Relationship between variation in conceptus development and differences in estrous cycle duration in ewes

The objective of this study was to examine conceptus development on Day 13 in ewes with estrous cycles of different durations. Ewes (n = 80) were screened according to the length of their estrous cycles. Subsequently, ewes that had either SHORT or LONG cycles were utilized (15.9 ± 0.1 or 18.6 ± 0.4 days; mean ± SEM, p < 0.01; 10 ewes per group). Jugular blood samples were collected twice daily from Days 0-6 after mating and then once a day until slaughter on Day 13. Concentrations of progesterone in plasma and amounts of ovine trophoblast protein-1 (oTP-1), protein, and prostaglandins (PG) E₂ and F(2α)(PGF(2α)) in uterine flushings were determined. Concentrations of progesterone were greater (Day by treatment interaction, p < 0.01) on Days 2-4 for ewes in the SHORT group. On Day 5 and thereafter, progesterone concentrations were not different between groups. More (p < 0.05) oTP-1 and protein (8.1 ± 1.3 μg and 1.8 ± 0.3 μg versus 2.4 ± 1.3 μg and 0.8 ± 0.3 mg) were recovered from uterine flushings from ewes in the SHORT versus LONG groups, respectively. The ratio of PGE₂:PGF(2α) was higher (p < 0.06) in flushings from ewes in the SHORT versus LONG group (1.4 ± 0.2 versus 0.9 ± 0.2, respectively). Conceptuses were classified by stage of morphological development. Conceptus development was accelerated (p < 0.01) in ewes of the SHORT group, as shown by filamentous conceptuses recovered from 78% versus 0% of SHORT versus LONG ewes, respectively. These data indicate that conceptus development and production of antiluteolytic signals occur sooner in ewes with shorter estrous cycles.