The following are digital copies of  original documents, sent to me by a friend who is farming in France.
(They are published together with my own translation, so apologies for any errors!).
It seems that French Scientists have discovered from tests they have conducted, that some rams that had been BT vaccinated were subsequently found to be positive for the virus and temporarily infertile.
(The results of these tests were published in August 2008)

This information seems to confirm that if a vaccinated animal is bitten by an infected midge(s) before or even soon after vaccination and before the full vaccine-induced immunity has had time to develop, the animals may not be ill themselves but may be affected with regard to their fertility and need some time to fully recover. 

I was concerned about this and contact Dr. Chris Oura at Pirbright who confirmed my suspicions and replied as follows, 'Yes,  they should have developed full immunity at the time the research was carried out however, they could have been infected only a couple of weeks previously at a time when full immunity had not developed. Also they could have been infected earlier which would mean that the fertility problem were more long-term.'

JB Translation -

'43 rams from 7 farms that had never appeared to have been infected with Bluetongue but had been BT Vaccinated more than a month previously, were at first blood tested to see whether or not they had been exposed to the BT virus. 

Their testies were also physically examined to see if they were normal or not,

Samples of sperm were taken from each animal and then examined in the laboratory under the microscope to check for the concentration and mobility of the sperms per sample.

It was found that among the 26 animals that returned a negative test result for exposure to the BT virus and on physical examination, were found to have normal adult testes, all showed a normal and vigorous sperm count in lab examinations of their sperm and were found to be fertile. Apart from 6 that were too young (under 8 months) and 4 that were described as not eager (?too thin). It was believed they would be OK within a few months.

Among the 17 animals that tested positive to BT virus exposure, it was found they had an 80% chance of not returning a normal sperm count and on physical examination the testes were sometimes found to be atrophied and the skin calloused. In those cases, 7 of the rams were found to have abnormal testicles and be temporarily sterile and unlikely to recover in time for tupping this autumn (if then). 10 rams had normal testicles and 6 of those were found to have a nil or poor sperm count and of the few sperms they had, some were abnormal. It was suggested they should have limited use on a ratio of 1 to 10 ewes. The remaining 4 rams in that group were found to be normal and fertile. (Published in France on the 26th August 2008)

Last updated - October 16, 2008