Evaluation and development of early pregnancy diagnosis in dairy cattle
Early chemical pregnancy tests for use in dairy cattle are necessary to aid in reducing the costs associated with days the animal is not pregnant. Identifying non-pregnant dairy cattle sooner would allow for efficient treatments and improve decision making for culling cows from the herd. A new rapid visual pregnancy associated glycoproteins test 25 days after insemination had equal sensitivity and accuracy to existing tests. With respect to on-farm application, the slightly lower specificity reinforces the need for a second pregnancy diagnosis (either chemical test or alternative method) after the period of embryonic loss has subsided. Measurement of interferon stimulated gene 15 in milk and blood cells was successful to detect non-pregnant cows but was not robust to serve as an imperfect early pregnancy biomarker. ISG15 expression in both blood and milk somatic cells was greater for pregnant compared with non-pregnant Holstein cows. The reason for increased ISG15 expression and variability among cows is still not understood. ISG15 expression in peripheral blood leukocytes was greater for pregnant compared with non-pregnant Holstein cows. ISG15 increased in the circulation during early pregnancy and responded to a minimal dose of 10 pg/ml when blood was tested in vitro. The in vivo response to pregnancy and in vitro responses to a known dose of IFNT, however, were not correlated. Individual cow differences for ISG15 were not explained by the sensitivity of PBL to IFNT. We failed to confirm a strong correlation between day 18 ISG15 expression and day 25 PAG concentration in pregnant dairy cows and heifers. Further investigation of novel biomarkers to develop a robust chemical pregnancy test in dairy cows 18 days after insemination is still needed.
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