Leptospirosis could affect dairy growth
The effect of leptospirosis on production is being researched at Massey University.
The results of deer studies show a correlation between vaccination and growth rates and weaning percentages; data from a sheep and beef cattle study is being analysed and a funding application is underway to do more research into the effects on dairy cows, says Professor Peter Wilson.
Wilson is one of an internationally-recognised team at the University's Institute of Veterinary, Animal and Biomedical Sciences alongside doctors Julie Collins-Emerson and Jackie Benschop and Professor Cord Heuer.
One point to know with leptospirosis is the difference between animals having the leptospirosis organism (being infected) and being sick. The infection is everywhere but the disease is not, Wilson says. Almost all sheep and beef farms and 85 per cent of deer farms have some level of leptospirosis infection.
There have been studies into infection effects on growth rates and reproduction, but he says some losses are clinical.
"But we don't have a good understanding of deaths or sickness because it's not investigated. It's not widely known as a cause of mortality. A death is usually put down to other causes or through misdiagnosis so leptospirosis is probably more common than we think."
Wilson says production and reproduction effects on dairy farms is a "current unknown".
"There has been widespread vaccination on most dairy farms since the late 70s, early 80s. Production impacts for abortion, mastitis and deaths of young calves has no doubt been considerably reduced due to the vaccine. We suspect because the vaccine is so widespread, it has created a belief leptospirosis is no longer an issue in the dairy industry. We believe it does remain a potential threat in herds with sub-optimum vaccination programmes. "
Screening of urine of adult cows has shown evidence of lepto shedding in 30 per cent of herds (44 herds were screened).
"It's not that the vaccine is not working. In sheep and deer, the vaccine was highly effective when animals were vaccinated before they were infected, as it likely is in cattle. Once infected, the vaccine reduced the number shedding by about 40 per cent. If dairy herds are first vaccinated at six months, there is six times more likely to be leptospirosis in the herd than if calves were vaccinated under three months of age."
An application for funding for a new dairy-based study has been made to the Sustainable Farming Fund and Agmardt, similar to the sheep and beef cattle study that has just been completed.
Two studies have focused on growth rates in deer. The first found a 3.4kg difference (live weight) at 12 months between deer that had been infected during growth and deer that hadn't. This equated to a 2kg carcass weight difference or a $16 difference in value (according to the venison schedule at the time). A second study was set up on another five farms to see if the findings could be replicated.
"On average, the vaccinated animals in herds that had significant infection rates were 6.4kg heavier at 12 months than non-vaccinated. That's 4kg of venison or a $32 difference in the value of the carcass. So again, this defied conventional beliefs about lepto. Not every animal is infected or harbours an infection. But where conditions meant a high level of infection in a herd, there was a profound difference in growth rates."
Two older studies on the effects of leptospirosis on deer reproductive performance showed the weaning rate in vaccinated hinds was higher than in non- vaccinated hinds. He says the results showed "the higher the prevalence of infection, the greater the effects".
In a three-year study into sheep and beef cattle, currently being analysed, Wilson says "preliminary findings show evidence in some beef herds of lower reproductive performance and evidence in sheep flocks of lower growth rates if infection occurred at a young age. But the results don't seem likely to show the same level of production effects overall as the studies showed with deer. This suggests infection behaves differently in different animals."