141EFFECT OF NUMBER OF LAMBS, THEIR SEX AND BIRTH WEIGHT ON OVINE PREGNANCY-ASSOCIATED GLYCOPROTEIN (ovPAG) CONCENTRATIONS

Abstract

Early pregnancy detection and prediction of the number of lambs would be profitable for sheep breeders, as this enables nourishment of pregnant ewes to their individual needs. Nonpregnant ewes can be separated and sold before winter. Prediction of sex is interesting for the curiosity of impatient breeders. Early pregnancy detection (before 45 days after mating) by means of ovine pregnancy-associated glycoproteins (ovPAGs) has proved to be a more reliable test than the commonly used transrectal ultrasound. The concentration of ovPAG has been claimed to be related to the number of lambs, their sex and birth weight, but contradictory results were obtained in different small-scale studies. In this study the correlation between number of lambs, their sex and birth weight and the ovPAG concentration in the serum of the ewes was examined. In a field trial, 160 and 70 ewes of the Texel and Suffolk breed, respectively, housed on 6 different farms, were synchronized by means of intravaginal sponges impregnated with 40mg cronolone (Chronogest®, Intervet, Boxmeer, The Netherlands). At the moment of synchronisation (T0) and at 25 (T25), 35 (T35) and 45 (T45) days after mating or artificial insemination, blood samples were taken by jugular vein puncture. A heterologous radioimmunoassay (RIA) was used to determine the ovPAG concentration. In the heterologous RIA boPAG molecules were used as tracer, and ovPAG molecules as standard, while rabbit antibodies against ovPAG were used as antiserum. At parturition, number, sex and birth weight of the lambs were registered and their effect on ovPAG concentrations was statistically evaluated. No significant difference in ovPAG concentration was found between ewes pregnant of a single male or female lamb (P=0.29). ovPAG concentrations were affected by the total birth weight (P<0.05). In ewes pregnant with multiples, the ovPAG concentrations were higher (P<0.01) than in ewes pregnant with singles at T25, T35 and T45, respectively. Because ovPAG concentrations were affected by the farm, it was impossible to predict the number of lambs by the ovPAG level. In conclusion, ovPAG concentrations were not affected by the sex of the lamb. However, ovPAG concentrations were related to the total birth weight. Within the farm, increased ovPAG concentrations may indicate pregnancy of multiples.