인공수정 및 수정란이식 후 젖소의 혈액과 유즙에서 Progesterone과 Estrogen 농도 변화와 수태율과의 상관관계

Progesterone and Estrogen Levels in Holstein Blood and Milk Following Artificial Insemination and Embryo Transfer

Early pregnancy diagnosis of bovine is an essential component for efficient reproductive plan in farms because long term of non-pregnancy results in economic losses by failure of offspring production and low milk yield in dairy cattle. The major steroid hormones related with reproduction are known to be progesterone and estrogen in bovine pregnancy. To evaluate detection level of hormones in milk, plasma and milk progestrone and estrogen of Holstein cows was analyzed during artificial insemination (AI) and embryo transfer (ET). Progesterone concentration at 21 days postestrus was significantly different in plasma and milk between pregnant and non-pregnant cows. Estrogen concentration at estrus was higher in pregnant recipients than that in non-pregnant recipients. To analyze correlation between hormone levels and conception rates in Holstein, the conception and return rates were checked following AI, and the returned cows were on the track of pregnancy after consecutive AI. Pregnant cows following first AI were considered as high conception group while pregnant cows following third AI were rated as low conception group. Proportion of high and low conception groups in this study was 78.2% and 9.1%, respectively. Hormone analysis indicated that high conception group had higher estrogen level during estrus than low conception group ($26.45{\pm}3.32$ vs $19.017{\pm}2.97$). Progesterone level was not different between high and low conception groups during estrus but increased significantly after 21 days postestrus (21 day: $4.95{\pm}1.12$ vs $0.95{\pm}0.23$, 35 day: $12.47{\pm}3.82$ vs $2.41{\pm}1.21$). In conclusion, the pattern of progesterone and estrogen secretion in Holstein milk samples could be a good candidate for early pregnancy detection and selection of recipients during ET.