Understanding border disease virus in sheep — causing congenital defects and welfare impairment.
Border disease causes significant welfare impairment across multiple presentations. Ewes infected during pregnancy experience reproductive failure — abortion, mummification, stillbirths, and weak neonates. Each failed pregnancy represents welfare loss for the ewe from reproductive stress and for the lost lambs.
Hairy shaker (persistently infected) lambs have the most visible welfare impairment. The continuous whole-body tremor — sometimes severe enough to prevent suckling — causes exhaustion, hypothermia risk, and failure to thrive. PI lambs that survive the neonatal period grow poorly and tremor throughout their lives. The tremor itself likely represents ongoing neurological discomfort.
The inevitable development of mucosal disease in PI sheep (as in BVD-PI cattle) causes severe terminal illness with oral ulceration and profuse haemorrhagic diarrhoea. Prompt identification and humane culling of PI animals provides welfare relief and prevents ongoing virus shedding to susceptible sheep in the flock.