Aging and genetic deterioration

by Jay Leimbach ©

Although there is an age-old debate as to whether stallions and mares decline at stud due to genetic deterioration or simply commercial opportunity, the tables of the great horses below certainly suggests that younger breeding stock does in fact outperform older stock - for whatever reasons.

Recently I read the October issue of Discover magazine, including an article about the genetic basis for illnesses. Although schizophrenia in humans was once thought to be largely psychological and environmental, it is now considered largely genetic and biochemical. Specifically it reported a study of schizophrenia which showed that men in their fifties were three times more likely to father children who developed schizophrenia than men in their twenties. It went on to say that genetic mutation is believed to be the culprit. Sperm cells divide and reproduce themselves 23 times per year, or 660 times over the three decades from 25 to 55. Occasionally, errors occur in this process so that a mutated gene, dominant for schizophrenic tendencies, occurs far more often in older fathers than younger ones.

Scientists have similarly discovered that such common traits as graying hair and wrinkled skin in aging humans are likewise the result of older, slightly mutated genes no longer producing the proteins needed for hair pigment and moist skin. All of which is not to say that older horses cannot produce greatness. Clearly they can, with Secretariat a case in point, conceived when his sire was 15 and his dam 17 years of age. Instead, we must simply conclude that the chances diminish into the late teens and twenties, but that the rate of this decline varies considerably from one individual to the next.

Female eggs are a slightly different story, inasmuch as they are all produced at the onset of sexual maturity and remain in the ovaries throughout the breeding years. Without question, they are subject to wear-and-tear, however, and it is well known that birth defects, including mongoloid babies (Downs' Syndrome), are more of a risk among pregnant women over 35 than among younger women.

Scientists, in general, often know little of what goes on outside their immediate specialty, and often are slow to change views after graduating from school. Many are still unaware of the growing evidence for genetic decline with age, but it is fact, not theory. While the extent of genetic deterioration and mutation was barely known a decade ago, it is now known widely enough to be referred to even in National Geographic and USA Today. Everything from graying hairs, to wrinkled skin, to birth defects and mental illness in humans may be related to older genes that have changed in their molecular structure. The establishment is often the very last to embrace new truths, but they simply cannot dispute this one.

Clearly younger mares have produced more than their share of great racehorses and sires, with age 5, 6, and 7 by far the most prevalent age for these dams. It should be noted from a statistical standpoint, however, that mares in the 5-10 age range produce the most foals. Older mares sometimes grow infertile or die, or are simply culled from the breeding stock. So while it is not unusual for younger broodmares to dominate, but to this extent, it is surely significant. As always, the proof is in the pudding.

Looking at this informal list of the great racehorses and sires of the past century (gleaned from export polls), we find that almost none had either parent over 17 at conception (those 15 or older are marked with an *), and none had a combined parent's age over 30 (those with combined ages of 25 or older are marked with **). ("You could look it up", as Casey Stengel used to say.)

Table 1. List of great American runners.

Runner
Age of Sire at conception
+
Age of Dam at conception
=
Combined Ages of parents at conception

Man O' War
11
+
6
=
17

Secretariat
15*
+
17*
=
32

Citation
9
+
6
=
15

Native Dancer
17*
+
6
=
23

Kelso
9
+
5
=
14

Seattle Slew
5
+
4
=
9

Dr. Fager
15*
+
9
=
24

John Henry
11
+
7
=
18

Forego
6
+
11
=
17

Spectacular Bid
13
+
5
=
18

Affirmed
9
+
12
=
21

Buckpasser
13
+
15*
=
28**

Count Fleet
14
+
9
=
23

Tom Fool
13
+
6
=
19

Graustark
10
+
10
=
20

Swaps
8
+
5
=
13

Nashua
11
+
9
=
20

Round Table
13
+
12
=
25**

Damascus
7
+
5
=
12

Cigar
8
+
7
=
15

Skip Away
10
+
11
=
21

Equipoise
16*
+
5
=
21

Exterminator
14
+
15*
=
29**

Sysonby
19*
+
5
=
24

Gallant Fox
6
+
6
=
12

War Admiral
16*
+
4
=
20

Seabiscuit
6
+
6
=
12

Bold Ruler
13
+
9
=
22

Gallant Man
9
+
14
=
23

Armed
5
+
7
=
12

Whirlaway
10
+
11
=
21

Northern Dancer
6
+
3
=
9

Colin
6
+
12
=
18

Discovery
7
+
4
=
11

Stymie
4
+
7
=
11

Assault
9
+
5
=
14

Alsab
7
+
7
=
14

Alydar
13
+
9
=
22

Riva Ridge
12
+
14
=
26**

Foolish Pleasure
6
+
13
=
19

Ack Ack
6
+
6
=
12

Majestic Prince
4
+
8
=
12

Slew o' Gold
5
+
10
=
15

Precisionist
22*
+
8
=
30**

Sunday Silence
16*
+
10
=
26**

Best Pal
13
+
7
=
20

Alysheba
8
+
13
=
21

Holy Bull
18*
+
10
=
28**

Silver Charm
15*
+
11
=
26**

Point Given
5
+
5
=
10

Average
10.5
+
8.5
=
19.0

In 29 of 50 stallions above (Table I), the sire was older, in 16 the dam was older, and in 5, the parents were the same age.

Table II. List of great racemares.

Runner
Age of Sire at conception
+
Age of Dam at conception
=
Combined Ages of parents at conception

Ruffian
5
+
8
=
13

Dahlia
4
+
6
=
10

Allez France
7
+
6
=
13

All Along
8
+
12
=
20

Bayakoa
6
+
9
=
15

Paeseana
5
+
9
=
14

Lady's Secret
11
+
6
=
17

Personal Ensign
7
+
9
=
16

Winning Colors
17*
+
11
=
28**

Serena's Song
6
+
8
=
14

Average
7.6
+
8.4
=
16.0

In the above table (Table II), none had a dam over 12.

Table III. List of great European runners.

Runner
Age of Sire at conception
+
Age of Dam at conception
=
Combined Ages of parents at conception

Nearco
14
+
6
=
20

Ribot
11
+
10
=
21

Sea-Bird II
5
+
5
=
10

Sir Ivor
5
+
11
=
16

Nijinsky II
5
+
7
=
12

Brigadier Gerard
7
+
11
=
18

Mill Reef
7
+
5
=
12

Nashwan
11
+
6
=
17

Dubai Millennium
10
+
9
=
19

Galileo
16*
+
8
=
24

Average
9.1
+
17.8
=
16.9

In the above list (Table III), no runner had a dam over the age of 11 years.

Table IV. List of sires of sires.

Sire	Age of Sire at conception	+	Age of Dam at conception	=	Combined Ages of parents at conception
Phalaris	10	+	7	=	17
Teddy	11	+	12	=	23
Gainsborough	8	+	7	=	15
Blandford	11	+	6	=	17
Average	7.6	+	8.4	=	16.0

Nasrullah	4	+	7	=	11
Princequillo	11	+	7	=	18
Hyperion	14	+	10	=	24
Northern Dancer	6	+	3	=	9
Mr. Prospector	8	+	7	=	15
Turn-to	8	+	10	=	18
Roberto	10	+	9	=	19
In Reality	7	+	6	=	13
Ribot	11	+	10	=	21
Damascus	7	+	5	=	12
Average	8.6	+	7.4	=	16.0

In the above table (Table IV), there was no dam over the age of 10 at the time of conception.

Table V. List of emerging sires of sires.

Sire
Age of Sire at conception
+
Age of Dam at conception
=
Combined Ages of parents at conception

Blushing Groom
19*
+
11
=
30**

Seattle Slew
4
+
4
=
9

Fappiano
6
+
6
=
12

Forty Niner
14
+
8
=
22

Cox's Ridge
7
+
12
=
19

Halo
10
+
15*
=
25**

Relaunch
11
+
10
=
21

Private Account
11
+
6
=
17

Pleasant Colony
9
+
9
=
18

Sadler's Wells
19*
+
5
=
24

Storm Cat
4
+
6
=
10

Deputy Minister
11
+
8
=
19

Average
11
+
9
=
20