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

The concentrations of urea, protein and macro-minerals and their interrelationships were investigated in lactating mares. Fifty-six samples including 17 colostrum and 39 whole milks were collected in 2011-2012 in Uremia, 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 (Ca), phosphorus (IP), magnesium (Mg), sodium (Na) and potassium (K) concentrations were 26.4 mg/dl, 4.66 g/dl, 43.2, 20.2, 7.33, 39.7, and 13.1 mmol/l, respectively. The concentrations of urea, Ca, IP and Na in whole milk were 24.4%, 2.8%, 14.3% and 9% greater than in colostrum and protein, and the Mg and K in colostrum’ were 505%, 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 Mg. The highest concentrations of urea, Ca, IP and Na were found in whole milk and for protein, Mg and K in colostrum. With the exception of the differences (P<0.05) in colostrum Ca concentrations between 5, 9 and 10 year olds, no significant differences were observed among the six age groups in milk and colostrum parameters. There were significant correlations between urea/protein (r=-.19, P<0.01), urea/Ca (r=.37, P<0.01), urea/IP (r=-.35, P<0.01), urea/Mg (r=-0.32, P<0.01), Ca/IP (r=0.47, P<0.01), Na/K (r=-0.49, P<0.01) and protein/Mg (r=-0.72, P<0.01), of which the greatest and strongest correlations were seen in urea and protein/magnesium, respectively. It is concluded that the concentrations of protein and Mg in colostrum of mares were higher and urea was lower than in whole milk. Milk urea revealed the greatest relationships with the other milk parameters, and can be considered as a useful index in studies related to milk production in lactating mares.