Downey-Slinker E D, Ridpath J F, Sawyer J E, Skow L C, Herring A D
Department of Veterinary Integrative Biosciences, Texas A&M University, College Station, TX 77843, USA.
Ruminant Diseases and Immunology Research Unit, National Animal Disease Center, USDA, Agricultural Research Services, 1920 Dayton Avenue, P.O. Box 70, Ames, IA 50010, USA.
Vaccine. 2016 Sep 30;34(42):5053-5059. doi: 10.1016/j.vaccine.2016.08.087. Epub 2016 Sep 3.
Subclinical illness associated with infection is thought to reduce performance and increase production costs in feedlot cattle, but underlying components remain largely unidentified. Vaccination is frequently used in feedlot settings but producers lack metrics that evaluate the effectiveness of vaccination programs. The goal of this study was to determine if levels of serum neutralizing antibody titers were predictive of levels of vaccine protection in a commercial setting. During this four-year study, Angus-Nellore steers housed in a production feedlot setting were assigned to 1 of 3 vaccine treatments: killed vaccine (kV), modified live virus (MLV) vaccine, or no vaccine (control), and were challenged with a noncytopathic 1b field strain of bovine viral diarrhea virus. Rectal temperature and levels of circulating lymphocytes and platelets were monitored following challenge. While no animals were diagnosed as clinically ill with respiratory disease, indicators of disease (pyrexia, lymphopenia, and thrombocytopenia) were observed. The MLV treatment elicited higher antibody titers to the vaccination than the kV, and calves in the MLV treatment had higher mean titers at challenge. The year that elicited the highest antibody response to the vaccination and the year with the lowest frequency of phenotypic responses to the challenge were not concurrent. The MLV treatment had the highest proportion, 34.68%, of animals that were protected against the challenge regardless of the pre-challenge antibody titer and had the fewest number of lymphopenia cases in response to the challenge. Both vaccine treatments mitigated thrombocytopenia when compared to the control treatment, and the MLV treatment reduced lymphopenia; however, these symptoms were not completely eliminated in vaccinated animals. Pyrexia was present in 40.11% of the animals, but no difference in the frequency of cases between treatments was observed. Pre-challenge vaccination response was not indicative of the level of protection nor was anamnestic antibody response correlated with health status.
与感染相关的亚临床疾病被认为会降低饲养场牛的生产性能并增加生产成本，但其中的潜在因素在很大程度上仍未明确。疫苗接种在饲养场环境中经常使用，但生产者缺乏评估疫苗接种计划有效性的指标。本研究的目的是确定在商业环境中血清中和抗体滴度水平是否可预测疫苗保护水平。在这项为期四年的研究中，将饲养在生产性饲养场环境中的安格斯 - 内洛尔阉牛分配到三种疫苗处理之一：灭活疫苗（kV）、改良活病毒（MLV）疫苗或不接种疫苗（对照），并用牛病毒性腹泻病毒1b型非细胞病变野毒株进行攻毒。攻毒后监测直肠温度以及循环淋巴细胞和血小板水平。虽然没有动物被诊断为患有临床呼吸系统疾病，但观察到了疾病指标（发热、淋巴细胞减少和血小板减少）。与灭活疫苗相比，MLV处理对疫苗接种产生的抗体滴度更高，并且MLV处理组的犊牛在攻毒时平均滴度更高。对疫苗接种产生最高抗体反应的年份与对攻毒产生最低表型反应频率的年份并不一致。无论攻毒前抗体滴度如何，MLV处理组中免受攻毒的动物比例最高，为34.68%，并且攻毒后淋巴细胞减少病例数最少。与对照处理相比，两种疫苗处理均减轻了血小板减少，并且MLV处理减少了淋巴细胞减少；然而，这些症状在接种疫苗的动物中并未完全消除。40.11%的动物出现发热，但各处理组之间病例频率没有差异。攻毒前的疫苗接种反应并不能表明保护水平，既往抗体反应也与健康状况无关。
