Farm Manager’s Guide To Progesterone Assays

1. ESTABLISH OVULATORY STATUS OF MARES

-Routinely sample mares when they arrive at your farm.
-If Progesterone level is greater than 1.0 ng/mL, mare is ovulatory.
-If Progesterone level is less than 1.0 ng/mL, mare is anovulatory or should be in heat.
-Check foaling mares in which foal-heat Estrus was not observed.
-Check any mares not showing Estrous behavior at normal
intervals.

2. IDENTIFY MARES WHICH HAVE EARLY FAILURE OF THE PRIMARY CORPUS LETEUM

-Sample at day 12 post-ovulation. Values should be greater than 4.0 ng/mL.
-Mares with values less than 2.0 ng/mL may have luteal
insufficiency, which is most likely due to uterine infection. If mare is not pregnant when ultrasounded, reculture reproductive tract. Uterine lavage may be indicated.
-Mares with values greater than 10.0 ng/mL likely double
ovulated and should be checked carefully for twins.

3. REINFORCE TESTING PROGRAM

-Determine status of mares missed by the teaser.
-Reduces amount of teasing necessary for good management.

4. DETERMINE MARES NEEDING PROGESTIN THERAPY TO
SUPPORT PREGNANCY

-Measure Progesterone levels at first ultrasound or manual
pregnancy check.
-Use Progestin Therapy in mares testing below normal for that
stage of pregnancy. Expect 8 to 10% to test below normal.
-Retest at various intervals of pregnancy to determine if mares
that were low in Progesterone have now become normal and
can be taken off progestin therapy.

5. IDENTIFY LOW PROGESTAGEN LEVELS DURING PREGNANCY

-Test at various stages of pregnancy. When levels are below
normal, retest to confirm and place on Progestin Therapy.
-Do not ship mares with low serum levels of Progestagens. If
possible, wait until at least 100 days of pregnancy before
shipping. If Progestagens levels are still low, place mare on
Progestin Therapy prior to shipping
-If Progestagens levels are low prior to weaning, place on
Progestin Therapy before weaning.
-If mare colics or is otherwise seriously stressed, measure
Progestagens.

Normal Serum Levels of Progestogens as determined by Radioimmunoassay

Days post ovulationng/mL
0Less than 1.0
21.0 – 3.0
5 – 124.0 – 10.0
15 – 183.0 – 10.0
213.0 – 10.0
25 – 302.5 – 10.0
454.0 – 10.0
604.0 – 15.0
80 – 3155.0 – 10.0
316 to term20.0 – 40.0+
Results are those used by BET Laboratories and were generated by radioimmunoassay (RIA), which measures progesterone and some of its major metabolites (progestagens).

Results are those used by BET Laboratories and were generated by radioimmunoassay (RIA), which measures Progesterone and some of its major metabolites (progestagens).