Comparison of radioimmunoassay and enzyme-linked immunoassay for the measurement of progestogen in equine plasma and milk.

The research article compares the use of radioimmunoassay and enzyme-linked immunoassay (ELISA) for measuring progestogen levels in the milk and blood of pony mares. It notes similarities and differences in trend lines, but advises caution in interpreting single sample results due to potential fluctuations in progestogen levels.

Study Methods

• The researchers tested samples of plasma and milk obtained from eight pony mares every 48 hours for 40 days after foaling, the process of giving birth.
• They measured the concentration of progestogen (a class of hormones that includes progesterone) in both the milk and plasma using ELISA.
• They further compared these ELISA results with the progestogen concentrations obtained through radioimmunoassay of the plasma. The radioimmunoassay is a method to measure antibodies or antigens from a solution, in this case, the plasma.

Findings

• Generally, they found that progestogen concentrations measured through the three assays showed similar trends in their changes. This suggests a level of consistency among the assays in tracking the fluctuations in progestogen levels.
• However, the absolute values— the actual amounts of progestogen detected— differed considerably across the assays. The reason for this discrepancy was not detailed in the abstract.

Interpretation Challenges

• The researchers observed that interpreting results from single samples could be challenging. This is particularly the case when progestogen concentrations were either rising (such as after ovulation) or falling.
• These fluctuations could make it difficult to accurately estimate the mare’s progestogen level from a single sample and therefore provide a clear understanding of the hormone’s function or impact on the animal’s health.

ELISA Practicality

• The researchers found that ELISA can be used on plasma obtained by allowing the erythrocytes (red blood cells) to settle for 30 minutes at room temperature or for two days at 4 degrees Celcius.
• This suggests the ELISA could be a practical option in field settings without access to specialized refrigeration equipment, as it can produce accurate results with samples left at room temperature for a short duration.