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Future-proofing winter-milk systems

The Johnstown Castle dairy herd was established in 2003 to provide a base for winter-milk research within Teagasc.

Johnstown Castle winter-milk herd receiving their indoor experimental diets 

 The Johnstown Castle dairy herd was established in 2003 to provide a base for winter-milk research within Teagasc.

Readily available, high-quality pasture during a long grazing season makes the Irish dairy industry highly seasonable. During the winter period, most spring-calving cows are non-lactating. As a result, winter-milk is a vital subsector in the dairy industry to achieve a consistent daily supply of quality fresh milk to our domestic market. In 2021/22, there were approximately 1,286 registered liquid milk producers that supplied just over 8% of national production (915 million litres). A further 600-800 producers are estimated to produce winter-milk under various non-registered price incentive schemes.

Due to the nature of winter-milk production from conserved forages, sustainability challenges such as reducing dependency on imported protein sources and reducing greenhouse gas emissions are particularly pertinent to these producers. Teagasc researchers have been performing experiments with the Johnstown Castle winter-milk herd to investigate strategies for improving the sustainability of winter-milk systems.

Investigating strategies

At the Johnstown Castle farm, a large emphasis is placed on maximising the proportion of high-quality grazed pasture in the cows’ diet. Current grassland management tools provide a strong framework for winter-milk producers to achieve this, subject to some slight adjustments. During the autumn period,
pre-grazing yield should be maintained below 1,800kg dry matter (DM)/ha, as the freshly calved cow can struggle on heavy autumn covers. Furthermore, a closing average farm cover of 650kg DM/ha should be targeted to allow a higher opening farm cover in early spring.

Strict breeding management rules (e.g. ten-week breeding period and no recycling of cows between breeding seasons) ensure that the herd has an optimal calving pattern for maintaining high feed efficiency, reducing annual feed costs and minimising the amount of surplus milk sold during November to February.

Experimental diets

During the winter-feeding period, there is an increased demand for high-protein feed ingredients due to the nature of conserved feeds. Currently, there is a major deficit in these ingredients, with the EU agricultural sector importing around 71% of its requirements. Home-grown or EU-grown protein sources (e.g. field beans and rapeseed) could provide economic and environmental benefits to European farmers, as well as food security to Europe as a whole. With this in mind, researchers performed an experiment to compare a standard winter-milk diet of grass silage, maize silage and concentrate containing imported protein sources with a diet of grass silage and concentrates containing native cereals and protein sources (i.e. barley and field beans). Initial life cycle assessment modelling suggests a lower carbon intensity per hectare and per kg of milk when cows consumed the home-grown treatment. However, reduced animal performance was observed (-20kg of milk solids/cow/lactation) when compared with cows fed the standard treatment as there were several dynamic factors among the treatments (i.e concentrate ingredients, concentrate feeding level, maize silage inclusion), it was difficult to ascertain the cause of the reduced milk production performance.

In a follow-up experiment, researchers compared home-grown concentrate protein ingredients (i.e. field beans and rapeseed meal) with imported concentrate protein ingredients (i.e. soybean meal and maize distillers). The experimental concentrates were formulated to be similar in terms of crude protein and energy concentration. Like the previous experiment, cows consuming the home-grown concentrate protein ingredients reduced milk production performance (-15kg of milk solids per cows across the 14-week experimental period) when compared with cows fed the imported concentrate protein ingredients. This was likely due to inadequate metabolisable protein/amino acid supply.

The experiments investigated the full replacement of imported ingredients, whereas currently in the industry, lower inclusion levels of home-grown protein sources occur in tandem with imported soybean inclusion, resulting in satisfactory animal performance. Furthermore, experiments from University College Dublin have demonstrated that when lower feeding rates and lower inclusion levels are offered to grazing dairy cows, there is no effect on milk production by the inclusion of home-grown protein sources.

 PhD scholar Neil Maher presenting experimental results to the Teagasc Moorepark Walsh Scholar discussion group

Reducing methane production

Enteric methane is responsible for 62.5% of Irish agricultural emissions; thus, the reduction of methane will play a critical role in achieving agriculture’s GHG reduction target of 25% by 2030. There are currently several mitigation solutions available such as animal genetics, pasture quality and methane-reducing feed additives.

At the Johnstown Castle farm, the researchers investigated a feed additive containing an ingredient (3-NOP) which potentially inhibits methane formation in the rumen. The feed additive was added to the diet feeder with the other dietary ingredients each morning and fed to the corresponding treatment group. Cows fed the feed additive treatment produced less methane (330g/day) when compared to cows fed the control diet not containing the feed additive (447g/day) – a 26% reduction. In addition, cows fed the feed additive treatment produced slightly higher milk solids yield (2.50kg/day) when compared to cows fed the control diet (2.45kg/day), a 2% increase.

Although home-grown protein sources can reduce the carbon intensity and increase the protein self-sufficiency of Irish winter-milk systems, reduced animal performance was observed. Future experiments will investigate strategies to alleviate this reduced animal performance, such as rumen-protected amino acid supplementation.

Finally, the methane-reducing feed additive that was fed to Irish winter-milk cows is promising; however, an array of mitigation technologies will be required to ensure that agriculture can meet its climate targets while also being mindful of economic and social sustainability. 



 Johnstown Castle winter-milk herd in numbers:

 90 high-EBI Holstein Friesians

370-day calving interval

6-week calving rate of 78%

Over the last four years, the herd has averaged:

7,450kg of milk, consisting of

  1. 66% protein, 4.52% fat, and 616kg of milk solids.

1,602kg of concentrate is supplemented per year.


This research was funded by the Irish Dairy Levy administered by Dairy Research Ireland, the Teagasc Walsh Scholarship Programme and VistaMilk.


Joe Patton, Hazel Costigan, James Dunne and Karina Pierce are gratefully acknowledged for their contributions to the research.


Michael Dineen
Senior Research Officer
AGRIP, Teagasc Moorepark.

Neil Maher

Walsh Scholar
Teagasc Moorepark.

Aidan Lawless

Dairy Unit Manager
Teagasc Johnstown Castle.

Ben Lahart

Research Officer

Teagasc Moorepark.

[picture credits] Teagasc