Waikato dairy farmer Verena Beckett knows how frustrating it can be when big, strong, healthy-looking replacement heifers fail to fire.
She runs a herd of 400 herd on her father's 160ha property at Rotongaro, west of Huntly, but it was on her own adjacent 165ha farm, also running 400 Friesians, where the trouble was brewing.
Her replacements are raised as part of a grazing scheme run by Franklin Vets (Te Kauwhata) on a separate sheep and beef property north-east of Te Kauwhata.
According to veterinary technician Jess Kingsland, they were "monster" heifers in great condition, but the naturally-mated animals were experiencing empty rates of 8 to 10 per cent, and calving was very spread out.
Ms Kingsland said blood tests carried out several years ago under a MSD Animal Health heifer screening programme had revealed exposure of stock to bovine viral diarrhoea virus (BVDv), so the disease was in the frame as a possible culprit for the less-than-stellar reproductive performance in the heifers.
Bulk milk tests for BVD were not showing anything significant, but the disease was a "sneaky" one, so couldn't be ruled out, she said.
Bulls were a well-known pathway for BVD infection, but those used for Ms Beckett's heifers were all tested and vaccinated. And no persistently infected (PI) animals were found among the heifers, so any transient infection with BVD may have come from "over the fence" contact with PI animals, or contact with other mobs on the property.
The property was also a working sheep and beef farm, and beef cattle were traded regularly, providing plenty of opportunity for the disease to find its way to the heifers, but it was not possible to prevent contact with other cattle.
On the advice of her veterinarian, Ms Beckett began an annual vaccination programme with Bovilis BVD, and noticed an immediate improvement.
"This year we had 80 per cent of our heifers calved within the first three weeks, and by the end of August only four were left to calve. The empty rate is also much lower now," she said.
The calves, once at least four months of age, received their initial sensitiser and booster shots four weeks apart before they went off to grazing.
As adults they received an annual booster, four weeks before mating. The entire herd was now vaccinated.
"There's definitely a cost involved, but it's hard to put a price on getting all your heifers in calf and calving early," she said, adding that she was now signed up to LIC's BVD testing scheme as part of an ongoing monitoring programme to shut the door on the disease.