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.

Prevalence of Bovine Leukemia Virus Antibodies in US Dairy Cattle

“…In the US, where there is no control program for BLV, the animal-level prevalence in the dairy cattle population has increased steadily from approximately 10% at that time to over 40% today [5–12]. Other major dairy producing countries that have not implemented large-scale eradication programs, including Canada, Argentina, Japan, and China, have also reported BLV prevalence in their dairy herds of 30-50% [11, 13–21]. In contrast, 19 member states of the European Union, the United Kingdom, New Zealand, and Australia have completely eradicated BLV from their dairy cow populations, and control programs are underway in the remaining member states of the EU resulting in an overall herd prevalence in the EU of less than one percent [11, 22, 23].…”

“…While some previous studies do not show significant negative effects of BLV infection on production and longevity or survival [13, 24, 25], the majority of recent studies have reported a negative association between BLV infection and both milk production and cow longevity [21, 22, 26–32]. Between 2010 and 2012, our research group conducted studies of BLV in 113 Michigan dairy herds using milk ELISA1 testing of a sample of 40 cows in each herd to estimate within-herd AP, which ranged from 0% to 80.6% with an average of 32.8% [9, 33–36].…”

Bovine leukemia virus: current perspectives

“…62 This increase of SCC may indicate that BLV-infected cattle could present higher incidence of mastitis than BLV-free animals. A high SCC in milk is undesirable for the dairy industry because it increases the acidity of milk and decreases the quality of cheese.…”

“…BLV-infected cows with ≥4 parities in their early and middle lactation stage had 13.2% and 14.9% reduction rate, respectively, compared with noninfected cows. 62 Another study analyzed the lactation history and BLV infection status of 4,052 cows from 348 herds and showed that infected cows in their 2nd and 3rd lactations had significantly lower life milk production compared with their negative counterparts with the same number of lactations. No significant differences were found between infected and noninfected cows with >3 lactations.…”

First Molecular Characterization of Bovine Leukemia Virus Infections in the Caribbean

“…The BLV FRET-PCR was performed as described previously [3] in a LightCycler 480 II real-time PCR platform to detect BLV. In brief, the gag gene sequences of representative BLV isolates were obtained from GenBank and the Clustal multiple alignment algorithm was used to identify a highly conserved region of the proviral polymerase DNA gene common to all the above BLV gene sequences.…”