Low protein degr adability and precision protein feeding improve nitrogen efficiency of dairy cows

The low efficiency of nitrogen (N) intake in dairy cows can increase feed costs and ammonia emissions.At the rumen level, decreasing degradable N to improve the urea reuse in microbial protein synthesis, canincrease N efficiency (Neff=Nmilk/Nintake). Moreover, at the animal level, the metabolisable protein(MP) efficiency varies greatly between dairy cows. Applying precision feeding, with adjustment of the dietaccording to individual observations, could increase this MPeff. The objective of this study was to improveboth N and MP efficiencies by combining a reduction in rumen degradable protein (RDP, factor N) withan individual adjustment of MP content in the diet (factor E) in a 2×2 factorial design with 4 groups of 11cows for 12 weeks fed maize-based diet. Factor N was either at the reference level of INRA for RDP (N0)or at a reduced level (N-10) of -1.4 g of degradable protein per MJ of net energy for lactation (NEL). FactorE was either constant with 14.8 g of MP per MJ NEL (EC), or variable (EV), from 12.0 to 15.5 g MP/MJ NEL and calculated for each cow according to its MPeff on a 4-week reference period. The lower theefficiency was, the lower the applied MP/NEL ratio was. No interaction occurred between the 2 factors. Thedecrease in RDP had no significant effect on intake and production. The milk production of EV was 1.7 kg/day lower than EC, but the energy ef¿ ciency (kg of milk/kg of DMI) was unchanged. The RDP reductionimproved Neff (35.7 vs 32.2%) and individual protein feeding mainly improved MPeff (69.1 vs 59.3%).Between extreme treatments (N0_EC vs N-10_EV), crude protein content decreased from 14.9 to 12.5%,Neff varied from 32.1% to 36.4%, and estimated urine urea-N excretion was reduced by 56%. Reducingdegradable N content of the diet and applying precision feeding to dairy cows fed indoors is thus a way tobetter use proteins and to reduce ammonia emissions.