Associations between calf factors of Japanese Black calves arriving at a backgrounding operation and bovine respiratory disease.

Bovine respiratory disease (BRD), a common and costly disease of beef cattle, has various causes. In Japan, Japanese Black calves aged 3-4 months were introduced to a backgrounding operation that raises calves until age 10 months. We assessed whether any associations relating to the calf information on arrival at the backgrounding operation and BRD incidence in Japanese Black calves exist. The data collected from a backgrounding operation in Miyazaki (Japan) included the records of 1843 animals entering the farm during 2012-2016. The information collected on arrival at the backgrounding operation was calf sex, age, blood line, weight and chest circumference, and the arrival season. Mixed-effect multivariable logistic regression modeling was applied to these data. The dependent variable was whether or not a calf showed the clinical signs of BRD and was subsequently treated with an antimicrobial between farm entry at 3-4 months of age and farm exit at 10 months of age (1 or 0). The first diagnosis of BRD after arrival was counted in this study. Average BRD incidence was 52.5 %, the relative frequencies of which at 0-30, 31-60 and ≥61 days after arrival were 58.7 %, 25.2 % and 16.1 %, respectively. BRD incidence was associated with sex, age and season (P < 0.05), but not blood line, weight, and chest circumference. Steers had 1.39 times higher odds than heifers of being diagnosed with BRD (P < 0.05). Calves entering in September to November had the highest BRD incidence (65.3 %), whereas those entering during March to May had the lowest BRD incidence (42.3 %; P < 0.05). Calves of ≤125 days old on farm arrival had higher BRD incidence than those ≥148 days old (P < 0.05). Thus, various factors on arrival at the backgrounding operation were found to be associated with BRD incidence in Japanese Black calves. It is important to carefully observe high-risk calves and monitor them for the clinical signs of BRD at the earliest opportunity on arrival at a backgrounding operation.