This is because some lambs are born contaminated with germs such as listeria, toxoplasma and chlamydia which may affect you and your unborn baby.

http://www.patient.co.uk/health/planning-to-become-pregnant

If you work with certain animals. For example:

• You should avoid contact with sheep and lambs at lambing time. This is because some lambs are born contaminated with germs such as listeria, toxoplasma and chlamydia which may affect you and your unborn baby.