Induced lactation with a dopamine antagonist in mares: different responses between ovariectomized and intact mares.

This research article examines the impact of repeated treatments with a certain drug, sulpiride, on horses’ prolactin secretion and lactation. The study particularly looks at whether the drug’s effects vary based on whether the horse is ovariectomized or in intact condition, and also whether the time of the year, at the beginning or end of the birth season, affects the result.

Research Design and Methodology

• The study was conducted in two experiment sessions, one in September (expt 1) and the other in March (expt 2), located in France (48 degrees N).
• In the first experiment, three groups of five mares were used for testing: one group that was intact and didn’t receive any treatment (intact-control), another intact group that received sulpiride injections (intact-treated), and a group of ovariectomized mares that received the same treatment (ovariectomized-treated).
• In the second experiment, selected mares, previously exposed to artificial photoperiod, were divided into two groups: four intact-control mares and five intact-treated mares.
• The intact-control mares in both experiments were previously synchronized with PGF2alpha injections, ensuring all the mares were in the follicular phase at the beginning of treatment.
• Sulpiride was administered intramuscularly at a rate of 0.5 mg/kg of body weight, twice a day.
• The mares were milked at four set times throughout the day.
• Blood samples were collected daily for hormone assay, including progesterone, total oestrogen, and prolactin.

Outcomes of the Experiments

• In both experiments, only the treated intact mares were found to produce milk, with a significant variation noted among the individual animals.
• The prolactin increase after sulpiride treatment in ovariectomized-treated mares was notably less than in the intact-treated mares.
• Significant correlations were discovered between prolactin, progesterone, oestrogen plasma concentrations, and daily milk production, with respective correlation coefficients of 0.57, 0.25, and 0.17.

Conclusions

• The research drew the conclusion that lactation can be induced in intact mares through sulpiride treatment throughout the entire birth season.
• However, this was not the case in ovariectomized mares, indicating that the presence of steroids is essential for this lactation induction process when treated with a dopamine D2 antagonist such as sulpiride.