Progesterone Levels in Cows Suspected of Embryonic Mortality

The competitive protein binding assay without chromatography was used to quantitate progesterone in the peripheral plasma of cows. The objective of this experiment was to estimate progesterone concentrations in cows suspected of experiencing embryonic mortality. Samples from 19 cows were assayed. The cows were divided into the following groups according to their estrous cycle length: (1) 20-22 days, (2) 26-32 days, (3) 40-69 days, and (4) pregnant.

Jugular vein blood samples were taken beginning 12 days after insemination. The blood sampling schedule was as follows: 12, 15, 17, 19, 21, 23, 26, 29, 32, 35, 38, 41, 44, 47, 58, 61, and 64 days post-breeding. Plasma was separated and stored at -20⁰C until assayed. The progesterone determinations were performed on 0.5 ml aliquots of plasma.

To monitor the effectiveness of each assay, steer plasma fortified with 3 ng of progesterone were assayed for progesterone. The progesterone content of steer plasma could not be distinguished from zero and the fortified steer plasma averaged 2.75±0.09 ng per ml. Tritiated progesterone was used to estimate the recovery percentage from cow plasma. the average recovery rate for all assays was 95.6±0.6 percent.

Analysis of variance on all groups through Day 21 indicated that Group 1 was different (P<0.05) from Groups 2, 3, and 4. A significant (P<0.10) day difference was found in Group 1 and no group-day interactions (P>0.05) were found in all groups. Group 2 had greater (P<0.05) progesterone concentrations than Group 1 indicating that the cows in the delayed estrus group (Group 2) may have been pregnant but experienced embryonic death shortly after implantation. This group was not different (P>0.05) from Group 4 (pregnant) at 21 days.

Comparison of Groups 3 and 4 through 47 days indicated that the progesterone level of Group 3 was significantly (P<0.01) less than the level of Group 4. From this analysis it was postulated that the cows in Group 3 may have had less progesterone than required for maintenance of pregnancy.