Department of Livestock & One Health, University of Liverpool, Liverpool, UK.
School of Veterinary Medicine and Science, University of Nottingham, Sutton Bonington, UK.
Vet Rec. 2023 Jun 3;192(11):e2731. doi: 10.1002/vetr.2731. Epub 2023 Feb 21.
Small ruminant lentiviruses (SRLVs) are lentiviruses of sheep and goats, formerly known as maedi-visna (MV) in sheep and caprine encephalitis and arthritis in goats. In sheep, SRLVs commonly cause progressive pneumonia, wasting and indurative mastitis. SRLVs have a long latent period, and chronic production losses are often not recognised until very late. Few studies quantifying the production losses in ewes have been published, and none have been published under UK flock husbandry conditions.
Production records of milk yield and somatic cell count (SCC) from a dairy flock of 319 milking East Friesian × Lacaune ewes identified as MV infected via routine serological screening for SRLV antibodies were used in multivariable linear regression modelling to estimate the impact of SRLV status on total milk yield and SCC.
Milk yield was reduced in seropositive ewes by 8.1%-9.2% over an entire lactation. SCC counts were not significantly different in SRLV-infected and unifected animals.
Further parameters, such as body condition score or clinical mastitis, that were not available may have clarified the underlying cause of milk yield drop.
The study demonstrates substantial production losses in an SRLV-affected flock and highlights the impact of the virus on a farm's economic viability.
小反刍兽瘟病毒（SRLV）是绵羊和山羊的慢病毒，以前在绵羊中称为梅迪-维斯纳（MV），在山羊中称为山羊脑炎和关节炎。在绵羊中，SRLV 通常会导致进行性肺炎、消瘦和硬化性乳腺炎。SRLV 的潜伏期很长，直到很晚才会发现慢性生产损失。已经发表了一些定量评估感染 SRLV 的母羊生产损失的研究，但在英国羊群饲养条件下尚未发表。
通过常规的 SRLV 抗体血清学筛查，从一个 319 头泌乳东弗里生 × 拉卡奴杂交母羊的奶牛群中获取产奶量和体细胞计数（SCC）的生产记录，这些母羊被确定为 MV 感染。使用多变量线性回归模型来估计 SRLV 状态对总产奶量和 SCC 的影响。
在整个泌乳期内，血清阳性母羊的产奶量减少了 8.1%-9.2%。SRLV 感染和未感染动物的 SCC 计数没有显著差异。
可能有进一步的参数，如体况评分或临床乳腺炎，没有被纳入，这可能会阐明产奶量下降的根本原因。
该研究表明，受 SRLV 影响的羊群存在大量生产损失，并强调了该病毒对农场经济可行性的影响。
