Agriculture Reference
In-Depth Information
constraints of having to use more than two breeds for
crossbreeding, substantial gain can be achieved from
average breed superiority and heterosis among comple-
mentary breeds. In goats, there is no practical evidence of
any serious attempt to exploit potential genetic merit
among multiple breeds. The crossing of does of the indig-
enous breeds with bucks of the more productive dairy
breeds to produce highly effi cient crossbred does in more
remote (or tribal) areas for use in terminal crosses under
more intensive production close to urban markets demon-
strates considerable opportunity.
duction of the imported Alpine, Toggenburg, and Saanen
breeds. The interbreeding of a number of goat breeds in
isolated regions has resulted in the development of small
meat breeds in Sri Lanka, India, Papua New Guinea, and
Fiji; various Criollo (syn. Creole) breeds of Latin America
and the West Indies; Spanish goats of southwest U.S.; and
Sem Ra รง a Defi nida goats of Brazil.
Composite populations with considerable genetic merit
are the Anglo-Nubian, Boer, French Alpine, Kilis,
LaMancha, and Peranakan Etawah breeds. The Boer breed
having excelled in meat production effi ciency has been
exported to a number of countries including Australia,
Canada, China, France, Germany, Israel, New Zealand, Sri
Lanka, and the U.S. to meet the growing demand for goat
meat (Skinner, 1972 ; Malan, 2000 ).
New Breed Development
Breeders expect the desirable qualities of two or more
breeds to be combined into a composite population to
approach the level of production from crossbreeding. In
addition to the operational advantage of having to maintain
a single breeding population, there is no need to purchase
new animals, minimizing the risk of introducing diseases.
Although many composite populations were developed for
specifi c objectives, methodologies today differ from those
used in the past principally in their intensity and deliberate
application of greater knowledge of quantitative genetics.
In theory, the genetic potential for performance in a newly
formed composite population when compared to specifi c
or rotational crosses involving the same number of breeds
is lower due to the reduced level of heterozygosity.
Heterosis in a composite breed based on two breeds is
two-thirds of that in single crosses, while in composites
made of three or more breeds heterosis can be three-fourths
or more of that in single crosses. One problem with the use
of a single composite population is that it is not capable of
exploiting breed differences in maternal versus individual
performance. Concept of the composite populations,
however, has become an integral part of breeding strate-
gies exploited by breeding companies for commercial pro-
duction of livestock and poultry.
Grading-up of indigenous breeds has occurred with the
Saanen breed in Korea; the Saanen and Toggenburg breeds
in the Russian Federation, Germany, and the Czech
Republic; the Angora breed in India; and feral goats in
Australia and New Zealand resulting in adequate produc-
tivity leading to the development of 80 composite breed
populations in 37 countries (Shrestha and Fahmy, 2007).
In developing countries, the replacement of indigenous
breeds through unplanned or accidental introduction has
contributed to the development of composite populations.
In Algeria, the introduction of the Murcia and Maltese
breeds of goats for crossbreeding with the indigenous
Berber, Makatia, and Arabia was followed by further intro-
Breeding Strategies
In a closed nucleus population, with all genetic evaluations
occurring in the nucleus herd, offspring with the highest
genetic merit in the nucleus are selected as parents to
continue improving the nucleus herd. Nucleus herds could
accelerate genetic response from the use of artifi cial
insemination, and multiple ovulation and embryo transfer
(MOET). Selected bucks and does of superior genetic
merit in the nucleus herd are placed in multiplier herds
to increase the number of goats with potential genetic
merit for transfer to commercial herds. The commercial
herds are exclusive in producing kids to provide animal
products for the customer. In this procedure, it may take a
generation or two to transfer the genetic improvement
from the nucleus to the multiplier and fi nally the commer-
cial herds.
In an open nucleus population, where evaluations occur
in the nucleus and multiplier herds, offspring with superior
genetic merit in the multiplier herds are used as parents in
the nucleus herd. Unlike the above procedure with a closed
nucleus where transfer of genetic merit occurs in one direc-
tion from nucleus to multiplier, exceptional offspring in
the multiplier herd contribute genetic merit to the nucleus
herd and can improve the rate of genetic change in the
nucleus. These breeding strategies have been modifi ed in
various countries according to segmentation of the com-
mercial goat industry.
CHALLENGES
There are numerous (about 1,153) breeds of goats in all
continents demonstrating the availability of a colossal
amount of genetic resources for increasing production effi -
ciency. The evaluation of breeds presents an opportunity
to characterize their qualities and shortcomings. There is
