The objective of this study was to examine the effects of metritis and subclinical hypocalcemia on reduction of uterine size in dairy cows using ultrasonography and sonomicrometry. Four piezoelectric crystals were implanted via laparotomy into the myometrium of the pregnant uterine horn of 12 pluriparous Holstein Friesian cows 3 weeks before the calculated calving date. Sonometric measurements were conducted daily from 2 days before parturition (= Day 0) until Day 14 after calving and then every other day until Day 28. Distances between adjacent crystals were expressed in relation to reference values obtained before calving. The diameter of the formerly pregnant uterine horn was measured using transrectal B-Mode sonography starting on Day 10. Cows were retrospectively divided into the following groups: cows without metritis (M–; n = 7), cows with metritis (M+; n = 5), cows with normocalcemia (SH–; Ca > 2.0 mmol/l on Days 1 to 3; n = 5) and cows with subclinical hypocalcemia (SH+; Ca < 2.0 mmol/l in at least one sample between Days 1 and 3; n = 7). Metritis did not affect (P > 0.05) sonometric measurements, but the diameter of the formerly pregnant horn was larger (P ≤ 0.05) between Days 15 and 21 in M+ cows than in M‒ cows. Reduction in uterine length in hypocalcemic cows was delayed (P ≤ 0.05) between Days 8 and 21 compared with normocalcemic cows, but the uterine horn diameter was not related to calcium status. In conclusion, both diseases affected reduction of uterine size until Day 28. Cows with metritis had a larger uterine diameter, possibly attributable to accumulation of lochia, and cows with subclinical hypocalcemia had delayed reduction of uterine length, presumably related to reduction of myometrial contractility.

Sonomicrometry allows the measurement of the distance between 2 piezoelectric crystals and has been widely used to investigate the contractility of the heart and gastrointestinal tract. The objective of this study was to determine whether this method can be used to quantify the reduction in uterine size in cows postpartum. Seven healthy pluriparous Holstein Friesian cows (3.7±0.7 yr old, parity 2.4±0.5, mean±SD) were used. Three weeks before calving, 4 piezoelectric crystals were implanted via laparotomy in the myometrium of the greater curvature of the pregnant uterine horn in a longitudinal direction. Sonometric measurements were conducted daily from 2 d before parturition until 14 d after calving, followed by measurements every other day until d 28. Changes in the distance between neighboring crystals were presented as relative changes (%) from baseline values before parturition. The diameter of the previously pregnant uterine horn was measured using transrectal B-mode sonography from d 10 to 28 after calving. The cows were slaughtered 39±6 d postpartum and the uterus was evaluated for fixation of the crystals. The distances between neighboring crystals underwent changes with a reduction of greater than 50% until d 1 postpartum, but no further changes were recorded from d 1 to 7. In the second week, changes in all distances were affected by day postpartum. One distance was affected by day postpartum in wk 3 and 4. There was a positive correlation between the diameter of the previously pregnant horn and the distances between the crystals. Examination of the uterus after slaughter of the cows revealed that 8 crystals (29%) were no longer fixed in the myometrium. Seven of these (25%) could be evaluated completely or partially and 1 (4%) could not be analyzed. Sonomicrometry seems to be suitable for the objective measurement of reduction in uterine length in cows.