Effects of the dam on equine chorionic gonadotropin concentrations during pregnancy.

This research study investigates how the mother horse, or mare, impacts the levels of a hormone called equine chorionic gonadotropin (eCG) during certain stages of pregnancy. It found that irrespective of the mate, the level of eCG hormone is primarily determined by mother horse.

Experimental Design

• This study explores the effect of the mother horse (‘dam’ in scientific terms) on the levels of a hormone called equine chorionic gonadotropin (eCG) during pregnancy. The study was carried during the period from Day 39 to Day 104 of gestation.
• The researchers conducted breeding trials where male horses (sires) were selected based on their mean eCG concentrations observed in groups of randomly selected female horses (mares) they were mated with.
• Mares were also ranked based on their eCG concentrations on specific days of gestation (Days 55, 71, and 85; Day 0 marking mating).
• The research design followed various combinations, for instance, in the 1986 breeding season, mares associated with high eCG levels were mated with sires linked to low eCG concentration pregnancies and vice versa.

Key Findings

• The study found that the highest eCG concentrations were detected on Day 55 of gestation in mares mated to low-ranked sire. This finding suggested that the mares had a significant influence on serum eCG concentration.
• A longitudinal comparison of eCG production by individual mares over the years (1985, 1986, and 1987) showed that irrespective of the rank or the eCG concentration of the sires they were mated with, mares maintained their rank.
• This underscores that the influence of the mare is predominant in determining eCG concentration.

Implications

• In 1987, an experiment involving highest-ranked sire mated with highest eCG producing mares produced two distinct subgroups.
• This suggested that a strategic choice of sire and mare combinations could be employed to maximize the production of eCG, yielding potential applications in equine reproduction and breeding strategies.