When sourcing dairy replacements, the overall Economic Breeding Index (EBI) figure is typically the first metric a farmer looks at. A high overall EBI is a fantastic baseline indicator of a profitable animal. However, buying based only on the headline number can mean missing out on the nuance of what makes a cow truly suited to your farm. For Irish spring-calving, grass-based systems, the real secret to long-term profitability lies hidden in two crucial sub-indices: Fertility and Milk Production.

Here is why digging into the sub-indices is critical before you buy, and how understanding them can transform your herd’s performance.

The Milk Production Sub-Index: Getting Paid for Solids

The Milk Production sub-index is designed to reward the production of milk solids (fat and protein yield) over sheer milk volume, which aligns perfectly with the A+B-C milk payment system used by Irish co-ops. Driving milk solids per cow is the most direct route to increasing your milk cheques without necessarily driving up your feed costs.

Research on commercial Irish dairy farms has demonstrated that herds with a higher genetic merit for milk traits achieve superior milk composition and, consequently, higher milk prices (Ramsbottom et al., 2012). Selecting animals with a strong milk sub-index ensures that you are bringing in genetics capable of efficiently converting grazed grass into the highly valued components the market demands. Furthermore, high EBI cows have been shown to be significantly more efficient in terms of the milk solids they produce relative to their bodyweight (Evers et al., 2021).

The Fertility Sub-Index: The Engine of the Spring-Calving System

While milk solids dictate the size of your milk cheque, fertility dictates whether you get to cash it year after year. The Fertility sub-index primarily measures a cow’s calving interval and her survival to the next lactation (Ramsbottom et al., 2012).

In a compact, seasonal grass-based system, a cow that slips her calving date or fails to go back in calf is a massive cost to the business. Excellent fertility genetics help maintain a tight calving block, ensuring peak herd demand coincides with peak spring grass growth. Animals with poor genetic merit for fertility often face delayed cyclicity, struggle with a negative metabolic status, and fail to maintain a 365-day calving interval (Butler & Moore, 2018). Simply put, cows with a high fertility sub-index last longer in the herd. This longevity reduces your costly replacement rates and gives you the option to sell surplus stock for additional income.

Finding the Balance

A high overall EBI driven by a balanced combination of these two sub-indices creates an animal practically custom-built for the Irish dairy industry. These cows provide the perfect blend of output and resilience. According to data from the ICBF and Teagasc, animals selected for both high milk solids and fertility show superior lifetime profitability and maintain a lower environmental footprint per kilogram of milk solids produced compared to lower EBI animals.

The Complete Picture: Factoring in the Wider EBI Traits

While Milk and Fertility are the heavy hitters—historically driving the bulk of farm profitability—the ICBF continuously updates the EBI to reflect modern farming realities. The index is comprised of eight sub-indices, and a smart purchasing strategy involves reviewing the complete genetic profile. When sourcing stock, you must also consider:

• Maintenance: With recent ICBF updates shifting heifer rearing costs into this sub-index, it is a vital metric for matching cow size to your land type and feed budget. A positive maintenance figure indicates a more feed-efficient, moderate-sized cow.

• Health: This sub-index targets mastitis, lameness, SCC, and increasingly, genetic resistance to TB. Buying heifers with strong health figures reduces veterinary interventions and labour demands.

• Calving & Beef: Calving difficulty and gestation length dictate how easily new stock transitions into the milking herd. Meanwhile, the Beef sub-index ensures there is residual value in cull cows and dairy-beef calves—a growing focus in the industry driven by updated Teagasc economic models.

• Management & Carbon: Selecting for good temperament and milking speed improves the daily working environment. The Carbon sub-index helps ensure your herd remains environmentally sustainable and compliant with future emissions targets.

Sourcing the Right Stock for Your System

A high overall EBI driven by a balanced combination of all sub-indices creates an animal practically bred for the Irish dairy industry. At Grasstec Group, we understand that every farm has a different baseline and distinct breeding goals.

That is why our Livestock Sourcing and Sales service does not just look at the headline EBI figure. We dig deep into the ICBF data, zeroing in on the fertility and milk sub-indices, while balancing maintenance, health, and beef traits to match the exact requirements of your system.

Whether you are seeking Friesians or crossbreds, we ensure the genetics you buy will drive profitability on your farm for years to come.

For more information on sourcing top-tier dairy livestock, visit our sourcing services here: https://www.grasstecgroup.com/livestock-services/source-quality-dairy-livestock/