title: Bovine leukemia virus infection in cattle of China: Association with reduced milk production and increased somatic cell score.
abstract: The main objective of this study was to investigate the individual cow effect of bovine leukemia virus (BLV) infection on milk production and somatic cell score (SCS). The fluorescence resonance energy transfer (FRET) quantitative PCR established in this study and a commercial ELISA kit revealed that 49.1% of dairy cattle (964/1,963) from 6 provinces of China and 1.6% of beef cattle (22/1,390) from 15 provinces were BLV positive. In a detailed study of 105 cows, BLV was found most commonly in buffy coat samples that also had highest copy numbers (10(4.75±1.56) per mL); all cows negative for BLV in buffy coat samples were also negative in vaginal swab, milk, and fecal samples. Copy numbers of BLV were 10(2.90±0.42)/gram of feces, 10(0.83±0.62)/mL of milk, and 10(2.18±0.81) per vaginal swab. The BLV-positive cows had significantly lower milk production in the early (26.8 vs. 30.9kg) and middle stages of lactation (22.2 vs. 26.1kg) in animals with ≥4 parities than the BLV-negative cows; they also had significantly higher SCS in early and middle lactation stages (early=5.2 vs. 4.3; middle=4.9 vs. 3.9) in animals with ≥4 parities. Milk production and SCS did not significantly differ between the BLV-infected and -uninfected cows when they were in the late lactation stage or in animals with ≤3 parities. Taken together, our results indicate that BLV infections are widespread in the dairy farms of China. Vaginal secretions and feces may be involved in BLV transmission. A BLV infection may result in reduced milk yield and increased SCS in a parity and lactation stage-restricted manner.
authors.affiliation: Jiangsu Co-innovation Center for the Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou University College of Veterinary Medicine, Yangzhou, Jiangsu 225009, China.
authors.forename: Y
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Laboratory of Zoonosis, China Animal Health and Epidemiology Center, Qingdao, Shandong, China.
authors.forename: W
authors.initials: W
authors.lastname: Fan
authors.affiliation: Yangzhou University College of Animal Science and Technology, Yangzhou, Jiangsu 266032, China.
authors.forename: Y
authors.initials: Y
authors.lastname: Mao
authors.affiliation: Yangzhou University College of Animal Science and Technology, Yangzhou, Jiangsu 266032, China.
authors.forename: Z
authors.initials: Z
authors.lastname: Yang
authors.affiliation: Jiangsu Co-innovation Center for the Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou University College of Veterinary Medicine, Yangzhou, Jiangsu 225009, China.
authors.forename: G
authors.initials: G
authors.lastname: Lu
authors.affiliation: Jiangsu Co-innovation Center for the Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou University College of Veterinary Medicine, Yangzhou, Jiangsu 225009, China.
authors.forename: R
authors.initials: R
authors.lastname: Zhang
authors.affiliation: Laboratory of Zoonosis, China Animal Health and Epidemiology Center, Qingdao, Shandong, China.
authors.forename: H
authors.initials: H
authors.lastname: Zhang
authors.affiliation: Faculty of Science, The University of British Columbia, Vancouver V6T, Canada.
authors.forename: C
authors.initials: C
authors.lastname: Szeto
authors.affiliation: Jiangsu Co-innovation Center for the Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou University College of Veterinary Medicine, Yangzhou, Jiangsu 225009, China. Electronic address: wangcm@yzu.edu.cn.
authors.forename: C
authors.initials: C
authors.lastname: Wang
mesh_terms: D000818:Animals; D002417:Cattle; D016583:Enzootic Bovine Leukosis / Q000821:virology*; D004797:Enzyme-Linked Immunosorbent Assay / Q000662:veterinary; D005260:Female; D007774:Lactation; D001909:Leukemia Virus, Bovine; D008892:Milk
keywords: China; bovine leukemia virus; milk production; somatic cell score