With 98% of ammonia emissions in NI coming from agriculture, there is a major focus on how farms can reduce emissions to help protect sensitive habitats.

That was a key talking point at the dairy open day held at the Agri Food and Biosciences Institute (AFBI) research centre in Hillsborough last week.

In his talk, Dr John McIlroy said six “relatively low-cost” measures can reduce ammonia emissions by up to 43% when they are all applied on a typical NI dairy farm.

The measures are reducing dietary crude protein from 18% to 16%, extending the grazing season by two weeks, scraping cubicle houses every two hours, covering slurry stores, spreading slurry with a trailing shoe and using protected urea fertiliser.

Switching from a splash plate to a trailing shoe was described as “the single most effective measure”, as it can reduce ammonia emissions from slurry spreading by 60%.

Emissions from a fully housed dairy herd with an average milk yield of 8,500l were compared to a herd which is grazing for half the year and is averaging 7,220l.

The fully housed system produces 57% more ammonia per cow than the grazed herd. This is mainly due to increased slurry production as ammonia forms when urine and faeces mix.

Even when calculated in terms of emissions per litre of milk, ammonia from the fully housed herd is still 33% higher than the grazing system.

Other mitigation measures which are much more expensive to implement and mainly relate to livestock housing design were also assessed by AFBI scientists.

Slurry acidification systems, which lowers the pH of slurry from 8.5 to 6.0 can cut ammonia emissions by 73%.

Similarly, a system which separates urine and faeces and then uses sulphuric acid to scrub ammonia from the air over floors and stores can cut emissions by 70%.

Dairy cow diets

Adjusting dairy cow diets to cut ammonia was expanded upon by Dr Conrad Ferris in his talk.

He said “with careful formulation” there is scope to reduce total crude protein levels to 16% and this will lead to lower ammonia emissions with no impact on cow performance.

Other research into dairy cow diets relates to phosphorus (P) losses from farms which is a long running water quality issue in NI.

Diet formulation is a key part of addressing the problem as between 60-70% of the P consumed by dairy cows ends up in manure.

Research at AFBI found that cutting P levels in concentrates by 38% in the winter and 46% in the summer had no adverse effect on feed intake, milk yields and milk composition.

Room to improve costly heifer rearing

Figures presented by Dr Gillian Scoley show that heifer rearing is an expensive part of dairy farming, as it makes up to 20% of total production costs.

The most recent CAFRE benchmarking results found the average cost of rearing a dairy heifer to the point of calving is £2,156.

This cost varies widely between farms, with an average difference of £1,134/heifer between the top 25% and bottom 25% of benchmarked herds.

A key issue is calving age, with the average age of first calving on NI dairy farms currently sitting at 27.7 months. Compared to calving at 24 months, it costs an extra £324/heifer to calve down at the NI average.

Cold, damp air in calf houses reduces the amount of energy available for growth and increases the risk of infections in calves

Monitoring body weight is proven to help hit the target calving age. Calves should be 40% of their mature body weight by nine months of age (puberty), 55% by 14 months (breeding) and 90% by 24 months (calving).

An AFBI study carried out on 66 dairy farms in NI, found improvements to calf housing could be made on many units, which would help pre-weaning performance.

Scoley said cold, damp air in calf houses reduces the amount of energy available for growth and increases the risk of infections in calves.

Across the 66 farms, average temperature was below 10°C in calf houses for 57% of the time. Also, average humidity was above the target range for 82% of the time.

Measurements of the dry matter of bedding on project farms were better, with the average figure of 70.2% being just above the 70% target. That said, there was a range across farms, with the dry matter of bedding ranging from 35.5% to 86.8%.

Scoley said “small changes” to calf house design and heifer rearing practices to ensure calves are warm, dry and well ventilated will make it easier to achieve the target weight gain of 0.8kg per day.

This includes having adequate air inlets and outlets for ventilation and drainage systems on floors.

Almost 90% of Holstein semen is sexed

The UK dairy industry has the highest rate of sexed semen use in the world, according to Marco Winters from the Agriculture and Horticulture Development Board (AHDB).

In his talk at AFBI Hillsborough, Winters said 84% of all dairy semen used in the UK is now sexed, with the figure standing at 88% for the Holstein breed.

Over 70% of dairy semen used in the UK is from genomic sires.