Diurnal and nocturnal concentration of essential minerals and trace elements in donkey milk

Donkey milk has been proposed as a food for sensitive consumers such as infants and elderly people. Circadian rhythm are report to affect donkey milk gross composition but no information is available on essential minerals and trace elements. Aim of this trial was to study the diurnal and nocturnal Ca, P, K, Na, Mg, Zn, Fe, Cu, Mn, Co, Se, and Mo concentrations in donkey milk. Four lactating donkeys (Martina Franca derived population) were used to provide milk samples. Donkeys were machine milked during the day (at 1800, and 1000 h) and during the night (at 2300 and 0200). Individual milk samples were analysed for the aforementioned elements by Inductively Coupled Plasma-Mass Spectrometry. Results from samples obtained at 1000am and 0600pm were grouped as day milk whereas samples obtained at 1100pm and 0200am were grouped as night milk. Data were processed by analysis of variance for repeated measures. The average milk concentrations of investigated elements (minerals: Ca 1100, P 459, K 875, Na 172, Mg 93 mg/L; Trace elements: Zn 1097, Fe 201, Cu 70.3, Mn 5.3, Co 0.67, Se 2.5, Mo 7.8 µg/L) were similar to literature data on donkey milk except for lower Zn and Se and higher Ca and Fe. The average concentrations of the investigated variables did not differ significantly between milk obtained during the day and during the night.