Volume 61 (2011) Issue: 2011 No#1

Diurnal variations in milk urea, protein and lactose concentrations in Holstein dairy cows

Author(s): Nozad S, Ramin AG, Moghadam GH, Asri-Rezaei S, Babapour A

Keywords:cows, daily milking, lactose, MUN, protein

Daily variations in milk urea, protein and lactose concentrations and their interrelationships were investigated in 36 and 40 moderate and high milk producer cows, respectively. Milk samples were collected from the morning and afternoon milking yield for up to one week from Holstein dairy cows in Urmia, Iran. The overall mean milk urea nitrogen (MUN), milk protein and lactose concentrations were 19.7 mg/dL, 3.6 g/dL and 4.13 g/dL, respectively. Daily mean concentrations for the milk parameters revealed the highest concentrations for MUN and milk protein in the afternoon and morning milking, respectively. Milk lactose was constant for both milking yields. Significant differences (p<0.01) were found for milk indicators for the moderate and high producers, morning and afternoon milking (p<0.01). The values for each cow within sampling times were also different (p<0.01). Positive correlations (p<0.01) were found between MUN/protein, MUN/lactose and protein/lactose in the morning, afternoon and daily milking except for protein/lactose in the afternoon milking. It was concluded that the concentrations in moderate producer cows were greater than in high producer cows. The values for MUN and milk protein were different between the afternoon and morning milking. MUN showed the highest relationships among milk parameters. Thus, MUN might be considered as a useful index in studies related to milk production and reproduction performance in cows.