[en] Early pregnancy detection and prediction of the number of lambs would be profitable for sheep breeders because it enables them to adjust nourishment of pregnant ewes according to the individual needs in order to prevent health problems around parturition. The concentration of ovPAG has previously been reported to be related with maternal parameters (farm, breed and age) as well as foetal parameters (number of lambs, their sex and birth weight), but contradictory results were obtained in different small-scale studies. This large-scale study evaluates the effect of these parameters on the ovPAG concentration, determined by a homologous radioimmunoassay (RIA), and it further investigates the possibility to predict the number of lambs by means of homologous ovPAG determination. Eighty-three and ninety-five ewes of the Suffolk and Texel breed, respectively, housed on four different farms (experiment 1) and 68 ewes of the Suffolk breed, housed on two different farms During the last 6 weeks of pregnancy determination of 3-OH butyrate can be used to determine a necessary nutrition correction . In conclusion, the present study has shown an effect of different parameters such as farm, breed of the ewes, and number and birth weight of the lambs on ovPAG concentrations at all time points. Prediction of litter size based on ovPAG concentrations at the individual ewe level was not useful due to small sensitivity and/or specificity, notwithstanding significantly increased odds of multiple lambs. Furthermore, age of the ewes and sex did not have an impact oil ovPAG levels.