Breeding Worth


24 min read

What is Breeding Worth? How BW is calculated How BW impacts herd value and farm profit International Dairy Sires Six Steps to a High BW Herd

Breeding Worth (BW) is an index that ranks cows and bulls on their ability to breed profitable, efficient replacements. This page explains how BW is used to create herds resilient to changes and disease, therefore increasing farm profits. It describes ten traits, split into 'Production Efficiency' and 'Robustness', contributing to a cow's BW score. By understanding BW, you can make informed decisions to improve your herd's profitability. It also introduces the concept of 'reliability', which measures the confidence in a BW evaluation.

Breeding Worth (BW) is the index used to rank cows and bulls on their expected ability to breed profitable, efficient replacements. Herds that are more resilient to farm system changes and illness are going to make you more profit as their rates of production vs input are likely to be higher and more reliable. The Breeding Worth Index helps farmers achieve a genetically strong herd and benefit from greater genetic gains faster, which means you can increase your farm profit more and more each year.

What is Breeding Worth?

Our National Breeding Objective (NBO) in New Zealand is to breed dairy cows that efficiently convert feed into profit. We rank cows and bulls on their ability to meet this objective using the index known as Breeding Worth (BW).

There are ten traits included in BW that have been identified as having a direct economic value to the NZ dairy sector. These traits can be categorised as either 'Production efficiency' traits or 'Robustness' traits.

The effective emphasis of the ten individual traits within BW are split between 63% production efficiency traits and 37% robustness traits (see pie chart). Updating the liveweight evaluation and adding udders to BW has resulted in a slight reduction in the emphasis on production efficiency traits and an increase in the emphasis on robustness traits.

Effective emphasis on individual traits within BW pie chart

Production efficiency traits

Milk protein and milk fat yield
Cows that produce more protein and fat will bring in more income for the dairy farm business.

Milk volume
Cows that produce the same quantities of fat and protein but with more volume incur costs to the dairy farm business.

Included in BW as the 'efficiency' part of production efficiency. There is a positive correlation between liveweight and milk production and between liveweight and feed requirements for maintenance and growth. If not included, selection would lead to successive generations getting heavier and the costs to feed these heavier cows would increase.

Robustness traits

Somatic cell
Cows with lower somatic cell counts have better survival, lower costs due to mastitis, and fewer penalties due to bulk somatic cell count being lower.

Fertile cows have better longevity and lower empty rates. Higher in-calf rates to high genetic merit bulls through artificial insemination reduces the need for natural mating bulls.

Gestation length
Short gestation length increases the number of days in milk, allows a cow more time to recover from calving and provides an opportunity for a condensed calving period.

Functional survival
Cows that fail for functional reasons such as udder breakdown have reduced longevity and lead to increased costs associated with rearing more replacements. Having more mature cows in the herd (the engine room of the herd) will positively impact profitability.

Body condition score
Cows that maintain condition easily can be dried off later. This increases lactation length and boosts potential production and profit, compared with cows that lose condition easily.

Udder overall
Cows with poor udder conformation add costs to the farm system due to an increased risk of developing mastitis or being culled due to their udder failing.

How Breeding Worth is calculated

BW is calculated by combining breeding values with the appropriate economic values for each trait and adding them all together.

Breeding Values (BV): An estimate of a cow or bull's genetic merit for a trait. e.g. Will his or her daughters produce milksolids efficiently, and be robust herd members?

Economic Values (EV): An estimate of the future dollar value of a unit change in each trait to an NZ dairy farmer.

BW is expressed as $ net farm income per 5 tonnes of dry matter. A bull whose BW is $300 is expected to produce daughters that are on average $150 (half of the bull’s BW) more profitable than a bull whose BW is $0. Importantly, animals can be compared using BW across different breeds, herds and ages.

How Breeding Worth impacts your herd value and farm profit

Herd quality has a direct impact on a farmer’s profitability. Herds that are more resilient to farm system changes and illness are going to make you more profit as their rates of production vs input are likely to be higher and more reliable.

The Breeding Worth Index helps farmers achieve a genetically strong herd and benefit from greater genetic gains faster, which means you can increase your farm profit more and more each year.

Your breeding plan will set you up for future seasons and have a lasting impact on your herd. That’s where Breeding Worth (BW) can help you make informed decisions to improve your herd’s profit through genetic gain.

The information you choose to focus on will depend on what your herd objective is. While you won’t see changes immediately in your herd, the decisions you make now will have an impact on your production for several seasons. Knowing you have accurate and meaningful data in Breeding Worth is critical to aid your decision-making.


The other number that is reported alongside BW is reliability. Reliability measures how much information has contributed to the BW evaluation for that animal. We show reliability on a scale of 0 to 100%, with reliabilities closer to 100% representing more information on progeny and ancestors being available for that bull.

High-reliability bulls are unlikely to have large shifts in their BW when more daughters are added. In contrast, bulls with lower reliabilities are more likely to have large shifts in their BW as we add more daughters. Learn more about reliability.

Delving deeper - no two bulls are the same

Two bulls can have exactly the same BW but will have reached it through very different strengths. The best bull for your herd is one that fits your herd breeding objective.

International Dairy Sires

Breeding values for international dairy sires are generated by Interbull, an international genetic evaluation organisation.

Interbull have an animal evaluation system which collates sire breeding values from all around the world. The relevance of how a bull’s daughters are performing overseas depends on how similar the environment and farming systems are between NZ, and the home country of each daughter.

Most dairy farms in New Zealand are predominately pasture based, and almost all NZ dairy cows graze pasture every day of the year. This makes our farming conditions somewhat unique, which means genetics that work overseas do not necessarily work well here.

Interbull account for the relationship between NZ and other countries, and then use daughter information from around the world as best they can to create NZ specific breeding values. 

These breeding values are received by NZAEL after each Interbull AE run (three times each year).

Because of the differences between NZ and other countries, Interbull breeding values on the NZ scale often have low accuracy. As a bull accumulates daughters in NZ, the performance information will be gradually blended with Interbull breeding values, until the international data is disregarded and the BVs are based entirely on the performance of a bull’s NZ born daughters.

Why are BWs for international bulls less accurate?

  1. NZ farming conditions are very different to the rest of the world.
    This means that daughter performance overseas is not a good indicator of how a bull’s daughters will perform in NZ
  2. NZ performance data is often limited.
    International bulls are not progeny tested in NZ, which means that there is less data collected, and they are compared against fewer bulls.

Why are BWs for international bulls typically low?

  1. Fertility
    In NZ, poor fertility in dairy cows has a very big impact on profitability. Overseas the economic impact is substantially less, as cows are often calving year around. For this reason, international bulls often have lower genetic fertility when compared to NZ bred bulls.
  2. Production efficiency
    The ratio of milksolids to mature liveweight is a key driver of cow profitability in NZ. Internationally bred bulls tend to produce daughters who have a higher mature liveweight. This creates cost for a farmer, as that animal requires more feed to be reared, and more feed for maintenance once fully grown. High liveweight cows must produce additional milk to justify the cost that their liveweight incurs, if they are unable to do so, a penalty will come through in their BW.

Six steps to a high BW herd

Genetic merit sets the foundation for the profitability of your dairy herd. The info below guides you through six steps to enhance your herd's genetic worth. The genetic merit of your herd will set the foundation for the profit you can achieve. Check out the six steps you can take to close that gap. Make these changes to help boost your annual profit.

The national herd improves every year, and the value of this compounds over time. The difference between the genetic merit of the median herd, and a herd in the top 10% is estimated to be worth $25,086 in profit every year.

Step 1: Use young sires

Using young sires with superior genetics can accelerate the rate of genetic improvement within your herd.

Read more

Step 2: Keep accurate and detailed records

Calving and mating records are used to assign a mother and a father to your replacement heifers.

Read more

Step 3: Use DNA sire verification

Mix ups with parentage will slow the rate of gain in your herd. Twice as many animals are DNA verified in top-ranking herds, compared to mid-range herds (top range 42%, mid range 24%). DNA sire verification is an effective tool to correct any mistakes.

Step 4: Measure cow performance

Did you know, 75% of top-BW herds are herd tested at least 3 times/season (compared to 60% of mid-range herds). Using herd testing, weighing, calving and mating records provide valuable information to cow performance.

Step 5: Use AI over your best heifers

Using AI over your best heifers will give you more choice when it comes to picking heifer calves to rear. It also means calves from those top heifers will be in the herd one year sooner.

Step 6: Target replacements from top cows

Use BW to help you decide which cows to keep replacement heifers from. Target your top BW cows.

Last updated: Feb 2024
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