Harem stability and reproductive success of Misaki feral mares.

The stability of relationships between harem stallions and mares (consort relations) was investigated and the durations of inter partum intervals were determined in order to establish if there was any correlation between the stability of consort relation and reproductive success of mares in Misaki feral horses. Thirty-four mares were observed continuously for more than 5 years. The lifetime stability was 80-100% (mean 92.4%) for 16 mares, 60-79% (mean 70.4%) for 10 mares and 0-59% (mean 27.9%) for 8 mares. The continuous length (years) of specific consort relations was 2-10 years and was found to correlate significantly with lifetime stability. There was a significant positive correlation of lifetime stability with lifetime reproductive success for 34 mares observed, and the correlation was higher when the data of 8 wandering mares (<60% in lifetime stability) were omitted. The mean +/- s.d. delivery interval of 25 stable mares was 364.5 +/- 11.0 days, whereas that of 8 unstable mares and stable mares who changed stallions was 387.0 +/- 40.2 days. There was a significant difference between delivery intervals of stable and unstable mares. Significant correlations between the stability of consort relations and both the foaling rates and delivery intervals suggest that mares may obtain major reproductive advantages if they maintain long term and stable consort relations with a particular stallion throughout their reproductive life span.