Effect of number of corpora lutea and fetuses on concentrations of progesterone in blood of goats

The objectives of this study were to assess relationships between 1) number of corpora lutea (CL) and concentrations of progesterone (P) in plasma of goats from onset of estrus (d 0) to d 45 of pregnancy and 2) concentration of P and number of fetuses on d 45. Blood from 79 pregnant goats was obtained on d 0 and 1 and at 48-h intervals thereafter to d 25 of gestation. Additional samples were collected every 5 d from d 25 to d 45. Plasma samples were analyzed for P by RIA. Fetuses and CL were counted at laparotomy on d 45 +/- 3. Six does had one CL, 47 had two and 26 had three or four. Concentrations of P were compared for 1) animals with different numbers of CL and 2) animals with the same number of CL but different numbers of fetuses on d 45. Concentration of P increased in all animals from d 3 to a maximum of 8.5 +/- .3 ng/ml on d 13, then P declined to 5 +/- .3 ng/ml by d 35. Goats with multiple CL had higher P than goats with one CL (P less than .01) from d 7 to d 30. Of goats with two CL, those with two fetuses at d 45 had higher P on d 13 than those with one fetus (P less than .01). The number of CL or fetuses did not influence the concentration of P after d 30.