The Australian Limousin Breeder's Society Ltd
The Carcase Breed
Understanding Estimated Breeding Values (EBVs)
Estimated Breeding Values (EBVs) are predictions of an animal's genetic merit, based on available performance data on the individual and its relatives.
In the calculation of EBVs the performance of individual animals within a contemporary group is directly compared to the average of other animals in that group. A contemporary group consists of animals of the same sex and age class within a herd, run under the same management conditions and treated equally. Indirect comparisons are made between animals reared in different contemporary groups, through the use of pedigree links between the groups.
Due to the establishment of the breed in Australia by artificial insemination and the continued use of artificial breeding, an extensive network of pedigree links has been established throughout the Limousin breed. These pedigree links enable the adjustment for environmental differences between herds, years and management groups. This allows comparisons between animals from totally different environments and management conditions.
EBVs are expressed in the units of measurement for each particular trait. They are shown as + ive or - ive differences from the breed base. For example, a bull with an EBV of +50 kg for 600-Day Wt is estimated to have genetic merit 50 kg above the breed base of 0 kg. Since the breed base is set to an historical benchmark, the average EBVs of animals in each year drop has changed over time as a result of genetic progress within the breed.
While EBVs provide the best basis for the comparison of the genetic merit of animals reared in different environments and management conditions, they can only be used to compare animals within the same breed. The EBVs for different breeds have different bases and are subject to different rates of change over time. Consequently, Limousin BREEDPLAN EBVs cannot be validly compared with EBVs for any other breed.
The absolute value of any EBV is not critical, but rather the differences in EBVs between animals. Particular animals should be viewed as being "above or below breed average" for a particular trait only if their EBVs are higher or lower than the average EBVs of all animals born in that year. The most useful "benchmark" is the average EBVs for calves born in their year drop.
EBVs are published for a range of traits covering fertility, calving ease, milking ability, growth, carcase merit and docility. When using EBVs to assist in selection decisions it is important to achieve a balance between the different groups of traits and to place emphasis on those traits that are important to your herd, your markets and your environment. One of the advantages of having a comprehensive range of EBVs is that you can avoid extremes in particular traits and select for animals with balanced overall performance.
EBVs are provided for the following traits:
Calving Ease Traits
· Gestation Length
· Birth Weight
· Calving Ease (Direct)
· Calving Ease (Daughters)
Fertility Traits
· Days to Calving
· Scrotal Size
Milking Ability
Weight Traits
· 200-Day Weight
· 400-Day Weight
· 600-Day Weight
· Mature Cow Weight
Carcase Traits
· Carcase Weight
· Eye Muscle Area
· Rump Fat
· Rib Fat
· Retail Beef Yield %
· Intra-muscular Fat % (Marbling)
Docility
Further details on each of the EBVs are listed below.
Calving Ease Traits
Calving Ease is an important economic trait because of its impact on calf and heifer mortality, labour and veterinary expenses at calving time and subsequent re-breeding performance of heifers.
EBVs for Calving Ease are calculated from calving ease scores, birth weights and gestation length information provided by breeders. Due to the many non-genetic influences on calving ease the trait has a low heritability.
Usually only proven bulls or cows with several progeny recorded have EBVs for Calving Ease with sufficient accuracy to be reported. Two Calving Ease EBVs are provided - Calving Ease (DIR) and Calving Ease (DTRS).
Gestation Length EBVs
Gestation Length EBVs are estimates of genetic differences between animals in the number of days from the date of conception until the calf is born. These EBVs are calculated from the joining and birth date records for calves got by AI or hand mating. The analysis accounts for differences in the "maternal" effect of dams on gestation length.
Shorter gestation lengths are usually associated with lighter birth weights, easier calving and improved cow re-breeding performance.
Lower, or more - ive Gestation Length EBVs are generally more favourable. For example, a bull with an EBV of -2.0 days would be expected to produce calves that are born earlier, with easier calving, than a bull with an EBV of +2.0 days.
Birth Wt EBVs
Birth Wt EBVs are estimates of genetic differences between animals in kg of calf birth weight. Calf birth weight is the biggest contributing factor causing calving difficulty in heifers. To minimise the risk of calving difficulty it is recommended that you only use bulls over your heifers that have similar, or lower, Birth Wt EBVs to the heifers.
While low Birth Wt EBVs are favoured for calving ease, they are also often associated with lower growth potential. Consequently, birth weight and later weights need to be carefully balanced.
Fortunately, animals do exist with moderate Birth Wt EBVs and above average weight EBVs.
Small, or moderate Birth Wt EBVs are more favourable. For example, a bull with an EBV of +2.0 kg would be expected to produce lighter calves at birth than a bull with an EBV of +5.0 kg, with a lower risk of a difficult calving if joined to heifers.
Calving Ease (DIR) EBVs
Calving Ease (DIR) EBVs are estimates of genetic differences between animals in the ability of their calves from two year old heifers to be born unassisted. The EBVs are reported as differences in the percentage unassisted calvings.
Higher, more + ive, Calving Ease (DIR) EBVs are more favourable. For example, a bull with an EBV of +2.0% would be expected to produce easier calving progeny from two year old heifers than a bull with an EBV of -2.0%.
Calving Ease (DTRS) EBVs
Calving Ease (DTRS) EBVs are estimates of genetic differences between animals in the ability of their two year old daughters to calve without assistance. The EBVs are reported as differences in the percentage unassisted calvings.
Higher, more + ive Calving Ease (DTRS) EBVs are more favourable. For example, a bull with an EBV of +2.0% would be expected to produce two year old daughters that have fewer calving problems than the daughters of a bull with an EBV of -2.0%.
Fertility Traits
Fertility is a critical component influencing the profitability of a breeding herd. EBVs are provided for two fertility traits - Days to Calving and Scrotal Size. These traits contribute important information to assist in making breeding decisions to maintain herd fertility. Days to Calving EBVs are calculated from the joining and calving date records provided by breeders.
Scrotal Size EBVs are based on measurements recorded on yearling bulls and the known genetic relationships with recorded growth traits.
Days to Calving EBVs
Days to Calving EBVs are estimates of genetic differences between animals in female fertility, expressed as the number of days from the start of the joining period until subsequent calving.
Variation in Days to Calving records is due mainly to differences in the time taken for females to conceive after the commencement of the joining period. Females with shorter Days to Calving EBVs tend to commence cycling earlier after calving and conceive earlier in the joining period. They also tend to attain puberty at a younger age as heifers.
Days to Calving EBVs for bulls are based on the performance of their daughters and female relatives. Differences in scrotal size among bulls can also contribute to variation in Days to Calving EBVs.
Lower, or more + ive Days to Calving EBVs are more favourable. For example, a bull with an EBV of -3.0 days would be expected to produce daughters that conceive earlier in the joining period and subsequently calve earlier than the daughters of a bull with an EBV of +3.0 days.
Scrotal Size EBVs
Scrotal Size EBVs are estimates of the genetic differences between animals in scrotal circumference at 400 days of age.
Increased scrotal size is associated with increased semen production in bulls and earlier age at puberty of bull and heifer progeny. Scrotal Size also has a favourable relationship with Days to Calving, such that bulls with larger scrotal size EBVs tend to have daughters with shorter Days to Calving intervals.
Larger, more +ive Scrotal Size EBVs are more favourable. For example,
a bull with an EBV of +2.0 cm would be expected to produce sons with larger
scrotal size at yearling age and daughters that reach puberty earlier than the
progeny of a bull with an EBV of
-2.0 cm.
Weight Traits
EBVs are provided for four traits: 200-Day Wt, 400-Day Wt, 600-Day Wt and Mature Cow Wt, enabling breeders to tailor their selection decisions to achieve desired growth rates for particular market requirements.
In general, with all other things being equal, higher weights will lead to higher profitability. However, it is likely that in most situations an optimum point is reached where less emphasis should be placed on further increases in weight. One of the consequences of continued selection for increased weight EBVs is an associated increase in body size at all ages, causing an increase in herd feed requirements.
Weight EBVs are calculated from weights submitted by breeders, adjusted to relevant age classes prior to analysis. In addition, birth weight data also contributes to variation in weight EBVs due to its positive relationship with later weights.
200-Day Wt EBVs
200-Day Wt EBVs are estimates of the genetic differences between animals in liveweight at 200 days of age. This is a measure of an animal's early growth to weaning. It is an important trait for breeders turning off animals as vealers or weaners.
Larger, more + ive 200-Day Wt EBVs are generally more favourable. For example, a bull with an EBV of +30 kg would be expected to produce heavier calves at 200 days of age (or weaning) compared to a bull with an EBV of +5 kg.
400-Day Wt EBVs
400-Day Wt EBVs are estimates of the genetic differences between animals in liveweight at 400 days of age. This is an important trait for breeders turning off animals as yearlings.
Larger, more + ive 400-Day Wt EBVs are generally more favourable. For example, a bull with an EBV of +50 kg would be expected to produce heavier calves at 12 to 14 months of age compared to a bull with an EBV of +30 kg.
600-Day Wt EBVs
600-Day Wt EBVs are estimates of the genetic differences between animals in liveweight at 600 days of age. This is an important trait for breeders targeting the production of animals suited for heavyweight grass or grain fed markets.
Larger, more + ive 600-Day Wt EBVs are generally more favourable. For example, a bull with an EBV of +60 kg would be expected to produce heavier progeny at 18 to 20 months of age than a bull with an EBV of +40 kg.
Mature Cow Wt EBVs
Mature Cow Weight EBVs are estimates of the genetic differences between animals for cow weight at 5 years of age.
Mature cow weight EBVs for sires are based on weights recorded on their daughters (following the weaning of their calves), plus the genetic relationships known to exist between mature weight and earlier weights.
While moderation in cow weight is desirable for reducing herd feed costs, it is also often associated with lower overall growth potential. Consequently, mature cow weight and early weights need to be carefully balanced to optimise overall herd productivity.
Sires with above average EBVs for 400-Day Wt or 600-Day Wt will also tend to have above average mature cow weight EBVs. However, following the analysis of weight records on their daughters, some sires have been identified that tend to have smaller (or larger) mature weights relative to that predicted from their early weights.
Moderate Mature Cow Weight EBVs are generally more favourable. For example, a bull with an Mature Cow Wt EBV of +20 kg would be expected to produce daughters with lighter mature weights and lower feed requirements than a bull with an Mature Cow Wt EBV of +40 kg.
Milk EBVs
Differences in calf growth are influenced by a combination of the genetic potential for growth among the calves and the genetic differences in maternal ability of their dams. The differences in maternal ability can largely be attributed to variation in milk production of the dams.
BREEDPLAN separates the growth and maternal components of 200-Day Wt and 400-Day Wt records to produce EBVs for milk production. A bull's Milk EBV is based on the milking ability performance of his daughters.
Milk EBVs are estimates of the genetic differences between animals in milk production expressed as differences in weight at 200 days of age.
A bull with a Milk EBV of +10 would be expected to sire daughters with higher milk production than a bull with a Milk EBV of +2 kg. This higher milk production should be reflected through higher weaning weights among the daughter's calves. There is a considerable time lag before a bull obtains a reasonable accuracy for its Milk EBVs due to the time taken before weight data is available from his daughter's calves. If a bull is to be used as a terminal sire with no daughters kept as female replacements then his Milk EBVs can generally be disregarded.
The optimum level of milk production potential in beef cows is dependent upon the production system and environment in which the cows are run. Selection for increased milk production might be warranted when cows are run under good nutritional conditions and calves are sold as weaners or vealers. However, not all environments will support high milking cows.
Larger, more + ive, OR moderate 200-Day Milk EBVs can be more favourable, depending on the environment.
Carcase Traits
Limousin BREEDPLAN uses data obtained from ultrasonic real-time scanning of live animals and abattoir chiller assessment data to calculate EBVs for carcase weight, eye muscle area, rib and rump fat cover, percentage retail beef yield and intra-muscular fat percentage (marbling).
To date, the majority of the data used in the calculation of carcase EBVs has come from ultrasound scan measurements taken by accredited scanning technicians. BREEDPLAN uses relevant abattoir carcase data collected on animals in structured progeny test programs, together with suitable overseas genetic information.
EBVs for carcase traits can be used, together with visual assessment for muscularity and maturity type, to assist in breeding cattle for specific market requirements.
Carcase Weight EBVs
Carcase Weight EBVs are estimates of the genetic differences between animals in untrimmed hot carcase weight at 650 days of age.
Differences in carcase weight EBVs are calculated from available abattoir carcase weight records and known genetic associations with weight traits. Animals with high 400 and 600-day weight EBVs will also tend to have high carcase weight EBVs.
Larger, more + ive Carcase Weight EBVs are more favourable. For example, a bull with an EBV of +30 kg would be expected to produce progeny with heavier carcases at 650 days of age than a bull with an EBV of +10 kg.
Eye Muscle Area (EMA) EBVs
EMA EBVs are estimates of the genetic differences between animals in eye muscle area (cm2) at the 12/13th rib site on a 300kg carcase. EMA has a positive relationship with retail beef yield.
Larger, more + ive EMA EBVs are generally more favourable. For example, a bull with an EBV of + 2.0 cm2 would be expected to produce progeny with a greater degree of muscle expression and higher retail beef yield at any particular carcase weight, than a bull with an EBV of -2.0 cm2.
Rib Fat EBVs
Rib Fat EBVs are estimates of the genetic differences between animals in fat depth (mm) at the 12/13th rib site, on a 300kg carcase.
If more fat is required on progeny you would select for higher EBVs for fat. Fat depth has a negative relationship with retail beef yield.
More positive (+ ive) Rib Fat EBVs may be more favourable, depending on your breeding goals. For example, a bull with an EBV of +1.0 mm would be expected to produce fatter carcases at any particular carcase weight than a bull with an EBV of - 1.0 mm.
Rump Fat EBVs
Rump Fat EBVs are estimates of genetic differences between animals in fat depth at the P8 rump site on a 300kg carcase.
There is a strong positive genetic relationship between rump fat EBVs and rib fat EBVs. Differences between Rib and Rump Fat EBVs for individual animals may indicate differences in carcase fat distribution.
More positive (+ ive) Rump Fat EBVs may be more favourable, depending on your breeding goals. For example, a bull with an EBV of +1.0 mm would be expected to produce fatter carcases at any particular carcase weight than a bull with an EBV of - 1.0 mm.
Retail Beef Yield % (RBY%) EBVs
RBY% EBVs are estimates of genetic differences between animals in percentage retail beef yield in a 300 kg carcase.
RBY% reflects economic differences in carcase value and refers to the bone-out yield of a carcase, trimmed to 2-3 mm of fat. Currently, variation in RBY% EBVs is determined largely from differences in ultrasound fat and EMA measurements between animals and a small negative relationship with weight EBVs.
Larger, more + ive RBY% EBV are more favourable. For example, a bull with an EBV of +1.0 % would be expected to produce calves with higher yielding carcases at any particular carcase weight than the calves sired by a bull with an EBV of -1.0 %.
Intra-muscular Fat % (IMF%) EBVs
IMF% EBVs are estimates of genetic differences between animals in percentage intra-muscular fat (marbling) in a 300 kg carcase.
In the markets that Limousin cross cattle are suitable for (domestic, Korean, Japanese grass fed and EU), marbling has little economic value. A bull with an EBV of +1.0 would be expected to produce calves with higher average marble score at any particular carcase weight than a bull with an EBV of -1.0.
Docility
Docility EBVs are estimates of the inherent genetic differences between animals for docility.
A bull with a docility EBV of +20 will produce more calves with a docile temperament than a bull with a docility EBV of 0.