Uterine Contractions in Nonpregnant and Early Pregnant Mares and Jennies as Determined by Ultrasonography1

Uterine contractions in 8 nonpregnant and 13 pregnant mares were studied using ultrasonography. A 1-min video tape recording was made of longitudinal real-time images of the uterine body. An overall uterine contractile activity score (0 = no or minimal activity to 4 = maximal activity) was assigned to each video tape segment. There was a day effect (P less than .01) and an interaction (P less than .01) of reproductive status X day. Uterine activity scores were highest on d 14 to d 18 (d 0 = day of ovulation) for nonpregnant mares and on d 10 to d 14 for pregnant mares. Uterine activity scores on d 10, d 12, and d 14 were greater (P less than .02) for pregnant mares (2.5 +/- .3, 3.1 +/- .3, and 3.2 +/- .1, respectively) than for nonpregnant mares (1.2 +/- .3, 1.5 +/- .3, and 2.6 +/- .3). Uterine activity scores for six pregnant and five nonbred jennies were assigned daily from d 0 to d 24. There were main effects of reproductive status and day (P less than .01) and an interaction of status X day (P less than .01). Uterine activity scores for pregnant jennies were highest on d 13 and d 14 and then declined. In the nonbred jennies, scores were highest on d 14 to d 20. The mean score on d 13 was greater (P = .05) in pregnant jennies (2.8 +/- .2) than in nonbred jennies (1.9 +/- .5).(ABSTRACT TRUNCATED AT 250 WORDS)