Agriculture Reference
In-Depth Information
cashmere goats are selected initially based on their fi rst
fl eece. However, as in most species, retention decisions are
ongoing throughout the productive life of the goat and if
the fl eece becomes excessively coarse at any point, the
animal would likely be culled.
Shelton (1993) noted that there are several qualitative
genetic traits (that is, those controlled by a single or a few
pairs of genes) such as color and developmental abnor-
malities, the latter having been selected against for many
years but which still crop up occasionally in Angora and
cashmere goats. These include peromelia (missing a leg),
missing ears (and ear length in general), wattles, cryptor-
chidism, no horns (polled), mouth deformities, and (pos-
sibly) in the case of Angora goats, sheepy fl eece. In
contrast, most of the economically important traits are
considered to be quantitative (that is, controlled by many
sets of genes). To design an effective selection program,
it is necessary to have the following knowledge for each
trait being considered: historic, current, or predicted eco-
nomic value, variability in the population to be selected,
heritability, and phenotypic and genetic relationships
between traits. Selection indexes can be constructed to
produce many different outcomes, but whatever the goals
of the breeder, it must be understood that the more traits
included in the index, the slower will be the progress in
any particular trait. Thus, rather than (or in addition to)
including a particular trait in a selection index, it may be
more effi cient to establish independent culling or retention
values for that trait.
issues. This index has generally resulted in the type of
animals desired by most breeders and commercial opera-
tors in the U.S. However, criticisms that have been leveled
at this and similar central performance test programs (for
example, those conducted in South Africa and Canada) are
that this type of test does not address fertility or ability to
raise kids. Further, the potential exists to produce animals
that cannot perform well in the range environments in
which they and their offspring will be maintained without
the provision of supplementary feed. This latter consider-
ation has led to the adoption in South Africa (and much
discussion in the U.S.) of a performance test conducted
solely on rangeland recognizing that the full genetic poten-
tials to grow and produce fi ber will likely not be realized
but also recognizing the need to identify animals that can
produce most effi ciently in a range environment.
Another approach being suggested by researchers uses
genetic evaluations in which pedigrees and all production
records are maintained by breeders and submitted on a
regular basis to a central organization that uses the data to
calculate “expected progeny differences” for each of the
measured traits for each contemporary animal. Although
this system has been used successfully in other species,
interest has been sparse among Angora and cashmere goat
breeders, although Boer goat breeders have initiated a
national genetic evaluation program for their breed in the
U.S., and programs for sheep are well established in
Australia, the U.S. (where they are still underutilized), and
elsewhere. The main objection appears to be that this type
of program involves more work for the breeder, and in the
case of fi ber-producing goats, numerous traits need to be
monitored whereas in some of the species where this type
of selection program has been almost universally adopted
(such as dairy cattle and pigs), relatively few traits are
being considered. This is one of many examples where
excellent technology has been developed and made avail-
able by researchers but for very practical reasons, produc-
ers are unwilling or unable to take advantage of it.
Heritability values reported for Angora goat traits in the
literature are highly variable (Table 15.3) but were catego-
rized by Shelton (1993) as high (
Angora Goats
In the Texas AgriLife Research Angora Goat Selection
Index used to evaluate yearling Angora males following a
112-d central performance test, the following traits are
included: clean fl eece weight, average daily body weight
gain, fi nal body weight, average staple length, average
fi ber diameter, face cover score, character score, and neck
cover score. This index was empirically derived and was
designed to reward animals with above-average clean
fl eece weight, body gain, fi nal weight, lock length, char-
acter, and neck cover scores, and those with below-average
fi ber diameter and face cover score. In addition, indepen-
dent culling criteria and minimum performance standards
were established for med and kemp content, fi nal weight,
clean fl eece weight, and average fi ber diameter. A sift
committee is also charged with disqualifying animals that
are defi cient in breed character or conformation (special
attention being paid to visible kemp and abnormal hind
legs), or have horns that are too close together, a sheepy
fl eece, scrotal irregularities, or any other discernible health
>
25%), moderate (15 to
25%) and low (
15%). Highly heritable traits in Texas
goats include staple length, clean yield, body weight (year-
ling and mature), face, neck, and belly covering, S (sec-
ondary follicle) to P (primary follicle) ratio, and scrotal
division. Moderately heritable traits include fl eece weight,
fl eece density, average fi ber diameter, medullation, and
weaning weight. Traits with low heritability are reproduc-
tive rate, longevity, and adaptability. Shelton did not report
any information for heritability of the subjectively assessed
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