Genome-wide association study for response to vaccination in Angus calves1

Background

Bovine respiratory disease complex (BRDC) is one of the most important sources of loss within the beef cattle industry in the USA. Steps have been taken to reduce the incidence of BRDC through vaccination. Despite the effectiveness of vaccines, large proportions of cattle still experience morbidity and mortality. Identification of genomic regions that are associated with variation in response to vaccination would allow for the selection of individuals genetically predisposed to respond to vaccination based on specific markers, while heritability and accuracy estimates would help facilitate genomic selection. This in turn may lead to selection for beef cattle herds that may have lower incidence rate of BRDC after vaccination. This study utilizes an Angus herd of more than 2000 head of cattle to identify these regions of association.

Results

Genome wide association studies were performed for viral neutralization antibody level and response to vaccination traits against four different viruses associated with BRDC: bovine viral diarrhea virus 1 and 2 (BVDV1 and BVDV2), bovine respiratory syncytial virus (BRSV), and bovine herpesvirus (BHV1). A total of six 1-Mb windows were associated with greater than 1% of the genetic variance for the analyzed vaccination response traits. Heritabilities ranged from 0.08 to 0.21 and prediction accuracy ranged from 0.01 to 0.33 across 7 different vaccination traits.

Conclusions

Although six 1-Mb windows were identified as associated with 1% or greater genetic variance for viral neutralization antibody level and response to vaccination traits, few genes around these windows could readily be considered candidates. This indicates the need for further functional genomic annotation, as these regions appear to be gene deserts. Traits ranged from lowly to moderately heritable, which indicated the potential for selection of individuals that are genetically pre-disposed to respond to vaccination. The relatively low amount of genetic variance accounted for by any 1-Mb window indicated that viral neutralization antibody level and response to vaccination traits are polygenic in nature. Selection for these traits is possible, but likely to be slow due to the low heritabilities and absence of markers with high genetic variation associated with them.

Evaluation of responses to vaccination of Angus cattle for four viruses that contribute to bovine respiratory disease complex

Although vaccination is an effective measure in reducing the risk of bovine respiratory disease complex (BRDC) in cattle, BRDC losses remain significant. Increasing the efficacy of vaccination depends on elucidating the protective immune response to different antigens included in vaccines, determining the best timing for vaccination, and understanding the impact of the age of the calf on vaccination. This study measured the serum antibodies present in calves following vaccination against 4 viruses commonly associated with BRDC: bovine viral diarrhea virus type 1 and 2 (BVDV1 and BVDV2), bovine respiratory syncytial virus (BRSV), and bovine herpesvirus 1 (BHV1). Serum antibody titers were measured in more than 1,600 calves at 3-wk intervals starting at the time of the first vaccination. This first vaccination occurred at weaning for approximately half of the individuals and 3 wk before weaning for the other half. Dam age (years), time of weaning (initial vaccination or booster vaccination), and age of calf within year-season (days within year-season) classification all were found to have a significant effect on measured traits such as the initial titer and overall response. An increased initial titer was negatively correlated with each response trait (initial, booster, and overall response). Calves that were weaned at initial vaccination had greater overall antibody response to BVDV1 and BVDV2 compared with calves weaned 3 wk before initial vaccination. In contrast, calves given their initial vaccination 3 wk before weaning had greater overall antibody response to BRSV and BHV1 compared with calves that were vaccinated at weaning. Furthermore, the circulating antibody titer at which each virus needed to be below for an individual calf to positively respond to vaccination was determined (log titer of 0.38 for BVDV1, 1.5 for BVDV2, 3.88 for BRSV, and 1.5 for BHV1). This information can be used to improve vaccination protocols to allow for a greater response rate of individuals to vaccination and, hopefully, improved protection.

Effects of two-stage weaning with nose flap devices applied to calves on cow body condition, calf performance, and calf humoral immune response

The effects of nose flap devices in calves before dam separation on cow BCS, pre- and postseparation calf performance, and humoral immune response were compared with traditional weaning. Primiparous and multiparous Angus and Hereford cows ( = 113) and their Angus, Hereford, and Angus × Hereford calves (179.4 ± 3.92 kg and 161 ± 22.7 d of age) were used. Cow-calf pairs were allocated to 1 of 2 treatments in a completely randomized design: 1) nose flap for 21 d before separation from the dam (NF) or 2) no nose flap for 21 d before separation from the dam (CON). Calves were separated from dams on d 0, and calves were placed in group feed-yard pens for 28 d. A subset ( = 75) of weaned calves were placed into 1 of 8 pens to evaluate DMI. Cow BCS was measured on d -21 and 56, and calves were given modified live vaccinations (d -21 and 1), challenged with ovalbumin (OVA; d 1), and weighed (d -21, 1, 7, 14, 21, and 28). In addition, blood samples were collected (d -21, 1, 14, and 28) to measure primary humoral immune response. Control calves tended to have greater BW on d 14 ( = 0.09) and 21 ( = 0.07) than NF calves, and CON calves had greater ( < 0.05) ADG from d -21 to 1 vs. NF calves. Treatments did not differ ( ≥ 0.27) for postweaning DMI, G:F, or morbidity. Serum neutralization tests for bovine viral diarrhea virus type 1 (BVDV-1) and bovine herpesvirus type 1 (BHV-1) were used to measure humoral response to a viral vaccination. Serum antibody titers to BVDV-1 for CON calves tended ( = 0.08) to be greater on d 1 and were greater ( < 0.05) by d 28 vs. NF calves. By d 28, a greater percentage ( < 0.05) of CON calves seroconverted for BVDV-1 than NF calves (82.1 vs. 66.7%, respectively). Serum antibody titers for BHV-1 were greater ( < 0.05) on d 1 and 28 for CON vs. NF calves. Humoral immune response to OVA during the 28-d postseparation period from the dam was evaluated in a subset ( = 57) of calves. There was no difference ( = 0.92) in OVA-specific IgG between treatments on d 14 or 28 ( = 0.76); however, OVA-specific IgM was greater ( < 0.05) in CON vs. NF calves on d 28. Results indicate that nose flap devices did not influence feed intake, feed efficiency, or morbidity during the initial postseparation period from the dam. However, preweaning ADG, serum BVDV-1 and BHV-1 titers, and humoral immune response to OVA were decreased in calves that received the nose flap treatment.

Efficacy of multivalent, modified- live virus (MLV) vaccines administered to early weaned beef calves subsequently challenged with virulent Bovine viral diarrhea virus type 2

Background

Vaccination of young calves against Bovine viral diarrhea virus (BVDV) is desirable in dairy and beef operations to reduce clinical disease and prevent spread of the virus among cattle. Although protection from clinical disease by multivalent, modified-live virus (MLV) vaccines has been demonstrated, the ability of MLV vaccines to prevent viremia and viral shedding in young calves possessing passive immunity is not known. The purpose of this study was to compare the ability of three different MLV vaccines to prevent clinical disease, viremia, and virus shedding in early weaned beef calves possessing maternal immunity that were vaccinated once at 45 days prior to challenge with virulent BVDV 2.

Results

At 45 days following vaccination, calves that received vaccines B and C had significantly higher BVDV 1 and BVDV 2 serum antibody titers compared with control calves. Serum antibody titers for BVDV 1 and BVDV 2 were not significantly different between control calves and calves that received vaccine D. Following BVDV 2 challenge, a higher proportion of control calves and calves that received vaccine D presented viremia and shed virus compared with calves that received vaccines B and C. Rectal temperatures and clinical scores were not significantly different between groups at any time period. Calves that received vaccines B and C had significantly higher mean body weights at BVDV 2 challenge and at the end of the study compared with control calves.

Conclusions

Moderate to low maternally-derived BVDV antibody levels protected all calves against severe clinical disease after challenge with virulent BVDV 2. Vaccines B and C induced a greater antibody response to BVDV 1 and BVDV 2, and resulted in reduced viremia and virus shedding in vaccinated calves after challenge indicating a greater efficacy in preventing virus transmission and reducing negative effects of viremia.