One ewe has even been made to believe that she has given birth to a goat kid by manipulating her sexual organs at a critical point in her reproductive cycle.
A technique for inducing phantom sheep pregnancies has been developed to address the problem of what to do with the million lambs born each year to mothers who for one reason or another cannot breast-feed them. Sheep fooled into believing they have given birth are more likely to foster another sheep's offspring.
Fostering is notoriously difficult because ewes quickly form bonds with their own lambs and reject all others. Farmers are forced to rear orphaned lambs themselves, and the lack of maternal contact can cause behavioural abnormalities.
Scientists at the Institute of Animal Physiology and Genetics Research near Cambridge believe they may have found the simplest solution by fooling sheep with only one lamb into believing they have had twins. The institute has shown how successful the method can be with a ewe that has suckled its own lamb and the kid of a goat.
Keith Kendrick, head of animal welfare and behaviour, said most sheep farmers would find the procedure simple as it involved manually stimulating the sheep's vagina and cervix for two minutes with a gloved hand smeared in antiseptic cream.
'Most farmers are used to the anatomy of sheep. Putting hands into these delicate regions is not unusual for them,' he said.
Gently stretching the neck of the cervix with two fingers sends nerve signals to the animal's brain that mimic those produced in labour. The sheep believes it has given birth to a second lamb. The orphaned lamb can then be introduced to its new mother with an 80 per cent chance that it will be accepted.
'The animal's own lamb can be re-introduced to it within 30 minutes and will not be rejected,' Dr Kendrick said.