Vitamin A effects on antibody responses to bovine coronavirus and rotavirus vaccines in feedlot calves

To understand the impact of vitamin A status in cattle on their immune responses, we investigated antibody (Ab) responses in feedlot calves naturally infected with BCoV as well as intramuscularly vaccinated with a commercial inactivated BCoV and BRV vaccine. These calves were fed either high or low dietary vitamin A, based on greater than or less than the 2200 international units (IU) Vitamin A/kg of dietary dry matter (DM), respectively as recommended by the National Research Council. Angus steers (n=40, average 199 days old) were randomly assigned to two groups. One group received low dietary vitamin A (LVA group; 1100 IU/kg of dietary DM, n=20) to simulate low levels in the vitamin A restricted feedlot calves and the other group received high dietary vitamin A (HVA group; 3300 IU/kg of dietary DM, n=20). Supplemental vitamin A was fed at post-arrival day (PAD) 0, then daily throughout the 140 day study period (PAD 140).;At PAD 0, the calves in both LVA and HVA groups showed statistically similar background levels of BCoV shedding and serum BCoV Ab. Therefore, no sub-categorical analysis was required. Twenty calves (50% of total calves) shed BCoV either in feces or nasally at least once shortly after arrival (at PAD 0 and 4). The prevalence of BCoV shedding increased from 21.05% at PAD 0 to 41.03% at PAD 4, but with no BCoV shedding detected thereafter (at PAD 35, 112 and 140). Before the decreased vitamin A levels in serum occurred (at PAD 0, 4 and 35), we investigated the isotype Ab responses induced at PAD 35 by natural BCoV infection at PAD 0 and 4. The BCoV fecal shedding was negatively associated with pre-existing serum IgA BCoV Ab titers at PAD 4.;After vitamin A decreased in serum (by PAD 112), we investigated BCoV and BRV Abs induced at PAD 112 and 140 by the inactivated BCoV/BRV vaccine given at PAD 112 and 126. Serum IgG1 BCoV Ab titers and the ratios of IgG1 to IgG2 Abs in the HVA group were significantly higher at PAD 140 than at PAD 112 (p < 0.005), whereas those in the LVA group did not differ significantly. At PAD 140, serum IgG1 BCoV Ab titers and the ratios of IgG1 to IgG2 Abs were significantly higher in the HVA than in the LVA group (p < 0.05). Calves naturally infected with BCoV in the LVA group (n=11) were compared to assess the impact of BCoV infection and BCoV vaccination on Ab responses before the decreased vitamin A (at PAD 0 and 35) and after the decreased vitamin A (at PAD 112 and 140) in serum. The calves naturally infected with BCoV had predominantly serum IgG1 BCoV Ab at PAD 35 (p < 0.05). However, the calves previously recovered from natural BCoV infection had a compromised serum IgG1 BCoV Ab response to an inactivated BCoV vaccine at PAD 140.;In contrast, there was no vitamin A effect on serum BRV Ab responses to the inactivated BCoV/BRV vaccine. All serum isotype BRV Ab titers were significantly higher at PAD 140 than at PAD 112, regardless of vitamin A dietary status. In addition, no statistically significant differences were observed between the HVA and LVA group at both PADs. In the LVA group, Ab responses to the inactivated BRV and BCoV differed since serum IgG1 antibody responses to the inactivated BCoV vaccine were compromised, whereas those to the inactivated BRV vaccine were significantly increased at PAD 140 compared with PAD 112.;To our knowledge, this is the first study to analyze the impacts of micronutrients, i.e., vitamin A on Ab responses to a BCoV and BRV vaccine in feedlot calves. The vitamin A status in feedlot calves had a significant effect on Ab responses to an inactivated BCoV vaccine. Serum IgG1 BCoV Abs were induced predominantly under the high vitamin A dietary regimen, whereas they were compromised under the low vitamin A dietary regimen, suggesting that the low vitamin A diet suppresses the Th2 associated Ab (IgG1) responses. However, the vitamin A dietary regimens did not affect Ab responses to inactivated BRV vaccine. This study suggests that vitamin A effects on antibody responses may be vaccine antigen-dependent. (Abstract shortened by UMI.)...