Genetic Variation

in Horse

Populations

By: E. Gus Cothran, PhD.,

Department of Veterinary

Science, University of

Kentucky

The fifth in a series of 13,

Session 2

Background

One of the major focuses of

conservation biology and

genetic management of small

populations is the preservation of genetic variability.

This topic is of particular

relevance to the Wild Horse

and Burro Program because

the majority of wild equid

populations managed by the

BLM are kept at population

sizes that are small enough

for the loss of genetic variation to be a real concern.

Because a loss of genetic variability can lead to a reduction

in fertility or viability of individuals in a population, it is

critical that genetic considerations be included in

management plans for wild

equid populations. An important aspect of utilizing genetic

information in management

planning is an understanding

of what is meant by the

term genetic variation and

how genetic variability can

be measured in horse and

burro populations.

Discussion

Genetic variation is the

amount of inheritable diversity in a population or an

individual. It can be observed

as morphological variation in

size, conformation or color,

but we are actually concerned

with variability of genes,

whether we can observe an

effect of this variation or not.

There are several different

measures of genetic variation

but two of the basic ways it is

expressed are heterozygosity,

the proportion of genes variable within an individual,

and some type of estimate of

allelic diversity, such as the

total number of genetic types

observed within the population. All of these different

measures of variation are calculated from data collected

from sampling a small set of

genetic marker systems in a

sample of individuals from a

population. Traditionally, the

genetic marker systems used

to measure genetic variation

in horses are a set of blood

group and biochemical genetic marker systems that have

been developed for parentage

verification analysis of domestic horses. The blood group

systems are tested by analysis

of variation of antigens on

the surface of red blood

cells using specific antibodies and standard serological

techniques. The biochemical genetic systems are serum

or red cell proteins or

enzymes detected by electrophoretic methods (relating

to a method of separating

large molecules such as

DNA fragments from a mixture of similar molecules by

passing an electric current

through a medium containing the mixture - separation

depends on each molecules

electrical charge and size).

Blood group testing requires a

fresh blood sample with intact

red blood cells. Biochemical

genetic testing can utilize

frozen blood or other tissues

such as a muscle biopsy. At

the University of Kentucky,

we routinely test seven blood

group and ten biochemical

genetic systems so that genetic variability measures are

based upon data from seventeen genetic loci.

Analysis of genetic variation

in populations also is done

by use of DNA genetic marker systems. In horses, these

DNA systems are primarily a

type of genetic marker called

microsatellites. Microsatellites

are highly variable sections of

DNA that can be tested by

use of PCR (polymerase

chain reaction - a method

for amplifying a DNA base

sequence) and electrophoretic

techniques. Direct testing of

DNA can utilize almost any

bodily product including

hair (if the hair root bulb is

RESOURCE NOTES

NO. 27 DATE 07/20/00

Range

Wild Horse andBurro Program
present) or even feces. The

estimates of genetic variation we can get from these

techniques perhaps do not

accurately correspond to

total genomic variation,

although that is not certain.

However, with a sufficient

comparative database, these

measures can be used to

determine the variation

within a population as it

compares to other horse populations and can be used to

make inferences about the

genetic health of the population at the time of sampling.

Conclusion

Genetic analysis of wild horse

and burro populations can

provide valuable information

about current levels of genetic

variation. This information

can then be used to make

predictions about how particular management strategies

will influence genetic variation

in the herd. Thus, genetic

analysis can be a useful tool in

the overall management of

wild horse and burro populations on public lands.

Contact

E. Gus Cothran, PhD.

Veterinary Science, Equine

Blood Typing and Research

Laboratory, 101 Dimock

Animal Pathology Building

University of Kentucky,

Lexington, KY 40546-0076

phone 606-257-3022

fax 606-257-4119

e-mail gcothran@pop.uky.edu.

Range

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