Ultrasonography and progesterone concentration at a single time point for the detection of puberty in dairy heifers

Data were available from 1657 heifers across 48 dairy farms which were visited once, on average 9days (±5.2) prior to the mating start date (23 April, ±12.6). Blood samples were collected via coccygeal venepuncture for progesterone (P4) analysis, and animals were scanned for the presence or absence of corpora lutea (CL), to determine the luteal status. A comparison of luteal status between ultrasound (CL identified) and P4 (≥1ng/ml), based on a single measurement point, showed poor agreement (K=0.32). The majority of animals were classified as luteal (76%) using both ultrasonography and P4. There was excellent agreement between luteal status detected by ultrasonography alone and luteal status assigned by a combination of ultrasonography and P4 (K=0.93). The agreement between luteal status assigned by P4 and luteal status assigned by the combination of ultrasonography and P4 was poor (K=0.37). These results indicate that at a single examination, ultrasonography is the preferred modality to determine the luteal status of maiden heifers.