PREGNANCY-SPECIFIC PROTEIN-B AND PROGESTERONE CONCENTRATIONS IN RELATION TO NUTRITIONAL REGIMEN, PLACENTAL MASS AND PREGNANCY OUTCOME IN GROWING ADOLESCENT EWES CARRYING SINGLETON FETUSES

The objective of this study was to investigate whether peripheral plas ma profiles of pregnancy specific protein B (PSPB) are predictive of p regnancy outcome in adolescent sheep in which growth of the placenta h as been compromised by the competing nutrient demands of maternal tiss ue synthesis. Embryos recovered on day 4 after oestrus from adult ewes inseminated by a single sire were transferred in singleton to prepube rtal adolescent recipients. After transfer, the adolescent recipients were individually offered a high or low proportion of a complete diet to promote rapid (RMG) or normal (NMG) maternal growth rates (n = 12 p er group). After day 100 of gestation the feed intake of the NMG group was adjusted weekly to meet the nutrient requirements of the gravid u terus. Blood was sampled three times a week throughout gestation and a nalysed for PSPB and progesterone. Liveweight gain during the first 12 0 days of gestation was 229 +/- 9.1 and 105 +/- 3.9 g day(-1) for the RMG and NMG groups, respectively. For ewes delivering live young, mean placental mass at term was 263 +/- 16.8 and 438 +/- 44.6 g (P < 0.002 ), while lamb birthweight was 2.74 +/- 0.25 and 4.34 + 0.27 kg (P < 0. 001) for the RMG (n = 8) and NMG (n = 11) groups, respectively The bip hasic pattern of PSPB secretion during gestation was similar in all ew es delivering live young, but individual concentrations within treatme nt groups were highly variable. Mean PSPB concentrations were lower in RMG than in NMG ewes throughout gestation (P < 0.05) and the major di fferences in relative terms were detected between days 50 and 100 of p regnancy. PSPB concentrations during this latter period were correlate d (P < 0.05) with placental mass at term but not with lamb birthweight . High dietary intakes, leading to rapid maternal growth rates were as sociated with low peripheral progesterone concentrations (P < 0.02) th roughout gestation. Irrespective of treatment group, progesterone conc entrations during the second half of pregnancy were positively associa ted with both placental mass at term (P < 0.002) and lamb birthweight (P < 0.01). The incidence of non-infectious abortion during late gesta tion (125 +/- 1.3 days) was higher (P < 0.001) in the RMG (4 of 12) th an in the NMG (1 of 12) group and was associated with abnormal PSPB pr ofiles in the former group. The mass of the fetus at the time of abort ion was highly correlated (P < 0.01) with mean PSPB concentrations up to day 120 of gestation, but was independent of peripheral progesteron e concentrations. These results suggest that sequential measurement of PSPB may provide a reliable indicator of fetal distress and adverse p regnancy outcome in singleton bearing ewes. PSPB and progesterone anal ysis may also have prognostic value as a biochemical marker of subopti mal placental growth and function in sheep.