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 compo sition of mare's colostrum and milk, and the biological value of milk protein during the first 45 days of lactation were studied. Milk sampl es (averaging 300-800 cm(3)) from 29 lactating mares were collected da ily 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 analys ed for total protein, true protein, whey protein, true whey protein, c asein and non-protein nitrogen (NPN) content using a Kjel-Foss nitroge n analyser and for amino acid composition wing a LKB amino acid analys er. The biological value of the milk protein was calculated on the bas is of amino acid composition by the method of Morup and Olesen (1976). The contents of ash and macro- and micro-elements in colostrum and mi lk were also determined. The total protein, whey protein, casein and N PN contents, respectively, were 16.41, 13.46, 2.95 and 0.052% for colo strum immediately after parturition; 4.13, 2.11, 2.02 and 0.043% for m ilk between the 2nd and 5th days and 2.31, 1.11, 1.20 and 0.031% for m ilk on the 8th to 45th days of lactation. The ratios of true protein a nd whey protein to total protein decreased, while the comparable ratio s 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 l actation. Most of the essential amino acids (threonine, valine, cystin e, tyrosine, lysine) decreased, while glutamic acid and proline increa sed in the milk protein after parturition. Therefore, the biological v alue of the milk protein was highest (132.3) immediately after parturi tion due to very high levels of threonine and lysine. This value decre ased 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 o f mare's milk protein was much higher than that of bovine milk protein s. 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/k g). Zinc and copper contents decreased after reaching a maximum on day 5, while manganese content increased to day 5 mid maintained that lev el. The concentrations of macro- and micro-elements (mg/kg) in colostr um and milk, respectively, were: potassium, 928.6 and 517.2: sodium, 3 20.0 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 1.20 9; copper, 0.606 and 0.249 and manganese, 0.0447 and 0.0544.