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24 Pages·2006·0.37 MB·English

by  Lynn Julian

Development of composite sheep breeds
in the world: A review
D.P.Rasali1, J.N.B.Shrestha2, and G.H.Crow2
1Department of Animal Science, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2;
and 2Agriculture and Agri-Food Canada, Dairy and Swine Research and Development Centre,
P. O. Box 90, Lennoxville, Quebec, Canada J1M 1Z3 ([email protected]).
Received 6 September 2005, accepted 21 December 2005.
Rasali, D. P., Shrestha, J. N. B. and Crow, G. H. 2006. Development of composite sheep breeds in the world: A review.Can.
J. Anim. Sci. 86: 1–24. In the 1850s, breeders established breed societies which maintained flock registries and actively partici-
pated in show rings, exhibitions and auctions promoting pure breeds that conformed to the breeders’ vision of uniform and dis-
tinct morphological characteristics. At that time, the performance of the pure breeds over grade sheep was overwhelming. As a
result influential government officials, specialists and scientists had to acknowledge their superiority. The supply of purebred seed-
stock that was initially adequate became sparse in the years following the World War II because demand arising from the increas-
ing human population exceeded the capacity for production. Thus, stimulated interest in higher productivity for commercial
production resulted in the development of multi-breed synthetic populations for specific objectives e.g. reproduction, meat quali-
ty, meat and wool combinations, wool for textile, carpet wool, fur, and milk production. Today, as many as 418 sheep breeds that
have been documented in nearly 75 countries are combinations of two or more distinct breeds, populations and landraces that have
records on pedigree and morphological characteristics, and in some cases, production performance similar to those for long estab-
lished breeds. The present day methods of forming composite breeds are based on a wealth of knowledge and creative skills passed
on from breeder to breeder over the centuries, as well as the application of quantitative genetic principles that had demonstrated
tremendous success in the development of hybrid corn. Research findings also suggested that in well-planned efforts to create com-
posite breeds, the genetic background of the foundation breeds should be as broad as possible to achieve increased additive genet-
ic variance and heterozygosity from a large proportion of segregating genes and lower probability for the expression of lethal
recessive genes. There was always the possibility of lower performance in the composite breeds compared with specific crosses
derived from two or more breeds, because of their inability to fully realise any benefit from individual and maternal heterosis (con-
sidered important in the mammalian species). Though unlikely, loss in performance of composite breeds could occur from recom-
bination of non-allelic genes and the migration of undesirable genes. Nevertheless, there is opportunity for accelerating genetic
response to selection as well as heterosis retention unless a rise in inbreeding occurs in the early generations causing loss in per-
formance. The real operational advantage of a multi-breed composite population lies in raising a single breed with nearly the same
productivity instead of two or more breeds for subsequent crossbreeding. Sheep in the domain of developing countries adapt well
to severe climatic conditions and arduous terrains that are often not suitable for cultivation or for raising the larger livestock and
are fully exploited for their ability to produce a variety of commodities without disrupting the cultural harmony. Likewise, more
breeds were developed in sheep than in other livestock species with the United Kingdom, Russian Federation, Australia, Poland,
China, France, the United States of America and New Zealand each having established 15 or more composite breeds that offer real
advantages. In North America and worldwide, there is further prospect for complementing established breeds with exotic breeds
to achieve potential biological ceiling in reproduction, lean muscle growth, feed efficiency and milk yield of sheep. In the future,
application of advances in molecular methodologies could possibly lead to the development of composite breeds for specific objec-
tives from a combination of widely different breeds, populations and landraces, probably, even from unrelated species.
Key words: Sheep, composite breeds, exotic breeds, indigenous populations
Rasali, D. P., Shrestha, J. N. B. et Crow, G. H. 2006.Panorama des races composites de moutons dans le monde. Can. J. Anim. Sci.
86: 1–24. Dans les années 1850, les éleveurs de moutons se réunirent en associations qui tenaient des registres et participaient activement
aux concours, aux expositions et aux encans promouvant des sujets de race pure conformes à la vision d’animaux illustrant une mor-
phologie distincte fondée des caractères uniformes. À cette époque, le rendement des sujets de race pure dépassait considérablement celui
des hybrides commerciaux. Les représentants des gouvernements, les spécialistes et les scientifiques étaient contraints d’admettre cette
supériorité. Dans les années qui suivirent la Deuxième Guerre mondiale, le nombre de géniteurs de race pure, adéquat au départ, a cepen-
dant commencé à s’amenuiser, la demande attribuable à la croissance démographique dépassant la capacité de production. L’intérêt pour
un meilleur rendement dans les élevages commerciaux a donc donné lieu à la création de populations multiraciales artificielles vouées à
des fins particulières, notamment la reproduction, une viande de qualité, la production de viande et de laine, la laine destinée aux textiles,
la laine à tapis, la fourrure et la production de lait. À présent, jusqu’à 418races dans près de 75pays combinent les caractères de deux
ou de plusieurs races, populations ou variétés indigènes distinctes dont on a enregistré la généalogie et la morphologie et dont la perfor-
mance au niveau de la production ressemble, dans certains cas, à celle des races établies de longue date. Les méthodes modernes
employées pour créer des races composites reposent sur une masse de connaissances et de méthodes transmises d’éleveur en éleveur des
siècles durant, mais aussi sur l’application des principes génétiques quantitatifs qui ont connu un succès retentissant dans l’amélioration
du maïs. Les résultats des recherches indiquent que, pour être bien conçu, un programme d’hybridation doit supposer que la base géné-
tique des races fondatrices est aussi vaste que possible de manière à garantir la meilleure variation génétique cumulative et l’hétérozy-
gotie de nombreux gènes ségrégants ainsi que la plus faible probabilité quant à l’expression de gènes récessifs dangereux.
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2 CANADIAN JOURNAL OF ANIMAL SCIENCE
Comparativement aux croisements issus de deux ou de plusieurs races spécifiques, les races composites couraient toujours le risque d’un
rendement inférieur, les animaux ne pouvant tirer pleinement parti des avantages de l’hétérosis individuelle ou maternelle (un aspect
important chez les mammifères). Bien qu’improbable, la diminution du rendement chez les races composites pourrait venir de la recom-
binaison d’autres gènes que des allèles et de la migration de gènes indésirables. Quoi qu’il en soit, on peut accélérer la réaction génétique
à la sélection et préserver l’hétérosis, à moins qu’une hausse de l’endogamie dans les premières générations n’entraîne une réduction du
rendement. Sur le plan pratique, le véritable avantage d’une population multiraciale artificielle réside dans l’élevage d’une seule race car-
actérisée par une productivité presque uniforme, au lieu de deux races ou davantage, pour hybridation subséquente. Dans les pays en
développement, les moutons s’adaptent bien aux conditions climatiques rigoureuses et aux terrains accidentés qui se prêtent mal à la cul-
ture ou à l’élevage d’animaux de plus grande taille; on les exploite pleinement en raison de leur capacité à fournir divers produits de base
sans pour autant perturber les coutumes ancestrales. Pareillement, on a créé plus de races de mouton que d’autres animaux domestiques
au R.-U., dans la Fédération russe, en Australie, en Pologne, en Chine, en France, aux É.-U. et en Nouvelle-Zélande, et chacune a donné
naissance à une quinzaine de races composites ou plus présentant de réels avantages. En Amérique du Nord et ailleurs dans le monde,
on prévoit améliorer les races établies avec des races exotiques qui permettront à l’espèce d’atteindre le plafond biologique pour la repro-
duction, la production de viande maigre, la valorisation des aliments et le rendement laitier. Dans l’avenir, l’application des progrès réal-
isés au niveau des technologies moléculaires pourrait aboutir à la création de races composites dans des buts bien précis à partir de
diverses races, populations et variétés indigènes, voire même d’autres espèces.
Mots clés: Mouton, races composites, races exotiques, populations indigènes
Raising sheep to fulfil the basic needs for meat, milk, fibre, ciency to remain profitable, at least in developing countries.
power, fuel, fertilizer and pleasure has been beneficial to the This has resulted in widespread use of the Merino breed to
human race for centuries. Sheep continue to provide a large improve fleece weight and fecund breeds to improve the
segment of the population with a variety of commodities, weight of lambs weaned, an ongoing trend for the past
whether raised on pastoral agriculture or family farms as 25–30 yr.
well as commercial production based on intensive manage- In the United States of America, open range states of
ment. Evolutionary forces such as selection (natural or arti- Montana, Idaho, North and South Dakota, Colorado, Utah,
ficial), migration, mutation and drift have contributed to etc., still manage the same breeds of sheep in a pastoral set-
domestic animal diversity among breeds, populations, or ting following husbandry practiced 30 to 50 yr ago. The
landraces within each habitat, ranging from sea level to high Rambouillet breed is still managed in west Texas the way it
mountains, desert to rain forests, and temperate climate to was 50 yr ago, but has been selected for increased produc-
hot tropics (Maijala and Terrill 1991). According to Osman tion. Again, in the United States of America, most sheep are
(1981), the reproductive isolation of many breeding popula- raised under the same management practice followed years
tions may be partly responsible for the colossal amount of ago, except for the provison of supplemental feeding to
variability and ability to physically function and adapt to pregnant ewes and shed lambing of more prolific ewes.
diverse environments. The most important characteristic in Pastoral animal agriulture continues to be practiced in the
the sheep species has been their ability to produce a wide Rocky Mountains of the United States of America, Russia,
variety of commodities while adapting to extreme agro-eco- China, Australia, New Zealand, South Africa, Brazil,
logical zones that vary in climatic conditions, diets, man- Kazakhstan, and many parts of the world.
agement, diseases, culture and religious rituals. This aspect Nevertheless, to meet the demand for more meat than
of sheep has, in all likelihood, been responsible for the wool arising from the popularity of synthetic fibre, the
development of a greater number of breeds, types and lan- major breeds of sheep in many countries have been moved
draces compared with any other domesticated species. In a away from their original habitats, and are adapting to
comprehensive assessment of livestock in the world, Mason changes in climate, housing, nutrition and disease condi-
(1967, 1980, 1996) documented approximately 418 com- tions, which are typical of present day management systems.
posite breeds (excluding those extinct) of sheep in nearly 75 The development of highly productive animal populations
countries that had been assembled by deliberate or uninten- and the intensification of production systems, which include
tional union of two or more diverse parental populations. mechanization, housing, feeding of diets balanced according
Many of these are breeds registered in Herd Books estab- to nutrient requirements, and control measures for conta-
lished by breed societies or associations similar to those for gious diseases and parasites, have contributed to productiv-
long-established pure breeds. ity increases of more than twofold. At the same time, the
In the years following World War II, the economic pres- ease with which potential sources of exotic breeds and their
sure for producing commodities to meet the growing germplasm could be imported into a country without jeop-
demand of the increasing human population put more ardizing the animal health status made it feasible to assem-
emphasis on the need to improve production efficiency. The ble composite populations for specific objectives. This has
consumption of lamb has been declining dramatically been achieved by combining desirable qualities from the
worldwide since World War II. People are not eating more established breeds in the country with those of exotic breeds
lamb, nor are more people eating lamb. Sheep numbers have that had already demonstrated genetic potential for traits of
been declining worldwide over the past two decades. Farm economical importance for commercial production. As an
prices for lamb and wool have not increased with production example, a number of studies confirmed the importance of
costs, so producers have been forced to improve animal effi- the Finnish Landrace and Romanov breeds in increasing
RASALI ET AL. — DEVELOPMENT OF COMPOSITE SHEEP BREEDS 3
reproductive rate, the Merino breed in increasing fine wool, establish rigid breed standards based on morphological
the East Friesian breed in increasing milk yield, and the characteristics, and promoted uniformity in closed popula-
Texel and Suffolk breeds in increasing lean muscle growth tions that were to serve as seed stocks. During this period,
for crossbreeding and formation of composite breeds breeders believed that purebred animals were superior, and
(Ricordeau et al. 1978; Maijala 1988; Shrestha and Heaney promoted the raising of livestock and poultry that excel in
2003, 2004). Although composite breeds were continually breed standards. The show rings, exhibitions and auctions
formed for centuries, present-day breeding methods differ further publicized purebreds as the seed stocks of choice and
from the older ones principally in their intensity and delib- promoted considerable interest among buyers. The inheri-
erate application of a greater store of knowledge of quanti- tance of characteristics in pure breeds was based on the
tative genetic principles (Dickerson 1969; Lopez-Fanjul leading doctrine of “race constancy” (Barton 1984).
1974; Hohenboken 1985). Prospects for increasing the pro- Presently, many breeders of modern sheep breeds continue
ductivity of composite sheep breeds have been reviewed in to practice the pure-breeding philosophy adhering to the
light of historical perspective, breeding methods, merits and rigid standards established by breed organizations, which
demerits of a multi-breed composite population, and future officially prohibit the introduction of any breeding animals
consideration. regardless of their potential genetic merit.
There is agreement among scientists that natural selection
HISTORICAL PERSPECTIVE played a key role in the development of sheep breeds. Later,
In the region bordering Iran and Iraq, remains of sheep skills acquired by breeders together with their ability to rec-
bones dating back to 7000–8000 BC have been uncovered ognize the benefit of alternating between moderate inbreed-
along side human settlements, and this, together with other ing in closed populations and the introduction of breeding
evidence, suggests that flocks of sheep were raised by pre- animals with potential genetic merit could possibly have
historic people at the end of the Mesolithic period (Zeuner contributed to the evolution of composite breeds for specif-
1963; Ryder 1983). The modern domestic sheep is believed ic objectives. Although many breeds were developed from
to have descended from three kinds of wild sheep, the the 1850s to the1950s, information on genealogy and per-
“Urial” found in southwest Asia, the “Mouflon” in Europe, formance has seldom been available. At the same time, the
and the large “Argali” in central Asia. Nomads caring for present day populations of many breeds have diverged con-
sheep along the usual migratory routes increased the possi- siderably from their original breed characteristics. There
bility of accidental or deliberate mating of migratory sheep are, however, indigenous breed populations in developing
with sedentary flocks. In some instances, the productivity of countries that remain in their natural habitat, and have not
the offspring exceeded those of their parents, and conse- been exposed to artificial selection. Many of the indigenous
quently, selected replacements derived from morphological- breed populations are likely to have retained specific genet-
ly diverse parents might have been retained for breeding ic combinations that may be of use in developing composite
(Zirkle 1952). This practice of assembling domestic animals breeds for the future with the potential to respond to chang-
from two or more divergent populations or landraces to cre- ing markets, climate change, and disease conditions.
ate new combinations could have continued by way of nat- The task of maintaining two or more breeds as indepen-
ural selection and human intervention, finally resulting in dent breeding populations with a more complex crossbreed-
new combinations. At that time, breeders likely had the ing protocol compared with attaining similar performance
skills and aptitude to recognize the importance of hybrid with a much simpler procedure has led to a revival of inter-
vigour in enhancing performance. est in the development of composite breeds from crossbred
Long before breeding records were kept there was a ten- foundations. In the 1960s, a large number of composite
dency to mate closely related animals and discard offspring breeds were developed from crosses among fine and long
with deleterious effects or those that did not conform to the wool breeds to promote meat production and wool of inter-
breeder’s vision. This practice might have continued over mediate fineness and length (Maijala and Terrill 1991).
generations and played an important role in establishing Furthermore, increased interest in meat, carpet, rugs and
breed characteristics. The domestic sheep that accompanied luxury products contributed to the modification of breeding
explorers and conquerors into various regions of the world objectives in the major sheep and wool exporting countries.
remained in the newly established colonial settlements due There has been considerable interest in describing sheep
to the availability of abundant forage and vegetation and populations in the world that may have potential genetic
freedom from predators and communicable diseases. In sub- merit for increasing productivity (Phillips et al. 1945;
sequent voyages, improved animals, including sheep, were Hodgson 1961; Epstein 1969 and 1974; Mason 1967; Terrill
introduced into the colonies and used in the grading-up of 1970; Yalcin 1979; Ghanem 1980; Fitzhugh and Bradford
livestock and poultry species that had been introduced pre- 1983; Skinner et al. 1985; Tu 1988; Dmitriev and Ernst
viously. Further details and description on the subject of 1989; Hall and Clutton-Brock 1989; Hallander 1989).
domestication, evolution and history of sheep have been Despite the existence of domestic animal diversity, the
extensively reviewed in the literature (Mason 1973; Ryder migratory patterns followed by humans, livestock and poul-
1991). try were subjected to trade barriers and considerable restric-
Since the latter part of the 18th century, detailed record- tions as a result of prolonged quarantine, limiting the ability
ing of animal pedigree and performance led to the emer- to sample potentially useful genetic resources (Dickerson
gence of breed societies in continental Europe. This helped 1993) that could have been made available for crossbreed-
4 CANADIAN JOURNAL OF ANIMAL SCIENCE
ing and the formation of composite breeds suitable for (Outaouais and Rideau). Furthermore, offspring sired by the
increasing productivity. In the past two decades, details and composite breed and the Suffolk breed, which is considered
description of sheep genetic resources have been of interest an industry standard in North America for growth perfor-
in developing an inventory of domestic animal diversity and mance, had similar productivity (Leymaster 1991; Shafto et
identifying breed populations that are endangered or at risk al 1996a, b) whereas fecund-type ewes exceeded the Suffolk
of extinction (Simon 1990; Wilson 1991; Delgado et al. breed and the Finnish Landrace in ewe productivity
1992; Wu et al. 1992; Simon and Buchenauer 1993; Board (Shrestha and Heaney 1992; Shrestha et al. 1992) demon-
of Agriculture 1993; Fahmy 1996; Mason 1996; Scherf strating the potential merit of the composite breeds for
2000). increasing productivity in the commercial sheep industry.
A simple procedure to create a composite population
BREEDING METHODS based on three divergent breeds (Lauprecht 1961) consists
In the 1940s, Winters (1953) at the University of Minnesota of producing three groups of two-breed cross offspring. All
pioneered a procedure based on exploiting breed differences the two-breed cross offspring are mated to the third breed to
for the genetic improvement of performance that led to the produce three breed cross progeny. This is followed by
development of composite sheep breeds (Minnesota 100, backcrossing a three-breed cross offspring to the two-breed
102, 103 and 105 breeds) for the mid-western United States. cross parents. The resultant crossbred offspring is back-
The concept of breed development based on crossbred foun- crossed to the three-breed cross parent. Finally, the cross-
dation was at that time, in contrast to the purebred philoso- bred population is closed after the second generation,
phy that was entrenched among the breeders. followed by inter se mating for a number of generations.
The breeding strategy for developing the Minnesota Procedures employed by researchers to create composite
breeds relied on keeping offspring of desirable types derived breeds have been well documented. Recently, Shrestha
from crossbreeding among breeds chosen for their potential (2005) described in detail the various crossbred combina-
genetic merit in morphological characteristics and produc- tions leading to the development of composite breeds based
tion performance. This was followed by additional cross- on two and three breeds.
breeding and subsequent inter se mating for the next few In theory, the greater initial heterozygosity in the com-
generations. Finally, the selection objective was for a ewe posite breed, unless lost through inbreeding in the early gen-
that would raise twin lambs, each weighing 40 kg at 140 erations could result in a higher initial performance and
days, possess sufficient quality to achieve a “top” market greater genetic variability providing opportunity for lasting
value for lamb carcasses, and produce 4 kg fleece per 45 kg response to further selection (Sumption et al. 1961).
of body weight (Winters et al. 1946; Winters 1954). Breed Selection will increase the frequency of specific linked gene
evaluation studies among the Minnesota breeds and their combinations and delay equilibrium in the newly formed
crosses have shown that lamb and ewe productivity vary combinations. In a three-breed composite population the
significantly in the pure breeds as well as for general com- contribution of three parental breeds would eventually sta-
bining ability while heterosis and specific combining ability bilize at one-third. Eventually, the newly formed population
had important effects (Shrestha et al. 1983). is expected to achieve equilibrium following five to six suc-
Crossbreeding has achieved success as an effective pro- cessive generations of random mating. Thereafter, any
cedure for exploiting the commercial value of highly fecund genetic improvement of the composite breed for desirable
sheep (Turner 1969, 1991; Dickerson 1977; Jakubec 1977; morphological characteristics and production performance
Meyer et al. 1977). An important extension is the develop- may be based on selection for optimal breeding objectives.
ment of composite breeds. Composite breeds have been In the newly developed breed, there have been reports of
developed for specific objectives by combining diverse higher estimates of heritability for some traits, but other
breeds with antagonistic characteristics (Aliev 1989) as well traits have had lower estimates (Mohd-Yusuff et al. 1988).
as also those with increased fecundity along with growth, In an accelerated lambing program over a 20-yr period, the
carcass and fleece attributes are combined for achieving per- heritability estimates for ewe productivity traits under 8-mo
manent increases in production efficiency (Carter 1976; breeding cycles and artificial rearing of lambs were report-
Smith et al. 1979; Hulet et al. 1981, 1984). Correspondingly, ed to be moderate, and in the desirable direction (Hansen
the breeding objectives for the improvement of both biolog- and Shrestha 1997, 1998). The parameter estimates were
ical and economic efficiency (Almahdy et al. 2000a, b) consistent across February, June and October lambing,
include the development of terminal sire breeds, the combi- demonstrating recurrent opportunity to continue achieving
nation of exotic breeds and indigenous populations for genetic response to selection (Hansen and Shrestha 2002),
desirable characteristics, and the development of breeds thus increasing the efficiency of sheep breeding programs.
from simple or more complex crosses. According to Mohd-Yusuff and Dickerson (1991) the
In Canada, breed complementarity of the parental breeds expected increase in genetic variability of composite breeds
of diverse genetic potentials has been exploited by con- was proportional to diversity in gene frequencies of the
tributing a number of desirable economic characteristics to parental breeds. Furthermore, simulation studies have
newly developed Arcott breeds of sheep (Shrestha and demonstrated that genetic variability is likely to increase
Heaney 2003, 2004). Rams and ewes from the composite only when dominance is partial or when frequencies of
breeds have been utilized in the breeding programs as meat- favourable dominance alleles are lower than their expected
type terminal sires (Canadian) and fecund-type dams equilibrium values. Such a change in genetic variability and
RASALI ET AL. — DEVELOPMENT OF COMPOSITE SHEEP BREEDS 5
greater potential selection intensity resulting from higher cost of introducing exotic breeds while minimizing the pos-
reproductive rate can be complementary to each other in sible risk of introducing diseases.
improving response to selection within the composite breed. Some developing countries have introduced one or more
Therefore, the use of highly fecund Finnish Landrace and exotic breeds from continental Europe into the indigenous
Romanov sheep as one of the parental breeds in the multi- populations through crossbreeding leading to the formation
breed composite population has achieved success in enhanc- of composite breeds. This practice has been more popular in
ing productivity (Fahmy 1996). Europe, Asia and the Americas. In India, Acharya (1982)
Prospects for complementing established breeds through described the newly developed Hissardale, Kashmir Merino
the introduction of exotic breeds (from global sheep genetic and Nilgiri breeds of sheep. These breeds developed from a
resources) that have demonstrated superiority in production narrow genetic base are variable in productivity. What
traits could shorten the time required for rapid genetic seems to occur in practice is that introductions from highly
improvement of economically important characteristics, productive exotic breeds into indigenous populations using
particularly those that have lower heritabilities. There have crossbreeding strategies, particularly in the developing
been extensive studies on the evaluation of a number of countries, have led to grading-up aimed at eventual breed
crosses of sheep breeds presenting a wealth of knowledge replacement. This practice greatly undermines the impor-
on their comparative productivity in various environments tance of utilizing desirable characteristics from the indige-
(Carter and Kirton 1975; Jakubec 1977; Dickerson 1977; nous populations.
Ricordeau et al. 1978; Nitter 1978; Rae 1982). The wide There is agreement among breeders that the quantitative
variation known to exist within breeds for economically genetic principles of heterosis retention, breed complemen-
important morphological characteristics and production per- tarity, reduction in rate of inbreeding and increased genetic
formance emphasizes the importance of adequate sampling variability need to be fully exploited for the development of
of rams and ewes. When choosing an imported breed with composite breeds. Though less likely, there is always the
potential for genetic improvement, primary emphasis must possibility of introducing undesirable genes and increased
be placed on characteristics such as high fecundity for year- risk from diseases or loss of genes that may have potential
round breeding, feed efficiency, production from ewe lambs merit in the future. Details and discussion of the genetic
and resistance to diseases, as these will likely be important principles when combining specific morphological charac-
in most biological objectives associated with commercial teristics, adaptability and improved productivity among
production. Year-round breeding and breeding of ewe lambs breeds to form composite populations have been reviewed
are not desirable or profitable for some regions or manage- (Dickerson 1969; Lopez-Fanjul 1974; Young et al. 1986;
ment systems. Although feed efficiency may be a desirable Maijala and Terill 1991; Rempel and Maijala 1991).
trait it is usually not measured. Disease resistance of import-
ed breeds is generally not known until the animals are in the MERITS AND DEMERITS OF A MULTI-BREED
new environment. The flocking instinct found in the Merino COMPOSITE POPULATION
and Rambouillet breeds, which may be lacking in many Composite populations have a definitive operational advan-
exotic breeds, is important to some producers. Evidence in tage because it is much simpler for a breeder to manage a
the literature does not support a genotype × environment single population of similar animals under uniform hus-
interaction, unless the differences among the genotypes or bandry. This is in contrast to a more complex commercial
environments are extreme (Turner and Young 1969). hybrid approach involving one or more levels of cross-
The cost of importing and testing breeds of sheep may be breeding that can be more difficult to implement, particular-
exorbitant, but the benefits in improving the efficiency of ly in a large number of family farms common in Canada.
sheep production should justify the investment. Restricting Also, in many developing countries, sheep are raised in
importation to those identified following extensive breed flocks of small numbers of animals that are easy to manage
evaluation studies minimizes any associated risk of intro- as a single population demonstrating potential for introduc-
ducing unwanted genes into the population. Financial ing a highly productive multi-breed composite population.
restrictions often make it impossible to purchase female The most widely accepted reason for combining two or
breeding stock chosen especially for their genetic potential. more breeds with divergent morphological characteristics
In practice, a sample of sires representing as broad a genet- and production performance, regardless of their contribution
ic background as possible from each breed would be desir- to heterosis has been “breed complementarity”. The benefit
able. Furthermore, in order to accelerate genetic response, it in the productivity of multi-breed composite populations is
is always advisable to utilize a large number of unrelated comprised of a combination of desirable qualities that occur
rams and reduce the ratio of the number of ewes mated to from the additive genetic effects of the parental breeds. The
each sire, thus increasing the effective population size. usual perception has been that the performance of the newly
Because of the quarantine and financial constraints, it may developed breed tends to remain intermediate between the
not always be possible to develop composite breeds to average of their parental purebreds and all possible single
achieve theoretical expectations. However, the number of crosses among constituent parental breeds. This is based on
breeds used in the foundation stocks should provide suffi- the assumption that the benefit from heterosis cannot be uti-
cient genetic variation for selection to achieve specific lized in a single segregating population.
objectives. Recent developments that permit the ease with In theory, the greater initial heterozygosity from a combi-
which semen and embryos can be moved could reduce the nation of desirable traits in the parental breeds should
6 CANADIAN JOURNAL OF ANIMAL SCIENCE
increase the proportion of genetic variation in the composite growth and carcass quality (Rastogi et al. 1982), and nega-
population and enhance response to long-term selection tive for prolificacy and longevity (Boylan 1985).
unless inbreeding in the early generations contributes to One major disadvantage of so many different composite
lower performance. A substantial proportion of the heterosis breeds is that in the market place this results in a gross lack
in the F generation due to dominant gene action resulting of uniformity of product. This is especially true in the meat
1
from increased heterozygosity could be retained even after packing industry, which prefers all carcasses to be uniform
several generations of inter se matings. There is evidence to and of the same size and grade. With so many different
suggest that an increase in initial heterozygosity followed by breeds of different mature size, uniformity of carcasses is a
retention of individual and maternal heterosis in the newly major problem in some areas.
formed breed could exceed that of the parental breeds. In a
crossbreeding study of D’man and Sardi breeds, a popula- NEWLY DEVELOPED SHEEP BREEDS
tion derived by crossing two breeds, followed by several The development of composite breeds from two or more
generations of inter se mating resulted in higher total lamb parental breeds does not appear to be strictly a domain of
production than either of the pure breed (Boujenane et al. any particular region of the world. The occurrence of com-
1991). In beef cattle, Gregory et al. (1999) have shown that posite breeds is prevalent across all regions irrespective of
in the advanced generations following the creation of com- their geo-climatic conditions, economies and prevailing pro-
posite breeds, heterosis retention for several desirable pro- duction-marketing situations. The contribution of the
duction characteristics was equal to or even greater than that parental breeds to the composite breeds developed for spe-
expected from crossbreeding. cific objectives have varied according to their potential
In theory, the genetic potential for productivity in a com- genetic merit for improving productivity. The majority of
posite population is expected to be lower than that of a spe- 418 composite breeds (Table 1) were developed from a
cific breed cross or rotational cross involving the same combination of two and three parental breeds, while others
number of parental breeds (Dickerson 1969). One can were derived from more than three parental breeds. The
reduce the loss in heterosis by increasing the number of regional distribution of 176 composite sheep breeds in the
breed combination to three, four or more, retaining two- world as documented in the database of domestic animal
third, three-fourth or more of the average superiority of the diversity of the Food and Agriculture Organization of the
single crosses among constituent breeds. United Nations is as follows: Central and Eastern Europe
There has been frequent reference made to optimizing the including Russia (34%), Europe (27.3%), Asia-Pacific
proportions of parental breeds that have demonstrated (9.7%), Oceania (10%), Africa and Middle East (6.3%),
genetic merit while assembling potential breeds for com- North America (8.5%), and South America (4%). An
posite breed development (MacNeil 1987; Kinghorn et al. exhaustive list of the composite breeds, strains, varieties and
1989; Hayes et al. 2000). Besides agreeing to set the fixed crosses of sheep includes country of origin, parental breeds,
proportions among breeds assembled during the develop- and available population sizes of breeding males and
ment of a composite breed, it is important to consider a large females registered (Mason 1996; FAO 2005).
segregating population with sufficient genetic variability, The United Kingdom (12%), Russian Federation (8.1%),
avoiding any possibility of increasing the rate of inbreeding. Australia (6.2%), Poland (5.5%), China (4.8%), France
At the same time, desirable morphological characteristics (4.3%), the United States of America (4.1%), New Zealand
and production performance will not be stable unless the ini- (3.6%), Bulgaria (3.4%), Italy (2.9%) and Kazakhstan
tial crosses are followed by at least four to five generations (2.6%) have developed the majority of composite breeds in
ofinter semating. This process is time consuming, and may the world (Table 2). The Merino, Romney, Rambouillet,
not be feasible unless the newly formed population consists Caucasian, Lincoln, Border Leicester, Dorset, East Friesian,
of genetic combinations, which exceed the performance of Leicester Longwool, Suffolk, Prêcoce, Corriedale, Tsigai,
the best parental breed. Mongolian and Finnish Landrace as parental breeds had the
There are also a number of drawbacks in developing a most impact in the development of composite breeds (Table
composite breed because a single breeding population may 3). The finewool and longwool breeds have been the more
not be capable of exploiting breed differences in maternal popular parental breeds compared with those that excel in
versus individual performance considered important in the growth, reproduction rate, meat quality, feed efficiency and
mammalian species. Nevertheless, breed development stud- disease resistance. This is because wool, a non-perishable
ies have shown that a substantial portion of the heterosis can product from sheep could be produced far away from the
be retained in the subsequent generations enhancing perfor- processing plant and sold at a good price. At the same time,
mance (Gregory et al. 1999). There is also a further decrease sheep have been more adaptive and widely utilized in pas-
in the performance of the composite breed due to recombi- toral agriculture.
nation loss among non-allelic genes, the lower proportion of According to Maijala and Terrill (1991), many composite
heterozygosity retained compared with systematic cross- sheep breeds across the world were developed for specific
breeding, and the occurrence of inbreeding and genetic drift, objectives. Examples include, the breeds of fine, medium
particularly if the base population is small (Dickerson and long wool-types capable of adapting to a wide variety of
1969). Despite several studies to demonstrate reduction in environmental conditions for textile wool; breeds with
the performance of sheep, deleterious effects in performance coarse or hairy medullated fleece for carpet wool; breeds for
due to recombination loss have been small or negligible for luxury fur or pelt market; fecund-type dam and meat-type
RASALI ET AL. — DEVELOPMENT OF COMPOSITE SHEEP BREEDS 7
size Parental breedsBreeding animals/registered; population size (yr) Askanian, Suffolk, Oxford Down, Tsigai Lincoln Longwool, Tsigai, Askanian English Longwool, Askanianm: 37417; t: 1 614000 (1980) East Friesian (32.5–62.5%), Israeli Improved Awassi Rambouillet, Malpura Local, Leicester longwool, South Down, Romneym: 39; f: 537; HB: 100; t: 576 (2001) Kedabek Merino, Bozakh, Askanian Romney, Tsigai Hissardale (25%), Damani (25%), Rambouillet (50%)m: 12; f: 382; t: 850 (1992) White Karaman, Libyan Barbary Basque, Béarnaism: 1805, f: 76000, t: >77900 (2001) Lleyn, Fingalway, High Fertility, Galway, Finnish Landrace Lleyn (45%), High Fertility (32%), Fingalway (18%), ProlificGalway (5%); m: 30; f: 1000; HB: 800; t: 1000–10000 (1997) Drenthe var of Dutch Heath, German Heathm: 112; f: 2499; t: >2611 (2001) Merino, Southdown, Leicester Longwool, Dishley Merino,Champagne and Boischaut variety of Berrichonm: 2970; f: 141000; HB: 3300; t: >144000 (2001) Africander, Wooled Persian, Blackhead Persiant: <100 (1999) Rambouillet, Soviet Merino, Chokla, Nali, Malpura
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animals/registered and po Composite breedCountry of origin (yr est.) Askanian BlackheadedUkraine Askanian CrossbredUkraine Askanian CorriedaleRuss. Fed. AssafIsrael (1955) AvikalinIndia (1970) AvranchinFrance (1928) Azerbaijan Mountain MeriAzerbaijan (1947) Azov TsigaiUkraine (1963) BaghdalePakistan Barbary HalfbredLibya Basco-BéarnaisFrance (1965) BelclareIreland (1976–1979) Belclare ImproverIreland (1981) BentheimerGermany (1934) Berrichon du CherFrance (1936) Bezuidenhout AfricanderSouth Africa (1918) Bharat MerinoIndia (1980)
g
edin 5%),7)
ds, country of origin, year established, parental breeds, bre Parental breedsBreeding animals/registered; population size (yr) Finnish Landrace (47%), East Friesian (24%),Border Leicester (17%), Dorset Horn (12%) East Friesian (25%), Awassi (50%), Dag˘lic (25%)t: 1000–10000 (1998) South African Mutton Merino (50%), Ronderib Afrikander (2South African Merino (25%); m: 83; HB: 2302; t: 3141 (199 Caucasian, Lincoln, Jaidara Sary-Ja, Précoce, Kazak Fat-Rumped Sary-Ja, Kazak Fat-Rumped American Rambouillet, Caucasian, Australian and SiberianMerinos; m: 68591; t: 3328000 (1980) Tsigai, Merino, Local coarsewool Altai, Précoce, Buryat Russian, Mongolian and Australian Merinosm: 1200, f: 15700; HB: 2650; t: >300000 (1983) Merino, Bergamasca, Sopravissanam: 273; f: 11601; t: 12334 (2002) Balbas, Rambouillet or Lincoln Cormo, Peppin Merino, Polled Merino, Corriedale,Beddale; m: 8500; f: 292200; t: 410000 (1992) Criollo, Spanish and Saxony Merinos, Rambouillet Chios or Anatolian Fat-tailed, Greek Zackel Rambouillet, Lincoln, Balbasm: 1831; t: 43390 (1980) Assaf, Barbados Blackbelly, Corriedale
e
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Table 1. Composite sheep Composite breedCountry of origin (yr est.) ABRO DamlineUK (1967) AcipayamTurkey AfrinoSouth Africa (1969–1976) Akhangaran Mutton-woolUzbekistan Aktyubinsk Semi-coarse woKazakhstan AlaiKazakhstan (1934–1981) Altai or AltaiskayaRuss. Fed. (1934–1949) Altai MountainRuss. Fed. (1940–1945) Angara MerinoRuss. Fed. (1974) Aohan FinewoolChina (1970) ApennineItaly (1981) AragatsArmenia Argentine CormoArgentina (1979) Argentine MerinoArgentina (1875–1990) ArgosGreece Armenian Semi-coarsewoolArmenia AsblackPeru (1990)
8 CANADIAN JOURNAL OF ANIMAL SCIENCE
West African, Criollo Bluefaced Leicester (16%), Polled Dorset (11.5%), East andWest Friesian (42%), Prolific (15%), Lleyn (13.5%), others (2%)f: 1232; t: 1000–10000 (2002) Stara Zagora, Pleven Blackhead, East Friesian Wiltshire, Suffolk, Border Leicester, Booroola Merino,Dorset Horn, Merino Australian Merino strains, Polwarth, (5–10%) South Australian Merino, English Longwool Barbado, American Tunis, Tunis Clun Forrest, Lleyn, Llanwenog, Finnish Landrace, BluefacedLeicester, Kerry Hill, Border Leicester, Radnor, Ryelandt: 100–1000 (2002) Tunisian Barbary, Local Thin-tailed sheep Ile de France (28%), Leicester Longwool (7%), Romnelet (6%),Suffolk (37%), North Country Cheivot (7%), other 7 breeds (8%)m: 89; f: 575 (1994) Corriedale, Lincoln, Rambouilletm: 28; f: 296; t: 100–1000 (1994) ××Da˘glic White Karaman, or Red Karaman Tuj Local, Paduan, Bergamascam: 57; f: 351; HB: 335 (1994) JCoarse wooled Border Leicester, Romney with Ngene,Coarse wooled Perendales; t: <100 (1995) Shetland, Mouflon or Soay, Manx Loaghtonf: 688; t: 688–1000 (2001) Lacaune, Berrichon, Ile de France, Roussillon Red German Mutton Merino (80%), White Karaman (20%)t: >1200000 (1990)
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Brazilian WoollessBrazil British MilksheepUK (1970) Bulgarian DairyBulgaria (1972) BumfdaleAustralia (1979–1992) Bundoran ComebackAustralia (1971) Bungaree MerinoAustralia California RedUSA (1971) CambridgeUK (1966–1976) Campanian BarbaryItaly (1971) Canadian ArcottCanada (1968–1988) Canadian CorriedaleCanada (1919–1934) ÇandirTurkey CarinthianAustria (1938) CarpetmasterAustralia Castlemilk MooritUK (1974) CatalanFrance Central Anatolian MeriTurkey (1952)
n
Polish breeds (Polish Merino and Wielkopolska), East Friesiaand meat breeds (Berrichon du cher, Ile de France, Texel)M: 160; f: 700; HB: 571; t: 1200 (1993) Polish Merino, Local from Polish Lowland ××Merino Tsigai or Merino Pramenka Ile de France, Palas Merino, Tsigai Leicester Longwool, Black Welsh Mountain Caussenard de la Garrigues, Caussenard dela Lozère, Race des Cévennes, Lacaunem: 7840; f: 400000; HB: 35684; t: >407840 (2001) Leicester Longwool, Wensleydale, Choletais)m: 970; f: 3000; HB: 1703; t: >3970 (2001 Border Leicester, Merino selected for fertility Lincoln, Tasmanian and Peppin Merino Border Leicester (7/8), Booroola Merino (1/8) carrying2 copies of Booroola gene; m: 20; f: 100; t: 400 (1993) Merino, Churro, Campaniça, Entre Douro e Minho,Saloia, Serra da Estrela Border Leicester, Corriedale Border Leicester (50%), Merino (50%) Border Leicester (50%), New Zealand Romney (50%) Scottish Blackface, Hebridean type of Tanfacef: 93, t: <100 (2002) Border Leicester, Merino Artois, Leicester Longwool, Dishley Merinom: 80; f: 3000; HB: 2313; t: >3080 (2001) Blackhead Persian, Localm: 3500; f: 72500; t: 120000–160000 (1992)
ol
Table 1. Continued Bialoglowa OwcaPoland BialyastokPoland (1963) Birkaformer Yugoslavia BîrsaRomania (1953) Black Leicester LongwoUK (1986) Blanc du Massif CentralFrance (1965) Bleu du MaineFrance (1938) BLMAustralia (1955) Bond Australia (1909) Booroola LeicesterAustralia BordaleiroPortugal BorderdaleNew Zealand (1930) Border-MerinoNew Zealand Border-RomneyNew Zealand (1930) BorerayUK (1870) BorinoAustralia BoulonnaisFrance (1963) Brazilian SomaliBrazil
RASALI ET AL. — DEVELOPMENT OF COMPOSITE SHEEP BREEDS 9
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Corriedale, Tasmanian Merinom: 700; f: 70000 (1992) Lincoln (or Leicester Longwool), Merinom: 180; f: 5200; t: 8000 (1992) Leicester Longwool, Local (Roussin de la Hague)m: 200; f: 2000; t: >2200 (2001) Leicester Longwool, Hampshire, Oxford Down, GermWhiteheaded Mutton Marsh; f: 712; t: >1000 (2 000) Hungarian Rambouillet, Booroola Merino Merinolandschaf (Württemberg Merino), Gunib Norsk Landrace, Leicester Longwool, Cheviott: 140000; HB: 42000 (2000) Polled Dorset, Border Leicester, Merino Swaledale, Scottish Blackfacef: 375000; t: <1000000 (2002) Swedish Finewool, Finnish Landrace Danish Heath, Merino, Leicester Longwool, Oxford Dm: 20; f: 200 (1992) German Mutton Merino, Caucasian or Askanian,Svishtov, Pleven Blackhead Spanca˘, Merino, Tsigai Original Dartmoor, English Longwoolf: 1685; t: <10000 (2000) Darvaz, Württemberg Merino, Caucasian Delaine Merino, Rambouillet(orig. 1920; named 1947; BS 1954) Shropshire, Précoce, Kazakh Fat-rumpedt: 124000 (1980) Leicester Longwool, Lonkf: 2250; t: <10000 (2002)
2)
CormoAustralia (1960) CorriedaleNew Zealand (1880–1910) CotentinFrance (1830–1900) CotswoldUK (1862) Csenger MerinoHungary (1982) Dagestan MountainRuss. Fed. (1926–1950) DalaNorway (1860–1920) DaldaleAustralia (1970) DalesbredUK (1930) Danish FinewoolDenmark Danish LandraceDenmark (1900) Danube FinewoolBulgaria (1950–1967) Danube MerinoRomania Dartmoor (Greyface)UK (1820–1909) Darvaz Mountain MuttonwoolTajikstan (1948) Debouillet;USA (1920–1943) Degeres Mutton-WoolKazakhastan (1931–1980) Derbyshire Gritstone(Dale-O-Goyt sheep) UK (189
n
Merino, Local Pyrenean Romney, Berrichon, Merino, Solognot, Tourainem: 1176; f: 20000; HB: 3800; t: 21176 (2001) Leicester, Longwool, Localm: 1576; f: 374000; HB: 10000; t: 400000 (2001) North Country Cheviot (50%), North Ronaldsay (50%) North Country Cheviot (50%), Corriedale (50%) Kuche, Kazakh, Karakul, Mongoliant: 60000 (1980) Australian Merino, Xinjiang, Mongolianm: 200; f: 30000; t: 50000 (1983) Buryat, Finewool Hill Radnor, Shropshire, Kerry Hillf: 4886; t: <10000 (2001) East Friesian, Clun Forest, Border Leicester, Dorset Hor(HB, 1962) Lincoln, American Rambouillett: 9512 (1990) Columbia, Southdale Border Leicester, Dorset Horn, Finnish Landrace,Rambouillet, Suffolk, Targhee English Longwool, Merinom: 4000; f: 200000; t: 500000 (1973) Maltese, Sicilianm: 3306; f: 106616; t: >138155 (2002) Polled Dorset, Suffolk, Hampshire, Wiltshire Horn,Leicester, Lincoln; m: 1500; f: 5000; t: 6500 (1994) Border Leicester, New Zealand Romneym: 1100; f: 48000; t: 60000 (1992) Merino, Corriedalem: 1600; f: 80000; t: >125000 (1992)
2)
Table 1. Continued Central PyreneanFrance CharmoiseFrance (1844–1952) CharollaisFrance (1963) ChevaldshayUK Cheviot-CorriedaleNew Zealand Chinese KarakulChina (1960) Chinese MerinoChina ChitaRuss. Fed. Clun ForestUK (1865) ColbredUK (1957) ColumbiaUSA (1912) Columbia-SouthdaleUSA (1943) Combo 6USA (1970) ComebackAustralia (1976) ComisanaItaly (1942) CoolaleeAustralia (1968–198 CoopworthNew Zealand (1968) CorinoArgentina (1970)
10 CANADIAN JOURNAL OF ANIMAL SCIENCE
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hos e (2 Mon
Cheviot, Local Coarsewoolm: 100; f: 779; t: 10000–1000000 Anatolian Fat-tailed, Local Thin-tailed Local Apennine, Bergamascam: 141; f: 2594; t: < 2854 (2002) Dall Sheep, Stone Sheepm: 495; f: 4015; t: >5000 (2002) Bergamasca, Bielleset: 4500 (1994) Finnish Landrace, Galway Finnish Landrace, Dorset Horn Finnish Landrace, Ile de Francem: 40; f: 1000; t: >1040 (2000) Rambouillet, Spanish Merino American Rambouillet, Australian Merino Local, Préalpes du Sud East Friesian, Local, Chios, Karagouniko, Zakyntt: >100000 (2001) East Friesian, Serra da Estrela East Friesian (37.5%), Sardinian (37.5%), Lacaun Australian Merino, Polwarth Caucasian, Salsk, Stavropol, Xinjiang Finewool, Tibetan; m: 200; f: 12000; t: 20000 (1983) Spanish Merino, Local, Saxony, Rambouilletm: 106; f: 5520; t: >5654 (2002) Tushin, Soviet Merino, Caucasianm: 67; f: 1166; t: 2018 (1980)
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Estonian WhiteheadedEstonia EvdilonGreece FabrianeseItaly (1974) Fannin sheepUSA FinardaItaly FinngalwayIreland (1970s) Finn-DorsetUK/Ireland FlevolandThe Netherlands (1975) Fonte Bôa MerinoPortugal (1902–1926) Fonthill MerinoAustralia (1954) French AlpineFrance (1952) FrisartaGreece (1946) FriserraPortugal (1962) FSLFrance (1967) GadasuChina (1970) Gansu Alpine FinewoolChina (1950) Gentile di PugliaItaly (1942) Georgian Fat-tailed FineGeorgia (1936–1958)
ol
Devon Longwool, South Devonf: 2750; t: < 10000 (2002) Devon Longwool, Exmoor Hornt: 4000–10000 (2002) Australian Dorset, Border Leicester, Suffolkm: 40; f: 208 (1989) German Mutton Merino, South African Merinot: 3500 (1997) Merino (75%), Dorset (25%) Dorset Horn (50%), German Mutton Merino (50%)m: 8700; f: 26000; t: >40000 (1992) Dorset Horn (50%) and Blackhead Persian (50%)m: 860000; f: 3900000; t: >7000000 (1992) Hampshire Down, Southdownf: 2034; t: <10000 (2000) Portland, Merinot: 1000–10000 (2002) Merino, Pramenkam: 5; f: 60; t: >65 (1996) Texel and Friesian with black colour gene, Drenthe, Schoonebeker; (HB: 1985) Altai, Transbaikal Finewool, Tsigai, Local Coarsewo Kazakh Fat-rumped, Kalmykm: 137798; t: 2419000 (1980) Drysdale, Border Leicester, Merino, hairy Romney,Homozygous for mutant carpet wool genem: 165; f: 9000; t: 12000 (1993) Bergamasca, Steinschafm: 136; f: 1381; t: >2035 (2001) Border Leicester (50%), Clun Forest; (BS: 1981) Soviet Merino, Caucasian, Mongolian Local North Short tail graded to Shropshirem: 110 ; f: 1 167; t: 10000–100000 (1998)
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Table 1. Continued Devon and Cornwall LoUK (1977) Devon ClosewoolUK (1923) DLSCanada (1989) Döhne MerinoSouth Africa (1940) DormerAustralia DormerSouth Africa (1941) DorperSouth Africa (1942–195 Dorset DownUK (1906) Dorset HornUK (1862) DubrovnikCroatia Dutch Black BlazeThe Netherlands (1979) East Mongolian SemifinMongolia (1962–1982) EdilbaevKazakhstan ElliotdaleAustralia (1963–1977) Engadine RedSwitzerland (1985) English HalfbredUK (1981) ErduosChina Estonian DarkheadedEstonia (1940)