Decisions that have to be made in improving the breed of dairy goats are dependent on the objectives of the goat breeding program. This will revolve around the desired products as determined by consumer trends, environmental factors such as climate, forage resources and social economic factors.
The other important factor is the selection criteria which relates to traits used in selection to meet the defined objectives.
Generally the emphasis is on a whole system approach whereby net returns are considered. In any one approach, meat, weights at weaning, yearling and litter size can be used. Challenges that might occur are due to fluctuation of product prices, the fact that genetic improvement is a long process therefore requires thinking ahead and a good flock structure is difficult to maintain. The flock structure determines the production system i.e. the male to female ratio, number of old animals in the flock etc.
Measurement of traits
A very organized system of identifying animals should exist. Objective measurements of traits are more beneficial than subjective ones. Note that recording of traits is very expensive therefore record only those useful in meeting the objectives of selection.
Measures of productivity include useful products such as milk, meat, and slaughter weight. This also includes measures of fitness such as survival, adaptability and fertility. Variations in the measurements are the basic ingredient of genetic improvement.
Traits of economic importance
These include adaptation to stress, heat, coat type, color, and resistance to diseases, temperament, neonatal survival and longevity.
In females fertility is measured in terms of:
- Prolificacy is measured by ovulation rate, embryo survival, kidding rate, parturition interval and weaning rate which is influenced by maternal traits like milk production which determine the vigor of the kid.
- Age at maturity
For males fertility you normally consider libido, semen quality in terms of concentration and abnormalities.
Size and efficiency
Growth and maturity rate e.g. body weights, birth weights which equates to kid survival, slaughter weights meaning meat yields, mature weight determining maintenance requirements and rate of gain determine the size of the animal and efficiency of feed conversion.
Production per lactation, length of lactation, persistency, milk composition (BF %) and ease of milking
Annual clean fleece weight, average fibre diameter, percentage kemp, staple length and tensile strength.
Tools of breeding
Animals that are to be parents of the next generation are determined. There are several factors that affect genetic improvement or rate of genetic response to selection. These factors are: -
- Phenotypic variation which reflects genetic variation
- Heritability – the higher the heritability the faster the response
- Accuracy of selection – is the correlation between the breeding value of the animal and the selection procedure. For example in angora goats fertility and fleece weight are negatively correlated.
- Intensity of selection – is the fraction of the total population that is used to become the parents of the next generation. It can be affected by the sales policy at the farm. Only the top animals should be chosen as parents.
In most of genetic improvement males are the ones selected. Females have a limit in terms of offspring they can produce whereas males have millions of sperms therefore many offspring if mated to many females.
- Generation interval is the average age of the parents when their offspring are born. it varies from one species to another. With shorter generation interval the response to selection is faster. this can be affected by gestation period, nutrition and other environmental factors.
- Number of traits – the lower the number of traits the faster the response to selection.
- Genetic correlation – if traits are antagonistic then response will be low
- Selection differential
- Repeatability of traits
The choice of procedure will be determined by
- For medium to high heritability selection on individual record of performance is sufficient. This is also true for medium to high repeatability traits.
- Where heritability is low as in traits expressed in one sex (e.g. reproduction, milk production), progeny testing or family selection is recommended.
- Cost of selection program
Productive traits in selection
The breed that is adaptable to a given environment is selected. Consider the ability to produce under given conditions, breeding seasons and foraging behavior. Breeds initially develop as a result of different environment, different consumer products and different management situations.
Heritability for this trait is low therefore response to selection will also be low. For efficiency of reproduction consider the number of kids or kilogram of kids weaned for reproductive efficiency. Life time productivity of an animal and frequency of multiple births can also measure reproductive efficiency. Cull all the animals that fail to conceive.
To select fertile animals identify twin or triplet born kids and use them for replacement. As the animal grows older there are increased incidences of multiple births therefore using young ones (both male and females) for replacement rather than the old ones eliminate chances for selecting fertility brought about by age.
First estrus should appear at 60 – 70% mature weight and those animals that attain this should be selected. Animals that get their first estrus either too early or too late should not be selected. Vasectomized bucks are used to detect the estrus periods.
This is Important in terms of meat production. Animals with high growth rate reach market weight very early. Growth rates can be measured using weaning weights, or weight at 18 months for both pre-weaning and post-weaning weight gain. There is a positive correlation between birth weight and weaning weight. Preweaning growth rate will depend on maternal influence and environmental factors.
In practical selection for growth
- Weigh all kids at weaning and correct the weights for type of birth, rearing, sex and age of the dam
- Determine daily weight gain – post and preweaning
- Performance testing – for 60 days for average daily gain, feed efficiency
Meat quality is measured through progeny testing, ratio of lean to fat and bone, loin eye area and fat thickness at the 12th rib.
Systems for selecting dairy goats
Traits for selection include
- Butterfat percentage
- Milk yield
- Type of animal
- Productive lifespan or longevity
- Milk production which is adjusted for milking twice per day for 305 days in a year
- Age of animals
- Butterfat percent at 4% fat corrected milk (FCM = 0.4 milk production + 15 Fat yield). There is a positive correlation between type and milk yield
Identify and keep those animals with the best traits. Selecting the sire is harder because progeny testing has to be carried out in form of Hermate comparison. Several dairy males are mated to different dams. The offspring milk yield are recorded and ranked. The ranking reflect the merits of the buck.
Most are highly heritable therefore respond well to selection. Clean fleece weight has the greatest effect on economic returns. Other traits like fleece length, fibre diameter, absence of kemp (% kemp).