Efficiency of Protein Utilisation in Dairy Cows

Efficiency of Protein Utilisation in Dairy Cows

 

A DEFRA funded project at the University of Reading Centre for Dairy Research (CEDAR) in collaboration with Aberystwyth University, Rothamsted North Wyke, the Basque Centre for Climate Change, SRUC (Scotland's Rural College), AHDB Dairy, and an Advisory and Dissemination Committee comprised of leading figures from across the dairy industry is continuing.

The aim of the project is to explore opportunities for reducing protein intake (i.e. reduced nitrogen intake) in dairy cattle without compromising lifetime productivity. In addition to determining the long-term impacts of reduced dietary protein concentrations for life-time production, fertility, and health, the project will evaluate the environmental and economic impacts for dairy systems in the UK. The 6.5 year project began in 2012 and will measure effects of reduced dietary levels of protein that are maintained from weaning through to the end of three lactations. An info-poster summarising the study can be downloaded here.

Efficiency of Protein Utilisation in Dairy Cows

Why is protein important?

Dairy cows are often fed diets with relatively high concentrations of crude protein (CP) to ensure an adequate supply of absorbable amino acids for maximal milk and milk protein production and to maintain health and fertility. Dietary protein supplies nearly all the nitrogen in dairy cow diets and is used less efficiently by dairy cows than in pigs and poultry. Approximately 75% of nitrogen intake is excreted in manure, in fact, dairy cows excrete more nitrogen in urine than they secrete in milk! Nitrogen excretion is a significant environmental concern due to atmospheric losses as nitrous oxide (N2O) and ammonia (NH3), and furthermore nitrate (NO3) leaching through the soil contributes to aquatic eutrophication. Nitrogen excretion in manure is highly correlated with dietary nitrogen intake, thus a simple option for reducing nitrogen excretion is to feed less protein. However, this strategy will only be acceptable to dairy farmers if it can be achieved without reducing milk production and without detrimental effects on cow health and fertility.

What is being measured in the study?

At the Centre for Dairy Research, measurements are being taken to determine the effects of reduced protein consumption on milk production and composition, fertility, body condition, and health in 215 cows of high genetic merit fed maize and grass silage-based diets at the start of their first lactation. Each cow has been assigned to one of three diets:

High: 18% CP; above metabolisable protein (MP) requirement

Medium: 16% CP; at MP requirement

Low: 14% CP; below MP requirement

Cows

Cows are individually fed these diets for three full lactations each with daily recording of intake, milk yield and weekly analysis of milk composition. The effects of these incremental reductions in dietary nitrogen on nitrogen losses in manure are also being measured. A companion study being conducted at Aberystwyth University is exploring the effects of feeding lower protein diets to growing dairy cattle on growth rate, manure output, nitrogen excretion and subsequent lactation performance. Scotland's Rural College is leading a practical demonstration study with dairy cows fed two levels of dietary protein using grazing and grass-silage based diets in an established farm system.

Efficiency of Protein Utilisation in Dairy Cows

During the final year of the study, researchers at Rothamsted North Wyke and the Basque Centre for Climate Change will integrate results from the experimental studies using simulation models to predict the effects of feeding lower protein diets on emissions of N2O, NH3, and NO3 from dairy farms of varying type, and the impact of these responses on national and regional emissions. Colleagues at the University of Reading will use the simulation model outputs, together with farm survey data, to assess the economic impact of feeding low protein diets on UK dairy farms.

Preliminary Results

Knowledge transfer of research results to the livestock industry will include practical information defining the long-term effects of reduced dietary protein intake on milk production, nitrogen excretion and environmental pollution for dairy cows. A series of three workshops were held during 2016 to engage the wider agricultural community in the ongoing project work (click here for hand out). Whilst final data will not be disseminated until the very end of the study once it has been robustly analysed, the following links show initial findings. More resources will be added here as they become available:

Poster 1: Lay summary.

Poster 2: Reynolds et al., (2016). Long Term Implications of Feeding Low Protein Diets to First Lactation Dairy Cows. Proceedings of the 5th EAAP International symposium on energy and protein metabolism and nutrition. Wageningen Academic Publishers, The Netherlands.

Contact us

Contact details for the project management team can be found here.

Contact details for the advisory and dissemination committee can be found here.

All enquiries should be directed to Professor Chris Reynolds (c.k.reynolds@reading.ac.uk) in the first instance.

Key references

Reynolds, C.K. (2000). Forage Evaluation Using Measurements of Energy Metabolism. In Forage Evaluation in Ruminant Nutrition (Eds. Givens, D.I., Owen, E., Omed, H.M., Axford, R.F.E.). CABI Publishing, Wallingford. pp. 95

Reynolds, C.K., Crompton L.A., Mills J.A.N., Humphries D.J., Kirton P., Relling A.E., Misselbrook T.H., Chadwick D.R., and Givens D.I. (2010). Effects of diet protein level and forage source on energy and nitrogen balance and methane and nitrogen excretion in lactating dairy cows. In G. M. Corvetto (ed.) Proceedings of the 3rd International Symposium on Energy and Protein Metabolism, EAAP Publ. No. 127, 2010, Wageningen Academic Publishers, The Netherlands, 463-464.

Weiss, W.P., St-Pierre, N.R. & Willett, L.B. (2009a). Varying type of forage, concentration of metabolizable protein, and source of carbohydrate affects nutrient digestibility and production by dairy cows. Journal of Dairy Science, 920:5595-5606.

Weiss, W.P., Willett, L.B., St-Pierre, N.R., Borger, D.C., McKelvey, T.R. & Wyatt, D.J. (2009b). Varying forage type, metabolizable protein concentration, and carbohydrate source affects manure excretion, manure ammonia, and nitrogen metabolism of dairy cows. Journal of Dairy Science, 92:5607-5619.

Find out more about our partners

Aberystwyth University, Rothamsted North Wyke, the Basque Centre for Climate Change, SRUC (Scotland's Rural College), DEFRA, AHDB Dairy

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