| Summary: | The aim of this study was to assess the relationships between the evolution of the corpus luteum size determined by ultrasonography and plasma progesterone concentration in Cheurfa cows during the estrous cycle. Luteal activity was evaluated daily by plasma progesterone concentrations determined by radioimmunassay at each ultrasound examination. The interovulatory interval was 20.5±0.6 days. The corpus luteum clearly delimited 2 days after ovulation reached its maximal size on day 10. The plasma progesterone concentration reached its maximum on days 14. There was a day effect of estrous cycle on corpus luteum size (P<0.0001) and plasma progesterone concentration (P<0.0001). During the growing and regression phases of corpus luteum, a significant correlation was found between plasma progesterone concentration and corpus luteum size. In conclusion, the relationships between the corpus luteum size and plasma progesterone concentrations throughout the estrous cycle in Cheurfa cow were similar to other cattle breeds.
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