114. Effect of grazing and feeding management on milk mineral concentrations

Application. Pasture intake and non-Holstein genetics were negatively correlated with milk I, Mn, and Cu, and positively correlated with milk Ca and P; but other feeds and mineral supplementation also influenced milk mineral concentrations. Introduction. Milk is a good source of minerals (Ca, Mg, P and K) and trace elements (I, Se, Zn), which are essential for optimum health [2]. Pasture intake may increase milk Ca and P concentrations but decrease Cu and Se concentrations, although pasture composition, plant maturity, and animal/environmental factors will also have an effect [1]. This study aimed to (i) investigate the milk mineral concentrations in herds with different pasture intakes, and (ii) assess the relative impact of individual feeds. Material and methods. Bulk-tank milk samples (n = 359) were collected monthly (over 12 months) from 30 dairy farms, and animal diet and breed were gathered via questionnaire. Three groups of 10 farms represented contrasting grazing management between April-September: high pasture intake (HP; 28–65% DMI), standard pasture intake (SP; 5–18% DMI), outdoors with low/limited pasture intake (LP; 0–3% DMI). Milk mineral concentrations were determined using ICP-MS. Analysis of variance by linear mixed effects models used pasture intake (HP, SP, LP), months (12 months), and their interaction as fixed factors. Farm ID was used as a random factor. A multivariate redundancy analysis (RDA; CANOCO 5) assessed the relative impact of breed and feeds on milk mineral concentrations. Results. When compared with HP and LP farms, milk from SP farms contained significantly less Ca (−50 mg/kg and −45 mg/kg, respectively) and P (−25 mg/kg and −29 mg/kg, respectively) (Table 1). The RDA indicated that pasture intake and non-Holstein genetics were negatively correlated with milk I, Mn, and Cu, and positively correlated with milk Ca and P. Grass/grass-clover silage and dry-straights were positively correlated with I, Mn, Cu, Mo, Zn and negatively correlated with Na. Intakes of maize silage, blends, moist by-products, oils and minerals were negatively correlated with Mn, Cu, Mo, Zn, Ca and P. Milk from low/no grazing periods contained, on average, more I (+21.1%), Mn (19.5%), Cu (+16.9%), Zn (+6.1%) and Mo (+5.5%), than milk produced from the grazing season, although between-month differences were not always significant.