The dairy centre at the College of Agriculture, Food and Rural Enterprise’s (CAFRE) Greenmount College in Co Antrim has 180 autumn-calving Holstein cows. Average yield is 8,853l at 4.10% butterfat and 3.40% protein.

With the herd well known for producing high yields, most farmers are suprised to hear that the average genetic index for milk volume across the herd is a negative value.

Under the UK-based Profitable Lifetime Index (PLI) system, the average Predicted Transmitting Ability (PTA) for milk in the Greenmount herd is -164kg. This means that CAFRE’s average cow will pass on genetics that give her daughter the potential to produce a milk yield that is 164kg below the genetic potential of the average Holstein heifer in the UK.c

At Greenmount, sires from the top 25% of PLI rankings are selected to improve the milk protein, fertility, lifespan and somatic cell count indexes

The baseline for a Holstein heifer under the PLI system is almost 8,300l, so having a low or negative PTA for milk will still give the genetic potential to deliver significant yields, probably in excess of 9,000l as mature cows.

Of course, a cow’s breeding index is only half of the picture, as the PTA of the bull is also added in to give the overall genetic merit of the heifer.

At Greenmount, sires from the top 25% of PLI rankings are selected to improve the milk protein, fertility, lifespan and somatic cell count indexes. This often results in bulls that have relatively low PTAs for milk being used. For example, across all bulls used last winter at Greenmount, the average PTA for milk was +56 kg.

there is more to high milk yields than genetic potential

With average yields of almost 9,000l, the Greenmount example shows that selecting sires with low PTAs for milk does not mean milk yields will tumble.

This is because the cows at the CAFRE dairy centre already have the genetic potential to produce high yields in terms of volume.

Also, there is more to high milk yields than genetic potential – the likes of fertility, management, forage quality and concentrate feed rate all have a big influence.

The same is true in many commercial dairy farms, where it is the likes of fertility and animal health that are the main limiting factors affecting milk yields, not the genetic potential of cow for milk volume.

Results

CAFRE’s approach to breeding for milk components appears to be working. Across the herd, the average PTA for butterfat and protein are +0.10% and +0.08% respectively. This is having an effect in the bulk tank, as the herd’s average butterfat and protein levels are above the Northern Ireland average of 4.04% and 3.29%.

Selecting bulls for fertility is often a slow burner and like milk volume, other factors can be at play aside from genetics, such as herd management and health status.

But picking bulls based on fertility index has improved the genetic potential of the Greenmount herd. For example, the average cow at Greenmount has a fertility index of +5.5.

Analysis of individual cows in the Greenmount herd shows that the breeding sub index for fertility does have an effect on actual fertility.

It backs up research by the Agriculture and Horticulture Development body, which suggests that every 1.0 increase in fertility index can reduce calving interval by 0.6 days and improve non return rates by 0.25%.

Breeding strategy on Dairylink farms

Dairylink Ireland participants with autumn-calving cows are currently finalising sires for use in the upcoming winter breeding season.

Several programme participants are going down a similar route as the Greenmount herd, by selecting bulls with high PTAs for butterfat, protein and fertility.

These farmers are not focusing primarily on a high requirement for milk PTA, as this could exclude a lot of bulls that have the potential to lift milk components and improve fertility.

If you’re going to improve variables like butterfat, protein and fertility, you need to select for them quite aggressively

This is not a major issue for Dairylink farmers, as their cows already have of plenty of genetic potential to deliver high yields.

Indeed, focusing on breeding for better fertility and not milk volume could be a more effective way of increasing annual milk yields per cow.

“If you’re going to improve variables like butterfat, protein and fertility, you need to select for them quite aggressively to make any significant in-roads,” said Dairylink adviser Aidan Cushnahan.

He has drawn up a selection criteria for programme farmers to apply when choosing bulls. When picking bulls from the PLI list, the PTA butterfat and protein should be at least +0.08% each and the fertility index should be at least +5 days.

Aidan has also included a requirement for at least +100kg for the PTA for milk.

Dairylink farmers are also assessing bulls that are listed under the Irish Estimated Breeding Index (EBI) system

This has been set relatively low, as it allows the best bulls for milk components and fertility to remain in the mix.

There are over 70 Holstein bulls in the PLI system that meet Aidan’s minimum criteria for all four traits.

Dairylink farmers are also assessing bulls that are listed under the Irish Estimated Breeding Index (EBI) system.

Aidan’s suggested criteria under EBI is for bulls to have milk between 0 to +200, butterfat of at least +0.15%, protein of at least +0.10% and a fertility sub index above €100.