Agriculture Reference
In-Depth Information
and their subsequent colonization in the world have had
signifi cant impacts on the choice, distribution, and method
of raising goats and its role in farming. Breed information
derived from the goat genome may help establish relation-
ships among goat breed populations worldwide, as well
as establish genomic inbreeding. Scientifi c studies of the
genome could contribute to genetic conservation. Genetic
principles investigated include polymorphism, gene fre-
quencies, genetic distances, and degree of heterozygosity
estimated from blood groups and genetic markers includ-
ing isozymes, microsatellites and single nucleotide poly-
morphism (SNP) in the DNA, and sequence variation in
the mtDNA (Shrestha et al., 2008).
The majority of endangered goat breed populations
worldwide rely on few male and female parents; this
results in small effective population sizes that contribute
to loss of genetic variation. The best way to reverse this
situation is to increase the effective number of parents,
particularly by using unrelated male parents. In closed
endangered populations, theoretically it is possible to min-
imize the infl uence of inbreeding and genetic drift by
dividing populations into several complementary breeding
groups of one male and one female parent. In the following
year, male offspring from the fi rst group may be bred to
female offspring from the subsequent group. This would
continue in the following years until the male descendent
of the fi rst group would be bred to the female descendent
of the last group according to a pedigreed breeding struc-
ture. This approach may not be practical in most popula-
tions of goats because in practice herds maintain about
1 buck for every 20 to 50 does (Shrestha et al., 2008).
Nevertheless, breeders with endangered goat populations
should attempt to increase the number of bucks that are
used as parents of the following generation, or risk loss of
genetic variation.
An increase in inbreeding at the rate of 0.1% per genera-
tion may be tolerated as long as the loss of genetic varia-
tion in commercial herds is prevented (Hill, 1982). This
same rate of inbreeding may be considered as the tolerable
level in the conservation of endangered breed populations.
Furthermore, populations with an effective population
size of more than 100 should be able to sustain a genetic
response to selection for economically important traits.
In the absence of records, a random breeding structure
where each male parent has an equal chance of mating
with a female parent may be appropriate. The rate of
inbreeding can be reduced by 50% with pedigreed breed-
ing compared to random breeding in a small population.
Concurrently, in theory, equalizing the number of male
and female parents could decrease the variance of progeny
numbers per parent, thus increasing the effective popula-
tion size.
The reestablishment of animal breeds, populations, or
landraces in one generation is possible with the cryoconser-
vation of spermatozoa and embryos for potential transfer to
an appropriate donor animal. There are reports of closely
related species having acted as surrogate dams to reproduce
implants from zygotes or clones of endangered domestic
animals that are at the verge of extinction. An alternate
approach is to backcross the endangered population to a
closely related breed for about seven generations resulting
in animals with 99% of the original breed. Among others,
Alderson (2003) has proposed qualitative criteria as a means
for prioritizing breeds of special genetic importance.
Conservation strategies should identify important
sources of interruption responsible for the endangerment
of the breed population. These may include habitat loss,
breed replacement, natural calamity, and loss of genes
within individuals. After the sources of interruption have
been identifi ed, appropriate policies and action plans to
sustain domestic goat diversity need to be developed and
implemented while resolving the unique status of the breed
population. Conservation breeding strategies for domestic
goats under threat of extinction or endangerment can
benefi t from the following: historical evidence that indi-
cates the unique status of goat populations; existing scien-
tifi c knowledge of application of quantitative genetic
principles; advances in husbandry and disease control
measures; and cryoconservation (Shrestha et al., 2008).
Conservation of an endangered breed or population can
best be realized by “conservation through utilization,”
(that is, fi nding ways to effectively use the breed in the
prevailing or a modifi ed production systems).
There are 80 composite breed populations of goats that
have been developed in 37 countries (Table 3.4). This list
is neither comprehensive nor does it necessarily imply that
these breeds/populations remain functionally present
today. A number of goat breeds with potential for improv-
ing effi ciency in the production of meat, milk, fi ber, and
skin under varying agroecological zones (Devendra, 1991)
could be used for developing composite breed populations.
There is an advantage in saving breeds considered less
productive by current standards, especially those that are
at risk of extinction that may become of value in the future
with changes in production system, environment, and con-
sumer preference for animal and animal products (Shrestha,
2005 ).
Development of composite breed populations from a
combination of an endangered breed with complementary
breeds of superior genetic merit for morphological
