Comparison of milk and blood plasma progesterone concentrations in cycling and pregnant mares.

This research study investigated the viability of using the progesterone concentration in mare’s milk as a pregnancy indicator by comparing it with progesterone levels in the blood plasma throughout a normal estrous cycle and early pregnancy stages.

Research Methodology

• The study involved 15 mares from which daily samples of milk and blood plasma were collected, starting from the foaling period until pregnancy was confirmed via rectal examination between 30 to 35 days of gestation.
• The progesterone concentration in the milk and blood samples was quantified using a radioimmunoassay.

Findings and Observations

• The study found mean progesterone concentrations in plasma and milk during different phases of the estrous cycle and early pregnancy.
• During the period from foaling to foal heat, and during estrus, the study observed higher progesterone concentrations in the milk than in the plasma.

Analysis and Conclusion

• The research aimed to identify the specific days of the estrous cycle during which progesterone in milk and/or blood plasma could be used to indicate pregnancy. To this end, the researchers compared the progesterone concentration in the milk of seven mares during a normal nonpregnant estrous cycle with the concentration during the first 25 days of a subsequent fertile estrous cycle.
• The study reports sharply lower levels of progesterone in the milk of the nonpregnant mares from days 17 to 22, as well as lower levels in the blood plasma of the nonpregnant mares from days 15 to 22.
• These findings suggest the potential use of progesterone concentration in milk as a marker for pregnancy in mares, although further studies would be required to confirm these initial findings.