Preliminary results on zinc, copper, selenium and manganese concentration in donkey milk

Donkey milk is well tolerated by infants suffering of cow milk protein allergy. Only few or no data is available on trace elements content of donkey milk. Aim of this study was to determine the content of Zinc (Zn), Copper (Cu), Selenium (Se) and Manganese (Mn) in donkey milk. Individual milk samples were obtained from 16 lactating donkeys (46-72 days from parturition) fed 8 kg of coarse hay and 2.5 kg of commercial concentrate daily. During the experimental period (3 months), donkeys were housed with their foals which was separated from the mother 3 hours before milking. Individual milk samples were collected by mechanical milking (11:00 a.m.) each 2 weeks (6 sampling time). Milk samples were analyzed for Zn, Cu, Se, and Mn concentration by inductively coupled plasma-Mass Spectrometry. Average Zn, Cu, Se and Mn milk concentration (mean±SE) was respectively 2246.92±8.12 μg/L, 97.57±2.98 μg/L, 4.48±0.15 μg/L and 3.57±0.11 μg/L. The concentration of all elements was significantly affected by the stage of lactation. A clear decrease of approximately 38% was observed for Cu (from 122 to 73 μg/L) and Se (from 5.31 to 3.3 μg/L) with the advancing of lactation. On the contrary, Zn and Mn tended to increase during the trial. Milk Zn was positively correlated with Mn (r=0.40) but inversely correlated with Cu (r= -0.28), and Se (r= -0.24). Copper was positively correlated with Se (r=0.63) and inversely correlated with Mn (r= -0.40). Correlations were also significant between Mn and Se (r= -0.27).