11 Impact of a Cache Valley Fever Outbreak on Lambing Performance in a Landrace Hair Sheep Flock: A Case Study

Abstract Cache Valley Fever (CVF) is a mosquito-born, viral disease endemic to North America. While generally not associated with clinical symptoms in ewes, it affects fetal development during the first trimester of pregnancy resulting malformations and loss. A suspected outbreak CVF was recorded flock Barbados Blackbelly St. Croix hair sheep managed under an 8-mo, accelerated mating system ewes bred March, July November. The breeding, summer unusually high rainfall standing water pastures. There had been no previous occurrence or other abortion storms (20+ years). Lambing outcome compared that three prior matings (CON). Ewes (n = 32-35) were pasture-based rotational grazing. mated two single sire groups 16 18 like-breed sires each breeding season. Pregnancy determined by transrectal ultrasound at end 21 d after 25-day lambed on pasture, lambs tagged, birth weights within 24 hours. Blood samples collected from all following lambing submitted for antibody testing. All showed titers. rate different CON (85.7 vs. 89.8%; P 0.512), whereas less both exposed (74.3 88.8%; 0.039) (86.7 98.9%; 0.004). Incidence stillborn neonatal death greater than (37.0 vs.5.6%; 0.002), as number malformed (13.0 0%; < 0.001). Malformed breech presentations. Litter size (1.77 vs 1.86; 0.471), but lamb weight tended be (2.80 3.04 kg; 0.055) while ewe postpartum (45.3 47.0 0.384). reduced increased incidence malformations. occurred may changing weather patterns linked climate change. Delaying considered mitigation strategy if feasible.