Team and Leader Drs. C Ferris, D Patterson, J Stevens and R Agnew

Organisations Involved ARINI, Hillsborough and Environmental Science Division

Background and Summary

A major proportion of the Northern Ireland dairy industry will remain on its present route of improving milk yield per cow within efficient traditional type, dairying systems. In these systems the key will be to efficiently increase milk output per farm, involving a mix of keeping more cows, increasing milk yield per cow, but most importantly achieving greater milk output per labour unit on the farm. 

But a key question is how do we continue to increase output per cow within simple management and feeding systems, which minimise labour requirement, from farms often with limited acreages?

In addition, there is growing public pressure on the industry to reduce the detrimental environmental impact of some agricultural practices. Phosphorus (P) in particular is of major public concern, with excess P entering watercourses and causing eutrophication and the rapid growth of aquatic weeds and algae, with a subsequent threat to fish and aquatic life. One of the key factors contributing to this P surplus is the high level of P in livestock diets. Dairy cow concentrates are particularly high in P and in addition, high yielding dairy cows often have access to high P free access minerals.

However, a recent Dutch study has concluded that dietary P can be reduced by approximately 25% without any impact on the animal although this study was for only 1lacation. Such reductions, if sustainable, would considerably reduce the loss of P from agriculture to the environment image of dairy farming, and also reduce feed costs. However before such diets are recommended to the industry in N. Ireland it is important that they are tested in controlled, long-term study, here. In addition, a lack of detailed knowledge concerning the availability of P from individual feedstuffs, both forages and concentrate components, makes the accurate formulation of low P rations difficult.

The objectives of the present study are:

(a)  Quality the inputs of P in the feed of dairy cows on 10 dairy farms across N Ireland.
(b)  Evaluate the effect of reduced P in dairy diets over a 3-year period.
(c)  Determine the availability of P in some commonly used Northern Ireland ration ingredients.
(d)  Compare animal performance and labour input of complete diet feeding versus twice weekly feeding of silage in an easy feed system plus concentrates in out-of-parlour feeders.
(e)  Compare two grazing systems, based on maintaining high cow yields, and milk quality.


Proposed Programme.

A total of 70 autumn calving, first lactation, high genetic merit Holstein Friesians will enter the study and remain for 3 years to measure full effects. These animals will be divided into two winter feeding and two summer feeding regimes. The project will aim for milk yields of around 8500 kg per cow. Over the 3-year period half of the animals will be maintained on normal P feed levels and half on new reduced P levels.

Measurement will include: milk production parameters; labour input; herd health and detailed P utilisation (including bone composition of animals)


(a)  Enable industry to decide if new P recommendations are appropriate for N. Ireland.
(b)  Help industry to decide if simple feeding systems are appropriate and can save labour.

Project News Update

Tackling the negative environmental impact of dairy farming, especially in relation to the pollution of rivers and lakes by phosphorus, will become increasingly important in Northern Ireland. This study aims to examine options by which phosphorus inputs on dairy farms can be reduced, without having a negative effect on animal performance. The main part of the study involves a comparison of dairy cow diets containing either "normal" or "reduced" levels of phosphorus. While the study will run over three successive lactations, preliminary findings from the first year of the study indicate that animal performance was unaffected by level of phosphorus inclusion in the diet. A second part of this study seeks to examine options by which labour inputs on dairy farms can be reduced.

During the first year of this study, two feeding systems, differing in labour inputs, were examined. A high labour input system (daily offering of complete diet), was compared with a reduced labour input system (silage component of the diet offered twice weekly), with concentrates offered via an out-of-parlour feeding system). Animal performance was unaffected by feeding system, while labour inputs were reduced by approximately 50%. Summer grazing systems, differing in labour inputs, will also be examined.

This study was extended and can be found under the title "Expanding output efficiently in environmentally friendly systems (Extension) - D-19-04."

FileDescriptionFile size
Download this file (Booklet_18_-_Reducing_Phosphorus_levels_in_dairy_cow_diets-1.pdf)Reducing phosporus levelsReducing phosporus levels in dairy cow diets 226 kB
Download this file (Booklet_17.pdf) Comparisons of dairy cow management strategies Comparisons of dairy cow management strategies which differ in labour inputs 537 kB