Effect of rumen degradable protein in concentrate on cow performance with two grazing strategies in 2016 and 2017: feeding trials supplemental feeding with grazing

Two grazing experiments were carried out to investigate the effects of 1. Compartmented continuous grazing 2. Strip grazing and 3. Protein supplementation strategy (Low and High rumen degradable protein (RDP) and high RDP plus additional metabolisable protein) on pasture intake, milk and milk solids yield in spring calving dairy cows. Neither grazing system nor protein supplementation strategy influenced pasture dry matter intake. However, high RDP resulted in higher milk yield and milk protein outputs. Additional high RDP plus additional metabolisable protein did not result in further improvement of milk performance. High RDP and high RDP plus additional metabolisable protein resulted in reduced nitrogen use efficiency. Despite similar diet compositions in both experiments, there were large differences in rumen NH3 and apparent OMD between experiments, suggesting strong year to year effects in rumen fermentation and rumen digestion which were not reflected in the feeding values.