ASSESSMENT OF FETAL NUMBER, AND FETAL AND PLACENTAL VIABILITY THROUGHOUT PREGNANCY IN CATTLE

Production of identical twin calves by embryo demisection requires a r eliable system for continual monitoring of pregnancy. Both halves of b isected embryos were replaced nonsurgically into one uterine horn on D ay 7 in 80 recipients. Monthly blood sampling began on Day 22 of pregn ancy and transrectal echography took place between 50 and 80 days. Fif ty-four recipients had elevated plasma progesterone concentrations on Day 22 (67% pregnancy rate). Of 21 pregnancies diagnosed as twins by e chography, 15 live sets were born, 3 singles accompanied by a stillbir th, and 3 complete abortions. Twenty-five singleton pregnancies result ed in 23 live calves, 1 still-birth and 1 abortion. It was not possibl e to monitor echographically the remaining 8 pregnancies. At all stage s of pregnancy studied, mean concentrations of bovine pregnancy-specif ic protein B (bPSPB) and estrone sulphate were higher (P < 0.01) in tw in (n = 17) than in single (n = 26) pregnancies, but the high individu al variation obviated any predictive value for fetal number. Although bPSPB and estrone sulphate concentrations were positively correlated a t most stages of normal pregnancies after Day 100, divergence was obse rved 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-bein g, whereas estrone sulphate may reflect placental viability.