Use of Pregnancy Associated Glycoproteins to Determine Fetal Age Throughout Gestation and Clearance Rate in Postpartum Beef Cattle

Study Description: Previously identified pregnant females from four different herds and postpartum females from one herd were utilized. Blood samples were collected (n = 1,753; study 1) between d 28 and 285 of gestation and (heifers n = 418 and cows n = 657; study 2) once a week for up to 12 weeks after calving. Serum was tested in duplicate using a commercially available blood pregnancy test, IDEXX Alertys Pregnancy Test. In study 1, procedures were modified to allow PAG concentrations to fall within the detectible range of the assay. Data were analyzed using the MIXED procedure of SAS with cow age and gestational age (also divided into four gestational age groups: 1) \u3c 30 d; 2) 30-90 d; 3) 91-180 d; 4) \u3e 180 d) in the model and then analyzed further using the REG procedure in SAS within gestational age group. In study 2, data were analyzed as repeated measure using the MIXED procedure of SAS with cow age, days postpartum (dpp), and cow age by dpp in the model, then data were analyzed further using the REG procedure in SAS. In study 1, there was a significant effect of gestational age and cow age by gestational age interaction (P \u3c 0.01) as well as a tendency of cow age (P = 0.08). Among heifers and cows, serum PAG concentrations did not differ between gestational age groups 1 and 2 (P \u3e 0.84), however, PAG concentrations differed between groups 2 and 3 (P \u3c 0.0001) and 3 and 4 (P \u3c 0.0001). There was a positive correlation between gestational age and PAG concentrations (P \u3c 0.01; r2 = 0.2604). In study 2, there was a significant effect of days postpartum (dpp; P \u3c 0.01) on PAG concentrations; however, PAG concentrations were not influenced by cow age (P = 0.73) or cow age by dpp (P = 0.55). Concentrations of PAGs rapidly decreased from d 0 to 50 postpartum and then continued to gradually decrease (P \u3c 0.01; r2 = 0.8083). Prior to 42 dpp, PAG concentrations were sufficiently elevated which resulted in false positive readings