Dairy Cows Experimentally Infected With Bovine Leukemia Virus Showed an Increased Milk Production in Lactation Numbers 3–4: A 4-Year Longitudinal Study

Abstract

Bovine leukemia virus (BLV) is widespread in global cattle populations, but the effects of its infection on milk quantity and quality have not been clearly elucidated in animal models. In this study, 30 healthy first-lactation cows were selected from ≈2,988 cows in a BLV-free farm with the same criteria of parity, age, lactation number, as well as milk yield, SCS, and composition (fat, protein, and lactose). Subsequently, these cows were randomly assigned to the intervention (n = 15) or control (n = 15) group, and reared in different cowsheds. Cows in the intervention group were inoculated with 1 × phosphate-buffered solution (PBS) resuspended in peripheral blood mononuclear cells (PBMC) from a BLV-positive cow, while the controls were inoculated with the inactivated PBMC from the same individual. From June 2016 to July 2021, milk weight (kg) was automatically recorded by milk sensors, and milk SCS and composition were originated from monthly performed dairy herd improvement (DHI) testing. Fluorescence resonance energy transfer (FRET)–qPCR and ELISA showed that cows in the intervention group were successfully infected with BLV, while cows in the control group were free of BLV for the entire period. At 45 days post-inoculation (DPI), the numbers of whole blood cells (WBCs) (P = 0.010), lymphocytes (LYMs) (P = 0.002), and monocytes (MNCs) (P = 0.001) and the expression levels of IFN-γ (P = 0.013), IL-10 (P = 0.031), and IL-12p70 (P = 0.008) increased significantly in the BLV infected cows compared to the non-infected. In lactation numbers 2–4, the intervention group had significantly higher overall milk yield (P < 0.001), fat (P = 0.031), and protein (P = 0.050) than the control group, while milk SCS (P = 0.038) and lactose (P = 0.036) decreased significantly. Further analysis indicated that BLV infection was associated with increased milk yield at each lactation stage in lactation numbers 3–4 (P = 0.021 or P < 0.001), but not with SCS and milk composition. Together, this 4-year longitudinal study revealed that artificial inoculation of BLV increased the milk yield in cows in this BLV challenge model.

Influence of BoLA-DRB3 Polymorphism and Bovine Leukemia Virus (BLV) Infection on Dairy Cattle Productivity

“…In this study, BLV infection had a positive effect on milk yield when analyzed considering farm differences, calving number, and lactation period. An experimental study of BLV infection reported that BLV-positive dams produced more milk, which is consistent with our report [38]. Additionally, a field study reported that herds with higher BLV prevalence actually produce more milk [40].…”

“…Several studies have reported the impact of BLV infection and BoLA-DRB3 on cattle productivity [4][5][6][7][19][20][21][22][23][24]38,[40][41][42][43]. Results from previous studies differed with regards to BLV infection, where it was found to have positive, negative, as well as no effect on cattle productivity [4][5][6][7]38,[40][41][42][43]. Additionally, BoLA-DRB3 reportedly has positive or negative effects on dairy cattle productivity [19][20][21][22][23][24].…”

“…Although the effect of BLV infection on milk yield was evaluated previously [7,38], the effect of this infection on other milk-related dairy cattle productivity has rarely been evaluated. Therefore, in addition to milk yield, the effect of a BLV infection on milk fat percentage, protein percentage, non-fat solids percentage, SCC, and MUN was evaluated (Figure 3).…”

Assessment of adaptive immune responses of dairy cows with Burkholderia contaminans-induced mastitis

“…Before the diagnosis of mastitis, these Holstein dairy cattle all had the same lactation number and had comparable individual performance and ages ( Table 1 ). In addition, with commercial ELISAs (Qiaodu, Shanghai, China) or PCRs ( Yang et al, 2022 ), it was preliminarily determined that none of the experimental cows infected any of the following pathogens: S. aureus ( Yang and Laven, 2022 ), Bacillus cereus ( Simbotwe et al, 2018 ), Streptococcus agalactiae ( Bu et al, 2015 ), Babesia spp., Brucella abortus , Anaplasma spp., or Theileria spp.…”

The Global Epidemiology of Bovine Leukemia Virus: Current Trends and Future Implications

“…Other research demonstrated that milk production in BLV-positive cows is comparable to that of healthy cows, and, in some cases, it may even be higher [13,205]. Additionally, a four-year study on the milking performance of cows experimentally infected with BLV reported that artificial infection with BLV can actually enhance the milk yield of dairy cows [206]. Hence, further research is necessary to thoroughly understand the impact of BLV infection on milk production in dairy cows and its underlying mechanisms.…”