60 Second Summary: When IBR is the missing piece in a repro puzzle

A North Island dairy practice, The Dairy Vet near Feilding, had a small group of high-performing herds where everything was tracking well — feeding, milking, non-cyclers, metabolic health — except reproduction. Conception and 6-week in-calf rates wouldn't budge.

After ruling out other causes, they screened for IBR and found an anomaly: well-performing herds sat at 65–70% IBR antibody positivity, but the problem herds were 90–100%. The team's theory was that the stress of calving and early lactation was reactivating latent IBR in these herds.

They trialled blanket Hiprabovis 3 vaccination at dry-off (May–June), aiming for peak antibody levels around calving. Results across the trial herds: empty rates improved by an average of 4%, and 6-week in-calf rates by 6–7%. Rolled out more widely, herds with persistent empty rates around 20% have dropped to 10–12%, and 97% of clients have stuck with the programme.

Dr Chris Chase (South Dakota State University) supports the mechanism: progesterone surges around calving and ovulation can reactivate latent IBR, with the virus showing a particular affinity for reproductive tissue — attacking follicles and the CL, and delaying conception. A killed vaccine like Hiprabovis 3 raises circulating antibodies to neutralise the virus before it causes reproductive damage.

The Takeaway: IBR isn't just a respiratory issue on first exposure. Reactivation in latently infected cows is an insidious second phase, and one worth investigating when repro performance can't otherwise be explained.

Poor dairy reproduction is not just bad for business. It can seriously mess with your clients' self-esteem, especially when on the face of it, they're doing everything 'right'.

So when a potential solution presents itself, even if it's right out of left field, is it not worth at least testing it, for the good of your farmers as well as their cows?

Back in 2016, one North Island dairy practice did just that.

The outcome has been so significant 97 per cent of clients have stuck with the programme.

Empty rates are down, six week in calf rates are up, and farmers feel much better about themselves and their business.

It started with high performing herds whose metrics under long-standing vet and farmer collaboration were all getting better every year, except for one thing – repro.

"The cows were well fed and milking well; the number of non-cyclers was dropping year on year, there were fewer metabolic issues every season, the whole system on these farms was consistently functioning better," says Fraser Abernathy.

"These were some of our top farmers, whom we'd been working with for years. But every year, conception and six week in calf rates were very poor. We couldn't shift them, and we couldn't explain it."

Abernathy's practice The Dairy Vet is based near Feilding and prioritises whole-farm system work with its clients.

The repro problem only affected some of their herds, not all of them, and one common factor that stood out for those with poor conception was early embryonic loss.

Having ruled out virtually everything else, the vets screened for IBR, and found an anomaly.

"In our herds with good repro, 65-70 per cent of cows would test positive to IBR antibodies, but in these herds with unexplained problems, the incidence was 90-100 per cent."

Accepted wisdom is that the strain of IBR found in New Zealand (BoHV-1.2b) does not impact cow reproduction to the same extent that the overseas strain (BoHV-1.1) affects herds in other countries.

Also, if the cows were full of antibodies, what would be the point of vaccinating for IBR in this particular context?

But what if the stress of calving and early lactation was causing the disease to flare up in these herds?

There was no real way of conducting a treatment trial, because so many of the animals had been exposed to IBR.

So The Dairy Vet team tried something new with just a handful of herds – blanket Hiprabovis3 treatment at dry off in May and June, with the aim being to achieve peak cow antibody levels around calving.

Average empty rates for the following mating improved by 4 per cent, and average 6WIC rates by 6-7 per cent.

That was enough to convert the farmers who took 'a leap of faith' at the start, and prompt the vets to deploy full Hiprabovis-3 vaccination at dry off, with annual boosters, across herds with an unexplained repro problem.

Empty rates that were consistently around 20 per cent are now down to 10-12 per cent.

"Sometimes we don't get as big a response as we expect. But continued treatment seems to consistently get the empty rate tracking down and the 6WIC rate tracking up. If conditions in spring are good, the IBR doesn't flare up as much, but generally it does."

The biggest expense is in year one, when two shots are required for every cow. After that, with just an annual booster, there's little pushback from clients about the cost.

"We've had one or two stop vaccinating, but most have continued, because they can see the value."

And it's not just better for their cows.

"We know clients who were beginning to doubt themselves, who thought they might be crap farmers because they just couldn't get their cows in calf. One of those in particular has more than halved their empty rate with vaccination, and they feel a lot happier as a result."