The maternal side of the 2015 Kentucky Derby

While sire lines are fairly simple to keep in mind, the greater variety of maternal lines calls for a little more dedicated scrutiny.

Tap-root mares from England have given rise to certain enduring female families over the centuries, with significant descendants sometimes establishing branches of their own. These families have been assigned numbers, which are further divided into subfamilies denoted by letters. (For example, the phenomenally successful *La Troienne branch of the No. 1 family is labeled 1-x). Other families taking early root in the colonies start with a letter, as in A1 for American Family 1.

I find the family numbers a handy tool to identify deep relationships through the maternal line that aren't readily apparent. Horses springing from the same family or subfamily might not have a direct maternal ancestress in common for generations, but if you trace back far enough, you'll find the connection.

Out of curiosity, I looked up the family numbers of the 2015 Kentucky Derby contenders, along with the family numbers of past Derby winners, on pedigreequery.com.

Just over half of this year's field descends from a subfamily that is already responsible for a Derby winner.

Carpe Diem and Bolo both hail from the prolific 23-b, whose honor roll includes I'll Have Another (2012), Mine That Bird (2009), Lil E Tee (1992), Winning Colors (1988), Affirmed (1978), Tim Tam (1958), Zev (1923) and Kingman (1891).

Mubtaahij (4-r) also traces to a family known for Derby success, with the likes of Monarchos (2001), Black Gold (1924), Donau (1910), Manuel (1899) and Halma (1895).

Far Right (A4) likewise comes from the productive family of California Chrome (2014), Kauai King (1966), Iron Liege (1957), Swaps (1955) and Clyde Van Dusen (1929).

El Kabeir (2-d) can claim Giacomo (2005) as a near relative, while Spectacular Bid (1979), Cannonade (1974) and Northern Dancer (1964) are at further removes.

Ocho Ocho Ocho (6-a) belongs to the same thread as Count Fleet (1943), Bold Venture (1936), Old Rosebud (1914) and Worth (1912), although his connection to them is more remote than usual (deep in the mists of time in 18th-century England).

Mr. Z (13-c) descends from the same ancestress as Ferdinand (1986), Seattle Slew (1977) and Jet Pilot (1947).

War Story (8-c) comes from the maternal line of Orb (2013) and Fusaichi Pegasus (2000).

Upstart (6-d) shares the family of fellow New York-bred Funny Cide (2003).

Frosted (16-g) descends from the same line as Shut Out (1942).

Dortmund (9-c) gets in on something of a technicality; the only other Derby-winning descendant of 9-c was Forward Pass, who was promoted upon the disqualification of Dancer's Image in 1968.

American Pharoah (14) can't point to a Derby winner from the undifferentiated No. 14 family, but Foolish Pleasure (1975) comes from an offshoot, 14-b. That ties in to Firing Line, who traces to 14-c, the branch founded by the immortal racemare Pretty Polly (whose dam founded 14-b).

Here are the others descending from a family that has yet to produce a Derby winner:

Stanford (2-f), Itsaknockout (3-i), International Star (4-g), Danzig Moon (5-f), Tencendur (8-f), Keen Ice (13-d) and Materiality (A5).

Of course, there's nothing immutable about that list, let alone a mark against otherwise terrific families.

Digging into the maternal families might not unearth a compelling handicapping angle, but it is catnip for pedigree buffs.

(Carpe Diem Photo: Keeneland/Coady Photography)