Effect of altrenogest-treatment of mares in late gestation on adrenocortical function, blood count and plasma electrolytes in their foals.

This research investigates the effect of altrenogest given to pregnant horses (mares) in late gestation on various aspects of their newborn foals, including adrenocortical function, blood counts, and plasma electrolyte levels. The study found that the treatment had no major effects on the foals’ adrenocortical function and potentially led to alterations in immune function or maturity.

Objective and Methodology

• The primary aim of this study was to determine the effects of treatment with altrenogest, a drug used to prevent abortion in mares with complicated pregnancies, on various physiological functions of their newborn foals. Specifically, the researchers were interested in the effects this treatment may have on the foals’ maturity, haematological changes, adrenocortical function and serum electrolyte levels.
• In order to investigate these effects, six mares were administered altrenogest (at a dosage of 0.088 mg/kg of body weight) daily from the 280th day of pregnancy until they gave birth.These treated mares were compared to a control group consisting of seven untreated mares.

Findings

• Compared to the foals born to the control mares, the foals from altrenogest-treated mares exhibited a significantly lower neutrophil/lymphocyte ratio on the first day after birth. This ratio is often used as an indicator of physical stress, and a lower value may suggest a potential immunomodulatory effect.
• Immediately after birth, the treated mares’ foals had higher basal plasma cortisol concentrations than the control group. Cortisol is a hormone produced by the adrenal glands and is often used as a measure of physiological stress. However, the cortisol release in response to an injection of adrenocorticotrophic hormone (ACTH) did not indicate any significant differences in adrenocortical function between the foals of the two groups.
• The study also found significant differences in the concentrations of certain electrolytes in the foals’ plasma. Specifically, foals from altrenogest-treated mares had significantly lower plasma potassium levels immediately after birth and lower ionised calcium levels three hours after birth compared to the control group.

Conclusions

• The treatment of pregnant mares with altrenogest, despite prolonging labour, did not seem to have major effects on the adrenocortical function in their foals.
• The lower neutrophil/lymphocyte ratio in the foals born to altrenogest-treated mares could be pointing towards possible immunomodulatory effects of the drug or a sign of the foals’ dysmaturity.