Variation of milk yield and contents of total casein and casein fractions in Murciano-Granadina goats

Data on 321 lactations of 252 Murciano-Granadina does were analyzed in orde r to describe the change through lactation of milk, protein and total alpha , beta and kappa-caseins contents, as well as to estimate the effect of the season of kidding, the lactation number and the number of suckling kids on these traits. Two hundred and ten day lactation yields and average concent rations were estimated from test-day data. Season of kidding had a signific ant effect on all parameters studied. Significant differences between lacta tion numbers were observed only for milk yield and protein contents. Number of suckling kids had a significant influence only on yield. Typical yield curves were obtained with peaks located between the second and the fifth mo nths, depending on the season of kidding. Protein and total casein contents showed variation through lactation, the magnitude of which depends on the season of kidding. The highest variation was observed in sprint kiddings. T his variation was much less marked in the case of a and K-casein fractions. (C) 1999 Elsevier Science B.V. All rights reserved.