Using Performance Records for Sheep Selection
|Last Reviewed:||13 April 2010|
|Written by:||Delma Kennedy - Sheep Specialist, Genetics, Reproduction and Performance Programs/OMAFRA|
Table of Contents
- Contemporary Group
- Complete Flock Testing
- Performance Information - What to Measure?
In order to select replacement animals in an objective manner and make "progress" or improvement, there must be performance records for the flock. Selection is based on estimated genetic merit of each individual and performance records are used to estimate the genetic merit.
A performance record is any recorded observation or measurement of a specific trait for an individual or a group. Average daily gain, wool weight and mature body size are all examples of traits that can be measured. There are an infinite number of traits that could be measured - the traits that should be measured are those that are economically important, directly affect the profitability of your operation, and are heritable.
The main objective of collecting performance records is to determine the:
- genetic merit of each individual animal, and
- performance of the breeding flock in your farming operation.
This information allows you to determine where, from a genetic and management standpoint, improvements can be made.
If the performance record is worth recording, it is worth recording accurately. Accuracy is important for obvious reasons, but the record must also be complete. All animals in the flock must be uniquely identified. Record sex, birth date, breed, contemporary group, sire and dam for each animal, along with the measurement or observation of the trait to make up the performance record. Since selection and management decisions will be made based on the performance records, the authenticity, accuracy and completeness of all records is essential to achieve improvement in the flock.
The phenotype or the expression of a trait as observed in an animal that is measured is made up of two factors -- environment and genetics. This is often expressed as P = G + E (phenotype = genetics + environment). The purpose of a performance-testing program is to identify animals that possess the genetics for a particular trait. To accomplish this, animals of a similar age are "tested" in the same environment and any differences in performance are deemed to be genetic.
Your selection program should concentrate on genetics, which equals phenotype minus environmental effects (G = P - E). Therefore, you measure the phenotype, but you need to be able to subtract the environmental effects. One way to do this is by making the environment the same for all animals whose phenotype you are measuring.
A contemporary group is a group of animals raised in exactly the same environment, with exactly the same management or as close to this as is practical. The phenotype or the expression of a trait is made up of environment and genetics. The environment includes such things as:
- number of lambs being raised by a ewe
- the weather
- feed availability
- ability of ewe to produce milk
- competition for creep feed
- incidence of disease
- season of the year, i.e. temperature
Varying temperature and weather conditions can have a large influence on traits like feed efficiency and growth rate. The location of the barn an animal is raised in can make a difference. For example, ventilation, lighting, and animal density are factors that can affect performance.
Clearly, it is almost impossible to make the environment for even just three or four lambs exactly the same. Even with twins, the ewe may favour one lamb over the other. It is important to make the environment as uniform as possible in order to evaluate a trait accurately. A uniform environment necessitates a small age range, as animals of different ages encounter different environments.
The size of the contemporary group also affects accuracy. As discussed, it is impossible to make the environment exactly the same for each lamb, but the group needs to be as large as possible while maintaining a uniform environment. A group composed of a large number of lambs from several sires and within a small age range gives the most accurate estimate of genetic merit. An ideal contemporary group for estimating genetic merit consists of lambs from a minimum of 3 sires and with 10-20 progeny per sire.
Complete Flock Testing
It is important when developing a selection program to test or measure all animals in the flock. This ensures a larger contemporary group and provides as much information as possible on all animals in the flock, thereby increasing the accuracy of the estimates of genetic merit in individuals and to measure flock performance. To produce estimates of genetic merit across flocks, information is needed on animals of similar breeding in more than one flock. By collecting information on all relatives, across flock comparisons are possible and estimates of genetic merit are even more accurate. Complete flock testing is also the only way to determine what, on average, is happening in your operation.
Performance Information - What to Measure?
Most commonly, performance information is collected in three general areas: ewe productivity, lamb growth and carcass merit.
There are a number of traits in each area that could be measured. Examples are listed in Table 1, Performance Traits.
Table 1. Performance Traits
- Lambing interval
- Pregnancy rate
- Pre-weaning gain
- Post-weaning gain
- Backfat thickness
- Loin eye area
- Lean meat yield
The number one consideration when deciding which traits to measure is economics. What is the cost to measure the trait(s) and what financial benefit will accrue through improving that trait(s). Determine the priority traits for improving your operation and the result will financially benefit your business.
In order to select animals based on economically important traits, collect accurate and complete records. All animals must be given an equal opportunity to perform, and to express their genetic potential. Contemporary groups, containing large numbers of lambs with as small an age difference as possible, will ensure minimal effect of environmental and management conditions. This generates accurate estimates of genetic merit.
In determining which traits to measure, consider the economic value of improving a trait to your operation. Other considerations include the cost of collecting the record(s).
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