Does feeding less protein over a longer period not only reduce nitrogen losses, but also affect methane emissions? Researchers at Wageningen University & Research (WUR) investigated this in a multi-year study with dairy cows.
The dairy sector faces a major challenge to reduce its environmental impact. Lower protein levels in the ration can lead to lower nitrogen excretion, particularly via urine, and therefore to lower ammonia emissions. At the same time, it is important that this does not come at the expense of animal performance or lead to unwanted side effects, such as higher methane emissions. This part of the research therefore focused specifically on nitrogen metabolism and methane excretion when feeding low-protein rations over a longer period.
In the study, 64 dairy cows were followed during two full lactations of at least 44 weeks each. The cows received rations with different protein levels, with realized average crude protein contents of 133, 143 and 154 g CP/kg DM for the low, medium and high protein groups (see also our earlier news article). The protein levels of all three groups were therefore below the Dutch practical average of 161 g CP/kg DM (CBS, 2024). The outcomes should therefore be interpreted in the context of a relatively low protein level. Throughout the entire lactation, feed intake, milk production and methane emissions were measured continuously. In addition, manure and urine samples were collected in early and mid-lactation to obtain a complete picture of nitrogen excretion alongside nitrogen intake.