Background – Milk can be an important source of minerals in the diet. In Australia, seasonal variation in the nutritive characteristics of pasture is likely to be associated with seasonal variation in the concentrations of minerals in milk.
Objective – To determine if there is seasonal variation in the concentrations of some minerals (table) in milk. Design – Milk samples representative of calving groups (autumn and spring) within commercial dairy herds located in northern Victoria were taken at 6 – 7 week intervals and analysed for concentrations of minerals. Summary statistics (table) are based on the entire data set, where 158≤N≤166 for the mean of each mineral; units are mg mineral/kg milk except for selenium where units are μg/kg milk. Seasonal variation in concentrations of minerals for mid autumn (April), mid winter (July), mid spring (October) and mid summer (January) are representative of the bulk milk supply, where N=12. Values with a subscript in common are not significantly different (P<0.05).
Outcomes – The range in concentrations for all minerals was large with maximum concentrations approaching twice that of minimum values for the macro-minerals calcium, magnesium, phosphorus and potassium, and exceeding twice that of minimum values for the micro-minerals selenium and zinc. The average concentrations of all components examined also varied with season.
Conclusion – Environmental factors (farm management and season) are important determinants of the concentrations of some minerals in milk produced in northern Victoria. Milk produced in pasture-based production systems should not be considered as a uniform product across seasons.