Effect of a Reduction of Dietary Protein on Milk Production and on Blood Components of Lactating Holstein Cows during Heat Stress

Document Type : Research Paper


1 Graduate Student, University of Zanjan, Iran

2 Associate Professor, University of Zanjan, Iran


   The aim followed in the present research was to study the effects of reduction in dietary crude protein on milk production and on blood components in lactating Holstein dairy cows when in heat stress. A number of 63 Holstein dairy cows (71 ± 16.5 DIM) were chosen to be made use of in a randomized complete block design. The cows were randomly assigned to any one of the three experimental rations (18.5, 17.5, 16.5% CP). Diets were formulated based upon rumen undegradable to degradable protein ratio in all the treatments as equal to 39 to 61%. Ideal proportions of essential amino acids (Lys to Met) were adjusted between 2.9 and 3.2. Results indicated that Dry Mater Intake, 3.5% Fat-Corrected Milk (FCM), percentage of milk protein and milk fat were not affected by experimental rations (P<0.05). In conclusion, a reduction of the level of crude protein in the diet (in comparison with the NRC (2001) recommendations) and an  increase in the ratio of rumen undegradable protein as well as an ideal proportion of essential amino acids (during heat stress) could maintain production levels, and as well reduces production costs. It could also reduce the environmental hazards arising from the emission of animal husbandry produced nitrogen into the air which in turn would be beneficial to the environment.