Use of blood collected onto and dried on filter paper for diagnosing pregnancy in cattle

The measurement of serum or plasma pregnancy-associated glycoproteins (PAGs) is increasingly used to diagnose pregnancy in cattle. This study evaluated whether a dried blood spot (DBS) collected on filter paper could be used as an alternative to serum or plasma for such tests. A total of 37 serum, 68 plasma and 68 DBS samples were collected from cows of known pregnancy status and tested using a commercial ELISA.None of the plasma or serum samples resulted in false positives or false negatives. No false positives (sample-negative (S-N) values >0.3 in non-pregnant cows) were observed with DBS samples, but false negatives were observed (S-N values <0.3 in pregnant cattle). The data suggested that PAGs in DBS samples were diluted during processing as samples from pregnant cattle had lower S-N values (0.111–0.494) than the corresponding serum (1.123–2.665) and/or plasma (0.764–2.042) samples.ROC analysis showed that lowering the cut-off S-N value from 0.3 to 0.1 for DBS samples prevented false negatives without increasing false positives. Modifications to the test protocol significantly increased mean S-N values of DBS samples from pregnant cows while those from non-pregnant cows were not affected. In conclusion, lowering the cut-off and modifying the protocol allowed DBS samples to be used for blood-based pregnancy testing.