Veterinary session

BRDC (bovine respiratory disease complex) is a multifactorial disease causing severe farm economic loss. Early diagnosis is essential for effective treatment, prevention and subsequent economic production. Ultrasound (US) is helpful in this, we can even diagnose subclinical pathologies. The aim of our research is the practical application of lung US for diagnosing BRDC in large dairy farms and investigating the effect of respiratory diseases in the calf period on the subsequent fertility index.

Our research examined 243 calves in the age group of 4-6 weeks on 10 large dairy farms in Hungary. All animals were subjected to a physical examination based on a scoring scale by the University of Wisconsin (0 points: no symptoms; 9 points: severe clinical signs). In addition, a US examination of the lungs was also performed on all animals, scored from 0 to 5 (0: no symptoms, 5: severe symptoms). We collected data on the diseases of the examined calves, their eventual culling, the insemination index, and the vaccination protocol against the BRDC of the inspected farms.

Based on the US examination, the mean of the scores was 1.92+1.42, while the mean of the clinical symptoms (Wisconsin score) was 0.86+1.33. Based on the statistical analysis, the correlation between the results of the two scoring methods is weak but significant (p<0.0001). The increase of the physical examination score by 1 was associated with a 0.44 higher US score.

Five out of ten farms vaccinated the calves against respiratory pathogens. There are no verifiable differences in US score, physical examination score and insemination index between vaccinated and non-vaccinated farms. However, the proportion of calves with a US score 5 was 4.8% in vaccinated and 10.3% in non-vaccinated herds. There is no significant correlation between the US score and insemination index in calves succesfully inseminated at the heifer age. Among the examined animals, the proportion of becoming pregnant and dying or culled animals is the same in vaccinated (88.5% pregnant; 11.5% died or culled) and non-vaccinated farms (89.5% pregnant; 10.5% died or culled). Based on our results, lung lesions can be detected with the US even before the appearance of clinical symptoms, already in the subclinical stage, or even after the clinical signs have disappeared. The US examination is more sensitive than the physical examination, the animals received a worse score than the physical examination, and US lesions could also be found in the lungs of asymptomatic animals.

Based on the similar results of vaccinated and non-vaccinated farms and the fact that the US score was not related to subsequent reproductive indicators, we can assume that the housing technology, the design of individual calf cages, the management of calf feeding and the vaccination protocol itself can influence these results, but further investigations would be needed to verify this.