Studies on the improvement of reproductive efficiency in Korean native cows -Plasma progesterone concentrations during the estrous cycle and early pregnancy-

한우(韓牛)의 번식효율(繁殖效率) 증진(增進)에 관한 연구(硏究) -발정주기(發情周期) 및 임신초기(姙娠初期)의 progesterone 농도변화(濃度變化)-

A study was conducted to improve the reproductive performance of Korean native cows. Plasma progesterone concentrations were determined by radioimmunoassay during the estrous cycle and early pregnancy. Plasma progesterone concentrations during the estrous cycle in the 15 cows were the lowest (0.30ng/ml) at estrus, gradually increased after 6 days, remained high from 8 to 17 days (3.87~5.59ng/ml) and drastically decreased thereafter to reach minimal concentrations at the next estrus. Plasma progesterone concentrations of the 10 pregnant cows at 20 days after insemination were $5.82{\pm}1.33ng/ml$ (mean${\pm}$SD) and those of 10 non-pregnant cows were $0.30{\pm}0.21ng/ml$, respectively. Therefore, plasma progesterone concentrations in the pregnant cows at 20 days after insemination were significantly higher than in non-pregnant cows (p<0.001).