Determination of pregnancy and estimation of litter size in gilts based on concentration of estrone glucuronide and estradiol glucuronide in plasma

Three experiments were conducted to determine the concentration of estradiol glucuronide (E2G), and estrone glucuronide (E1G) in the blood of gilts after mating (Day 0). Blood samples were taken from 20 mated gilts at weekly intervals from Day 14 to Day 34 and analyzed by radioimmunoassay (RIA) for concentration of E2G and E1G. The concentrations of both hormones rose from about Day 19 to a peak at Day 26 and then declined. The concentration of E2G rose to 1700 pg ml−1 and E1G rose to 8000 pg ml−1 at Day 26. Eleven mated gilts in a second study were bled on Days 20, 22, and 24 and plasma analyzed for E2G and E1G. At slaughter on Days 29–35, gilts with more than 100 pg ml−1 of E2G or more than 1000 pg ml−1 of E1G on Day 20 or later were pregnant. In a third study, 31 gilts were bled at 48 h intervals from Day 20 to 28 and plasma was analyzed for concentration of E2G and E1G. All gilts with over 100 pg ml−1 of E2G and 30 of 31 with over 1000 pg ml−1 of E1G were pregnant when killed at Days 30–35. When gilts were classified according to the concentration of E2G at Day 20, 86% of gilts with over 200 pg ml−1 had eight fetuses or more and at Day 24, 77% of gilts with over 1100 pg ml−1 had eight or more fetuses. When gilts were sorted on the basis of over 1500 pg ml−1 on Day 20 and on Day 22 for over 3400 pg ml−1 of E1G, the percentages of correct classification for eight or more fetuses were 87% and 81% respectively. Concentration of E2G or E1G from Day 20 to 28 after mating can be used to detect pregnancy and estimate litter size at the time of analysis.