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14 July 2009
 

FOR WHOM THE BELL CURVE TOLLS

by Tom Reed
Horse International Vol 6 2009


The goal we have set for ourselves of breeding and producing world-class athletes is a tough one. If we are to achieve this goal on a systematic basis we must use world-class stallions and mares in our breeding program and make informed, creative, and bold choices about which particular genetic endowments to combine each year to produce a foal. That's the fun part: analyzing bloodlines, genotypes, phenotypes, and the actual production of mares and stallions to decide which stallions and mares are paired each year.

The not-so-fun part is deciding which mares (and stallions) to remove from our breeding program. Morningside Stud culls a minimum of 10% of our female herd each year (in practice we have been culling 10 - 15% each year). How do we decide which mares and fillies to cull?

In my last article (Brother Can You Spare a Sigma?) I discussed how the bell curve -- the so-called normal distribution -- is a useful tool for understanding how traits such as jumping ability are distributed across a population of horses. I encouraged breeders to critically analyze each mare in his or her herd and to judge where each one falls on the bell curve.

If you do not have a culling policy a useful place to start is to do is to draw a bell curve like the one shown as Figure 2 in last month's article (issue 5, page 37) and write the names of your mares in the appropriate segment in the bell curve. The key is to be brutally honest with yourself about your mares' genetic endowments and their actual production. Does the mare have world-class genetics? (If not, how can one expect to have a realistic chance of breeding a world-class athlete?) Even if your mare has world-class genetics, has the mare been producing progeny that are excelling in sport? (If not, why should her lack of success change in the future?) Has the mare's damline been producing progeny that are excelling in sport? (If not, are you expecting the stallions you use to be miracle workers?)

The next step is to rank order your foals from the best to the worst. Assess each foal using any set of criteria and metrics you like but for me the most important variable is always athleticism.

If a mare produces a foal that is in the bottom 10% (10th percentile) of its cohort in terms of athleticism, movement, type and conformation the mare should be put on a "watch list".

The following year if the mare produces another foal that is in the bottom 10% of its cohort the mare should be culled. If she produces a foal that is between the 11th and 25th percentile of its cohort the mare should maintained on the "watch list" for another year.

The next year if the produces another foal that is below the 25th percentile she should be culled.

If a suspect mare produces an extraordinary filly -- and far superior to its dam in terms of athleticism, movement, type, and conformation -- consider repeating the breeding. Later on you may decide to cull the mare and keep one or more of her daughters for your breeding program.

If your breeding program is small and you do not have a cohort of five or more foals each year then you can visit other breeders, shows, breed inspections, auctions, etc. to create a virtual cohort of foals for the sake of comparing your foal(s) to others foals.

Once you have in place a system to evaluate each year's foal crop you should develop a system to track and evaluate those foals as they enter sport. Remember that our goal is to produce world-class athletes, not world-class foals. Mare that produce very good foals that simply turn out to be average or below average athletes should also be culled from the breeding program.

What does one do with mares culled from a breeding program?

Some breeders put the mare to other uses (such as riding, embryo transfer recipient, etc.).

Other breeders sell the culled mares to other breeders. Morningside Stud never sells mares to other breeders if the mare has been producing incorrect foals. If the mare serially produces incorrect foals she is removed from the breeding population through euthanasia. We have had a couple of mares like this over the years. These mares produced foals with terrible leg conformation despite using a variety of stallions that normally produce good leg conformation. We believe it is our duty to ensure that these mares are not bred again and we consider it our absolute duty not to sell these mares to an unsuspecting client.

If the mare produces correct foals but they are simply not good enough for Morningside Stud's breeding and competition program we give the mare to a good friend whose breeding aspirations are not as high as ours.

As a stallion owner the biggest mistake I see many mare owners make is that they spend a lot of time and intellectual energy analyzing stallions but very little time and brain power analyzing their mares. Just as a stallion has to prove himself worthy of the breeding shed each mare should be evaluated on an annual basis based on what she is producing and their subsequent success in sport.