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Irish Limousin Cattle Society, Kilglass, Mitchelstown, Co. Cork

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Looking at a catalogue nowadays in order to select the next AI bull or stock bull for your herd can be a daunting task given the range of information provided. This article attempts to give you a better insight into what the figures are and where they have come from. To do this we have to use some well known terms (but often not well understood!!) used in animal breeding circles.

Phenotype:

This is the observed performance of an animal ie. For an example animal this could be a difficult calving at birth, 325kg liveweight at 7 months of age or scoring 5 out of 10 doe docility.

Genotype:

This is the part of that observed performance in the phenotype which was due to the genes that animal inherited from its parents. Some traits are more heritable than others, liveweight and carcass conformation and more heritable that fertility and survival traits.

Environment:

This is the remaining part of the observed performance which is due to the on-farm conditions e.g of the dam at the time of calving may have affected her ability to calve and the size of the calf, whether the animal was getting feeding at the time of the 8 month liveweight measurement.

Breeding Value:

This is related to the genotype and it is that part of the genotype which we try to measure and alter by selection.

Unfortunately we never know the true breeding value of an animal, though we can come close to it by performance recording very large numbers of offspring. Hence for young animals we have to rely on predicted or estimated breeding values (EBVs) in order to rank candidates for selection. Strictly speaking, breeding values are predicted, because they relate to future breeding performance, but the terms predicted and estimated get used interchangeably.

The information that geneticists use to predict breeding values include records of performance from:

  • The animal itself
  • The animal’s ancestors
  • The animal’s full or half sibs
  • The animal’s progeny
  • Any other relatives of the animal
  • Combinations of the classes of relatives listed above.

Information from all the above sources contribute to completing the picture of an animals true breeding value. However some sources are more informative than others. Records from progeny are of most value. This is why widespread progeny tests produce the most accurate and unbiased estimation of a bulls breeding value.

What is a contemporary group?

An effective genetic evaluation system for ranking animals on their genetic merit must be able to disentangle the effects of genes and the environment. This is to allow the selection of animals that have high genetic merit and not those that perform well simply because they are well fed and managed. This is why a strong contemporary group is so important.

The genetic evaluation process rests heavily on comparisons of the performance of animals which have been treated in a similar way, e.g. born over a relatively short time period, on the same farm, and fed and managed similarly. These animals are often called contemporaries and the groups they belong to are called contemporary groups.

Ideally, contemporary groups should be as large as possible with all animals under similar treatment. to allow the best possible separation of genetic and environmental effects on performance. The Irish Cattle Breeding Federation (ICBF) has set the size of a contemporary group for linear scoring at 5 or more and preferably by 2 or more different sires. Sires give important links across herds.

The genetic evaluation system uses all information available including records on pedigree beef animals, dairy and both crossbred beef and crossbred dairy x beef animals. Including all breeds in a single analysis is possible due to the substantial crossover that exists in Ireland between genes from different beef breeds and also between dairy and beef breeds. The genetic evaluation also accounts for whether an animal is crossbred or not and removes this effect from the figures. Hence bulls used on dairy cows have a correction for the reduced beef merit of the progeny relative to the progeny from a bull used in a beef herd

Predicted Differences:

Up to now we have discussed breeding values as the benchmark for measuring the genetic merit of an animal. This can cause confusion among breeders and buyers of bulls because when they breed from this bull they can expect to see only half of this breeding value in terms of extra progeny performance, as only half the genes of the progeny come from the sire, with the dam contributing the other half. Breeders and buyers of bulls need to start thinking about the merits of a bull in terms of the extra profit produced by his offspring both male and female. In other words it is the genetic merit of the progeny of that bull rather than the merit of the bull himself. This is why the new figures are called predicted differences or PDs. They can be visualised as expected progeny differences

PD’s are presented in the unit of measurement for the particular trait. For example, the unit of “kgs” for liveweight or “days” for gestation length. They are presented for a range of traits covering fertility, calving events, growth and phenotype, slaughter and maternal characteristics. An advantage of having a comprehensive range of traits is that it is possible to select for balance between different traits and avoid extremes in particular traits.

PD’s are adjusted to a common genetic base. A base allows the comparison of the genetic merit of current animals to a group of animals from a number of years ago. This base will be fixed for a number of years allowing a measure of genetic improvement over a period.

The full range of PD’s and their units are as follows:

Calving Difficulty (%) expressed as a percentage and is derived from calving difficulty rating (1-5) recorded during calving. For example a PD of +6.5% indicates that, on average, the calving difficulty of the sire will be 6.5% higher that the common base. Negative or low values are desirable.

Gestation Length (days) expressed in days as the time between conception and birth of the calf recorded from insemination records and birth dates. For example, a PD of +2.7 days indicates that, on average, the gestation length of the progeny of the sire will be 2.7 days longer that the common base. Negative or low values are desirable.

Calf Mortality (%) expressed as a percentage derived from the recording of calf deaths between birth and 1 month of age. For example, a PD of +1.5% indicates that, on average, the mortality of the progeny of the sire will be 1.5% higher that the common base. Negative or low values are desirable.

Weaning Weight (kgs) expressed in kilograms derived from the weight recording of animals at weaning. For example, a PD of +15.5kgs indicates that, on average, the progeny of the sire will be 15.5kgs heavier at weaning compared to the common base. Positive or high values are desirable.

Calf Quality (%) expressed as a percentage and derived from price per kg data from the livestock marts but also related traits such as muscle linear score values mart weights and carcass conformation. Assuming that calves sold at weaning can be divided 3 value categories, an increase in the calf quality percentage increases the percentage of calves in the high value category. For example, a PD of +28% indicates that, on average, 28% more the progeny of the sire will be of higher value compared to the common base. Positive or high values are desirable.

Carcass Weight (kgs) expressed in kilograms derived from the recording of carcass weights at the time of slaughter. For example, a PD of +27kgs indicates that, on average, the carcass weight of progeny of the sire will be 27kgs heavier that the common base. Positive or high values are desirable.

Carcass Conformation (grade) expressed as the 15-point EUROP grading of carcasses after slaughter. For example, a PD of +2.75 indicates that, on average, the carcass conformation of progeny of the sire will be 2.75 grades higher that the common base. Positive or high values are desirable.

Carcass Fat (grade) expressed as the 15-point scale for grading carcass fatness after slaughter. For example, a PD of –0.56 indicates that, on average, the progeny will grade 0.56 units lower for carcass fat score compared to the common base. In general low values are desirable but are dependent on differing markets.

Feed Intake (kgs) expressed in kilograms and derived from dry matter intake levels recorded in at Tully test centre. For example, a PD of –0.13kgs indicates that, on average, the progeny of the sire will require 0.13kgs less dry matter intake per kg live weight gain compared to the common base and therefore considered to be more efficient. Negative or low values are desirable.

Maternal Weaning Weight (kgs) expressed in kilograms derived from the weight recording of animals at weaning. The PD estimates how much of the calfs performance is due to the dam i.e milk ability and general mothering ability. For example, a PD of +10.5kgs indicates that, on average, daughters of the sire will have calves with 10.5kgs heavier weaning weight compared to the common base. Positive or high values are desirable.

Cow Survival (%) expressed as a percentage derived from CMMS recording of reappearance (calving) from year to year. Cow survival is defined as the proportion of a sires daughters having a 2nd calf. For example, a PD of +0.8% indicates that, on average, 0.8% more of a sires daughters will reach their 2nd calving compared to the common base. Positive or high values are desirable.

Calving Interval (days) expressed in days and derived from CMMS recording of reappearance (calving) from year to year. It is defined as the time in days between two consecutive calvings. For example, a PD of +2.0 indicates that, on average, the calving interval of a sires daughters will be 2 days longer than the common base. Negative or low values are desirable.

Age at First Calving (days) expressed in days and derived from CMMS recording of the first calving of heifers. For example, a PD of –20.5 indicates that, on average, the age of first calving of the sires daughters will be 20.5 days earlier than the common base.

Maternal Calving Difficulty (%) expressed as a percentage and is derived from calving difficulty rating (1-5) recorded during calving. For example, a PD of +4.1% indicates that, on average, the sires daughters will experience 4.1% more calving difficulty when calving compared to the common base. Negative or low values are desirable.

Cull Cow Carcass Weight (kgs) expressed in kilograms derived from the recording of carcass weights at the time of slaughter. For example, a PD of +18.0 indicates that, on average, the carcass weight of a sires daughters will be 18kgs heavier that the common base.

Positive or high values are desirable.

€urostar Profit Indexes:

All of the individual traits listed above are considered important traits to maximise the profitability of a beef production system. Accordingly, each trait is given an economic value (€), which allows breeders to see the benefit of increasing or decreasing individual traits. For example, we can calculate the increased value of a higher weaning weight when an animal is sold at a mart, or alternatively the increased veterinary cost associated with an increase in calving difficulty. These economic values are updated according to market prices and costs of production.

There are many different types of production systems in operation on Irish beef farms ranging from herds selling weanlings for export, herds specialising in fattening cattle for Irish factories, to the all inclusive suckler to slaughter operations. Each of these systems have different goals which need focus in terms of breeding decisions. A selection index is simply an optimal way of combining several traits of economic or functional importance. Individual traits are then grouped together, depending on their importance in different aspects of beef production, to produce a profit based €urostar Index (see below).

Index

Traits

Weighting

Description

Overall Suckler Beef Value (€)

 

 

This is an overall profit index combining all of the indexes below based on the expected proportions of calves born which are: Sold at weaning for live export, Retained for slaughter in Ireland, Sold or retained as replacement females.

Calving Traits (€)

Calving Difficulty (%)

Gestation Length (days)

Calf Mortality (%)

53%

25%

22%

Estimates the direct cost of calving events in a suckler herd, combining the economic cost of calving difficulty, gestation length and calf mortality.

Weanling Export (€)

Weaning Weight (kgs)

Calf Quality (€)

55%

45%

Estimates how good a sire is at producing high value weanlings for export. Combines the economic values of weaning weight and calf quality.

Beef Carcass (€)

Carcass Weight (kgs)

Weaning Weight (kgs)

Feed Intake (kgs)

Carcass Conformation (grade)

Carcass Fat

46%

24%

12%

11%

7%

Estimates how good a sire is at producing progeny with high value carcasses combing the economic values for carcass weight, weaning weight, feed intake, carcass conformation and carcass fat.

Maternal Replacement Value

 

 

 

Milk & Fertility (€)

Maternal Weaning Weight (kgs)

Cow Survival (%)

Calving Interval (days)

Age at 1st Calving (days)

Maternal Calving Difficulty (%)

29%

26%

18%

10%

10%

7%

These two indexes can be used where a suckler farmer is selecting to breed replacements. The Milk & Fertility index focuses in the performance of a sires daughters for true maternal traits. The Calf Quality index focuses on the future profit of calves born to a sires daughters.

Both indexes should be used in tandem when selecting sires to breed replacements.

Calf Quality (€)

Weaning Weight (kgs)

Carcass Weight (kgs)

Feed Intake (kgs)

Carcass Conformation (grade)

Calving Difficulty (%)

Calf Mortality (%)

Carcass Fat

Gestation Length (days)

32%

29%

13%

10%

6%

4%

4%

2%

 

Star Ratings:

Star ratings were introduced to allow each breeder to see how good each animal is in relation to all other animals of that breed (within breed) but also in relation to other breeds (across breed). The number of stars allocated to an animal is directly linked to the € value index as follows:

5 Stars – Excellent – Top 20%

4 Stars – Above Average – Top 20 to 40%

3 Stars – Average – Top 40 to 60%

2 Stars – Below Average – Bottom 20 to 40%

1 Star – Poor – Bottom 20%

Farmers interested in selecting for terminal sire characteristics, with no intention of selling bulls from which replacement heifers would be kept for breeding, should focus on the Calving, Weanling Export and Beef Carcass indexes. Where future bulls are to be mated to mature suckler cows with no history of calving difficulty, relatively less emphasis should be given to the Calving Index than to the Weanling Export, or Beef Carcass indexes. Relatively more emphasis should be given to the Calving in

The Overall Suckler Beef Index is for the breeder who sells bulls from which replacement heifers (daughters) would be kept for breeding. It combines all of the 5 indexes (Calving, weanling export, beef carcass and the 2 maternal indexes) in a way that it takes account of the proportions of calves born which end up being exported, slaughtered or kept as replacements. Currently this proportion is 16% exported, 69% slaughtered in Ireland and 16% kept as replacements. Some animals which rank highly for the Overall Suckler Beef Index  may not be at the top of any of the specialised indexes but may have a good balance across all the indexes. It will also be used as a benchmark as to the increase in genetic merit of the herd as a whole.

Other Genetic Indexes:

Before the development of the new €urostar indexes, Irish genetic indexes were centred on the BLUP (Best Linear Unbiased Predictor) model for animal evaluation. This model was used to analyse linear score data recorded at the time of weaning. A minimum of 14 traits are scored at weaning and subsequently composited to into Muscle, Skeletal, Functionality and Docility indexes (see table below)

MUSCULAR DEVELOPMENT:

Linear Traits

Scale (1 – Bad, 10/15 Good)

Description

Width between Withers

1-15

Used to estimate the ability of the bull to transmit high muscling ability and shape to his progeny

Width behind Withers

1-15

Loin Development

1-15

Width of Hindquarter

1-15

Development of Hindquarter

1-15

 

SKELETAL DEVELOPMENT:

Linear Traits

Scale (1 – Bad, 10/15 Good)

Description

Height at Withers

1-10

Used to estimate the ability of a bull to transmit a large frame to his progeny

Length of Back

1-10

Length of Pelvis

1-10

Width a Hips

1-10

 

 

 

FUNCTIONALITY:

Linear Traits

Scale (1 – Bad, 10/15 Good)

Description

Front legs – front view

1-10

Used to estimate the ability of a bull to breed functional progeny with good legs & feet.

Hind legs – side view

1-10

Hind legs – rear view

1-10

Locomotion

1-10

 

 

 

DOCILITY:

Linear Traits

Scale (1 – Bad, 10/15 Good)

Description

Docility

1-10

Used to estimate the ability of a bull to breed quiet & docile progeny.

Intermediate value of 5 is best for FLFV, HLSV & HLRV)

Breeding values for muscle, skeletal, functionality and docility are expressed in index form. The index is scaled to a mean of 100. Such an index indicates the relative position of an animal in the wider population of that breed.

Predicted differences (PD’s) are also available for each of the individual traits listed above but are generally only used for AI sires with high reliability. These linear type indexes are predominately used by the pedigree breeders to help to improve the phenotype of their animals. The docility index has been used to genetically improve the temperament of Irish Limousin cattle.

Currently, the composite indexes of muscle, skeletal, functionality and docility are evaluation on a within breed basis – therefore direct comparisons cannot be made between breeds. Developments are taking place to evaluate these composites on an across breed basis and these new indexes will be released in the near future.

Reliability – The reliability is a very important factor to consider when examining individual trait predicted differences or indexes

The reliability (%) of an index is based on a number of factors;

  • the amount of information from the animal itself
  • the amount of information from the relatives of the animal
  • the heritability of the traits
  • the genetic correlations between traits
  • the size and genetics within the contemporary group

Reliability figures are presented with each index to indicate how accurate the figures are. Hence, the reliability indicates the “confidence level” of the index. The higher the reliability the lower the likelihood that the index will change as more information is analysed from the animal and its relations. Equally a low reliability value indicates that there is a high chance that the index will change, and there is an equal chance that the index will increase in value or decrease in value.

Reliability values range from 0-99%. The following guide is given for interpreting reliability:

Reliability Range

Interpretation

Less than 30%

Low reliability. Little or no own performance information available. Index is predicted from pedigree. Index is preliminary and may change substantially as more performance information becomes available. Confidence in index is low

30–50%

Low-Medium reliability, usually based on animals own performance records and pedigree. Index may change substantially as more information becomes available.

50-70%

Medium reliability, some progeny information included in the index. Index may change slightly with the addition of new data.

70-90%

Medium-High reliability, index dominated by performance information of progeny. Index change less likely.

More than 90%

High reliability, Index is accurate estimate of animal’s true breeding value. Change of index is unlikely and confidence in index is high.

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