Image caption There are about 20 million deer in the US today

US scientists say they have developed a contraceptive vaccine for deer that reduces fertility and eliminates aggressive mating behaviours.

They claim that in captive animals a single shot of the vaccine can be effective for up to five years.

The aggressive mating causes an estimated $1bn (£600m) in damage to property each year and an upsurge in collisions with cars.

But it is unclear whether the vaccine will be a cost-effective solution.

The burgeoning populations of white-tails are a testament to successful human intervention to protect them from unregulated hunting.

From around half a million in the early 1900s, the animals have prospered to the extent that there are about 20 million of them in the US today.

Across many parts of the country, their seasonal mating presents a serious threat to both the environment and human populations, with males chasing females across busy highways.

Ballooning populations

It is not just legal protection that has helped the deer thrive.

Natural predators such as mountain lions and wolves have declined, and humans have inadvertently created the types of landscape in many eastern states that provide excellent forage for the animals.

I think the ideal is to control the deer population with the least negative impact as possible Dr David Goldade, USDA

Over the years, state officials have tried to limit deer populations by the controversial means of organised culling. But these have proved neither popular nor particularly effective.

Birth control has also been tried before - but those trials did little to reduce the associated aggression.

Now, a vaccine called GonaCon, developed over the past 20 years by the US Department of Agriculture (USDA), claims to be effective against both fertility and disruptive behaviour.

It works by inducing the production of antibodies to the sex drive hormones in both males and females.

Dr David Goldade is a supervisory chemist at the National Wildlife Research Centre, a part of the USDA. He says that after the shot, the vaccinated deer do not even try to mate.

"It removes the oestrous cycles from the females and the males have no interest in females that are not in oestrous, so they don't pursue them."

Public attitudes

But critics say the deer still have to be caught and injected with the compound, which is estimated to cost up to $1,000 (£600) per animal.

And there are also worries about how effective the treatment really is.

Even though a single shot was shown to last up to five years on captive animals, there are concerns that a year after the deployment of the vaccine in wild deer, its effectiveness was reduced to around 50%.

David Goldade agrees that the vaccine has limits.

"It's not a single solution to the problem; it's a tool to use," he says. "This alone can't bring a population down in a reasonable amount of time; it can manage the population that's there."

The jab is also said to work with a range of other animals such as California ground squirrels and wild horses. It also shows promise with household pets such as cats, reducing both their fertility and their inclination to fight and wander off.

So far, only the States of Maryland and New Jersey have licensed the vaccine for deer. Both have major problems with them in urban areas.

But with the population of white-tails ballooning around the rest of the country, many other states will be watching to see if the vaccine approach proves more effective than shooting.

And despite the limitations of the vaccine, it does have one major advantage: it is seen as humane.

"I think the ideal is to control the deer population with the least negative impact as possible, to be sensitive to public perception of the control of the population and to do things that are more publicly acceptable," said David Goldlade.

Details of the new vaccine were presented at a meeting of the American Chemical Society in Denver, Colorado.