Thoracic ultrasound assessment of lung consolidation at weaning in Holstein dairy heifers: Reproductive performance and survival

Abstract

The objective of this study was to determine the association of lung consolidation at weaning with later reproductive performance and survival. Ultrasonography of the lungs was performed at 60 d of life in recently weaned Holstein heifer calves from a single farm in New York State. Thoracic screening covered the right 2nd through 10th and left 3rd through 9th intercostal spaces and was performed using a 6.2-MHz linear transducer. Each calf was classified as not having lung consolidation (hyperechoic line with reverberation artifact with or without comet tail) or with lung consolidation (any detectable heterogeneous hypoechoic area). A total of 613 heifer calves were enrolled in the study, with 489 (79.8%) classified as not having lung consolidation and 124 (20.2%) classified as having lung consolidation. No difference in mortality was observed from 60 to 350 d of life between heifers with lung consolidation (1.6%) and without lung consolidation (2.0%). Six hundred and one nulliparous Holsteins became eligible for insemination at 350 d of life; the hazard of being removed from the herd between 350 d of life and first calving for heifers with lung consolidation at weaning was higher (hazard ratio = 4.7, 95% confidence interval = 2.1 to 10.7). Additionally, heifers without lung consolidation tended to have improved pregnancy to first artificial insemination (62.0%) compared with heifers with lung consolidation (52.5%). Overall reproductive performance was also affected as heifers with lung consolidation at 60 d of life had a lower hazard of pregnancy compared with those without lung consolidation (hazard ratio = 0.7, 95% confidence interval = 0.6 to 0.8). From 601 animals that entered the breeding period, 565 entered the milking herd and were followed during the first 3 mo of lactation. No differences in weekly average milk production were observed between animals with or without lung consolidation at weaning. Our results show that heifers with lung consolidation at weaning were less likely to get pregnant and more likely to be culled before their first parturition than heifers without lung consolidation; this difference did not continue into first lactation milk production, risk of culling, or reproductive performance.