The variation in the content of total protein, total casein, whey protein, α-casein, β-casein, k-casein, α-lactalbumin, β-lactoglobulin and ‘other’ whey proteins of the mammary secretion was studied in 44 goats of the Murciano-Granadina breed (Spain) from the 1st to the 4th day after parturition.
The concentration of all the protein variables showed a marked decrease from the 1st to the 4th day after parturition (P < 0·001). In whey proteins this decrease was more marked from the 1st (67·1 g/1) to the 2nd day after parturition (21·6 g/1), whereas the total caseins sharply decreased from the 2nd (62·6 g/1) to the 3rd day after parturition (39·0 g/1).
Stepwise discriminant analysis revealed that, except for the k-casein, all the proteins resulting from the electrophoretic fractionation had a discriminant power between the dates of sampling (P < 0·001). The multivariant analysis did not show statistical differences in the electrophoretic fractions corresponding to the samples on the 3rd and 4th days after parturition. According to such fractionation, the transition from colostrum to milk should take place on the 2nd day after parturition.