Martin S W, Nagy E, Shewen P E, Harland R J
Ontario Veterinary College, University of Guelph.
Can J Vet Res. 1998 Oct;62(4):257-61.
The association between bovine respiratory disease (BRD) and antibody titers to bovine coronavirus (BCV) was studied in 604 calves (19 different groups in 4 different feedlots from 2 provinces). Almost all calves had antibody titers on arrival in the Alberta feedlot and 82% of the calves had an antibody titer on arrival at the Ontario feedlots; titers in calves in Alberta were almost twice as high as those in calves in Ontario. The incidence of infection, in the first mo after arrival as judged by seroconversion, ranged from 61% to 100%; titer increases were much greater in calves in Ontario feedlots. Titer variables were not significantly related to BRD, except on a within-group basis (group was a confounding variable for BCV-BRD associations). Given control of group effects, calves with an antibody titer on arrival appeared to be protected against BRD for the first 28 d in the feedlot, and the association was reasonably linear over the range of titers. Each titer unit on arrival decreased the risk of BRD by about 0.8x (odds ratio). Titer change was not strongly related to the risk of BRD and the relationship was not linear over the range of titer changes. Titer change was strongly and negatively correlated with titer on arrival, and titer change was not significantly related to BRD in the presence of arrival titers. Arrival titer retained its relationship with BRD in the presence of titer data for other putative pathogens. Each higher unit of titer to BCV on arrival increased the 28-day weight gain (controlling for group, initial weight and the occurrence of BRD) by slightly more than 1 kg. Titer change was associated with decreased weight gain, when initial titer was not in the model. The lack of a linear or multivariable association between BCV titer change and BRD, and weight gain, may indicate that BCV is not a major pathogen; or, its lack of significance may merely be due to its strong correlation with arrival titer. Given the associations found in this study, particularly the interprovincial differences in arrival titers, more and different approaches to studying the possible effects of BCV on BRD are in order.
在来自两个省份4个不同饲养场的604头犊牛（19个不同组）中，研究了牛呼吸道疾病（BRD）与牛冠状病毒（BCV）抗体滴度之间的关联。几乎所有犊牛抵达艾伯塔省饲养场时都有抗体滴度，82%的犊牛抵达安大略省饲养场时具有抗体滴度；艾伯塔省犊牛的滴度几乎是安大略省犊牛滴度的两倍。根据血清转化判断，抵达后第一个月的感染发生率在61%至100%之间；安大略省饲养场犊牛的滴度增加幅度要大得多。除了在组内基础上（组是BCV - BRD关联的混杂变量），滴度变量与BRD没有显著相关性。在控制组效应的情况下，抵达时具有抗体滴度的犊牛在饲养场的前28天似乎受到BRD的保护，并且在滴度范围内这种关联相当呈线性。抵达时每一个滴度单位使BRD风险降低约0.8倍（优势比）。滴度变化与BRD风险的相关性不强，并且在滴度变化范围内这种关系不是线性的。滴度变化与抵达时的滴度呈强负相关，并且在存在抵达滴度的情况下，滴度变化与BRD没有显著相关性。在存在其他假定病原体滴度数据的情况下，抵达滴度与BRD仍保持其关系。抵达时BCV滴度每升高一个单位，28天体重增加（控制组、初始体重和BRD的发生情况）略超过1千克。当初始滴度不在模型中时，滴度变化与体重增加减少有关。BCV滴度变化与BRD以及体重增加之间缺乏线性或多变量关联，可能表明BCV不是主要病原体；或者，其缺乏显著性可能仅仅是由于它与抵达滴度的强相关性。鉴于本研究中发现的关联，特别是抵达滴度的省际差异，需要更多不同的方法来研究BCV对BRD可能产生的影响。
