Levels of bPSPB throughout single and twin pregnancies after AI or transfer of IVM/IVF cattle embryos

Blood plasma measurements of bovine pregnancy-specific protein B (bPSPB) during gestation in Alentejano beef cows were used to characterize twin pregnancies resulting from transfer of in vitro fertilized embryos (TWIN IVF; n = 25, beef crosses), single pregnancies resulting from transfer of similar embryos (SING IVF; n = 35, beef crosses) and single gestations resulting from artificial insemination (SING AI; n = 36, pure breed), as well as late embryonic mortality associated (HS; n = 10) or not associated (EM; n = 16) with heat stress. Blood samples were collected monthly starting at 40 days of pregnancy. Levels of bPSPB at 40 days were significantly lower in cows with EM (0.56 ± 0.18 ng ml−1) and HS (0.15 ± 0.09 ng ml−1) than in cows finally calving twins (3.63 ± 0.43 ng ml−1) or singletons (1.87 ± 0.14 ng ml−1) . In six out of ten cows of the HS group, levels of bPSPB rose above the detection limit only at 70 days after estrus, while in the EM group only 1 of 16 cows presented the same pattern (P ⪕ 0.035). PSPB concentrations in TWIN IVF cows were significantly higher than those of SING IVF cows at 40 and 240 days of pregnancy (3.85 ± 0.30 vs. 2.04 ± 0.26 ng ml−1, and 715 ± 63 vs. 415 ± 58 ng ml−1, respectively; P < 0.001). The TWIN IVF group of cows presented significantly higher concentrations of bPSPB than SING AI cows at all stages of gestation, except at 180 days. In the single pregnancy groups, cows carrying fetuses originated by IVF embryos, when compared with cows carrying fetuses originated by AI, presented significantly higher concentrations of bPSPB from 100 to 210 days of pregnancy and at calving. The rate of increase in bPSPB from 40 to 240 days of gestation, taken from the slope of multiplicative regressions, was significantly higher in SING IVF than in TWIN IVF and SING AI groups of cows (3.284 ± 0.085 vs. 2.750 ± 0.101 and 2.852 ± 0.086, respectively; P < 0.0001). After spontaneous calvings, calves born from the SING IVF cows were significantly heavier than those born from either SING AI or TWIN IVF cows (58 ± 3 vs. 42 ± 2 and 39 ± 2 kg, respectively; P < 0.0001). Twin gestations were 8 days shorter than single ones (P < 0.0001). In conclusion, bPSPB measurements at 40 and 70 days of gestation are useful to diagnose embryo losses occurring later then 21 days of gestation. Heat-stressed cows with embryo losses presented a retarded pattern of bPSPB production, suggesting an impaired metabolic function of the trophoblast until near 70 days of gestation. Significantly higher amounts of bPSPB are produced at 40 days in twin pregnancies. A larger variation and higher bPSPB production were observed in cows carrying crossbred fetuses derived from IVF techniques than in purebred AIʹed cows. These results suggest that there is a relationship between fetal growth rate and PSPB increase during pregnancy in cattle.