Dairy cows on a long-term low-protein diet: Dairy Campus research successfully completed
- AH (Axel) van Ruitenbeek
- Onderzoeker diervoeding
Wageningen University & Research has successfully conducted a large-scale study on the effects of feeding dairy cows a long-term low-protein diet. The practical execution of the research, financed by the Dutch Association for Feed Research (VDN), LVVN and the Dairy Cattle Fund, has now been completed after a period of more than two and a half years. The project aims to provide valuable insights into the effects of reducing dietary protein on cow health, milk production and metabolism. The dairy sector faces the challenge of reducing nitrogen emissions, and lowering crude protein (CP) in cows’ rations is one way to achieve this. But what are the long-term impacts on cow health, milk production and metabolism? Wageningen University & Research researchers set out to answer this question. Methane emissions were also measured in this trial using so-called GreenFeed units.
The study ran from September 2022 until mid-May 2025. In total, 64 dairy cows, all in their second or higher lactation, were followed over two complete lactations. The animals received one of three diets with different protein levels, targeting average lactation CP contents of approximately 16.0%, 14.5% and 13.0%. To achieve this, a basic ration was fed that was supplemented with different concentrate mixes. The basic ration consisted of grass silage, maize silage and rapeseed meal, was the same for all cows, offered ad libitum, and had an average protein content of 12.4% CP. The concentrates included a high-protein (30.4% CP) and a low-protein (14.6% CP) variant, plus an attractant mix for the GreenFeed units (14.1% CP). These concentrates were supplied in fixed amounts but in different proportions, resulting in the desired differences in dietary protein between the test groups. The protein content varied over the weeks of lactation, with the highest values around peak lactation and lower values toward the end.
The practical execution of the study has been completed successfully. It was possible to keep both the basic ration and the concentrate types relatively stable in composition and quality throughout the entire experimental period. It was also possible to feed three distinct protein levels, with achieved lactation averages of approximately 15.4%, 14.3% and 13.3% CP. Due to higher intake of the basic ration by some cows in the highest two protein groups, the realized protein levels for these two groups were somewhat lower than initially calculated. Nonetheless, the differences between the groups were maintained.
The completion of the practical phase marks an important milestone in this long-term research. The collected data will now be further analyzed to map the effects on milk production, metabolism and health. The results may contribute to practical advice for dairy farmers who want to aim for lower nitrogen emissions without compromising cow performance and health.
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