Plasma progesterone levels throughout the oestrous cycle and release of LH at oestrus in sheep with different ovulation rates

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Abstract
The concentrations of progesterone in the peripheral plasma throughout the estrous cycle and the preovulatory LH [lutropin] discharge were examined in Finnish Landrace, Galway and Fingalway (Finnish Landrace .times. Galway) ewes. Progesterone levels were significantly higher in Finnish Landrance ewes during the luteal phase of the cycle (Days 10-13) than in Galways or Fingalways in which the concentrations were similar. Luteal-phase progesterone levels were almost 50% higher during December than during October in all 3 breeds. The relationship between the number of CL [corpus lutea] and plasma progesterone was not a simple linear function. All aspects of the preovulatory LH discharge were similar in the 3 breeds with the exception of the timing of the LH release in relation to the onset of estrus. This occurred earliest in the Galway and latest in the Finnish Landrance while the Fingalway was intermediate.