Stocking density versus national milk output: What is the proper balance?

Given the environmental constraints coming down the track for the Irish milk sector, scientists at University College Dublin (UCD) Lyons Dairy Education and Research Facility have been seeking an answer to the fundamental question: is it feasible to maintain Ireland’s current milk output from a reduced number of cows?

The last five years have seen staff at the Lyons facility monitoring the performance of a bespoke herd of 60 high Economic Breeding Index (EBI) cows, managed specifically to allow the aforementioned issue to be addressed.

The results generated by the project to date, which is about to enter its sixth and final year, were the focal point of a recent webinar. The event was hosted by members of the UCD research team, all of whom are involved with the Lyons Systems herd.

Grazed grass

Associate Prof. Finbar Mulligan confirmed that Irish dairy farmers’ ability to incorporate high levels of grazed grass into cow diets gives them a cost of production and marketing advantage, when compared with their counterparts in many other countries.

“The last decade has seen a 40% increase in Irish dairy cow numbers. However, Irish dairy farming has a very fragmented structure, with the result that many grazing platforms are now peaked out,” Prof. Mulligan said.

“But with increasing pressure coming on the sector from a methane, ammonia and water quality point of view, growing environmental challenges may well create the tipping point that leads to a reduction in the size of the national dairy herd.

This matter would be further exacerbated if Ireland was to lose its Nitrates Directive derogation.

Challenges

Prof. Mulligan told the webinar that one way of addressing a challenge of this nature is to effect change on the basis that more milk could be produced from individual spring calving cows with a higher genetic merit, having access to higher meal feeding levels but still making optimal use of grazed grass.

The Lyons Systems herd was established in early 2016 to allow us investigate these matters. In essence, it constitutes a high-output, grass-based, spring milk production system.

The production targets set for the Sytems herd are as follows: stocking rate on milking platform – 3.4 LU/ha livestock units/hectare; stocking rate across the whole farm – 2.4 LU/ha; milk yield cow – 7,500 to 8,000kg; milk solids (ms) per cow – 625kg; six-week in-calf rate – 75%; concentrate feeding rate – 1,500kg/cow/year; proportion of diet as grazed grass – greater than 51% and proportion of diet as grazed grass and grass silage – greater than 75%.

The concentrate feeding levels built into the Systems management model are approximately four times the quantities of meal offered to cows on benchmarked low-output grass farms.

Feed budget

“The annual feed budget contains 93% to 94% grazed grass and silage on as-fed basis,” Mulligan further explained.

During the first period of the trial, milk solids (ms) per cow hovered just below 600kg per annum but then reached their target level of 625kg in 2020. With regard to fertility performance six-week calving rates rose from 83% in 2016 to 93% in 2019.

Mulligan further explained:

We are treating the results obtained in 2018 very much as outliers, due to the drought-like conditions that prevailed for much of that summer.

Grass grown across the Systems unit increased from 13,060kg/ha in 2016 to 14,535kg in 2019. During the same period, total herbage utilisation rose from 11,417kg/ha to 13,528kg.

“A high-output, grass based, spring milk production system can be profitable when built on a foundation of good grassland management while also meeting performance targets.

“Moreover, such an approach has a place in a sustainable Irish dairy industry,” Mulligan concluded.