The research article investigates the impact of low progesterone levels during early pregnancy in horses, concluding that those with reduced progesterone during the early luteal phase experienced delayed fetal growth and higher rates of pregnancy loss than those with normal progesterone levels.

Objective of the Study

• The aim of the study was to understand the effects of low progesterone concentrations during the early luteal phase on the growth and development of the fetus, and the overall outcome of pregnancy in horses.

Methodology

• In the study, 12 mares were inseminated and two kinds of treatments were administered. The first group, PGF, received a prostaglandin F analogue (cloprostenol) for the first three days after ovulation to induce low progesterone concentrations. The second group, CON, remained untreated as a control group.
• The type of treatment (PGF or CON) was alternated for each mare in the following year. Throughout the pregnancy, blood samples were collected and the size of the conceptus was determined by transrectal and transabdominal ultrasonography.
• Once born, the foals were weighed, measured, and given a clinical examination.

Findings

• The findings demonstrated that low progesterone concentrations in the early luteal phase resulted in fewer successful pregnancies when comparing PGF to CON treatments.
• While all foals from CON pregnancies were healthy and mature, 4 out of 7 PGF pregnancies resulted in embryonic death, abortion, or compromised foals.
• Differences were also identified in the size of the conceptus and embryo between the two treatments. However, by the time of birth, these differences had decreased and there was no significant variation in size between PGF and CON foals.

Conclusion

• The research ultimately concluded that reduced progesterone concentration during the early luteal phase can delay conceptus growth beyond placentation and increase the risk of pregnancy loss in horses.