In April 2022, NZAEL launched the next round of enhancements to its genetic evaluation system for dairy bulls. Read more about these changes here.
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.
Trait definitions
The nine traits in BW are categorised as either Production efficiency traits or Robustness traits.
Production efficiency
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 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.
Robustness
- 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 fertility are expressed as the percentage of cows calving within 42 days (6 weeks) of the start of calving.
- A higher fertility breeding value indicates that a bull is expected to have more early calving daughters than a bull that has a lower breeding value for fertility.
- 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 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 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.
Farmer opinion
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.
Click the arrows on 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.
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.
Click the arrows to learn what each score represents, and how you can use them to breed improved conformation in your herd.
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.
Click the arrows to learn what each score represents, and how you can use them to breed improved udders in your herd.
Additional traits
Gestation length
Gestation length breeding values are estimated from the difference between a cows planned calving date given her mating date, and her actual date of calving. Bulls with negative gestation length breeding values are expected to have calves that are born earlier than the average gestation length.
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.