Breeding Values

• 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.

• 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.

• 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 three 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.

• Breeding values for fertility are expressed as the percentage of cows pregnant within the first 42 days (six weeks) of a herd's mating period.

Breeding values for fertility are estimated using information that comes from calving and mating dates.

Starting in the first calving, it uses heifer calving date relative to the planned start of calving (CSD0), cow submission rate within the first three weeks of the planned start of mating (PM21) for the first three lactations as predictor traits and back calculates pregnancy rate data (PR42) for the first three lactations from calving and mating dates.

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.

• 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 calves that have a shorter gestion length than a bull that has a higher breeding value for gestation length.

• 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.

• 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.

• 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.

Calving difficulty breeding values are estimated from calving assistance information collected from farms that have good recording of calving difficulty.

Bulls being mated to yearling heifers should have a low breeding value for heifer calving difficulty. NZ Animal Evaluation publishes heifer calving difficulty and cow calving difficulty breeding values for dairy bulls.

Calving difficulty includes both direct and maternal effects. This means it considers not just the genes of the calf, but also the genes of the dam (the mother).

From a bull perspective:

• The direct effect refers to the likelihood of his calves experiencing a difficult calving when they are born.
• The maternal effect refers to the likelihood of his daughter experiencing a difficult calving when she gives birth.

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 lower heifer calving difficulty breeding values are expected to produce calves that exhibit fewer calving difficulties in first calving heifers than those with higher 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 lower cow calving difficulty breeding values are expected to produce calves that exhibit fewer calving difficulties in cows aged three and over than those with higher breeding values for cow calving difficulty.