Plasma Estrogen, Progesterone and Luteinizing Hormone Levels During the Estrous Cycle in Pigs1

Abstract

Plasma estrogen progesterone and luteinizing hormone (LH) were det ermined during the estrous cycle in 6 pigs and during 24 hours on the 1st day of estrus (Day 0) in 4 pigs. Estrogen was low (less than 20 pg/ ml) during the cycle until Day 16 or 17 when it increased to a maximum of more than 50 pg/ml 1-2 days prior to estrus. Progesterone increased from 5.1 to 25.2 ng/ml between Days 2 and 6 and reached a maximum of 33.2 ng/ml by Day 12. Estrogen levels increased only after progesterone levels began to fall. LH decreased from 2.5 ng/ml on Day 0 to below 1 ng/ml until the next estrus when it increased to more than 5 ng/ml while estrogen was greater than 20 pg/ml and progesterone remained at 1 ng/ml.