Breeding Values
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A breeding value is an estimate of an animal's genetic merit for a particular trait. Breeding values define the superiority or inferiority of the offspring of an animal. An estimate of the breeding value for a particular trait is obtained from pedigree and performance information. Using breeding values to select cows and bulls to be the parents of the next generation is the most effective way to achieve genetic improvement.
Breeding Values (BV) reflect our knowledge of a cow or bull's genetic merit for a trait.
Breeding values explained
A breeding value is an estimate of an animal's genetic merit for a particular trait. Breeding values define the superiority or inferiority of the offspring of an animal. An estimate of the breeding value for a particular trait is obtained from pedigree and performance information. Using breeding values to select cows and bulls to be the parents of the next generation is the most effective way to achieve genetic improvement.
The genetic relationships between an animal and all known ancestors and descendants are used when estimating breeding values to identify animals who are likely to produce progeny that is better or worse than average for each trait.
Importantly, breeding values for NZ dairy cattle can be compared across different breeds, herds, and ages.
Breeding values are calculated using information which is collected by farmers, on-farm. For example:
- Herd testing data
- Scale liveweight data
- Body condition scores (when collected for each individual cow)
- Traits other than production (TOP) scores
Cows that are measured on more occasions will have more reliable breeding values.
When a calf is born, the first estimate of its breeding values will be calculated as the average of its parents. This means it is critically important that the mother of a calf is identified correctly at birth, as dam information is linked to the father of the calf through mating records.
The reliability of a bull’s breeding value for a particular trait increases as more of his daughters are measured in the same herd in comparison to daughters of other bulls.
The NZAEL Animal Evaluation system publishes breeding values for dairy bulls on a wide variety of traits. Nine of these traits have been identified as having a measurable economic value to NZ farmers, and those breeding values are combined with the relevant economic values to produce the index Breeding Worth (BW).
In addition to traits included in BW, farmers can access Breeding Values for a range of TOP traits (Conformation and Udder traits) as well as gestation length and calving difficulty in order to select bulls best suited to their herd.
Breeding value trait definitions
The ten traits in BW are categorised as either Production efficiency traits or Robustness traits.
Production efficiency traits
Protein yield, fat yield, milk volume
- Breeding values for protein yield, fat yield, and milk volume are expressed as a whole season value.
- Higher protein yield, fat yield or milk volume breeding values indicate a bull will have daughters that are expected to produce more protein, fat or volume than a bull used in the same herd that has lower breeding values for these traits.
Breeding values for protein yield, fat yield, and milk volume are estimated using information that comes from herd testing during a cow’s first 6 lactations.
The performance of each cow is compared with the cows in her herd that were tested on the same day, are of the same age and calved in the same season. This grouping of herd, test-day, age and season define each animal’s 'contemporary group'.
The general assumption is that cows that perform better than other cows in their contemporary group (known as 'contemporaries') are of superior genetic merit and those that perform worse than their contemporaries have inferior genetic merit.
That said, there are a range of factors that influence an animal’s performance and some of these factors are not passed on to subsequent generations. The effect of these non-heritable factors should be disregarded from breeding values. In the case of protein, fat and milk volume, these factors include stage of lactation, hybrid vigour, inbreeding, inductions and what is termed the ‘permanent environmental effect’ for example, the effect of rearing to two years of age.
Liveweight
- Breeding values for liveweight are expressed as 5-year-old mature liveweight in kilograms.
- A higher liveweight breeding value indicates that a bull will have daughters that are expected to be heavier than a bull that has a lower breeding value for liveweight.
Breeding values for liveweight are estimated using information that comes from scale weight records of cows measured during one or more of their first 6 lactations.
The weight of each cow is compared with the cows in her herd that were weighed on the same day, are of the same age and calved in the same season. This grouping of herd, weigh-day, age, and season define each animal’s 'contemporary group'.
The general assumption is that differences among cows within a contemporary group have a genetic basis.
That said, there are a range of factors that influence an animal’s liveweight and some of these factors are not passed on to subsequent generations. The effect of these non-heritable factors should be disregarded from breeding values. In the case of liveweight, these factors include stage of lactation, hybrid vigour, inbreeding, and what is termed the ‘permanent environmental effect’ for example, the effect of rearing to two years of age.
Robustness traits
Somatic cell score
- Breeding values for somatic cell are expressed as an average somatic cell score (SCS) that is calculated by what is called a ‘log transformation’ of the somatic cell counts.
- A lower somatic cell breeding value indicates that a bull will have daughters that are expected to have lower somatic cell counts than a bull that has a higher breeding value for somatic cell. In this case a negative breeding value is a good thing.
Breeding values for somatic cell are estimated using somatic cell count information that comes from herd testing during a cow’s first 3 lactations.
The somatic cell information of each cow is compared with the cows in her herd that were tested on the same day, are of the same age and calved in the same season. This grouping of herd, test-day, age and season define each animal’s 'contemporary group'.
The general assumption is that cows that perform better (lower somatic cell) than other cows in their contemporary group (known as 'contemporaries') are of superior genetic merit and those that perform worse (higher somatic cell) than their contemporaries have inferior genetic merit.
That said, there are a range of factors that influence an animal’s performance and some of these factors are not passed on to subsequent generations. The effect of these non-heritable factors should be disregarded from breeding values. In the case of somatic cell, these factors include stage of lactation, hybrid vigour, inbreeding, inductions and what is termed the ‘permanent environmental effect’ for example, the effect of rearing to two years of age.
Fertility
- Breeding values for fertility are expressed as the percentage of cows calving within 42 days (6 weeks) of the start of calving.
Breeding values for fertility are estimated using information that comes from calving and mating dates.
Starting in the first calving, it uses calving season day (the number of days between the herd’s planned start of calving and a cow’s calving date) to assess fertility success in first, second, third and fourth calving.
It also uses information collected before calving that reflects whether a cow was mated in the first 21 days of mating (PM21) during lactation 1, 2 and 3.
The calving or mating performance of each cow is compared with the cows in her herd that are of the same age and calved in the same year and season. This grouping of herd, age, year and season define each animal’s 'contemporary group'.
The general assumption is that cows that perform better than other cows in their contemporary group (known as 'contemporaries) are of superior genetic merit and those that perform worse than their contemporaries have inferior genetic merit.
That said, there are a range of factors that influence an animal’s performance and some of these factors are not passed on to subsequent generations. The effect of these non-heritable factors should be disregarded from breeding values. In the case of fertility, these factors include age at calving, hybrid vigour and inbreeding.
Gestation length
- Breeding values for gestation length are expressed as days from last recorded mating to subsequent calving date.
- A lower gestation length breeding value indicates that a bull is expected to have more early-calving daughters than a bull that has a higher breeding value for gestation length.
Functional survival
- Breeding values for functional survival are expressed as the likely percentage of cows surviving to the next lactation independent of culling for low production or poor fertility.
- A higher functional survival breeding value indicates that ignoring culling for low production or for low fertility, a bull is expected to have more daughters surviving to the next lactation than a bull with a lower breeding value for functional survival.
Breeding values for functional survival are estimated using information from only those herds that provide high-quality data, reflecting direct cow culling for functional reasons other than poor fertility or low milk production.
The survival performance of each cow is compared with the cows in her herd that are of the same age and calved in the same year and season. This grouping of herd, age, year and season define each animal’s 'contemporary group'.
The general assumption is that cows that perform better than other cows in their contemporary group (known as 'contemporaries') are of superior genetic merit and those that perform worse than their contemporaries have inferior genetic merit.
That said, there are a range of factors that influence an animal’s survival performance and some of these factors are not passed on to subsequent generations. The effect of these non-heritable factors should be disregarded from breeding values. In the case of functional survival, these factors include age at calving, hybrid vigour and inbreeding.
Information on daughter survival only becomes available as a bull’s daughters are culled from herds that record the fates of cows. For this reason, to help identify promising young bulls prior to that time, the functional survival breeding value makes use of several predictor traits that are collected during 'Traits Other than Production' (TOP) inspections, these include the breeding values for conformation of the legs, and udder as well as milking speed and body condition score.
As a bull’s daughters get older the reliance on the direct cow culling increases and the reliance on the predictor traits decreases.
Body condition score
- Breeding values for body condition score (BCS) are expressed in BCS units and reflect the genetic merit for reserves of adipose tissue or fat.
- A higher BCS breeding value indicates that a bull will have daughters that are expected to have higher BCS than a bull that has a lower breeding value for BCS.
Breeding values for BCS are estimated using information from 2 year old heifers generally collected in early lactation with the majority coming from CRV and LIC progeny test herds.
It is difficult to compare BCS breeding values between different breeds because there are fundamental differences in the way each breed exhibits their fat reserves throughout the milking season. Therefore, BCS breeding values have a 'breed-neutral' adjustment applied to fairly compare breeds. This means that the 2005 birth year average BCS breeding values for one breed are no different to the 2005 birth year average BCS breeding values of another breed.
The BCS of each cow is compared with the cows in her herd that were scored on the same day, are of the same age and calved in the same year and season. This grouping of herd, score-day, age, year and season define each animal’s 'contemporary group'.
The general assumption is that differences among cows within a contemporary group have a genetic basis.
That said, there are a range of factors that influence an animal’s BCS and some of these factors are not passed on to subsequent generations. The effect of these non-heritable factors should be disregarded from breeding values. In the case of BCS, these factors include stage of lactation, hybrid vigour, inbreeding, and what is termed the ‘permanent environmental effect’ for example, the effect of rearing to two years of age.
Udder overall
- Breeding values for udder overall are expressed as an overall score of udder conformation.
- A higher udder overall breeding value indicates that a bull is expected to have daughters with more desirable udder conformation than a bull with a lower breeding value for udder overall.
Udder scores from first lactation (two-year-old) cows that are assessed by certified ‘traits other than production’ (TOP) inspectors are used to estimate breeding values for udder overall (as well as six other udder traits, described further down). Each scored heifer’s data feeds into their own breeding value, as well as those of their sire, dam and other relatives.
The udder overall score of each cow is compared with the cows in her herd that were scored on the same day, are of the same age and calved in the same year and season. This grouping of herd, score-day, age, year and season define each animal’s 'contemporary group'. The general assumption is that differences among cows within a contemporary group have a genetic basis. That said, there are a range of factors that influence an animal’s udder overall score and some of these factors are not passed on to subsequent generations. The effect of these non-heritable factors should be disregarded from breeding values. In the case of udder overall, these factors include age of the cow at calving, stage of lactation, hybrid vigour, and inbreeding.
Farmer opinion traits
Farmers that participate in progeny testing and 'Traits Other than Production' (TOP) assess first lactation (two-year-old) heifers for ‘opinion’ traits. Each scored heifer’s data is used to estimate their own breeding values, as well as those of their sire, dam and other relatives.
See the slider below to learn what each score represents, and how you can use them to breed improved temperament and milking speed in your herd.
Adaptability to milking: How quickly the animal adapts to the milking routine and how long it takes for milk to be let down spontaneously.
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Shed temperament: The temperament of the animal in the shed after it has settled into the milking routine.
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Milking speed: The length of time it takes for an aminal to milk out.
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Overall opinion: A farmer's overall feeling about the animal.
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Farmers' score two-year-old heifers for four traits: Adaptability to milking, Shed temperament, Milking speed and Overall opinion.
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Body and Dairy Conformation Traits
Body conformation scores from first lactation (two-year-old) heifers that are assessed by certified TOP inspectors are used to estimate breeding values for the following six traits. Each scored heifer’s data feeds into their own breeding values, as well as those of their sire, dam and other relatives.
Scroll through the images below to learn what each score represents, and how you can use them to breed improved conformation in your herd.
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Udder Conformation Traits
Udder scores from first lactation (two-year-old) cows that are assessed by certified TOP inspectors are used to estimate breeding values for the following seven udder traits. Each scored heifer’s data feeds into their own breeding values, as well as those of their sire, dam and other relatives.
Scroll through the images below to learn what each score represents, and how you can use them to breed improved udders in your herd.
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Additional breeding value traits
Calving difficulty
Calving difficulty breeding values are estimated from calving assistance information collected in progeny test herds or from cows that have been TOP inspected as heifers.
Bulls being used on yearling heifers should have a minus figure on calving difficulty with a greater minus indicating an easier calving sire.
NZAEL publishes heifer calving difficulty and cow calving difficulty breeding values for dairy bulls.
- Heifer calving difficulty:
- The heifer calving difficulty breeding value for a sire is calculated from the difficulty its calves have, being born from a two-year-old dam.
- Sires with more negative heifer calving difficulty breeding values are expected to produce calves that exhibit less calving difficulties in first calving heifers than those with more positive breeding values for heifer calving difficulty.
- Cow calving difficulty:
- The cow calving difficulty breeding value for a sire is calculated from the difficulty its calves have, being born from a three-year-old or older dam.
- Sires with more negative cow calving difficulty breeding values are expected to produce calves that exhibit less calving difficulties in cows aged 3 and over than those with more positive breeding values for cow calving difficulty.