Improved Herd Fertility is in the Details

BY LAURA HANDKE

For George Perry, associate research professor – beef cattle reproductive physiology, Texas A&M AgriLife Research and Extension, the equation of reproduction is the measure of a herd’s overall fertility.

In a recent Beef Reproductive Task Force webinar, Perry and Ph.D. student, Kaitlin Epperson, discussed the importance of heifer vaccinations in relation to the administration of modified live virus (MLV) vaccines. The team looked at the fertility of naïve heifers when given MLV, killed vaccine, or saline (control) in relation to estrous and conception.

To begin the webinar, Perry shared with producers that there are four main things that can impact reproductive efficiency:

1. Animals detected and inseminated

2. Inseminator efficiency, regardless of whether insemination occurs via AI or natural service

3. Fertility of the herd

4. Semen fertility level

And noted that when we think about things that can impact herd fertility, it’s important that we consider every aspect, “I tell people all the time to get the highest level of reproductive efficiency, ‘it’s in the details,’” he says.

And those details include timing: not just if we’re giving the vaccinations heifers and cows need to be healthy and prolific, but when we are giving those vaccinations.

Perry says that two reproductive viruses that standout are Bovine Viral Diarrhea (BVD) and Infectious Bovine Rhinotracheitis (IBR).

“Both BVD and IBR are viruses that we focus on and vaccinate for because they can actually impact both fetal infection and pregnancy losses, and both of these viruses can impact the ovary directly to cause estrous cycle disruption to impact the success of breeding season,” he says.

Citing work done in the 1970’s on heifers that had been previously exposed to either MLV or a killed virus vaccine at weaning, Perry and Epperson wanted to investigate what happens when a vaccination is given at the start of a synchronization program or natural service breeding season into naïve, or never vaccinated, animals – work that had not previously been done.

The team started with naïve heifers because many times the vaccination history of a group of purchased heifers is unknown.

When the Modified Live Virus (MLV) was given, even after a follow-up estrous, 40% of the animals were observed to have had abnormal estrous cycles. When the inactivated [killed] vaccine, was given, there were still between 10 to 15% of heifers that had abnormal cycles. Eye opening was the group of heifers that just received saline of which there were no abnormal cycles detected.

The research, conducted in 2020, has led Perry to caution producers, “We really want to avoid using a MLV near the start of breeding season,” he says, noting that a true naïve animal is one that has never been exposed to that antigen.

“I can tell you about many examples where I’ve been called in to help troubleshoot problems where the producer bought a group of heifers that were supposedly vaccinated, so they gave them the same vaccine and then saw problems because something wasn’t actually given or a different vaccine was used,” he says. “What I tell people is that unless you know it was administered, consider those animals naïve to avoid problems.”

Epperson says that there are many differences occurring today in terms of pregnancy rates when modified live or killed vaccines are administered close to the breeding season.

“What we’re realizing is that after viral infection, either from the natural virus, itself or the virus contained within the vaccine, there’s several things that can happen in terms of the functional and cellular changes on the ovary, including inflammation or cellular degeneration, invasion of plasma cells, which secrete antibody, or even infection of the egg,” she says, and adds, “What our research is telling us right now is that modified live vaccination does negatively influence the development of the corpus luteum and also its function and ability to produce progesterone which, in turn, can have implications on [a producer’s] breeding season in terms of pregnancy rates.”

The take-aways, Perry concludes, are that producers need to be vaccinating before or at weaning to get heifers set-up correctly. Both heifers and cows should be vaccinated at least 45 days before the start of the breeding season, and if they have never been vaccinated before, avoid a modified live near the time of breeding. It’s important to get vaccines administered on a timeline that allows a cow or heifer’s ovaries to heal prior to breeding season – a protocol that Perry says increases fertility.

Editor’s note: Visit the Beef Reproductive Task Force website to learn more about this study and watch the educational webinar, along with others, in its entirety. With a mission to optimize the productivity and improve the profitability of cow-calf operations by facilitating the adoption of cost-effective, applied reproductive technologies, the Beef Reproduction Leadership team is dedicated to educating producers on sustainable reproductive management. The education provided is truly a resource for any size herd. www.beefrepro.org