Validation of a luciferase bioassay to detect the progestative activity in gilts whose estrus was induced by an uterotonic herb (Ligusticum chuanxiong)

Ligusticum chuanxiong (LC) is an uterotonic herb. Ethanol extract of LC has potent progestative activity. The progestative activity in rat serum was well documented after oral and subcutaneous administration of LC. The objective of this study was to investigate the possibility of LC for estrus synchronization of gilts in place of synthetic progesterone. Eighteen gilts were randomly assigned into three groups, control group fed normal feed, positive control group supplemented with 20 mg of altrenogest (Regumate®) and treatment group supplemented with 100 g of LC daily for 22 consecutive days in feed. Blood samples were collected from jugular vein of gilts on the 22nd day before altrenogest or LC feeding. Estrus was monitored every day in the morning and the evening by observing the vulva swelling and reddening as well as nose to nose fence line contact between the boar and sow. Estrus was confirmed by testing the standing reflex in the presence of boar. All gilts in LC-fed group and 5 gilts in altrenogest-fed group came in estrus within 2–6 days after withdrawal of feeding, but did not show estrus during the feeding period. Whereas, all gilts in control group came in estrus during the feeding period. Progesterone responsive reporter plasmid was constructed by incorporating the progesterone response elements and TATA box at the multiple cloning site of pGL3 basic vector. Gilts serum progestative activities were measured by using luciferase reporter gene bioassay. Serum analysis showed that progestative activities of altrenogest- and LC-supplemented groups had a similar pattern. It is concluded that LC is a potential feed additive to be used for estrus cycle synchronization in swine industry.