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Biological Warfare Against Rabbits

Commonly found pasture species may play a key role in controlling rabbits in the future, providing compounds that could interfere with rabbit breeding. That's what AgResearch Invermay scientists are hoping, as they start on a new research programme with this in mind.

Ironically, New Zealand pasture scientists have been trying to get rid of such compounds for years. For instance, ewes grazing some strains of subterranean clover and red clover become infertile, and many years ago Australian scientists found these plants contained high concentrations of plant oestrogens. Considerable effort has since been put into breeding plant species for farms that do not contain oestrogenic compounds.

However it has also been demonstrated that some compounds which have no effect on ruminants such as sheep, cattle, goats and deer, have potential effects on non-ruminant species. Dr Bernie McLeod plans to screen a wide range of plant compounds for potential toxic effects on rabbit reproduction.

He has taken an interesting approach to his trial. Rather than feeding plants to the animals, he is using laboratory culture systems to test the compounds directly. Tissue from the rabbits' reproductive tract is grown under carefully controlled conditions, so the effects that compounds have on the function and survival of tissue is easily monitored. This provides a cheap way of screening large numbers of compounds quickly.

Once compounds that disrupt reproductive function under these laboratory conditions have been identified, their effects will be studied in live animals. This will be followed by research into the best way of incorporating these compounds into the ecology, and the effect of this pasture on the environment. Obviously, this is long-term research, but McLeod believes there are major advantages in this line of rabbit control research.

"The reason why it is so difficult to control rabbits is their very high reproductive rate. This means that even after a successful poison operation, with a kill of over 95% of adult rabbits, the population soon recovers. To keep rabbit numbers down, we need to suppress reproduction," he says.

"An advantage of the approach we are taking is that it doesn't involve the introduction of bugs or viruses into the environment, but simply uses naturally-occurring compounds found in plants."