Nitrogen use efficiency of sixty individual dairy cows under intensive grazing

The Dutch dairy sector aims to improve nitrogen (N) use efficiency (NUEN) at intensive dairy farms, while supporting grazing. Managing NUEN in intensive grazing systems is challenging, because of the high feed supplementation levels combined with varying and unknown grass (N) intake at cow level. To gain insight in the NUEN at intensive dairy farms, we need insight in the NUEN at cow level. We performed a two-by-two factorial grazing trial with sixty Holstein Friesian cows (7.5 cows ha-1), in which we compared NUEN of individual cows under two grazing systems, i.e. compartmented continuous grazing (CCG) and strip grazing (SG), and two levels of dietary rumen-degradable protein balance (OEB), i.e. low and high (contrast of 500 g OEB cow-1 day-1). Grass and supplementary intakes, and faecal and milk outputs were quantified and analysed for N content, during two weeks in July and September 2016. Results showed a higher NUEN for cows in CCG (39%) compared to cows in SG (36%) in July, due to a lower grass (N) intake in CCG. Low OEB showed a higher NUEN (40%) compared to high OEB (34%). Our results are key to explore strategies to improve NUEN at farms that apply innovative grazing systems.