Genetics of Feet and Legs … Importance of Bull Selection

Mary Beth Grove,
Dairy/Environmental Agent, Lancaster County, Pa
November 1, 2002

How important is it to select bulls that transmit good (above average) feet and legs for your
herd? How should these bulls be selected?

Common sense tells us that when deciding which A.I. bulls to use for the dairy herd, the
traits we select on should have a definite economic value. Everyone knows the economic value
of milk pounds and butterfat percentage - in most cases, more milk means more money in your
pocket. Unfortunately, the relationship between foot and leg traits and production or cow
longevity is much more difficult to measure.

Dr. Ben McDaniel at North Carolina State University conducted interesting research to
evaluate the importance of feet and legs on production. Much of this work was done at several
state-owned dairy herds in the Carolinas. The researchers actually measured the hoof angle and
hoof length on several thousand cows to determine if these measurements could be associated
with production traits. Table 1 exhibits the finding of this study:

Table 1. Correlations between measured foot traits and production/longevity characteristics of
dairy cows in North Carolina institutional herds.

Trait                 Foot Angle                     Claw Length              Heel Depth
Milk, pounds           .01                            .18                     -.12
Fat, pounds           -.40                            .24                     -.06
Days Open             -.44                            .26                      .59
Survival to 5 years
of age                 .21                           -.01                      .36
Age at culling         .87                           -.34                      .47

These results showed that as foot angle increased (became steeper) by 5 degrees in first
calf heifers, there was an associated 503 pound increase in second lactation milk production. A
decrease in 10mm of toe length in first calf heifers equated to a 1475 pound increase in second
lactation milk production. Steeper foot angles and shorter claw length were associated with
fewer days open, earlier breedings, and a greater survival to five years of age. Deeper heels
tended to increase days open, but also increased longevity of that cow in the herd. Cattle with
deeper heels did exhibit more sole ulcers.

Longer claws and lower angles were also associated with lower survival rates. It was also
suggested that legs that are neither too straight (posty) nor too crooked (sickled) are apparently
the best for increasing longevity in cattle.

As you can see from this research, there is an economic value in steeper foot angles in
dairy cattle. Unfortunately, this does not mean that they are easily improved by using better
genetics.

There is another important factor in making bull breeding decisions – the "heritability" of
that trait. What is heritability? In simple terms, it is the portion of the "visible" differences in a
trait that are due to genetic factors. The higher the heritability, the greater is the genetic control
on the trait, and the more rapidly selection will result in genetic progress. Some traits are highly
heritable; for example stature has a heritability of about .42 or 42%. This means genetics
accounts for 42% of the variation in stature (measured at hip height), and the environment (or
way the animal was raised) accounts for the remaining 58%. Unfortunately, foot and leg traits
are not nearly as heritable, in part because the animal's environment can easily affect the feet on
a cow. In Table 2, you will see the linear score and heritabilities for the foot and leg traits.

Table 2. Heritabilities for Foot and Leg Traits of Dairy Cattle

Trait                    Heritability 
Foot angle               .10-.15
Rear Legs (Side)         .15-.21
Rear Legs (Rear)         .10-.15

This data suggests that, while increased foot angle and proper leg set are very important
for cow longevity, much of the improvement to be made on feet and legs on individual cows will
be through environmental changes. These environmental changes might include grooved
concrete and more stall bedding, allowing cows access to pasture, and an adequate nutritional
program.

Unfortunately, with these "low to moderate” heritability values, bull selection to improve
feet and legs through genetics will be a long, slow process. This also explains why you may not
always be able to see measurable changes from generation to generation in regards to foot
confirmation. This does not mean you should ignore foot and leg composite or foot angle PTA's
on bulls - just that you may want to make it a secondary trait to select. Why not choose bulls
that meet your production goals first, and then choose from this pool of bulls for those with
higher foot angle and more intermediate leg set traits? When attempting to correct a “twoway”
trait such as rear legs (side view), select an intermediate (+.00) bull – this bull will tend to
sire daughters with legs of an intermediate set. Using a bull that tends to sire daughters with
straight “posty” legs will not correct a “sickled” cow faster.

There are also some indexes that include the sire's genetic merit for foot angle in the
overall index – one such index is Net Merit. According to many industry leaders, the top Net
Merit bulls transmit the best combination of superior genes for production, longevity, somatic
cell score and type traits for most commercial dairy herds.

For more information on sire selection for improved feet and legs, you can reach Beth
Grove at (717) 394-6851 or contact your local extension office.