How to assess and improve dairy herd genetics

Making the right decisions on breeding strategy can mean the difference between profit and loss for dairy farmers.

Even with the best management, there is a limit to animal performance, which can only be optimised by bringing superior genetics into the herd and breeding from the best stock.

Below, Fern Pearston, animal genetics manager at AHDB Dairy, talks through the five key steps for improving herd profitability through better genetics. 

See also: How the dairy industry is making genetic improvements

1. Make a wish list for your herd

Before you even begin to look at bull proofs or genetic differences, it’s essential to consider what you are trying to achieve from the herd. Give thought to factors such as:

  • Yield
  • Fat and protein levels
  • Somatic cell count
  • Fertility
  • Longevity
  • Maintenance feed costs

2. Assess the strengths and weaknesses of your current breeding programme

The AHDB Dairy Herd Genetic Report is available to any dairy farmers who are fully milk recording, and it quickly illustrates strengths and weaknesses within a herd.

When it comes to picking out areas to address, it is important to take into consideration your milk contract and your production system.

The chosen bulls should target weaknesses while maintaining the existing strengths of the herd.

3. Benchmark against other UK herds

Benchmarking allows farmers to compare their individual herd performance against the national average.

The outcome of benchmarking can form a practical basis for target setting – are you in the top 20% of dairy herds? Do you want to move into the top 10%? In which areas are you excelling or falling behind?

However, it is important to select bulls that are right for your management system – don’t get caught up with being at the top of the table for each trait if the breeding isn’t right for the individual situation (see tables below for targets).

4. Decide which economic profit index is right for you

Economic indices were developed to easily rank animals that transmit the most profitable combination of genetic traits to suit a specific farming system.

Breeding decisions can be overwhelming, but these indices are split into three groups, making it simple for farmers to match a bull to their system:

  • £PLI – Profitable Lifetime Index for all-year-round calving herds
  • £ACI – Autumn Calving Index for autumn block-calving herds
  • £SCI – Spring Calving Index for spring block-calving herds

The indices represent the additional profit that a high-ranking bull is predicted to return via each of its milking daughters over her lifetime (compared with an average bull of £0). As discrete systems have different costs and returns, the value and ranking of bulls on each of these three indices varies.

The £PLI should be used to compare bulls within a breed, but both the £ACI and £SCI can be used to compare genetic qualities of animals from different breeds directly with each other.

Estimated Breeding Index

As well as AHDB indices, other tools such as the Estimated Breeding Index (EBI) can also be used to help farmers identify the most profitable bulls and cows for breeding dairy replacements.

EBI is a single profit index based on data collected from Irish dairy farmers and the industry. The information is split into seven sub-indexes, all related to profitable milk production.

These include: milk production, fertility, calving performance, cow maintenance, cow management, health and beef carcass.

Each trait within a sub-index is given an economic weight (expressed in euros) and a percentage for the trait emphasis.

5. Use genetic indexes to select specific traits

A genetic index is a measure of an animal’s ability to pass its genes on to the next generation – any trait that can be measured and inherited can be influenced by breeding through the development and availability of a genetic index for that trait.  

Genetic merit is based purely on genetic information – not in combination with environmental factors – meaning the genetics of a 12,000-litre cow from a high-input system can be compared with one in an extensive herd averaging 6,000 litres.

Dairy cattle genetic indexes are expressed as Predicted Transmitting Abilities (PTA), which forecast the amount that the trait will be passed on to offspring.

Some of the most desirable traits include:

  • Milk, fat and protein

Expressed as kilograms or a percentage and can be used to increase yield and milk quality.

For example, daughters of a bull with a PTA of 650kg of milk are – on average – predicted to produce 650kg more milk in a lactation than the daughters of an average bull whose PTA is 0.

  • Somatic cell count

Expressed as a percentage ranging from -40% (good) to +40% (bad) and can be used to breed lower cell counts into dairy cattle.

For example, negative PTAs are desired – a daughter of a bull with a -10% SCC is expected to have cell counts 10% lower than daughters of a bull with an SCC PTA of 0.

  • Fertility Index

Expressed as a financial figure (£) based on calving interval and non-return rates – for every £1 increase a bull’s daughter’s calving interval is predicted to shorten by just under half a day.

For example, a +15 bull’s daughters are expected to have – on average – a seven-day shorter calving interval than the daughters of a bull with a fertility index of 0.

  • Lifespan

Expressed in terms of lactations and used to predict reduced or increased survival rates.

For example, daughters of a +0.5 bull are predicted to survive, on average, 0.5 lactations longer than the daughters of a bull with a lifespan PTA of 0; equating to around an extra 150 days in milk.

  • Lameness advantage

Expressed as a percentage ranging from -5% (bad) to +5% (excellent) and can be used to reduce lameness within the herd.

For example, a bull with a +5% lameness advantage is expected to have 5% fewer cases of lameness in his daughters (per lactation) compared with a bull with a PTA of 0%.

  • Calf survival

Expressed as a percentage ranging from -6% (bad) to +6% (excellent). This new index differs from lifespan as it is based on BCMS records of calf deaths between tagging and 10 months old – rather than the survival of animals once they are in the milking herd.

For example, a bull rated +6% is expected to produce calves with a 92% survival rate – from tagging to 305 days of age – compared with a bull with a PTA of 0 whose progeny would have an 86% survival rate.

  • Mastitis

Expressed as a percentage ranging from -5% (good) to +5% (bad) and can be used to reduce the likelihood of mastitis through genetic selection.

For example, a bull with a -5% mastitis PTA is expected to produce offspring with 10 fewer cases of mastitis per year (per 100 cows) than a bull with a +5% PTA.

  • Dairy carcass index

Expressed as a percentage ranging from -5 (bad) to +5 (good) and can be used to improve dairy cow carcasses in order to progress the 55% of UK beef that originates from the dairy herd.

For example, for each one-point increase, an improvement is predicted in both carcass conformation and average daily carcass gain in a bull’s progeny.

Which are appropriate genetic tables to benchmark against?

This may vary depending on the type of system you are operating.

Block calving systems

Key Performance Indicators

Excellent performance

Good performance

Average performance

Cows & heifers calved within the first six weeks 




Herd replacement rate




Milk solids output per hectare (kg MS/ha)




Milk from forage (litres and solids)

>5,000 litres


4,000 litres


2,750 litres


Overheads (excluding rent & finance) (ppl)




Genetic merit

Top 5% 

Top 25% 

Top 50% 

All-year-round calving

Key Performance Indicators

Excellent performance

Good performance

Average performance

Pregnancy rate (%)




Age at first calving (months)

23 months (but not less than 22 months)

24 months

27.5 months

Total purchased feed costs (ppl)

8,000 litres – 7ppl

10,000 litres – 7.8ppl

12,000 litres – 8ppl

8,000 litres – 7.5ppl

10,000 litres – 8.5ppl

12,000 litres – 8ppl

8,000 litres – 8ppl

10,000 litres – 9ppl

12,000 litres – 9.5ppl

Average daily lifetime yield (litres/day)

>19 litres

14.5 litres

12.5 litres

Overheads (excluding rent & finance) (ppl)




Genetic merit

Top 5%  

Top 25% 

 Top 50%