|
              
| |
 
Breeding Strategies:
Which is Which, and Which is Right for Your Alpaca?
by D. Phillip Sponenberg, PhD, DVM
In alpaca breeding, as in any other worthwhile pursuit, establishing a
guiding philosophy and then outlining your goals can eliminate a lot of wasted
effort. Developing a philosophy is a rarely done but all-important first
component of any breeding program.
Your guiding philosophy is really just your reasons for breeding alpacas, and
once you identify what they are, you will know what your goals are. For you,
these might be show ring wins, temperament, conformation, soundness, color, or
fiber characteristics. Every breeding program places different emphases on
different components. Matings that are accomplished simply because males and
females are conveniently available are frequently less rewarding than matings
that are planned by carefully matching males and females for traits of interest.
Two useful philosophies in common use concentrate on slightly different
aspects of animal breeding. One, often followed by show participants, is the
production of excellent individual animals. This approach generally tolerates a
fair degree of variation in animals just as long as some excellent ones are
produced. These excellent animals are skimmed off the top and used to good
advantage as show animals and as breeding stock. A second common approach is the
"uniform population" philosophy, often followed by commercial
livestock production breeders, whose goal is to produce genetically predictable,
uniform offspring. Usually this means that the breeding program aspires to
develop a uniformly good population, and therefore it accomplishes some of the
goals of the "excellent individual" philosophy. The difference between
the two philosophies is that the "uniform population" philosophy is
more concerned with narrowing the overall range of variation.
Neither of these philosophies is right for all situations. The importance of
considering them is to realize that different strategies are necessary to
accomplish them. Many other philosophies can govern animal breeding, but this
essay deals primarily with these two because genetic phenomena and breeding
strategies have especially dramatic impacts on them and less on some other
possible philosophies. For example, a less-useful philosophy is "anything
will do." Little direction and progress are made possible by this approach,
and we can only hope that few alpaca breeders are content with reproducing
animals for the sole reason that they are alpacas.
What Is Genetics Anyway?
Genetics is the science that studies the transmission of traits from one
generation to the next. For those of us involved in its practical application,
we use genetics to determine how the activities of animal breeding interact with
the transmission of traits. Genes are ultimately responsible for most of the
traits of animals, although they can be imperfectly represented in the
individual final animal. The other way to say this is that the phenotype (external
appearance of the animal) does not always reveal the genotype (the full
complement of genes in the animal). The imperfect representation is due in part
to the modifying effect of the environment. A genetically perfect animal in a
hostile environment is going to look and perform shabbily. A genetically
inferior animal in an ideal environment might actually end up looking pretty
good.
The interactions among genes are complicated-another reason the phenotype can
imperfectly represent the genotype. Genes may be expressed or hidden. Some genes
or some gene combinations mask or cover up other genes. One of the challenges
facing animal breeders is to unlock genetic combinations so that the animals
reveal their true genetic potential. Once the genetic potential is revealed,
knowledgeable breeders can pick and choose breeding stock to make great progress
in the production of alpacas that accomplish the goals of their breeding
programs.
The importance of genetics to animal breeders is really twofold. First, the
genes and the environment of the animal combine to produce the individual
animal, and either one can limit its level of perfection. Most breeders are
preoccupied with the genetic makeup of individuals. A second and very
significant aspect of genetics is the makeup of the population. since the
positioning of genes throughout a population affects the pattern of their
expression in individuals within the population. The genetics of the population
sets the pattern of occurrence for all traits, both bad and good. Maintaining a
healthy viable population made up of sound, productive individuals should be a
major goal of all alpaca breeders.
It is fairly obvious that any population is made up of individuals. What can
be less obvious is the way those individuals relate to the overall population.
Genes can be relatively evenly dispersed through a population. Alternatively,
genes can be present in only certain subpopulations of an overall population,
and absent from other subpopulations. If a population is subdivided into
different isolated pockets of interbreeding animals, then each of these is going
to produce different genetic combinations. Those combinations that are
deleterious can then be eliminated without involving the whole population. Those
that are advantageous can be fostered and introduced more widely across the
whole population. One major advantage of at least some isolation of strains is
that each strain will house its own array of genes. These can be more easily
identified and manipulated in smaller groups. They can then work their way out
of the small groups, to have advantages for the population as a whole. These
different situations are going to govern the pattern of gene expression
throughout the population.
Breeding Strategies: What They Are
Three common breeding strategies for domesticated livestock are outbreeding,
linebreeding, and inbreeding. These have become charged with positive and
negative connotations, especially in the breeding of alpacas and llamas, when in
actuality each has a place in any domesticated population.
Inbreeding is usually defined as the mating of animals that have common
ancestors. Parent to child, brother to sister, aunt to nephew, and a host of
other combinations are classed as inbreeding. What inbreeding accomplishes is
the pairing up of genes so that they are homozygous(both members of a
gene pair are identical). Being homozygous can be either good or bad depending
on the genes. Inbreeding in and of itself is neutral-the outcome of inbreeding
depends on which specific genes are present to be paired up. "Good"
genes pair up to make good sound animals; "bad" genes can pair up to
produce defective animals. The key point is that inbreeding generally exposes
the entire range of genes to view. Nothing is hidden; everything can be seen in
at least some of the animals produced by inbreeding.
Linebreeding, a less extreme form of inbreeding, is generally considered to
be the mating of individuals that have a single ancestor in common. One example
is the mating of half brothers to half sisters. Usually this takes the form of
mating sons and daughters of a single outstanding sire or dam. This mating is
frequently used in order to regenerate an animal as close to the original
outstanding animal as is possible.
Outbreeding, linecrossing, outcrossing, and crossbreeding are all variants of
a strategy opposite to inbreeding. They involve the mating of animals that have
totally different ancestors. Crossbreeding is usually considered to be mating
between different breeds. Examples from lamoids could include llama-to-alpaca
matings. Usually the mating together of sun and huacaya types of alpacas is
considered crossbreeding, although it might also be considered outcrossing since
these two fall short of being breeds in the narrow sense.
Linecrossing is usually considered to be mating that is accomplished within a
general type or breed, but to animals that represent different lineages of that
type or breed. Examples here could include the crossing of English, Bolivian,
Peruvian, or Chilean huacaya alpacas. They are the same general type but are
representatives of different portions of the population and therefore are
unlikely to have common ancestors. Mating of animals from within these various
countries but from different regions or herds also qualifies as outbreeding. The
problem at this stage of alpaca breeding in North America is determining just
exactly the relationship between potential mates, since the South American
background of these is frequently a black box. As a consequence, just exactly
which type of mating is being accomplished is difficult to know in any given
situation involving recently arrived animals.
Breeding Strategies: What They Do
Inbreeding and linebreeding serve to pair up genes in such a way that both
members of a pair are the same (homozygous).This pairing does not occur
in each inbred or linebred mating but does occur much more frequently than it
does with the other breeding strategies. Like pairs of genes result in animals
of consistent genetic makeup, so that they produce predictably. On the positive
side, these strategies can produce prepotent breeding animals that stamp their
offspring with uniformity since they themselves have only a single sort of gene
to pass along. The uniformity is a reflection of low levels of genetic variation
within individuals.
The flip side of the inbreeding coin is the need to cull substandard
variants. This can be difficult, but if culling isn't done, problems in a
population can be expected to increase. For example, many defects in
domesticated animals are due to recessive genes. Few of these are proven in
lamoids, but if the general rule holds, then many (but not all) alpaca defects
are due to recessive genes. Inbreeding and linebreeding are going to bring them
to the surface. Defects that are revealed then need to be removed from the
breeding population. The trick, though, is to realize that many (though not all)
of the normal siblings and half siblings of a defective animal are also likely
to have the genes for the defect although in an unexpressed heterozygous
state (in this situation, each member of a pair of genes is different rather
than the same). All that inbreeding does in this situation is alert the breeder
to the presence of these weaknesses within the population. Actually identifying
and removing the genes from the populations is complicated, time consuming,
often emotionally painful, and expensive. Strategies for this will be outlined
below.
Inbreeding, if taken to extremes, can lead to general diminishment of vigor
Decreases can occur in disease resistance as well as in general reproductive
vigor It is, however, a useful strategy for detecting any weaknesses that might
be present in a population if it is used wisely and with intense selection for
animals that have vigor and are free of genetic defects. Without such selection,
inbreeding can be a disaster.
Outcrossing accomplishes a result opposite to that of inbreeding. Genes in
outbred animals are likely to be in unlike pairs (heterozygous), and few
recessives are likely to be expressed. The upside of this is that few genetic
diseases are expressed. The downside is that few really prepotent breeding
animals are likely to be produced by this strategy because most outbred animals
lack the genetic consistency to produce evenly. With outbreeding, an important
factor to consider is that recessive genetic diseases are unlikely to be
expressed, but they are still being passed along to carriers in the population.
Outbreeding is unlikely to reveal carriers until the gene responsible for the
defect gets to high frequencies in the population, at which point it will be
expressed periodically because carriers will be mated on occasion, providing the
opportunity for the expression of the recessive genetic disease in the
offspring. Very rare recessives are unlikely to be detected in populations that
are bred by outcrossing; more common recessive are much more likely to be
detected. Widespread use of outcrossing ensures that carriers will be
undetected, especially when recessive diseases are relatively rare.
So Which Is Best?
No simple answer will determine which breeding strategy is best-it all boils
down to philosophy. Each strategy has favorable and adverse consequences. Using
a combination of strategies and knowing how they drive selection and breeding in
various portions of the population can help you choose among them, depending on
the goals of your breeding program.
Inbreeding (and to a lesser extent linebreeding) makes for more consistent
and more predictable animals, which can be good in some situations. It is useful
if selection for vigor is going to be possible (save the vigorous, chuck the
wimps). In South America, selection is accomplished fairly readily, since a meat
market is functioning to absorb the less-desirable animals, although identifying
carriers of defective genes is nearly impossible because of the absence of
verifiable pedigrees. In North America, we do not have the same mechanism for
removing defective animals from the breeding population, nor for the removal of
their relatives. Inbred populations have little variation, so that performance
(fiber, conformation, color) can be accurately predicted. Inbreeding can also
bring recessive defects to light. This too can be either good or bad. It is bad
if selection is not going to remove (or at least identify) carriers from the
population. It is good if the identification of carriers is going to act to
reduce their frequency in the population.
With outbreeding, vigor goes up, especially reproductive vigor. Uniformity
generally goes down, although one notable exception is the first cross between
inbred or linebred animals that are from different tines. Crossing inbred lines
usually generates very uniform animals, but these uniform animals do not in
their own turn produce uniform offspring. An extreme example is the crossing of
Hereford and Angus cattle. All the resulting calves are black baldies. If the
black baldies are used for reproduction (and they do reproduce very well), they
can throw black, red, black baldy, and red baldy offspring. So the initial cross
is uniform but cannot itself produce uniformly Still, for the production of
stunning individual specimens, outbreeding certainly has merit. Think show
winners here!
Outbreeding also tends to decrease (at least initially) the chance that rare
recessive genes are brought to light. The good news is that many diseases are
probably due to rare recessive genes, and therefore outbreeding is one way to
avoid their expression. The bad news is that they will eventually show up in a
population, for carriers eventually become common enough that outbreeding pairs
them up and the diseases or deformities are expressed. In a deliberately outbred
population the expression of defects can indicate that the genes responsible
(for those defects that are genetic in origin) are widely dispersed throughout
the entire population.
So what is my choice? Generally, I prefer to have both linebreeding
and outbreeding going on in a population. My overall choice is for outbred
females and linebred males. A single strategy to accomplish this is somewhat
tricky but possible. In this system it is essential that the linebred males come
from carefully documented lines, and that they are not carriers of any
deleterious genes. Not just any male will do!
Selection Is the Key
Selection is the force that allows reproduction of some individuals and not
others. It operates independently of any type of breeding system in animal
populations. Selection is therefore a force for change in the overall genetic
makeup of a population. Selection is a powerful tool, one that can irreversibly
change a population. In a single decade, for example, fleeces presented to
markets in Arequipa changed from 70 percent colored to 70 percent white-a change
brought about because only white males were allowed to reproduce.
Selection can involve any trait whatever: size, staple length, fiber color,
fiber fineness, conformational type. Selection can be intense and cause fairly
rapid change over a few generations, or it can be more relaxed and change the
population more slowly in the desired direction. Because selection can
irreversibly change a population, the breeder needs to carefully consider his or
her goals.
Selection can be responsible for changing the incidence of recessive alleles.
If a malformation is due to a recessive allele and the defect can be treated,
then it is possible for the defective animals to reproduce. All offspring of
these animals will carry the gene for the defect, whether or not they actually
express it. This transmission, repeated in many individuals, can act to increase
the frequency of genes for defects. Other alternative plans have different
consequences.
Limiting reproduction of known carriers is important for the long-term
genetic health of the population, although its practice will always be unpopular
with owners of otherwise-outstanding individual breeding animals that happen to
be carriers of genetic defects. Such a phenomenon occurred in Arabian horses
with the lethal recessive defect of combined immunodeficiency. Currently about
20 to 25 percent of Arabian horses carry this gene so that 4 percent of Arabian
foals are born with the defect. The widespread use of carriers ensures that this
will be the case, and the difficulty is that, if left unchecked, the genes can
become so common in a population that selection becomes a difficult pill to
swallow, because then a high number of individuals must be removed from
reproduction. Some of the carriers are bound to be otherwise exceptional, and
these are the animals for which the choices become very difficult.
Identification of carriers can come about in different ways. One way is to
simply let individual breeding practices eventually bring carriers to light.
This works reasonably well for defects of low incidence, since they are unlikely
to overwhelm the population. The danger of this approach is that a single
undetected carrier sire that is used widely can spread the defective gene far
and wide before it is detected. Examples occurring in various other livestock
species are relatively common. Once these genes become common, reducing their
incidence is a real headache.
In the case of more common or severe defects, it is possible to test for
carriers more deliberately One of the most powerful tests for genetic defects is
the mating of parent to offspring. In alpacas, this generally takes the form of
sire mated to daughters because only a single offspring is produced per
pregnancy. The reason this is such a powerful test is that it simultaneously
tests the male for all defective genes. That is, if anything weak is present it
will be exposed. Unfortunately, the number of matings needed for this type of
test is relatively high. To be 95 percent sure that the animal is not carrying
deleterious recessives, it takes twenty-three normal offspring from daughters.
To be 99 percent sure, it takes thirtyfive normal offspring. Obviously, any
abnormal offspring produced at any point along the way implicates the sire as
having the genes for that defect. Nevertheless, this conclusion would be
something of an intuitive leap because few defects are proven to be genetic in
alpacas. The logic works only if the defects are genetic.
If a carrier is detected, by whatever means, then the next step needs to be
pondered carefully. If selection is aimed at decreasing the number of carriers,
many different routes can be taken. One method is to neuter the affected
individuals as they become known, the parents of the defective individual, and
all of their previous offspring. This is the most radical selection against a
defect, and it effectively removes carriers from the population as they are
detected as well as some noncarriers simply because, based on the law of
averages, they are more likely to be carriers by virtue of their relationship to
known carriers. At very low gene frequencies carriers are unlikely to be
detected because they are unlikely to be mated to another (equally rare)
carrier. So while the "neuter all carriers" approach will work to
dramatically reduce the number of carriers in a population, it rarely completely
eliminates all carriers since some slip through the cracks of the system.
Other selection plans that work against carriers are better than nothing, but
less drastic than neutering all carriers. One such plan is to neuter the sire
because he can spread the gene more widely than can the dam, which produces
fewer offspring. Still, half of the offspring of the carrier dam will be
carriers. One approach to this problem is to geld all of her sons but allow her
daughters to reproduce. About half of these will be carriers. If these are in
turn used for reproduction, the carrier rate goes down to about one-fourth,
although which specific fourth is uncertain without a breeding test. If
excellent males are generated, an alternative to this scheme would be to
test-mate them to known carrier females to determine which of the males do not
carry the defective gene. Those documented as free of the gene can then be used
widely and safely for breeding of animals free of the specific defect. In this
way, the positive traits of the line can be continued while leaving behind the
defect. The process is long and involved but well worth the effort in some
circumstances.
Alpacas in North America: Just What Do We Have?
Alpacas come to us in North America as an interesting population, and various
aspects of their origin have consequences for any breeding program. Breeding
strategies throughout most of the alpaca range in South America involve fairly
rigid isolation into small subpopulations, with little transfer of genetic
material among them. As a result, the subpopulation-to-subpopulation variability
can be great. Putting this factor to good use is one of the challenges facing
the alpaca breeders of North America.
A second important factor is that pedigree mating is not accomplished
throughout most of the South American range. That is, the specific sire of a
cria is usually unknown. Couple that with somewhat casual culling of various
deformities, and the result is that very little documentation of background or
family characteristics exists for most alpacas coming to North America. In most
cases, all that is known is the animal's visual appearance and perhaps its
geographic origin. This lack of information makes breeding and selection
decisions difficult, but rich opportunity for progress is likewise possible.
The alpacas imported into the United States can usually be assumed to be
inbred or linebred to some extent, and in some situations greatly so. The
problem with this is that the overall extent of linebreeding is undocumented, as
is the relationship of the different lines to one another As a result, the North
American breeder who has imported animals is never really certain of which sort
of breeding strategy is actually being accomplished. One strategy, then, is to
cross the various lines to one another, to the extent it is known that different
lines are represented. This is linecrossing, a form of outbreeding. Very little
expression of recessive genes is expected for a generation or so under this
breeding scheme. Great individuals will be produced, although few of them may be
prepotent enough to reproduce uniform offspring themselves. A disadvantage is
that the strategy can spread defective genes far and wide before their existence
is discovered.
Alpacas in North America: Selection and Breeding Practices Determine What
They Will Become
Alpaca breeders in North America have a few advantages over South American
breeders. One is the requirement for pedigree breeding. With the accurate
identification of sires, dams, and crias comes the information needed to make
intelligent and wise breeding and selection decisions. Accurate pedigrees and
monitored performance of animals will demonstrate which animals are truly
excellent and can improve the population. Wise and talented breeders can use
accurate pedigree information to good advantage.
Knowing the exact pedigree and production characteristics of their alpacas
also allows North American breeders to put more selection pressure on traits of
interest than is possible in South American systems, which are characterized by
multisire matings in subsistence situations. North Americans have the luxury of
using alpacas not for subsistence but for enjoyment. It is entirely possible
that North Americans will be able to unlock the genetic combinations of some of
the preconquest Alpaca types, which can then be used to good advantage
internationally. The challenge confronting them is huge, but the opportunity is
likewise immense, and the ultimate accomplishment will be very satisfying.
About the Author
D. Phillip Sponenberg, DVM, PhD, is professor of pathology and genetics at
the Virginia-Maryland Regional College of Veterinary Medecine located in
Blacksburg, Virginia. Educational endeavors there include a special senior
rotation dealing with sheep, goats, llamas, alpacas, and farmed deer.
Professional interests include reproductive pathology, genetics, breed
conservation, and the inheritance of color in animals. Dr. Sponenberg is the
convener for the sheep color group of the Committee on Genetic Nomenclature for
Sheep and Goats. An avid handspinner, he is hoping that alpaca breeders can
re-create some of the preconquest types of alpacas and that the full range of
colors is fostered in this most wonderful fiber. He blade-shears sheep and
angora goats; he used to do alpacas until owners objected to the ridges left by
blade shearing!
Dr. Sponenberg serves as the technical coordinator for the American Livestock
Breeds Conservancy, an organization involved in the conservation of rare
livestock breeds. ALBC's educational program recently published A
Conservation Breeding Handbook by D. P. Sponenberg and C. J. Christman. For
information, contact the conservancy at PO Box 477, Pittsboro, NC 27312.
Selection of Alpacas for Breeding
Chris Tuckwell
At present, the U.S. and Australian alpaca industries are based on small
populations that are widely dispersed throughout each country. Most alpacas are
maintained in herds of fewer than fifty head, and there is a large within-herd
variability in quantity, quality, and color of fiber produced. There is
obviously scope for genetic improvement in the production characteristics of the
U.S. and Australian alpaca through application of breeding methods based on
sound genetic principles.
When commercial profitability is considered, selecting for high fleece
weight, fiber diameter, yield, and perhaps body weight seems desirable. This can
be achieved only through the use of objective measurement, recording and
analysis of animal performance (commercially important traits), and application
of this information to select genetically superior animals for use in
well-designed genetic improvement programs.
This discussion will consider breeding programs where selection is based on
characteristics that are economically important in commercial production and
where the breeding program is designed to lead to genetic improvement of
commercial production.
METHODS OF SELECTION
Selection refers to the method of choosing the parents of future generations.
The two main techniques for selecting individuals are family selection and mass
selection. In family selection, the breeder considers the relatives of the
individuals under selection. Examples of family selection are pedigree selection
and progeny test. Mass selection is the simplest form of selection of
individuals and involves selecting the animal on the basis of its own
performance relative to the performance of other animals that are the same sex
and age and affected by a similar environment.
DESIGN OF BREEDING PROGRAMS
The first stop in designing a breeding program is to define breeding
objectives--that is, the economically important production characteristics
involved in alpaca breeding for fiber production. Breeding objectives need to be
continually reviewed.
In addition to breeding objectives, the development of a breeding program
requires information on genetic parameters (heritabilities, genetic
correlations), phenotypic parameters (means, variances, repeatabilities,
phenotypic correlations), and environmental effects (age of dam, type of birth
and rearing).
PRODUCTION CHARACTERISTICS OF IMPORTANCE
Alpacas primarily produce fiber (wool); meat and skins are likely to be
important only in the long-term future. Breeders should be concerned with the
alpacas' ability to produce fiber in sufficient quantity and of an acceptable
quality in a given environment at minimum cost. Therefore, many production
characteristics will be of interest, but it must be remembered that the fewer
the characteristics in a selection program, the more rapid the progress that may
be made in each.
For alpaca fiber production, the economically important production
characteristics are the following:
Reproduction rate (aim to maximize annual weaning rate, ideally one cria per
hembra per year)
- Body size (only as large as is necessary to maximize fleece production
economically)
- Greasy fleece weight (as high as possible)
- Fiber diameter (fiber of a lower diameter is likely to command a higher
price per pound in the long term)
- Fleeces of single uniform color (reduces skirting and clip preparation
needs; in addition, large volumes of single-color fiber are more attractive
to processors)
Before deciding which characteristics should or should not be subjected
to selection, the breeder must determine whether the characteristic can be
objectively measured, whether it is heritable, and what phenotypic and
genetic correlations exist between the characteristics.
MEASUREMENT OF CHARACTERISTICS
The objective measurement of those production characteristics mentioned
above provides information that can be used in direct selection for
productivity. All of these characteristics can be measured; some are
relatively simple and cheap to measure (examples: body weight and greasy
fleece weight); others are time consuming and expensive (such as fiber
diameter) to measure.
Greasy fleece weight can be easily measured with a spring balance and
weighing pan, but to measure fiber diameter and clean scoured yield requires
some special equipment, such as a projection microscope or air-flow testers.
It is important to remember that a test giving a mean fiber diameter of,
say, 30 microns does not mean that the animal will always produce 30-
micron fiber. Older animals produce coarser fiber than younger animals, and
nutrition influences fiber diameter.
The phenotype (appearance or performance) of each animal is the result of
the genetic makeup of the animal's genotype and the environment in which it
is run (phenotype = genotype + environment). Therefore, valid comparisons
can be made only between animals of the same type (sex, age), run under the
same conditions (same property), and at the same time (that is, same
shearing dates).
HERITABILITY OF CHARACTERISTICS
Heritability refers to the degree to which an animal of a superior
phenotype (performance) will transmit to its offspring that advantage. For
example, if the heritability of body weight at tuis age is 50 percent and
each parent has a selection differential of 22 pounds (10 kg), then on
average they would transmit 50 percent (11 pounds, or 5 kg) of their
advantage to their offspring. The remainder of their advantage may not have
resulted from their genotype but rather from having been reared in a
favorable environment. This part of their advantage cannot be handed on to
the next generation. It must be remembered that the machos and hembra
contribute equally to the genotype of their offspring, so therefore, when
estimating the improvement in the offspring, gains expected from each parent
must be averaged (selection differential of the sire x heritability x
1/2 + selection differential of the dam x heritability x 1/2).
In the example above, the total gain expected in the next generation would
be 22 x 50/100 x 1/2 + 22 x 50/100 x 1/2, or 11
pounds in body weight at tuis age.
There are no Australian estimates of heritability for production
characteristics of alpacas, and therefore we have to rely on overseas
information, which itself is limited and of a preliminary nature. However,
the heritability values shown in Table 1 have been estimated by research
workers in Peru. Characteristics can be classified as having high (greater
than 0.30), medium (0.15 to 0.30), and low (less than 0.15) heritability).
| Table 1. Alpaca Heritability
Estimates |
|
|
| (Peruvian research data) |
|
|
|
|
|
Characteristics |
Age |
Heritability
Estimates |
|
|
Body weight |
Birth |
0.34; 0.53 |
|
|
|
|
Weaning |
0.39 |
|
|
|
|
First shearing |
0.55; 0.69 |
|
|
|
Fleece weight |
First shearing |
0.21; 0.22; 0.35 |
|
|
|
Survival to weaning |
0.10 |
|
|
The heritability of a characteristic
indicates whether selection for that
characteristic will be effective. The fleece
characteristics outlined above have
moderate-to-high heritability estimates,
suggesting that gains in these characteristics
can be made relatively quickly.
ASSOCIATION BETWEEN CHARACTERISTICS
A phenotypic correlation estimates the
degree of association between two
characteristics in the same animal. For
example, if data suggest that significant and
positive phenotypic correlations exist between
greasy fleece weight, clean fleece weight,
fiber diameter, and staple length, and if a
selected animal has a fleece weight higher
than the average of the herd, then the
selected animal is one with higher than
average fiber diameter and staple length. A
high negative correlation has the obvious
reverse implications. The phenotypic
correlations shown in Table 2 have been
estimated by researchers in Peru.
| Table
2. Phenotypic Correlation Estimates
(Peruvian research data) |
|
|
|
Characteristics |
Age |
Machos |
Hembras |
|
|
|
Body Weight |
|
|
|
|
|
|
|
|
with fleece weight |
Juveniles (< 4 yrs) |
|
0.40 |
|
0.58 |
|
|
|
with fleece weight |
Adults (> 4 yrs) |
|
0.45 |
|
0.32 |
|
|
|
with
survival |
|
|
0.26 |
|
0.26 |
|
|
|
Fleece
Weight |
|
|
|
|
|
|
|
|
with
staple
length |
Juveniles
(< 4
yrs) |
|
0.30 |
|
|
|
|
|
with
staple
length |
Adults
(>
4
years) |
|
0.32 |
|
0.20 |
|
|
|
Fiber
Diameter |
|
|
|
|
|
|
|
|
with
fiber
length |
Adults
(3
years) |
|
|
|
0.27 |
|
|
|
with
yield |
Adults
(3
years) |
|
|
|
0.42 |
|
|
|
with
%
grease |
Adults
(3
years) |
|
|
|
0.28 |
|
|
|
Fiber
Length |
|
|
|
|
|
|
|
|
with
yield |
Adults
(3
years) |
|
|
|
0.40 |
|
|
|
with
%
grease |
Adults
(3
years) |
|
|
|
0.18 |
|
|
A
genetic
correlation
estimates
the
extent
to
which
selection
for
one
characteristic
in
the
parent
will
cause
a
change
in
another
characteristic
in
the
offspring.
As
an
example,
if
a
significant
positive
genetic
correlation
exists
between
greasy
fleece
weight
and
fiber
diameter,
there
is
an
implication
that
as
parents
are
selected
for
greasy
fleece
weight,
fiber
diameter
may
increase
in
their
offspring.
No
genetic
correlations
have
yet
been
measured
on
Australian
alpacas.
It
is
worthwhile
to
note
that
the
genetic
correlation
between
greasy
fleece
weight
and
fiber
diameter
in
Australian
merinos
is
not
strong
(+0.13
to
0.19),
and
that
it
is
possible
to
hold
fiber
diameter
relatively
constant
while
selecting
for
fleece
weight.
THE
IMPORTANCE
OF
SIRE
(MACHOS)
SELECTION
Increases
in
commercial
profitability
from
genetic
improvement
programs
can
be
substantial
over
time,
and
selecting
the
best
sire
replacements
for
the
sire
breeding
flock
provides
the
greatest
opportunity
for
genetic
improvement.
Determining
from
which
stud
to
buy
sires
is
the
machos
buyer's
most
important
decision.
Genetic
differences
between
studs
can
be
substantial,
while
only
minor
genetic
differences
can
be
made
to
a
commercial
flock
by
buying
different
grades
of
sire
from
a
particular
stud.
For
long-term
genetic
gain,
the
machos
buyer's
flock
is
entirely
dependent
on
improvements
made
in
the
sire
breeding
flock.
INDUSTRY
BREEDING
STRUCTURES
In
the
common,
traditional
flock/herd
breeding
structures
used
in
Australia's
animal
industries,
parent
studs
are
closed
to
outside
introductions,
whereas
daughter
and
general
studs
buy
sires
mostly
from
parent
studs.
Sires
and
some
females
move
down
from
parent
studs
to
daughter
and
general
studs,
but
never
upwards.
Culling
of
females
in
commercial
flocks
has
no
impact
on
the
breeding
program
in
studs.
Only
selection
of
sires
and
females
in
the
stud's
sire
breeding
flock
can
influence
the
stud's
genetic
improvement
program.
The
commercial
sire
buyer's
flock
is
entirely
dependent
on
improvements
made
in
the
sire
breeding
flock
source
for
long-term
genetic
gain.
An
alternative
breeding
structure
used
in
some
industries
is
a
nucleus
breeding
scheme.
In
contrast
to
a
more
traditional
structure,
females
can
be
taken
to
higher
levels
from
lower
down.
Although
selection
of
females
in
the
top
and
lower
tiers
influences
the
program
at
the
top
tier,
the
selection
of
sires
remains
the
main
way
of
making
genetic
improvement.
IMPORTANT
CONSEQUENCES
OF
INDUSTRY
BREEDING
STRUCTURES
Commercial
flocks
"lag"
behind
stud
flocks
in
genetic
merit,
on
average,
by
two
alpaca
generations
(five
to
seven
years).
Table
3
shows
the
length
of
time
it
takes,
from
the
decision
on
which
sire
replacement
is
selected
in
general
studs
to
sire
progeny
that
are
ready
for
sale
to
commercial
flock
owners,
about
two
years.
For
an
assessment
of
offspring,
replacement
sires
likely
need
to
be
at
least
three
years
of
age.
Pregnancies
will
result
in
tuis
available
for
shearing
two
years
after
conception.
| Table
3.
Breeding
Timetable |
|
|
| Sires
selected
"today"
will
produce
progeny
for
sale
in
two
years. |
|
|
|
Event |
Time |
|
|
|
Final
sire
selection |
January
1996 |
|
|
|
Joining |
March
1996 |
|
|
|
Cria
drop |
February
1996 |
|
|
|
Tuis
measurement |
January
1998 |
|
|
|
Sale
of
tuis |
January
1998 |
|
|
Figure
1.
Genetic
lag
between
|
