18 ng/ml) approximately. 24 h prior to the end of estrus. The levels of LH was. 10-15 ng/ml. (baseline) throughout diestrus. Levels of progesterone were low. (
BIOLOGY
OF
REPRODUCTION
14,412-415
(1976)
Levels of Luteinizing Hormone and Progesterone During Estrous Cycle and Early Pregnancy in Mares T. M. NETT,
B. W. PICKETT,
J.
and Animal
G. E. SEIDEL,
Colorado Fort
State
Collins,
JR.
L. VOSS
Reproduction of Physiology
Department
the
Laboratory, and Biophysics, University,
Colorado
80523
ABSTRACT Jugular venous blood was collected from 16 mares at daily intervals throughout the estrous cycle. Twelve of these mares were bred to fertile stallions. Of the twelve, four were palpated daily throughout the estrous cycle, four were palpated daily during estrus and four were not palpated. The remaining four mares were not palpated or bred and blood samples were collected at 6-h intervals during estrus. Serum was harvested from all blood samples by centrifugation. The serum samples were analyzed for luteinizing hormone (LH) and/or progesterone by radioimmunoassay. Levels of LI-I in serum increased gradually beginning at the onset of estrus and reached a peak (85 ± 18 ng/ml) approximately 24 h prior to the end of estrus. The levels of LH was 10-15 ng/ml (baseline) throughout diestrus. Levels of progesterone were low (