1Department of Animal Science, College of agricultural sciences, University of Mohaghegh Ardabili, Iran.
2Department of Animal Science, Campus of agriculture and natural resources, University of Tehran, Karaj, Iran.
The aim of this study was to evaluate the effects of balancing low protein diets for methionine and lysine on performance of early lactation Holstein cows under hot environmental temperature. Twenty one multiparous Holstein cows in early lactation were allocated to three experimental rations including, 1) High protein ration with 17.5% CP, 2) Medium protein ration with 16% CP and 12 g/d rumen protected methionine (RP Met), 3) Low protein ration with 14.5% CP, 14 g/d RP Met and 5 g/d rumen protected lysine. There was no effect of ration on milk yield and milk fat percentage, but milk protein percent, N efficiency for milk production, milk urea nitrogen (MUN) and blood urea nitrogen (BUN) were affected significantly. N excreted in urine, N balance and creatinine concentration in urine decreased significantly by feeding low protein diets. Plasma concentrations of non-essential AA were not affected by treatments but, Methionine, Valine and Leucine concentrations were affected significantly. These results suggest that low protein diets with rumen protected amino acids can be an alternative for high protein diets for dairy cows under hot climates.