Association between clinical respiratory signs, lung lesions detected by thoracic ultrasonography and growth performance in pre-weaned dairy calves

Authors: CUEVAS-GOMES, INMACULADA - Teagasc (AGRICULTURE AND FOOD DEVELOPMENT AUTHORITY); MCGEE, MARK - Teagasc (AGRICULTURE AND FOOD DEVELOPMENT AUTHORITY); SANCHEZ, JOSE MARIA - University College Dublin; O'RIORDAN, EDWARD - Teagasc (AGRICULTURE AND FOOD DEVELOPMENT AUTHORITY); BYRNE, NICKY - Teagasc (AGRICULTURE AND FOOD DEVELOPMENT AUTHORITY); McDaneld, Tara; EARLEY, BERNADETTE - Teagasc (AGRICULTURE AND FOOD DEVELOPMENT AUTHORITY)

Submitted to: Irish Veterinary Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/11/2021
Publication Date: 3/25/2021
Citation: Cuevas-Gomes, I., McGee, M., Sanchez, J., O'Riordan, E., Byrne, N., McDaneld, T.G., Earley, B. 2021. Association between clinical respiratory signs, lung lesions detected by thoracic ultrasonography and growth performance in pre-weaned dairy calves. Irish Veterinary Journal. 74. Article 7. https://doi.org/10.1186/s13620-021-00187-1.
DOI: https://doi.org/10.1186/s13620-021-00187-1

Interpretive Summary: Background: Bovine respiratory disease (BRD) is the biggest cause of mortality among 1–5 month-old calves in Ireland, accounting for 34.3% of deaths in this age group. Diagnosing BRD based on clinical signs limits the identification of sub-clinical cases and using thoracic ultrasonography (TUS) may improve identification of lung abnormalities and help identify sub-clinical BRD cases. The aims of this study were to: (i) investigate the relationship between BRD-associated clinical signs and lung abnormalities detected by TUS and (ii) assess their effect on growth performance in preweaned artificially reared dairy calves. Results: Forty-three percent of calves showed clinical respiratory signs while 64% had lung abnormalities from purchase until weaning. While no associations were found between mild lung abnormalities detected by TUS and respiratory signs, moderate associations were found between cough and severe lung abnormalities on days 0 and 7 post-arrival and between fever and lung consolidation on days 7 and 14 post-arrival. The average daily gain of calves with or without respiratory signs did not differ, however, calves with severe lung abnormalities grew at 0.1 kg/d less than calves with healthy lungs. Conclusions: These findings emphasize the importance of implementing the use of TUS in calf health monitoring for an early and accurate detection of BRD and sub-clinical forms of BRD and also identifying those calves at high risk of poorer growth outcomes.

Technical Abstract: Background: Bovine respiratory disease (BRD) is the main cause of mortality among 1-to-5 month old calves in Ireland, accounting for approximately one-third of deaths. Despite widespread use of clinical respiratory signs for diagnosing BRD, lung lesions are detected, using thoracic ultrasonography (TUS) or following post-mortem, in calves showing no clinical signs. This highlights the limitation of clinical respiratory signs as a method of detecting sub-clinical BRD. Using 53 purchased artificially-reared male dairy calves, the objectives of this study were to: (i) characterise the BRD incidence detected by clinical respiratory signs and/or TUS, (ii) investigate the association between clinical respiratory signs and lung lesions detected by TUS, and (iii) assess the effect of BRD on preweaning growth. Results: Clinical BRD (based on Wisconsin clinical respiratory score and/or rectal temperature > 39.6ºC) was detected in 43% and sonographic changes (lung lesions) were detected in 64% of calves from purchase (23 (SD; 6.2) days of age) until weaning, 53 days post-arrival. Calves with clinical BRD were treated. Sixty-one per cent calves affected with clinical BRD had lung lesions 10.5 days (median) before detection of clinical signs. Moderate correlations (rsp 0.70; P < 0.05) were found between cough and severe lung lesions on arrival day, and between rectal temperature > 39.6ºC and lung lesions = 2 cm2 on day 7 (rsp 0.40; P < 0.05) post-arrival. Mean average daily live weight gain (ADG) of calves from purchase to weaning was 0.75 (SD; 0.10) kg; calves with or without clinical BRD did not differ in ADG (P > 0.05), whereas ADG of those with severe lung lesions (lung lobe completely consolidated or pulmonary emphysema) was 0.12 kg/d less (P < 0.05) than calves without lung lesions. Conclusions: Thoracic ultrasonography detected lung consolidation in calves that did not show signs of respiratory disease. The presence of severe lung lesions was associated with reduced pre-weaning growth. These findings emphasise the importance of using TUS in addition to clinical respiratory scoring of calves for an early and accurate detection of clinical and sub-clinical BRD.