Donkey milk composition is altered by lactation stage and jennies age

Abstract

The aim of this study was to evaluate whether lactation stage and animal age influence the milk composition of grazing donkeys. Jennies were maintained in an exclusively free-range system during the summer season and grazed on a mixed pasture of native grass. Milk samples were collected by manual milking twice a day, two days a week. Acidity, density, total solids, solids-non-fat, fat, protein, casein, lactose, somatic cell count (SCC), and the proportion of nitrogen fractions of the milk were determined. Milk production was 0.61 kg/animal/day. Lactose, fat, acidity, SSC, and whey protein were not affected by the lactation stage. However, milk total solids, solids-non-fat, protein, casein, and nitrogen fractions (non-protein nitrogen and true protein) decreased as the lactation stage progressed. Total solids and protein decreased with the lactation stage, whereas aging was associated with increased protein and fat concentration in milk. These results indicate that the impact of jenny's age on milk fat was lower than on protein content; for every year of age, milk fat percentage increased by 0.023 and milk protein increased 0.13% units. Therefore, the lactation stage and jenny's age are the determinants of milk composition in grazing donkeys.