Dairy cattle fertility is
declining at a rate of 1% a
year in the UK.Reasons old
and new were debated at
the Nottingham Cattle
Marianne Curtis reports
WHAT is the biggest single cause of cattle abortion in the UK? If you answered BVD, lepto or brucellosis, think again. It is neosporosis: It causes 6000 abortions a year, leads to lower milk production and higher culling rates, and there is no vaccine.
Speaking at the Nottingham Cattle Fertility Conference, Carmarthen VLA vet, Arthur Otter, outlined the latest research on neosporosis. "Recent figures show that neosporosis is the most frequently recorded infectious abortion diagnosis in England, Wales and Scotland. It accounts for 12.5% of all abortions.
"Foetal loss can occur at any stage of pregnancy, including stillborn and mummified calves. Decreased milk production and premature culling also lead to significant economic losses," he added.
Although 6% of the UK herd is likely to be infected with neosporosis, most show no signs of the disease, according to Diana Williams, researcher at Liverpool vet school. But infected cattle are up to seven times more likely to abort than healthy cattle, said Dr Otter.
Because not all infected cattle abort, one of the most worrying aspects of the disease is that more than 95% of calves born to infected dams will be infected themselves and could go on to abort. This has implications for breeding herd replacements, he warned.
"Uninfected stock should be selected for future breeding. Where replacements are home-bred, this is best achieved by screening potential replacement heifers at less than a week old. They are easy to blood sample at this age and infected animals can quickly be identified," he said.
Checking bought-in heifers, however, is less easy. For unknown reasons, the blood test for neospora is unreliable for 12-14-month old heifers – the age when many are purchased.
"Where it is unclear whether bought-in heifers are infected, it is best to test their calf at calving." Positive calves indicate a positive dam and progeny should not be kept for breeding, he advised.
Furthermore, producers should consider culling infected animals, particularly in herds producing breeding stock. "Culling should reduce a herds current and future abortion rate by removing infected breeding stock."
But infected high genetic merit stock neednt necessarily be lost. Embryo transfer to uninfected cows should offer an opportunity to maintain high genetic potential in a herd, he told delegates.
Although the disease is most commonly transmitted from mother to calf before birth, dogs and aborted foetuses may pose a risk to uninfected animals.
Dogs can become infected with neosporosis, and may pass the disease to cattle. "We dont yet understand the role of dogs in transmitting the disease. But producers should take precautions by keeping cattle feed and water protected from dogs," he advised.
Hygiene at calving can also help minimise infection risk, said Dr Otter. "Maintain high hygiene standards at calving by efficiently disposing of placentae, aborted calves and dead calves."
Further research into the actual cost of the disease is on-going. Vaccine development is likely to be someway off because of the difficulty in developing vaccines for animals born with an infection, according to Dr Williams.
lResponsible for 12.5% of abortions.
lCull infected stock.
lTest replacements as calves.
• Responsible for 12.5% of abortions.
• Cull infected stock.
• Test replacements as calves.