COMPOSITION OF MARES COLOSTRUM AND MILK - PROTEIN-CONTENT, AMINO-ACID-COMPOSITION AND CONTENTS OF MACROELEMENTS AND MICROELEMENTS

Changes in the protein content, protein fractions and amino acid composition of mare's colostrum and milk, and the biological value of milk protein during the first 45 days of lactation were studied. Milk samples (averaging 300-800 cm(3)) from 29 lactating mares were collected daily at the beginning of lactation and weekly from the 5th to 45th days post-partum. Colostrum samples were obtained by hand milking without oxytocin administtation, while the foals nursed and milk samples were obtained from the mixed total daily production. Each sample was analysed for total protein, true protein, whey protein, true whey protein, casein and non-protein nitrogen (NPN) content using a Kjel-Foss nitrogen analyser and for amino acid composition wing a LKB amino acid analyser. The biological value of the milk protein was calculated on the basis of amino acid composition by the method of Morup and Olesen (1976). The contents of ash and macro- and micro-elements in colostrum and milk were also determined. The total protein, whey protein, casein and NPN contents, respectively, were 16.41, 13.46, 2.95 and 0.052% for colostrum immediately after parturition; 4.13, 2.11, 2.02 and 0.043% for milk between the 2nd and 5th days and 2.31, 1.11, 1.20 and 0.031% for milk on the 8th to 45th days of lactation. The ratios of true protein and whey protein to total protein decreased, while the comparable ratios of casein and NPN increased from foaling to 45 days. The amino acid contents of colostrum and milk decreased during the first 45 days of lactation. Most of the essential amino acids (threonine, valine, cystine, tyrosine, lysine) decreased, while glutamic acid and proline increased in the milk protein after parturition. Therefore, the biological value of the milk protein was highest (132.3) immediately after parturition due to very high levels of threonine and lysine. This value decreased in the course of 5 days to 119.7 and to 107.9 on the 45th day of lactation. The essential amino acid composition and biological value of mare's milk protein was much higher than that of bovine milk proteins. The ash content of colostrum (0.592%) was significantly higher than that of normal milk (0.405%). Calcium content was lowest immediately after foaling (747.7 mg/kg) and reached a maximum at day 5 (953.7 mg/kg). Zinc and copper contents decreased after reaching a maximum on day 5, while manganese content increased to day 5 mid maintained that level. The concentrations of macro- and micro-elements (mg/kg) in colostrum and milk, respectively, were: potassium, 928.6 and 517.2: sodium, 320.0 and 166.6; calcium, 747.7 and 822.9; phosphorus, 741.7 and 498.8; magnesium, 139.7 and 65.87; zinc, 2.95 and 1.99; iron, 0.996 and 1.209; copper, 0.606 and 0.249 and manganese, 0.0447 and 0.0544.