Influence of Season and Nutrition on Luteal Plasma Progesterone in Rambouillet Ewes

Abstract

Plasma concentrations of progesterone in the ewe reach a plateau by about the 10th day of the estrous cycle, though there is considerable variation between days and animals (Stabenfeldt, Holt and Ewing, 1969; Thorburn, Bassett and Smith, 1969). Thorburn et al. (1969) observed variation in the luteal phase peak values of progesterone in the same ewes in successive cycles, which they speculated was due to variation in number of CL. Season and nutrition influence annual reproductive rhythms and also affect the suppressive action of exogenous progesterone on estrus and ovulation (Lamond, 1963, 1964). The purpose of the present study was to relate luteal phase plasma progesterone concentration to number of CL in ewes maintained for an 8-month period on three nutritional regimes. Animals and Treatments. Grade Rambouillet ewes were obtained rom Southwest Texas in 1969 and were allotted to three treatment groups in March, 1970, at 2 years of age. Copyright © 1972. American Society of Animal Science . Copyright 1972 by American Society of Animal Science.