PROTEIN-CONTENT, AMINO-ACID-COMPOSITION, BIOLOGICAL VALUE AND MICROELEMENT AND MACROELEMENT CONTENT OF MARES MILK

Changes in the ash, macro- and microelement, protein content, protein Fractions and amino acid composition of mare's colostrum and milk, and 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 the lactation and weekly from the 5th to 45th days postpartum. Colostrum samples were obtained by hand milking without oxytocin administration, 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 by 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 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 in 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 day. 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 is highest (132.3) immediately after parturition due to very high levels of threonine and lysine. This value decreases 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. Ash content of colostrum was significantly higher (05923%) than that of normal milk (0.4051%). Among the macro elements, calcium content is lowest right after foaling (747.7 mg/kg), reaches its maximum at about the 5th day (953.7 mg/kg) and later on decreases during the lactation, just right the other macro elements. Among micro elements zinc and copper content decreases after its maximum at the 5th day, manganese content increases till the 5th day of lactation and later on stays on a constant level in the analysed section of the lactation. For the macro- and micro element content of colostrum (first data) milked right after foaling and that of normal milk (second data) - in average of genotypes - the following data were obtained: potassium: 928.6 and 517.2 mg/kg; sodium: 320.0 and 166.6 mg/kg; calcium: 747.7 and 822.9 mg/kg; phosphorus: 741.7 and 498.8 mg/kg; magnesium: 139.7 and 65.87 mg/kg; zinc: 2.95 and 1.99 mg/kg; iron: 0.996 and 1.209 mg/kg; copper: 0.606 and 0.249 mg/kg; manganese: 0.0447 and 0.0544 mg/kg.