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

Abstract

Plasma estrogen, progesterone and luteinizing hormone (LH) concentrations were determined during the estrous cycle in six pigs and throughout the day on the first day of estrus (Day 0) in four pigs. Fifty-seven blood samples were collected during the cycle and 16 samples on the day of estrus. The mean plasma estrogen level was low (< 20 pg/ml/ animal) during the cycle until Day 16 or 17 when it began to increase reaching a maximum level (> 50 pg/ml/animal) one or two days prior to estrus. The mean progesterone level increased rapidly from 5.1 to 24.2 ng/ml/animal between Days 2 and 6, and continued to increase to reach a maximum level (33.2 ng/ml/animal) by Day 12. The mean estrogen level began to increase only after the progesterone level began to fall. The mean LH level was 2.5 ng/ml/animal on Day 0, then decreased below 1 ng/ml/animal until the next estrus. At estrus, the LH level increased to a high level (> 5 ng/ml/animal), while the estrogen level was high (> 20 pg/ml/animal) and progesterone remained below 1 ng/ml/animal.