Project code:  DB-16-03 

Duration 2 years

Team and Leader J.P. Frost and T.W.J. Keady

Organisations involved ARINI, Hillsborough; Environmental Science Division, DARD

Background and Summary

Under EC Council Directive 91/676/EEC, Nitrate Vulnerable Zones (NVZ) have been designated in catchment areas in the British Isles where nitrate from agricultural land is reported to be a source of pollution of watersources. Within NVZ the application of N from animal manures must be less than 250 kg/ha total N each year over the area of grass on the farm, and 210 kg/ha total N averaged over the area not in grass. These limits apply to all manures, including those deposited by grazing animals. 

Clearly these limits have significant implications for stocking rates on dairy and beef farms in Northern Ireland. In addition, there is the possibility of the whole UK being designated as a NVZ and that total organic N limits will be reduced further. Should this be the case there would be further restrictions on dairy cows and beef cattle stocking rates. Reducing organic N output in the manure from dairy cows and beef cattle would be one possibility for maintaining existing stocking rates on dairy and beef farms in Northern Ireland. Very little information is available on the effects of dietary manipulation on manure N output, whilst maintaining animal performance. Raw data are available at ARINI that would enable N inputs and outputs to be modelled for different diets. This would be the first time that this data would be utilised for this purpose.

The objectives of the proposed study are:

1. Collate data from across many dairy cow and beef cattle studies undertaken at ARINI, evaluating the effects of many different diet types on N input, output and animal performance.
2. Develop a model to relate N output to diet and animal performance
3. Provide recommendations to EU on N outputs from dairy cows and beef cattle fed on different diets commonly offered to dairy cattle in NI.
4. Enable stocking rates of dairy cows and beef cattle appropriate to NI production systems to be recommended.

Proposed Programme:

Data from digestibility studies undertaken at the institute during the last 10 years will be collated. A comprehensive database will be collated incorporating N inputs and outputs and animal performance with beef cattle and lactating dairy cattle at Hillsborough. The database will include information on beef cattle and lactating dairy cows differing in levels of performance offered diets consisting of varying qualities of grass silages, grass silage/maize silage mixtures and zero grazed grass supplemented with varying levels of concentrates differing in energy source and protein level. 

The data will be modelled to determine:

a ) actual organic nitrogen outputs,
b) effect of diet and animal characteristics on nitrogen output.


January 2003 study commences (subject to DARD approval)

Year 1:

i) collate database
ii) determine organic nitrogen output for diets commonly fed in Northern Ireland
iii) identify the effects of forage and concentrate characteristics on organic nitrogen output

Year 2:

i) undertake nitrogen output studies evaluating a number of different diets on organic nitrogen output and possible animal performance effects.


a) Provide dairy and beef farmers in Northern Ireland with important information on dietary factors influencing organic nitrogen output.
b) Enable development of dairying and beef systems which may operate at current stocking rates with reduced organic nitrogen output.

Project News Update

Project has been completed and information leaflets have been published and sent to all farmers.

See the final report for this project here.

FileDescriptionFile size
Download this file (FinalReportdb1603.pdf)FinalReportdb1603.pdfFinal Report - Reducing organic N outputs from dairy cows and beef cattle in NVZ's (DB-16-03)738 kB
Download this file (Book_9_-_Reducing_Organic.pdf)Reducing organic nitrogen outputsReducing organic nitrogen outputs from dairy cows and beef cattle in Nitrate Vulnerable Zones - DB-16-03 600 kB