Bovine Pregnancy Associated Glycoproteins in Beef Cattle: Effects of Embryo Size and Various Methods of Handling of Plasma and Serum Samples
Abstract
Accurate assessment of pregnancy associated glycoproteins (PAG) in biological samples is fundamental for early pregnancy diagnosis and prediction of embryonic mortality in cattle. Two experiments were conducted to determine the effects of embryo size and various methods of handling of plasma and serum samples on PAG in beef cattle. The objective of experiment 1 was to determine a relationship between embryonic size and growth throughout gestation and circulating PAG concentrations. A total of 137 multiparous beef cows at three different locations were used for this experiment. Embryonic crown to rump length (CRL) was measured via transrectal ultrasound and PAG concentrations were determined using an in-house enzyme-linked immunosorbent assay (ELISA). Data were analyzed using PROC CORR (SAS 9.4). Birthweight was not significantly correlated with PAG concentrations on days 28 and 67 at Location 1 (r=-0.24; P=0.12 and r=-0.11; P=0.47, respectively). PAG on day 42 was associated with day 70 CRL at Location 3 (r=0.43; P= 0.04); however, no other CRL measurements were significantly associated with PAG concentrations. Few significant correlations between embryo-fetal growth and PAG concentrations were only detected at Location 3; however, the strength of the relationship lacked statistical power. In conclusion, PAG concentrations throughout different stages of gestation do not appear to be associated with embryo size or development. The objective of experiment 2 was to identify the effect of plasma or serum samples, time to centrifuge, repeated freeze-thaw cycles and antibody handling on PAG concentrations. Plasma and serum samples were collected from 2 pregnant and 2 open multiparous beef cows and evenly distributed to be centrifuged on the same day or one day post-collection. Samples were submitted to one, two and three freeze-thaw cycles, a no-thaw sample (pre-freezing), and an intact sample (no freeze-thaw cycles)were analyzed with an in-house ELISA. Data were analyzed using PROC GLM (SAS 9.4). A decrease in PAG concentrations was detected for serum compared to plasma (P<0.0001); however, plasma PAG concentration was not affected by multiple freeze-thaw cycles (P= 0.19) although serum concentrations were (P= 0.03). Interestingly, centrifugation day did not alter PAG concentrations in either plasma or serum (P= 0.50 and P= 0.59, respectively), nor did the utilization of frequently used monoclonal antibodies versus unfrequently used monoclonal antibodies (P= 0.89). In conclusion, plasma appears to be a more reliable source for detecting PAG concentrations.
Citation
Fernandez Montero, Lohana (2020). Bovine Pregnancy Associated Glycoproteins in Beef Cattle: Effects of Embryo Size and Various Methods of Handling of Plasma and Serum Samples. Master's thesis, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /192969.