Relationships among urea, protein and macro-mineral concentrations in colostrum and whole milk in lactating mares

The concentrations of urea, protein and macro-minerals and their interrelationships were investigated in 56 samples including 17 colostrums and 39 whole milks in lactating mares in 2011 in Urmia, Iran. Milk parameters were evaluated by auto-analyzer using commercial kits after separation of the milk casein in 0.1 normal HCl. The overall means for urea, protein, calcium, phosphorus, magnesium, sodium and potassium concentrations were 26.4mg/dl, 4.66 g/dl, 43.2, 20.2, 7.33, 39.7, and 13.1 mmol/l, respectively. The concentration of urea, calcium, phosphorus and sodium in whole milk were 24.4%, 2.8%, 14.3% and 9% greater than in colostrum and protein, magnesium and potassium in colostrums were 500%, 91% and 9% greater than in whole milk of mares. Mean comparison between colostrum and whole milk parameters revealed significant differences (P<0.01) in the concentrations of urea, protein and magnesium and not for other parameters. The highest concentrations of urea, calcium, phosphorus and sodium were found in whole milk and for protein, magnesium and potassium in colostrums. With the exception of the differences (P<0.05) in colostrum calcium concentrations among 5, 9 and 10 years old, no significant differences were observed among 6 age groups in milk and colostrum parameters. There were significant correlations between urea/protein (r=-.19, P<0.01), urea/calcium (r=.37, P<0.01), urea/phosphorus (r=-.35, P<0.01), urea/magnesium (r=-0.32, P<0.01), calcium/phosphorus (r=0.47, P<0.01), sodium/potassium (r=-0.49, P<0.01) and protein/magnesium (r=-0.72, P<0.01), which the greatest and strongest correlations were seen in urea and protein/magnesium, respectively. It is concluded that the concentrations of protein and magnesium in colostrum of mares were higher and urea was lower than in whole milk. Milk urea revealed the greatest relationships with other milk parameters which can be considered as the useful index in studies related to milk production in lactating mares.