified live and then switching over when cattle are pregnant to a killed was a really good herd health measure and provided a lot of protection against severe exposure.”
Summary takeaways
Jones continually reminds producers that MLV build a stronger, quicker and longer immunity with some cross-protection to other strains. But the most effective strategy for heifers, cows and calves requires a balancing act with both types of vaccines.
Logistically, the biggest hurdle in rebreeding is that MLVs may cause transient reduction in fertility early in the breeding season, even if vaccines are given with strict adherence to label directions (30 days prior to breeding).
“It may be more prudent to consider the use of a killed virus vaccine instead in lactating cows.”
Studies show the highest protection uses a combination MLV and killed vaccine in preventative schedules.
The MLVs can still be considered for herd health protection in calves and replacement heifers. But Jones added that vaccinating calves with an MLV when they’re nursing from pregnant cows that haven’t been vaccinated in the past 12 months is extra-label.
The best approach, Jones said: Get three doses of MLVs in replacement heifers at pre-breeding, with the last one given at least 30 days prior to breeding.
Then utilize killed vaccines in pregnant or nursing cows previously vaccinated with an MLV.
“The safety of modified live, quite frankly, is up to you and your veterinarian. I seriously recommend and suggest that you use the modified-live in your herd because it provides optimum protection. But again, a really, really good tool does have potential side effects.”
