Effects of altrenogest treatment of mares in late pregnancy on parturition and on neonatal viability of their foals.

The research studied the effects of a hormone treatment called altrenogest on late-term pregnant horse mares and their foals. The conclusions indicated that use of this treatment may not prevent preterm birth, and it might also affect the ability of newborn foals to adapt to their environment.

Research Method

• The researchers selected a total of 13 animals for the study, which was conducted on mares during their late pregnancy until they give birth. Of these, 6 mares were given a daily dose of altrenogest (0.088 mg/kg) and were identified as ‘the treatment group’, while the remaining 7 were the ‘control group’ and were not given any hormone treatment.

Impact on Gestation and Parturition

• The research found that the gestation period, i.e., the term of pregnancy, tended to be shorter in mares given altrenogest. However, the birth weight of the foals and the placenta did not vary between the control and treatment groups.
• Interestingly, the second stage of parturition, the process of giving birth, was longer in mares that were treated with altrenogest.

Effects on Newborn Foals

• The study observed that the foals born to mares treated with altrenogest exhibited a significantly lower respiratory rate than those born to the control group during the first half-hour of life.
• However, at no point were differences found between the two groups in terms of heart rate and body temperature of the new-born foals.
• The research also indicated that foals born to the altrenogest-treated mares had higher venous plasma pH levels, a measure of the acidity or alkalinity of blood, 15 and 30 minutes post-birth. Intriguingly, these foals also exhibited higher base excess, an indicator of the buffering capacity of blood, up to 12 hours after birth.
• Moreover, the study also pointed out a significant increase in perinatal problems among foals born after their mothers were treated with altrenogest.

Conclusions

• The study concludes that altrenogest treatment does not prevent parturition, and thus its effectiveness in preventing abortion or preterm births in mares with disturbed pregnancies can be questioned.
• Additionally, treating mares with altrenogest seemed to affect their foals’ adaptation to the environment outside the uterus after birth.