Abstract
Changes in the ovaries and plasma progesterone (P) and estradiol-17β (E2) levels were examined and compared to pregnancy and twinning rate in 17 Holstein-Friesian cows with twin ovulations after insemination. Plasma P and E2 levels of 8 cows that conceived following a single ovulation were used as normal controls. Of the 17 cows, 11 cows conceived; 5 cows delivered twins, 4 cows had a single, and remaining 2 cows aborted fetuses at 95 and 106 days of pregnancy, respectively. In 6 other non-pregnant cows, 2 cows ovulated again 20 & 21 days after insemination, and 4 cows ovulated 26-58 days after the service. Plasma P levels in all cows changed within the range of mean±2SD of the levels in control cows during the period of 12-13 days after insemination. The levels decreased coincident with the regression of either of the 2 corpora lutea in 1 cow which delivered a single, and in 4 non-pregnant cows which showed a prolonged estrous cycle. Plasma E2 levels in pregnant cows changed within the range of the control level, but the levels in non-pregnant cows changed above or over the control level. The results indicated that there was a high incidence of the embryonic death after twin ovulation, and an increase of plasma E2 level after ovulation may adversely affect embryo survival rate. No relationships between plasma P profiles and pregnancy rate were observed.
