Defra - Department for Environment, Food and Rural Affairs.

Science Search

Science and Research Projects

Return to Science Search homepage   Return to Project List

Optimising the efficiency of dietary nitrogen use to reduce emissions and waste in dairy systems - AC0122

Dairy farmers typically feed diets with higher concentrations of crude protein (CP) than the animals require, ensuring an adequate supply of metabolisable protein to achieve the maximal production of milk and milk protein. Dietary protein is used inefficiently by dairy cows, with approximately 72% of nitrogen intake excreted in manure. Nitrogen excretion is a significant environmental concern due to nitrate (NO3) leaching contributing to aquatic eutrophication, and nitrogen lost to the atmosphere as ammonia (NH3) and nitrous oxide (N2O). Nitrogen excretion in manure is highly correlated with dietary nitrogen intake, thus one option for reducing nitrogen excretion is to feed less protein. Thus while there may be clear benefits of offering lower protein diets, this strategy will only be acceptable to dairy farmers if it can be achieved without a significant reduction in milk and milk solids production and without having any detrimental effects on health and fertility.
Objectives: The overall objective of this project is to determine the longer-term impacts of feeding lactating dairy cows diets lower in protein concentration than currently used by UK dairy farms (i.e. reduced nitrogen intake) over consecutive lactations on milk production and composition, fertility, body condition, and health. These effects will be measured in cows of high genetic merit fed maize- or grass-based diets. The effects of incremental reductions in dietary nitrogen intake on manure output and associated excretion of nitrogen in urine and faeces will also be measured across multiple lactations, parities, and stages of lactation. In addition, the effects of feeding lower protein diets to growing heifers on growth rate, manure output, nitrogen excretion in urine and faeces, and subsequent lactation performance will be measured.

Results of these experiments will be integrated using simulation models to predict effects of feeding lower protein diets on emissions of nitrous oxide (N2O), ammonia (NH3), and nitrate (NO3) from dairy farms of varying typographies. Together these and current farm survey data will be used to assess the economic impacts of reduced protein feeding on UK dairy farms.

The specific objectives of this research are:

1. To determine the scope for increasing efficiency of N use in dairy systems based on a review of published and archived research data.

2. To measure the longer-term effects of incremental reductions in protein concentration of maize silage-based diets for high yielding dairy cows on:
a. Feed intake, milk production and composition, and body condition.
b. Longevity (fertility and health) over three lactations (comprising first, second, and third calvings).
c. Feed conversion efficiency, manure output and excretion of nitrogen in urine and faeces.
d. the proportion of urinary nitrogen excreted as urea.

3. To determine the longer-term effects of reduced dietary protein concentration on production, fertility, and health of lactating dairy cows fed grass silage-based diets.

4. To determine the effects of reduction in dietary protein concentration on growth rate of dairy heifers, nitrogen excretion in urine and faeces, and subsequent lactation performance.

5. To determine the extent to which reductions in dietary protein concentrations for multiple lactations alter predicted excretions of N2O, NH3, and NO3 across varying dairy farm typographies.

6. To evaluate the economic consequences of reductions in total dietary protein concentration and associated greenhouse gas emissions and the use of home-grown protein sources across representative farm types."
Time-Scale and Cost
From: 2012

To: 2018

Cost: £3,532,896
Contractor / Funded Organisations
University of Reading
Agriculture and Climate Change              
Sustainable Farming and Food Science