Improvement in the
genetic quality of goats can contribute to production, efficiency and
profit. Selective breeding is how you improve genetic quality. You
need to identify the traits that are important to your production - define
your breeding goals. Identify the goats which are superior for the
traits defined. Limit the selection of breeding goals to one or two
items; you cannot improve all traits in one season.
All animals have characteristics
of performance which can be observed and measured. Some traits are
phenotype, some are genotype. Genotype is the actual genetic makeup of
an animal as determined by its genes. Phenotype characteristics can be
measured or observed values for an individual trait. Phenotype is
the combination of genotype plus environment.
The overall
environment affecting production includes a whole host of factors. i.e.
feed, housing, weather, nutrition, bedding, etc. The production environment
is typically the easiest area for a producer to control and usually identify
areas of success and factors which need improvement. Goats which are
kept in a similar environment can be considered a contemporary group or
management group. You can have two or more management groups which have
common genetics (sire), for example does which have kidded the first time
compared to mature does which have previously kidded. The difference in
the management groups would be the environmental factors, for example keeping
the young does on a higher nutritional plane or in the barn, any environmental
change. Comparison based on phenotype can be useful within management
groups.
Some of these
traits include milking ability, average daily gain, conception or proflicacy,
ease of birthing etc. While environment has a large effect on some
traits such as fertility, it has no effect on others such as color.
Average daily gain has a high heritability factor, and is a trait which can be
most affected by genetic selection. Heritability values range from 0 to
100% for various traits. If the heritability is high, the majority of
the phenotypic differences between animals are due to differences in genotype
and less subject to environmental factors.
All animals do not
have the same genetic value. The actual breeding value or genetic value
of an animal cannot be measured directly; it must be estimated through
evaluation of performance information. Accurate performance
records are required for the evaluation and comparison of animals.
Assuming a
breeding goal is increasing weight gain, you should record birth weights,
weaning weights and post-weaning
weights on contemporary groups. The comparison of these records will
identify animals with superior genetic value. To improve the overall
genetic merit of the herd for a given trait, only those goats with superior
genotype should be selected as parents.
Birth Weight:
Birth weight is the earliest growth measurement for a kid and is dependant on
the age of doe, breed of sire and dam, sex of kid (s), number in litter,
length of gestation, nutrition level of doe and other environmental factors
plus genetics. Increases in birth weights for does kidding for the first
time have resulted in dystocia. Kids which are heavier at birth are
expected to be heavier at weaning provided all management factors are
positive. Due to the difficulties at kidding associated with larger
kids, the emphasis should be for an optimum size and not a maximum size.
In our herd, we like to have does producing twins, with birth weights of eight
to ten pounds (3.5 to 4.5 kg) for doe kids and nine to eleven pounds (4.0 to
5.0 kgs) on buck kids. The preference being the kids which have less
than one pound (0.5 kgs) difference in body weight within litter.
Weaning Weights:
Weaning weight is one of the most important weight/size traits affecting
productivity. It is primarily determined by two factors: the kids
genetic potential to grow or its own growth impetus and the maternal
environment. At least 50% of the variation in weaning weight is due to
the milk production of the dam and the kids ability to obtain its share of
that milk. Weaning weight is about 40 - 50% repeatable suggesting that a
doe which weans heavier kids one year will do it again next. Thus
culling does which produce kids with lower weaning weights will improve the
breeding herd, but before you make this selection and adjustment is required
for age of doe, size of litter and age of kids at weaning. A host of
environmental factors may influence weaning date, which subsequently need to
be applied as an adjustment factor to weaning weights. Comparison
without adjustment is limited to contemporary groups.
Post-weaning
Weights: This trait is usually taken 30-60 days post weaning and is a further
measure of the kids potential to grow or its own growth impetus. It is
important that only contemporary groups with common environments be
compared. Nutritional values in natural forage can vary substantially
between spring and summer. Protein levels in the nutrition available
will affect growth weight and size. As this is a critical period for
growth, progress through selection of contemporary groups should be expected.
Performance
Weights: These weights will be an indication of each goats ability to
add to the overall value of the herd, throughout the year.
Genetic progress
will enhance production. Identify your breeding goal, evaluate
production by reviewing your production records and select the goats which are
superior for the traits defined.
