The Dam Quality Revolution: Part 3 — The Colt–Filly Divide
When analysing a global population of more than one million thoroughbreds, a clear pattern emerges: dam quality influences colts and fillies differently. Both sexes benefit meaningfully as mare class improves, but the nature and scale of this improvement varies in important ways.
Colts maintain higher absolute stakes-winner rates at every dam level. However, fillies gain more proportionally as mare quality rises. This duality is often overlooked, yet it has significant implications for breeding, buying and long-term planning.
Part 3 explores how these patterns behave across dam categories and what they mean for the upcoming Northern Hemisphere 2026 and Southern Hemisphere 2025 breeding seasons.
Overall Stakes-Winner Rates by Sex
Across the global dataset, colts show a higher overall stakes-winner rate than fillies, reflecting long-standing performance patterns in major racing jurisdictions.
Colts: 5.48%
Fillies: 2.63%
This consistent difference provides the baseline for understanding how each sex responds as mare quality improves.
Dam Class Changes the Trajectory
The stakes-winner rate rises in both sexes as dam class improves, but the shape of the curve differs.
Absolute performance:
Colts outperform fillies at every dam level. A colt from a G1 mare remains more likely to win at stakes level than a filly from the same mare.
Relative performance:
Fillies gain proportionally more from dam class. The uplift from non-stakes mares to stakes-winning mares is significantly larger for fillies than for colts.
This creates a two-part story: colts convert mare quality into higher raw performance, while fillies demonstrate greater sensitivity to the mare’s class.
Stakes-Winner Rates by Dam Class × Sex
The following percentages show how both sexes respond as mare quality rises.
G1 Dams
Colts: 12.31%
Fillies: 7.71%
G2 Dams
Colts: 10.23%
Fillies: 7.44%
G3 Dams
Colts: 9.47%
Fillies: 6.98%
Listed Dams
Colts: 6.83%
Fillies: 5.89%
Non-Stakes Dams
Colts: 5.24%
Fillies: 2.43%
Three patterns are immediately clear:
- Colts outperform fillies at every dam category.
- Fillies gain proportionally more from improved dam quality.
- The uplift behaves differently in the mid-tier bands (G2/G3), where value is strongest.
Relative Uplift: Where Fillies Gain the Most
When comparing relative improvement against non-stakes-winning mares:
Colts
Non-Stakes → G1: +135%
Non-Stakes → G2: +95%
Non-Stakes → G3: +81%
Fillies
Non-Stakes → G1: +218%
Non-Stakes → G2: +207%
Non-Stakes → G3: +188%
A filly from a G1 mare is more than three times as likely to become a stakes winner compared with a filly from a non-stakes mare. Colts improve as well, but not at the same rate.
This is the central insight: colts convert mare quality into higher absolute performance, while fillies experience a larger proportional uplift.
Why These Differences Occur
Genetic variance
Colts show wider performance dispersion, allowing superior mares to lift the top end more visibly.
Commercial opportunity
High-class mares are more likely to be matched with higher-quality stallions. While this benefits both sexes, colts are typically campaigned more aggressively, amplifying outcomes.
Development pathways
Colts bred from higher-level mares receive more intensive placement and management strategies, widening the raw stakes-winner rate.
These factors make colts more likely to sit at the top of the performance curve while allowing fillies to demonstrate stronger proportional gains relative to their baselines.
Practical Implications for Breeders
When planning matings
For breeders seeking high-performance colts, upgrading mare quality—especially into the G2/G3 tier—offers a sharper rise in absolute stakes performance.
For fillies, mare class remains important, but the uplift is more proportional than absolute. This distinction helps breeders set clearer expectations.
When selecting broodmares
Breeders focused on long-term fillies for the broodmare band may gain more by broadening the mare base while focusing on stakes-level mares for colt-oriented programs.
Tools like the G1 Goldmine Broodmare Report help quantify these differences within individual broodmare bands.
Implications for Buyers and Sellers
Yearling buyers
A colt from a high-class mare carries a strong absolute performance signal. A filly carries a strong relative improvement signal. Understanding this distinction sharpens yearling evaluations.
Vendors
The market’s long-standing premium for colts out of high-class mares is supported by the data. However, the proportional uplift in fillies may represent an undervalued segment, particularly when aligned with long-term breeding goals.
Stallion Match’s sales analysis platform helps track how dam class influences yearling performance and pricing outcomes across both sexes.
The Practical Breeding Reality
Most breeders face the same annual question:
“Which stallion should I send my mare to?”
Only a small number of stallions globally have the luxury of selecting mares. With declining foal crops and rising stallion counts, most stallions accept broad mare books.
This makes the mare the more stable and predictable element in most mating decisions.
As Matthew Ennis, Managing Director of G1 Goldmine and Stallion Match, explains:
“The mare is the fixed point in most breeding decisions. Understanding how her quality expresses differently in colts and fillies allows breeders to make stallion choices with far greater accuracy.”
The Stallion Quality Context
Higher-class mares tend to visit higher-class stallions, which contributes to overall uplift. Even when comparing mares within similar stallion-fee brackets, the colt–filly divergence remains clear: colts show stronger absolute performance, fillies show stronger proportional gains.
Methodological Note
This analysis reflects performance outcomes, not financial profitability. It excludes nomination fees, production costs, training expenses and sales results. The purpose is to measure how dam class affects the probability of producing a stakes winner, not net return.
What This Means for Upcoming Breeding Seasons
As breeders prepare for the 2026 Northern Hemisphere and 2025 Southern Hemisphere seasons, these sex-based patterns should guide both mating and commercial decisions. Understanding how dam class influences each sex—both absolutely and proportionally—helps breeders design matings that are aligned with their performance goals.
To explore how these insights apply to your mares:
• Use G1 Goldmine to assess dam-class performance across colt and filly outcomes.
• Use Stallion Match to evaluate stallion compatibility and sales performance trends.
Conclusion
Dam quality does not influence colts and fillies in the same way. Colts convert mare class into higher raw performance; fillies show larger proportional improvement. This duality matters for mating decisions, buying strategies and the long-term structure of broodmare bands.
Part 4 completes the series by examining how dam quality interacts with stallion choice—and the mating patterns behind the highest-performing crosses in the dataset.