[Pregnancy Diagnosis by Detection of Pregnancy-associated Glycopoteins in Milk: Evaluation of a Commercial Available ELISA]

In order to increase fertility in modern dairy farming, the interval between first insemination and conception should be as short as possible. Therefore, one approach is to diagnose non pregnant animals early to re-inseminate them as soon as possible. Commercial milk pregnancy assays are available to detect throphoblast derived bovine pregnancy-associated glycoproteins (bPAG) in milk. The aim of the present study was first to evaluate pre-analytical factors interfering with the correct detection of bPAG in milk. To achieve this aim, the stability of the bPAG was tested after repeated freezing and thawing cycles, as well as after a storage of seven days at room temperature and at 37°C. Secondly, the diagnostic performance of a commercially available PAG-ELISA was evaluated for pregnancy diagnosis between 28 to 60 days after artificial insemination by comparing the results with transrectal ultrasonography in a field study (n = 291 cows). After one freezing and thawing procedure the optical density (OD) increased and afterwards stayed stable. The storage of milk samples at room temperature had no effect on the OD, but after five days of storage at 37 °C the OD dropped sharply. It is therefore recommended to add an appropriate microbicidal preservative for shipment and storage of milk samples for bPAG analysis . The results of the field study showed that PAG-ELISA results and ultrasonography results agreed in 95.7% of the cases. Nine samples were tested as "false negative"and five as "false positive", however a re-check revealed that all "false positive"and "false negative" tested cows suffered from embryonic/fetal mortality. In conclusion, the pregnancy diagnostic by bPAG detection in milk samples is an accurate method to diagnose early pregnancy in lactating cows.