Relationship between ultrasonic assessment of the corpus luteum and plasma progesterone concentration in heifers

Abstract

In nulliparous Holstein heifers, ultrasonography was used to measure cross-sectional areas of corpora lutea, central luteal cavities and luteal tissue on Days 2, 5, 8, and 11 and daily on Days 14 to 21 (pregnant heifers, n = 7) or Day 14 to the day of the subsequent ovulation (nonbred and bred nonpregnant heifers, n = 7 and n = 8, respectively). A blood sample for progesterone assay was collected prior to each ultrasound examination. Combined for the three reproductive statuses, luteal tissue area and plasma progesterone concentration increased (P < 0.0001) over Days 2, 5, 8, and 11; the rate of increase was not significantly different between the two endpoints (12 and 13% of the maximum/day, respectively). There were significant main effects of day and interactions of day by reproductive status for luteal tissue area and for plasma progesterone concentration over Days 14 to 20; luteal tissue area and plasma progesterone concentration were first significantly lower on Days 19 and 17, respectively, in nonbred and nonpregnant heifers than in pregnant heifers. Combined for nonbred and nonpregnant heifers, both luteal tissue area and plasma progesterone concentration first decreased significantly between Days -6 and -4 relative to the second ovulation. Luteal tissue area decreased slower (P < 0.01) than plasma progesterone concentration (mean rates combined for nonbred and nonpregnant heifers, -20 and -28% of the maximum/day, respectively). The correlation coefficients combined for all reproductive statuses were 0.76 and 0.72 during Days 2 to 11 and following Day 14, respectively. The presence and size of central luteal cavities did not affect luteal tissue area or plasma progesterone concentration. Results indicated that ultrasonic assessment of the corpus luteum is a viable alternative to the determination of peripheral progesterone levels for assessment of luteal function in nulliparous Holstein heifers. © 1990.