The Effect of Reducing Ration Protein Level Using Commercial Premixes on the Performance and Blood Parameters of Holstein Dairy Cows

The aim of this experiment was to evaluate the effects of concentrate premixes containing of by-pass proteins (BP) in balanced low protein diets for essential amino acids on performance, blood metabolites and nitrogen efficiency of lactation Holstein dairy cows. Twenty-four multiparous Holstein cows (in 3rd parity and DIM 80±10) randomly were divided to three experimental rations including, 1) control ration with 17.5% CP based on NRC 2001 recommendations, 2) Low protein ration containing concentrate premix with 16.5% CP and 3) Low protein ration containing concentrate premix with 15.5% CP. The ratio of the rumen undegradable protein (RUP) to rumen degradable protein (RDP) in experimental diets was 37:63 and the ratio lysine to methionine was adjusted by concentrate premix up to 3:1 and 2.8:1 in the diet 16.5% and 15.5% CP, respectively. The results showed that the dry matter intake (DMI) increased linearly with a reduction of CP in the diets (P=0.048). The highest 3.5% fat corrected milk yield (FCM) and energy corrected milk (ECM) was recorded for 16.5% CP diet that showed a significant difference than other groups (P=0.038). Milk protein yield and milk nitrogen efficiency (MNE) showed significantl difference between control and 16% CP diets (P=0.05 and P=0.03, respectively). This study showed that decreased in CP levels compared to recommended NRC values (2001), and providing an optimal ratio of limiting amino acids can increase nitrogen yield while maintaining production.