Assessment of fetal number, and fetal and placental viability throughout pregnancy in cattle.

Production of identical twin calves by embryo demisection requires a reliable system for continual monitoring of pregnancy. Both halves of bisected embryos were replaced nonsurgically into one uterine horn on Day 7 in 80 recipients. Monthly blood sampling began on Day 22 of pregnancy and transrectal echography took place between 50 and 80 days. Fifty-four recipients had elevated plasma progesterone concentrations on Day 22 (67% pregnancy rate). Of 21 pregnancies diagnosed as twins by echography, 15 live sets were born, 3 singles accompanied by a stillbirth, and 3 complete abortions. Twenty-five singleton pregnancies resulted in 23 live calves, 1 still-birth and 1 abortion. It was not possible to monitor echographically the remaining 8 pregnancies. At all stages of pregnancy studied, mean concentrations of bovine pregnancy-specific protein B (bPSPB) and estrone sulphate were higher (P<0.01) in twin (n = 17) than in single (n = 26) pregnancies, but the high individual variation obviated any predictive value for fetal number. Although bPSPB and estrone sulphate concentrations were positively correlated at most stages of normal pregnancies after Day 100, divergence was observed in the unsuccessful pregnancies between the concentrations of all 3 hormones, suggesting synthesis/release is under independent control. Measurement of bPSPB may be useful for prediction of fetal well-being, whereas estrone sulphate may reflect placental viability.