Agriculture Reference
In-Depth Information
weights and 12% for mortality. Furthermore, Abdelsalem
et al. (2000) reported Barki-sired does of Damascus
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Barki
Two-breed rotation
Three-breed cross rotation
Barki cross produced
more milk for a longer lactation, had heavier litters, and a
more effi cient milk conversion ratio. Relative to contem-
porary Barki does, crossbreds produced more milk and
heavier litter weights.
There has been extensive research (Flamant and Morand-
Fehr, 1982) directed toward genetic improvement of goat
breeds from continental Europe. Studies suggest increas-
ing milk yield in the female parent results in increased
growth rate of their crossbred offspring. In Mexico,
Sánchez et al. (1994) used a stall-fed system to evaluate
the grading-up of local goats derived from high (
cross compared to those of Zaraibi
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Parents
A
B
A
B
Offspring
AxB
AxB
Parents
A
AxB
C
AxB
Offspring
Ax(AxB)
Cx(AxB)
Parents
B
Ax(AxB)
A
Cx(AxB)
≥
7/8) and
Offspring
Bx{Ax(AxB)}
Ax{Cx(AxB)}
7/8) proportions of the Alpine, Granadina, Nubian,
Saanen, and Toggenburg dairy breeds from continental
Europe. The authors concluded that crossbred kids from
high and low proportions of the Alpine, Saanen, and
Toggenburg breeds were similar to the Nubian breed but
heavier than the Granadina breed. Concurrently, Montaldo
et al. (1995) reported crossbred kids from high and low
proportions of the Alpine, Saanen, and Toggenburg breeds
were more productive compared to their contemporary
local goats in milk production, lactation length and effi -
ciency, litter size, and weight.
The mating of crossbred bucks to purebred or crossbred
does can capitalize on paternal heterosis and contribute
toward libido and sperm production with possible infl u-
ence on fertilization and embryonic survival (Notter,
1987). Lopez-Perez et al. (1998) showed crossbred off-
spring from Boer
low (
<
Parents
A
Bx{Ax(AxB)}
B
Ax{Cx(AxB)}
Offspring
Ax[Bx{Ax(AxB)}]
Bx[Ax{Cx(AxB)}]
Given A, B and C are parental breeds.
Figure 4.3
Rotational crosses based on two and
three parental breeds.
nate breeds not used to produce the crossbred doe may be
purchased as required for use as male parents.
The crossbreeding of two or more breeds in rotation
involves mating does from a specifi c breed with bucks of
an alternate breed (Figure 4.3). In this procedure, bucks
may be purchased from reputed breeders. Crossbred off-
spring from the previous mating are bred to bucks of an
alternate breed not used previously to sire the female
parent in succession. The drawback arises from large dif-
ferences in performance of offspring from the different sire
breeds. This can contribute to a lack of uniformity in the
marketing of animal products to the consumer. In theory,
the performance of two- or three-breed rotational cross is
reduced due to lower heterozygosity, by one-third or one-
seventh the average difference in performance between
single crosses and parental breeds, respectively. There is
no special benefi t from breed differences in maternal
versus individual performance. Also further loss in perfor-
mance can occur in the offspring from interbreed recom-
bination in the gametes as a result of contribution of genes
from the dam and maternal granddam.
In the U.K., regional segmentation of sheep production
involves raising the Hill breeds in the mountains, and
the Down breeds in the lowland followed by their cross-
breeding to produce market lambs. Despite the practical
Spanish bucks and Spanish does
exceeded the Spanish breed in body weights at birth and 90
days by 11 and 16%, respectively. There is also the poten-
tial for lower performance due to rearrangement or segre-
gation of genetic combinations between the chromosomes
of the crossbred parent as well as the inability to benefi t in
performance from maternal heterosis and favorable genes
in the crossbred doe. Nevertheless, crossbred bucks may
be suitable in environments that may be stressful, due to
unfavorable climate, grazing condition and disease.
The mating of bucks from crosses between two meat-
type breeds with does from crosses between two fecund-
type breeds results in a four-breed cross offspring. The
resulting cross can capitalize on the full potential of mater-
nal, paternal, and individual heterosis. The drawback is the
need to use four breeds. However, in large scale commer-
cial production of goats there is the possibility of maintain-
ing one or two parental breeds or their crosses within the
farm to produce does for use as female parents (Figure
4.2). At the same time, crossbred bucks derived from alter-
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