Breeding Worth
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Genetic merit sets the foundation for the performance of your dairy herd. Breeding Worth (BW) is an index that ranks cows and bulls on their ability to meet the National Breeding Objective (NBO); to breed dairy cattle that efficiently convert feed into profit. This page describes the traits, split into 'Production Efficiency' and 'Robustness', contributing to an animal’s BW ranking. By understanding BW, you can make informed decisions to improve your herd's profitability. The page guides you through five ways to enhance your herd's BW. It also introduces reliability, which measures the confidence in each animal’s BW evaluation.
Further reading
What is Breeding Worth?
Our National Breeding Objective (NBO) in New Zealand is to breed dairy cows that efficiently convert feed into profit. Cows and bulls are ranked on their ability to meet this objective using the index known as Breeding Worth (BW).
Using BW to make decisions on which bulls and cows to breed replacements from helps you achieve a genetically strong herd and increasing farm profit each year. Your breeding plan will set you up for future seasons and have a lasting impact on your herd. That’s where 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.
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 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.
Ten traits included in Breeding Worth
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 individual traits within BW are split between 66% production efficiency traits and 34% robustness traits (see 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.
Liveweight
Included in BW as the 'efficiency' part of production efficiency. There is a positive relationship between liveweight and milk production and between liveweight and feed requirements for maintenance and growth. If not included, selection on milk production 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 tank somatic cell count being lower.
Fertility
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 days in milk 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.
Reliability
The other number that is reported alongside BW is reliability. Reliability measures how much information has contributed to the BW evaluation for that animal. Reliability is shown 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.
Five ways to a high Breeding Worth (BW) herd
Genetic merit sets the foundation for the performance of your dairy herd. The information below guides you through five ways to enhance your herd's Breeding Worth. Each action contributes to building a stronger herd, and the more strategies you combine, the better the results.
The national herd improves every year, and the value of this compounds over time. However, the underlying foundation is herd reproductive performance. Getting more of the right cows in-calf to high-genetic merit bulls will enable options to select the best replacements and accelerate genetic gain.
Use high BW sires
If you can only do one thing – choose high BW sires. Select the bulls that aligns with your goals for the animals you want to be milking. The higher BW of the bulls you use, the faster your herd’s genetic gain.
View the top bullsTarget replacements from your top BW cows and heifers
Keeping replacements from top BW cows and using AI over your heifers gives you more options when selecting heifer calves to rear. It also means calves from those top heifers will be in the herd one year sooner – a boost to genetic gain.
Read more on heifer matingKeep accurate and detailed records
From pregnancy scanning through to accurate calving records, data is key to your herd BW and reproductive performance. Detailed calving and mating records support better mating and culling decisions, including tracking cases of calving difficulties.
Read more on accurate recordingUse DNA parentage verification
Around 25% of calves are mismothered at birth or when completing data entry. DNA parentage verification helps avoid accidentally keeping replacements from low performing cows, preventing a loss in genetic gain.
Read more on genomicsMeasure cow performance
Regular herd testing helps you accurately identify which cows are productive and which cows are costing you. Liveweight is a key component of BW. Consider weighing the herd to gain insights into overall efficiency, and to identify individual cow performance.
Read more on cow performanceChoosing the best bull for your herd
No two bulls are the same. Two bulls can have exactly the same BW but will have reached it through very different strengths.
Which bull is the best?
In the table below, Bull A has superior milk production traits while Bull B has superior Fertility, Somatic Cell and BCS. Out of these two bulls, the best bull for your herd is the one that fits your breeding objective.
| BULL A | BULL B | |||||
| Trait | BV | BW contribution |
BW $546/75 |
BV | BW contribution |
BW $546/75 |
| Production | ||||||
| Milkfat (kg) | 67 | $353 |
$523 |
55 | $290 | $363 |
| Protein (kg) | 45 | $319 | 38 | $270 | ||
| Milk Volume (L) | 699 | -$80 | 866 | -$100 | ||
| Liveweight (kg) | 41 | -$69 | 58 | -$97 | ||
| Robustness | ||||||
| Fertility (%) | 1.5 | $9 | $23 | 6.8 | $40 | $183 |
| Gestation length (days) | 1.3 | -$3 | -8 | $10 | ||
| SCC (score) | -0.09 | $4 | -0.75 | $35 | ||
| Functional survival (%) | 2.5 | $5 | 4.4 | $8 | ||
| BCS (score) | -0.02 | -$3 | 0.33 | $58 | ||
| Udder overall (score) | 0.2 | $11 | 1.2 | $32 | ||
International dairy sires
Choosing the right genetics is crucial for New Zealand's pasture-based grazing systems. The performance of international bulls’ daughters depends on how similar the environment and farming systems are. This means that how well daughters perform overseas doesn’t always indicate how they’ll do here.
Interbull, an international bull genetic evaluation organisation, generates breeding values for international dairy sires. They collect sire data from around the world and estimate breeding values for New Zealand based on known relationships between our breeding values and other countries estimated breeding values. NZ Animal Evaluation receives these breeding values three times a year after each Interbull Animal Evaluation run.
International bulls aren’t progeny tested here, leading to less data and fewer comparisons. As internation bulls sire more daughters in New Zealand, their performance data will be gradually included in Interbull’s breeding values, making them more reliable.
When selecting an international sire, consider these two factors:
Fertility: In New Zealand, poor fertility impacts profitability because our cows calve once-a-year. Overseas, cows often calve year-round, reducing the economic impact of poor fertility. Some international bulls can have lower genetic fertility than New Zealand bred bulls, but many still have daughters with good fertility here.
Production efficiency: The ratio of milksolids to mature liveweight is vital for cow profitability in New Zealand. International bulls often sire daughters with higher mature liveweights, increasing feed costs. These cows need to produce more milk to offset the extra feed required.
Choosing the right sires can lead to better performance and profitability on your farm.
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