Mineral and Citrate Concentrations in Milk Are Affected by Seasons, Stage of Lactation and Management Practices

This study was conducted to examine associations between nutrition, time of year and season of calving on milk mineral concentrations in 24 pasture-based dairy farms. There was substantial variation in the concentrations (mean with range in parentheses) of Ca 1072 (864–1310) mg/kg; citrate 1579 (880–2080) mg/kg; P 885 (640–1040) mg/kg; Mg 98 (73–122) mg/kg; Na 347 (248–554) mg/kg; K 1534 (1250–2010) mg/kg; and S 295 (155–372) mg/kg with most of the variation associated with stage of lactation, although the influence of days in milk was different for different minerals. Feeding practices were also important in determining the concentrations of some components. Milk Ca, citrate, P, and K concentrations were greater (p < 0.05) in cows receiving mineral supplements, while Ca, P and Mg were positively correlated (p < 0.05) with the amount of concentrates fed. Milk citrate and K concentrations were positively correlated (p < 0.05) with herbage allowance. Milk Se (15 (<3–37) µg/kg) and Zn (3.4 (2.2–4.9) mg/kg) also varied with time of year, with Se concentrations also greater (13.7 vs 11.6 µg/kg) in spring compared with autumn calving herds and positively correlated (p < 0.05) with the amount of concentrates fed and mineral supplementation. These data indicate that calving pattern and feeding practices could be used to reduce variation in the measured milk mineral concentrations.