HEIFER reproductive performance, a strong driver of profitability in cattle herds, may be compromised more often than producers realise by the hidden effects of pestivirus.
Pestivirus, or Bovine Viral Diarrhoea Virus (BVDV), is a common virus of cattle which can cause lost pregnancies, or poorly developed calves that go on to die or have a short life expectancy.
Managing for pestivirus is an important factor in getting the best results from maiden heifers, and for subsequently maximising genetic gain.
Negotiating the hidden aspects of the virus is the subject of a live webinar to be hosted by pestivirus vaccine manufacturer, Zoetis Australia, to be held on Friday, August 30, 2013, from 12pm – 1pm.
The reproductive losses from pestivirus around joining or insemination may not be noticed until pregnancy testing or even weaning.
“When producers invest heavily in top bulls, artificial insemination (AI) and the time and energy of a breeding program, it can be devastating not to get a full crop of calves from maiden heifers,” said Dr Neil Farmer of Comanche Grazing Co. near Rockhampton, one of the webinar hosts.
Another host, Dr Neil Charman from Zoetis, says this can even be the case when herds have been exposed to the virus, but individual animals fail to build immunity against the disease.
“While about 90 per cent of herds are estimated to have been exposed to this virus at some point in time, testing of individuals in a mob commonly shows mixed levels of immunity," Dr Charman said.
"This means that a proportion of the herd is at risk to the effects of pestivirus."
In some cases, there may no obvious signs of the virus, meaning that some producers dismiss it as a non-issue.
“Take the example of a producer implementing an AI program. If a heifer gets infected around the time of AI, she may fail to conceive to the top AI bull she’s been inseminated with. Instead, she comes back to cycle some time down the track, and may get joined to the mop-up herd bull instead."
"It’s a lost opportunity in terms of genetic gain and early calving."
Another myth is that pestivirus can always be controlled by running cows with heifers. Dr Charman believes this is a flawed.
“There are a lot of pitfalls in establishing immunity in unexposed animals by running an infected animal with them. You need to know that the virus is being shed and circulating in the mob, and you need to check that animals have developed an immune response after exposure, both of which require testing.”
“Heifers may fail to get enough exposure and protection, and are still at risk of the disease. When you weigh up the cost of these tests, and the risk of failure to protect, it’s usually easier to just vaccinate.”
Zoetis's Pestigard vaccine, developed in Australia specifically for Australian circumstances, can be integrated with other management practices and involves two doses prior to joining. The first shot can be administered between six months and six weeks before joining and then again two to four weeks before joining.
“A six month window in which to vaccinate prior to joining offers producers flexibility to fit around their own marking and weaning schedule," said Dr Lee Taylor from Zoetis.
"A single annual booster shot each year after that will maintain protection. Ideally you’d vaccinate the whole herd, but the maiden heifers in a herd are a must-do. They are the most valuable part of the herd, and the most heartbreaking not to be able to get a calf from.”
The Zoetis "Get a handle on pestivirus" webinar will feature Dr Neil Charman (Zoetis Australia), Dr Neil Farmer (Comanche Grazing Company), Dr Lee Taylor (Zoetis Australia), Alistair Smith (Charles Sturt University) and Professor Mike McGowan (University of Queensland).
