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Estimated Breeding Values
Breeding Values (EBVs) estimate the genetic worth of animals. They are produced for each animal for each recorded trait from Beefbreeder and Society records using BLUP technology. EBVs use the same units as the recorded traits (eg kg for liveweight) and are expressed relative to a common baseline for all animals in all contemporary groups. In the UK, the baseline is set so that the average of the breeding values for all animals born in 1980 is zero.
Because BLUP takes environmental influences into account and all EBVs are expressed relative to a common base, direct comparisons can be made across herds (as long as they are linked genetically). Across-herd BLUP increases the size of the genetic pool from which replacements can be accurately chosen, thus increasing selection intensity and reducing the risk of inbreeding.
Comparisons can also be made between animals across time allowing measurement of genetic progress. Genetic progress in a breed can be charted year by year, both nationally and on an individual herd basis. This provides a valuable check for breeders and can be an important marketing tool for convincing commercial customers that the breed is improving.
BIRTH WEIGHT (KG)
High birthweights are more likely to be associated with difficult calvings. A bull with an EBV of -1 is expected to produce calves 0.5kg lighter at birth than calves sired by a bull with an EBV of 0.
GESTATION LENGTH (DAYS)
Gestation length affects birth weight and consequently calving ease (ie a shorter gestation length results in easier calvings because birth weights are lower). A shorter gestation length is also important because it increases the interval between calving and the start of mating, which gives the cow more time to recover.
The more negative a bull's EBV, the shorter the expected gestation length when his offspring are born. A bull with a gestation length EBV of -2 is expected to produce calves that are born one day earlier than calves sired by a bull with an EBV of 0. To maximise accuracy, Beefbreeder currently only uses gestation length records that refer to an AI mating, although the use of data from some natural matings is being considered.
CALVING EASE
This EBV predicts the effect of using a particular bull on the percentage of unassisted calvings when his calves are born. It is recorded subjectively using 5 categories: category 1 indicates no assistance is required; category 5 refers to surgery section other than elective caesarean. Approximately 3% more of the calves sired by a bull with an EBV of +6 for calving ease are expected to be born easily compared to calves sired by a bull with an EBV of 0.
200-DAY GROWTH (KG)
The EBV is a measure of an animal's genetic potential for growth from birth to weaning at about 200 days. A bull with an EBV of +20 for 200 day growth is expected to produce calves 10kg heavier at weaning compared to calves sired by a bull with an EBV of 0.
400-DAY GROWTH (KG)
The 400 day growth EBV is a measure of the animal's genetic potential for growth to 400 days of age. A bull with an EBV of +40 for this trait is expected to produce calves 20kg heavier at 400 days than calves sired by a bull with an EBV of 0. Selection for faster growth (ie high 400 day EBVs) results in animals which will have heavier carcases at a constant fat class or leaner carcases at a constant age. Selection for high growth rates also results in an overall increase in mature size for that breed (and therefore higher birth weight).
MUSCLING SCORE (POINTS 1-15)
This EBV is a visual assessment of an animal's conformation at around 400 days of age. Animals are assessed on a 1 to 15 point scale based on the EU carcase classification system. A score of 1 indicates very poor conformation (equivalent to P) whereas the muscles of animals with a score of 15 will be extremely well formed (equivalent of E). The scale is adjusted for fat.
A bull with a muscling score of 1.0 is expected to produce calves 0.5 points better on the conformation scale than calves sired by a bull with an EBV of 0. To cater for the extreme muscularity of the Belgian Blue the upper end of the muscling score point range has been extended to 17. However, scores 15, 16 and 17 are considered to be of the same value in the BLUP analysis.
MUSCLE DEPTH (MM)
This is based on the ultrasonic measurement of eye muscle depth at around 400 days and provides a direct measure of carcase worth in live animals. A bull with an EBV for muscle depth of +0.2 is expected to produce calves with 0.1mm greater eye muscle depth compared to calves sired by a bull with an EBV of 0.
FAT DEPTH (MM)
Fat depth is based on an ultrasonic measure of backfat depth at around 400 days of age. Negative EBV's for fat depth indicate leanness. A bull with an EBV of -0.2 for fat depth is expected to produce calves 0.1mm leaner at 400 days than calves sired by a bull with an EBV of 0.
A negative fat depth EBV suggests that if the animal was slaughtered at the same weight as an animal with a positive EBV for this trait it would produce a leaner carcase or, if required, it could be taken to a heavier weight to achieve a similar carcase fat cover.
MATERNAL TRAIT EBVs
Maternal traits are only expressed by females so a bull's EBV for 200-day milk, when halved, gives an indication of how well a bull's heifer calves will perform as mothers when they themselves are mated.
200-DAY MILK (KG)
The maternal component of the 200 day weight record estimates how much of the performance of the calf up to 200 days (weaning) is due to the dam's maternal performance. For example milkiness, uterine capacity and general mothering ability. A bull with an EBV of +4 for 200 day milk is expected to produce heifer calves which will have above average maternal characteristics leading to their calves being 2kg heavier at 200 days than calves from heifers sired by a bull with an EBV of 0.
Information to derive 200 day milk EBVs comes from two main sources - the most valuable one being the 200 day weights of offspring (of cows) or grand offspring (of bull or cows). Other things being equal, families with high genetic merit for 200 day milk will leave calves with higher weaning weights than families with lower EBVs.
However, it takes a long time to get many records on offspring or grand offspring and, in the meantime, records of 200 day weight (and correlated traits) from the animal and its relatives can help. In this case 200 day milk EBVs are based on the fact that, in general, families with high genetic merit for weight gain are slightly poorer than average for milk yield, ie there is a negative correlation between milk production and growth. (This is similar to the situation across breeds where faster growing breeds tend to be poorer milk producers.)
BEEF VALUE
The Beef Value ranks animals on the expected carcase financial merit of their offspring. The objective of the Beef Value is to improve financial returns by improving carcase weight, fat and conformation scores in line with current commercial carcase pricing structures.
For example, a Beef Value for a bull of 20 means his carcase is estimated to be £20 more valuable than the carcase from a bull with a Beef Value of 0. As with the EBVs a bull's Beef Value must be halved to estimate the value of his calves. If the cow's Beef Value is also known (eg in a pedigree herd) the best estimate of the value of the calf is half the cow's Beef Value plus half the bull's Beef Value. For example, if a cow with a Beef Value of 10 is mated to a bull with a Beef Value of 20 the expected Beef Value of their calve is 5 + 10 = 15.
All Beef Values are expressed relative to a common base year which is defined so that an average animal born in 1980 had a Beef Value of £8. Beef Values cannot be compared across breeds and to avoid confusion they are prefixed with two letters which indicate which breed they refer to. This is LM for Limousin, eg LM15.
CALVING VALUE
The objective of the Calving Value is to improve financial returns by reducing the costs associated with difficult calvings (eg veterinary costs, loss of production) and longer gestation lengths (eg feeding/housing the pregnant cows, extended calving intervals). It is designed to help producers select terminal sires that will produce calves that do not have extended gestation lengths and which are born easily.
The Calving Value is presented as a cash value per head and must be halved in the same way as the Beef Value. For example, a bull with a Calving Value of 4 is expected to produce calves which save an average of £2 in calving and gestation length costs compared to calves sired by a bull with a Calving Value of 0.
All Calving Values are expressed to a common year which is defined such that an average animal born in 1980 had a Calving Value of £2. The values cannot be compared across breeds and to avoid confusion with the Beef Value they are suffixed with the letter C, eg LM4C indicates a Calving Value of +4.
Having two indexes provides users of the Beefbreeder genetic evaluation scheme with flexibility. The economic importance of the various traits differs substantially across breeds and production systems and two indexes allow trade-offs to be made between the emphasis put on calving traits and on growth and carcase traits.
EBV ACCURACY
There are several factors that affect EBV accuracy:
- the amount of information available on the trait from the animal itself;
- the amount of information on the trait from relatives of the animal;
- the heritability of the trait concerned;
- the amount of information from the animals and its relatives on traits correlated with the trait of interest and the strength of the correlation's;
- the number of contemporaries recorded.
Accuracy values are presented along with the EBVs and they indicate how close the EBVs are to the true breeding values of the animal. In the UK they are expressed as percentage points ranging from 0 to 100.
Accuracy's provide a guide to the likelihood of an EBV changing (up or down) as more information on the animal becomes available, for example a low accuracy value indicates that there is a high chance the EBV will change. However, it is important to note that the BLUP evaluations will have already compensated for a lack of information on an animal by adjusting its EBVs towards the average.
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