Prevalence of bacteria involved in bovine respiratory disease in dairy heifers in Spain: influence of environmental factors.

Abstract

INTRODUCTION: Bovine Respiratory Disease (BRD) is a multifactorial condition and a major health and economic concern in dairy production. METHODS: This study aimed to determine the prevalence of five key bacterial pathogens-,,,, and-in Spanish dairy heifers and to evaluate the influence of seasonality, geographical location, farm size, and antibiotic use. In 2017, samples (deep nasopharyngeal swabs, transtracheal aspirates, and blood) were collected from 855 heifers (<12 months old) in 50 farms across Spain. Bacterial isolation and serological testing (ELISA) were performed. RESULTS: spp. showed the highest overall prevalence (26.7% at the individual level by culture; 75.7% of cultured farms), with PCR confirmingin 89% of Mycoplasma-positive farms. Serology revealed 16.3% individual-level positivity forand 63% farm-level positivity.was also notable, detected in 6.0% of animals (45% of farms). Lower isolation rates were observed for(2.5%) and(3.5%), whilewas not detected. Larger farm size, winter season, and certain regions were significantly associated with higher prevalence ofand. DISCUSSION: These findings underscore the need for improved management practices-such as better ventilation, reduced stocking density, and targeted vaccination-to mitigate BRD risk in high-prevalence settings.