Estimated Breeding Value: A Tool for Genetic Improvement of Swine

Agdex#:	440/42
Publication Date:	01/88
Order#:	88-014
Last Reviewed:	08/03
History:	Original Factsheet
Written by:	Cathy Aker - Swine Specialist/Orangeville; B. W. Kennedy - Animal & Poultry Science/University of Guelph

Table of Contents

1. Performance Testing of Swine
2. The Canadian Swine Genetic Evaluation Program
3. Estimated Breeding Values
4. Sire and Dam Report
5. Herd Activity Monitor
6. Using EBV's

The performance of any animal is determined primarily by two factors - genetics and environment (management). Often environment can affect an animal's performance as much or more so than the animal's genetic make-up. The key to genetic improvement of livestock is to distinguish between genetic and environmental factors influencing performance and select only those animals which are genetically superior. Performance that is the result of good management will not be passed on to the next generation, whereas performance due to genetic superiority will be repeated.

Performance Testing of Swine

Supervised performance testing of swine began in 1967 with the development of the Record of Performance (ROP) Swine Testing Program. Its purpose was to help pork producers to identify and select superior replacement breeding stock.

Through the ROP Program, breeders have been provided with performance test information on pigs tested either on the home farm or at a central test station. Central testing has provided performance comparisons of young boars from a number of different herds. All boars are tested under similar environmental and management conditions, therefore, differences in performance can be attributed to genetics rather than herd management. The central test station also gives an indication of the genetic merit of a herd relative to other herds in the province using the test station. The number of boars that can be tested each year, however, is limited to approximately 1500. The home test component allows performance testing of larger numbers of young boars and gilts. Home test evaluations have been of limited value because comparisons of breeding stock are valid only for the herd in which the pig was raised. The comparisons are only valid within a herd because evaluations for each pig are expressed relative to the average performance of all pigs in that herd only, and herds can differ greatly in genetic merit and management (environmental) conditions.

Performance test information, generated either on the farm or at the test station was based strictly on the pigs own performance and did not take into account information on tested relatives. Information on related animals is useful in determining the genetic merit of a pig, together with the pigs own performance data. Because related animals are similar in their genetic make-up, their test results can also be used to predict an animal's genetic worth.

The Canadian Swine Genetic Evaluation Program

To overcome these limitations, the Canadian Swine Genetic Evaluation Program was developed in 1985. It provides pork producers with Estimated Breeding Values (EBV's) for backfat thickness and days to 90 kg on performance tested pigs. EBV's are estimates of the genetic (breeding) values of an animal for a particular trait.

Estimated Breeding Values

Estimated Breeding Values are simply an extension of the ROP Program. Data are collected in the same way; however, the analysis of the data is quite different. EBV's take into account the following factors:

1. the heritability of the trait, or that part of a trait that is expected to be inherited;
   
2. the amount of information available on each boar or sow i.e. number of relatives as well as number of progeny, number of litters, and number of herds;
   
3. the genetic merit of the herd in which the pig was raised; and
   
4. the genetic trend (change) in the breed over time for all ROP-tested pigs in the region (Ontario).

EBV's take into account performance information (backfat and days to 90 kg) on the individual as well as all related animals (sire, dam, littermates, etc.) and progeny as their test information becomes available. The more information that is available on related animals, the greater the accuracy of the EBV. This is referred to as 'repeatability'. Theoretically repeatability values can range from 0 to 100% but in practice published values on sires and dams will range between 45 to 99%. The higher the repeatability value, the more accurate is its EBV. For example, sires with many progeny will have repeatability values approaching 99%. As performance information becomes available on progeny, the importance of the animal's own record as well as records on its other relatives diminish since the performance that the selected animal has passed on to its progeny becomes the most important factor.

EBV's also account for the effect of management on an animal's performance. This is achieved through the use of genetic links between herds. Genetic links are created through the use of artificial insemination, the central test station and the sale of breeding stock from one herd to another. Through these methods, animals of a related genetic background are raised in different herds, thus herds become "linked". Because EBV's account separately for the effects of environment and genetics, the management effect can be removed, allowing valid comparisons of breeding stock in different herds. This means that an individual can be compared genetically to all other ROP tested pigs of the same breed.

The Canadian Swine Genetic Evolution Program provides producers with two valuable reports:

(1) Sire and Dam Report
(2) Herd Activity Monitor

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Sire and Dam Report

A separate sire and dam report is produced for each breed (Yorkshire, Landrace, Hampshire, Duroc, Lacombe) and region (Maritimes, Quebec, Ontario, Western). To be listed in the report a boar or sow must meet the following criteria:

(1) the animal must have a complete identification, including herd letters, pig number and year letter (according to Canadian National Livestock Records); and
(2) must have at least 1 progeny and a repeatability on EBV index of at least 45%.

The report lists animals identification, EBV's for backfat thickness and days to 90 kg, as well as an index combining EBV's for backfat and days and its repeatability. The report also lists for each breeding animal the number of progeny tested, the number of litters and the number of herds (including the test station) in which progeny were tested. The last herd in which the sire or dam had progeny is also given. EBV's are expressed relative to the average of all pigs of the same breed born and tested in ROP herds within the last two years. Because the goal is to reduce backfat and days to 90 kg, sires and dams with negative EBV's are breed improvers. Their use will result in a decrease in backfat and/or days. The EBV index is useful for breeders who wish to select for growth rate and backfat thickness at the same time. The traits are weighted so that a change of 1 mm in backfat has approximately the same value as a change of 4 days in growth rate. The average index for each breed is 100, but the average,in genetically superior herds will be greater than 100 and the average in genetically poorer herds, will be less than 100.

Sire and dam reports are published quarterly and are provided to all producers enrolled on the ROP Program. Additional copies can be obtained from: Supervisor, Sheep and Swine Performance Testing, Guelph Agriculture Centre, Box 1030, Guelph, Ontario, MIH 6Nl Phone: (519) 836-3560.

Herd Activity Monitor

The Herd Activity Monitor (HAM) is a confidential report provided to each ROP breeder on a quarterly basis. This report allows the breeder to assess genetic and management progress in the herd. The report lists the number of pigs tested in the last two years as well as the average EBV of pigs tested during this time period (compared to all other ROP herds in the region). The report also gives a measure of environmental or management performance of the herd, both in absolute terms and relative to the average herd. Trends in genetic and management performance over time are also given based on six-month periods. These trends can be used as an indicator of the effectiveness of a breeding program, provided that reasonable numbers of pigs are tested in each six-month period. The trends are also useful for determining the results of a change in management.

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Using EBV'S

The Canadian Swine Genetic Evaluation Program provides breeders and commercial producers with a means of identifying and selecting genetically superior breeding stock. Because EBV's account for the effect of management on an animal's performance, the selection of breeding stock is greatly simplified. Within a breed and region (i.e. Ontario), comparisons can be made between all pigs in ROP-tested herds. Prior to the development and use of EBV'S, accurate comparisons of breeding stock in different herds could not be made. The environment under which the animal was raised was not accounted for. Therefore an animal's performance could not be attributed strictly to genetics or management but some combination of the two factors. Genetic improvement results from the selection and use of genetically superior animals, not animals that have been raised under ideal management conditions. Table 1 compares two methods of selection of breeding stock - one using the traditional ROP Index and other, the EBV Index.

Accurate selection of breeding stock is only the first step. Designing an effective breeding program is essential for the selection process to be of any benefit. EBV's can be used by breeders to predict the outcome of a specific mating. By simply averaging the EBV's of the parents the genetic merit (value) of the progeny can be determined. An example is given in Figure 1.

 

Figure 1. Genetic (Breeding) Value of progeny from mating a boar with an EBV of -6.0 days and a sow with an EBV of -2.0 days.Not all progeny would have a genetic value of -4.0, however over a large number of matings the progeny would, on average take 4 days less to reach 90 kg than progeny of parents with breed average.

Breeding programs must be evaluated on a regular basis in order to determine their effectiveness, Breeders can use the Herd Activity Monitor (HAM) to assess their breeding strategies. The HAM lists trends in genetic performance over time, indicating the amount of genetic improvement, or lack of it, in the breeder's herd. Similar trends are given for management performance, allowing the breeder to determine the effectiveness of management practices in the herd.

The Canadian Swine Genetic Evaluation Program will also allow evaluation of current breeding practices and testing programs on a national level. Routine monitoring of genetic trends (genetic change) in performance - tested breeding stock ensures continued genetic improvement for the entire industry.

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