Urinary Estrone Sulfate for Monitoring Pregnancy of Dairy Cows

The purpose of this study firstly was conducted to establish a radioimmunoassay (RIA) of estrone sulfate ( E1S ), secondly to monitor the reproductive status of dairy cows using their urine samples. Urine and blood samples were collected in series within a day from four pregnant Holstein-friesian cows to evaluate the relationship between E1S levels in blood and urine with or without urinary creatinine basis. The urine was then collected biweekly from three cows in estrous and those artificially inseminated; collection from pregnant cows was made on a monthly basis. Results indicated that sensitivity for the E1S RIA was 5 pg/tube and the recovery rate was 100%. The daily urinary creatinine concentrations fluctuated within a day, but changes were slighter in midday, whereas the changes of concentrations of E1S in urine were relatively smaller. The concentrations of serum E1S during the estrous cycle were undetectable due to the limitation of assay, but the urinary E1S level could be measured with no obvious changes during the cycle. The urinary E1S levels increased remarkably around 7.7 to 8.3 ng/ml, 80 to 100 days after pregnancy but the serum E1S levels did not elevate until 120 to 150 days. The level of E1S increased gradually during pregnancy and eventually reached its peak before parturition at around 40 ng/ml and finally decreased to its basal level 2 days postparturition. During pregnancy, E1S concentrations of urine increased earlier than those in blood. The correlation coefficients between urinary and serum E1S concentration during pregnancy and postparturm were higher than those adjusted with creatinine (creatinine ratio). The concentrations of E1S in urine could be maintained unchanged for 8 days storing the samples in room temperature, which was extended to 8 days when the samples were pretreated by boiling for 30 minutes or treated with autoclave. In conclusion urinary E1S concentrations can be used directly for monitoring the pregnant status and fetal viability of dairy cows and can assist accurate confirmation of pregnancy in cows at least 80 to 100 days after insemination much earlier than by serum E1S. (Asian-Aust. J. Anim. Sci. 2003. Vol 16, No. 9 : 1254-1260)