Dairy herds in the top 25% for genetic merit earn £173 more a cow a year than herds of average genetic merit, a reassessment of the value of profitable lifetime index has shown. This translates to a £34,600 benefit in a 200-cow herd.

See also: Why genetics are critical for improving dairy cow fertility

Each profitable lifetime index (PLI) point is now said to be worth £2.09 a cow a year – a substantial rise since the previous independent assessment in 2021, when each point was worth £1.58.

The new study, commissioned by the AHDB and carried out by Promar, analysed fully bank-reconciled data from 66,000 Holstein cows across 249 herds using the consultancy’s farm business accounts.

Herds were grouped by genetic merit into a top and bottom quartile and an average group, and the higher PLI herds consistently outperformed the rest.

Performance data

This included average milk yield of 11,149 litres a cow a year in the top group (PLI £229), 9,816 litres in the average group (PLI £141) and 7,960 litres in the lowest group (PLI £30). High PLI herds also generated more calf income but had slightly higher spending on vet and artificial insemination services.

Net replacement cost was marginally higher in the top group. Feed use in this group was also higher, at 4.38t a cow a year, compared with 3.73t in the average group. And feed costs for the top group were greater, at £1,620 a cow a year, compared with £1,392.

However, any extra costs were more than offset by improved performance, leaving a margin over purchased feed of £2,949 a cow per year (top group) against £2,635 (average group).

Economic value

Promar also used the concept of a genetically influenced margin (GIM) to better pinpoint which of the financial gains were related to genetics. This meant excluding costs like electricity and buildings, while including those directly linked such as feed and replacement costs.

This gave a GIM of £2,664 a cow a year in the top PLI group, £2,350 in the average group and £2,042 in the lowest group.

 “The GIM gives us an unambiguous economic endorsement of PLI in real farming situations,” said Peter Hoyle, research and data analyst at Promar.

“It clearly quantifies the influence of genetics and confirms that the formula for PLI continues to reflect modern market demands.

“Provided there is no relationship between genetics and any other costs, the extra margin in high PLI herds will directly translate through to pre-tax profits.”

Herd management

However, he said it was important to recognise that factors other than genetics also influenced a farm’s bottom line, such as cow nutrition and comfort, and other aspects of good herd management.

“But none of these factors alone can account for the magnitude of improved performance in the higher PLI herds, and much of their advantage is unambiguously due to genetics,” he stressed.

Marco Winters, head of animal genetics at the AHDB, explained that the fourth study of its kind was commissioned in the face of significant rises in costs of production, most notably in the price of feed.

“So, we wanted to test whether the £1.58 previously calculated remained relevant today. From this new study, we can conclude that the influence of genetics on profitability remains consistent – if not even greater – in the face of rising costs.”

However, he said the scale of the index may need to be reassessed by the Genetics Advisory Forum, which periodically reviews PLI as inflation, market conditions and industry needs change.

Fully milk-recording producers can benchmark their herds’ £PLI using the AHDB’s Herd Genetic Report.

What is profitable lifetime index?

Profitable lifetime index is the UK’s national genetic index for year-round calving dairy herds. Expressed as a single financial figure, it balances milk production (34%) with feed efficiency and health (66%). PLI is designed for use as an initial screening tool for genetic selection.