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Based on previous farm-level studies, this study hypothesised that production system (conventional, CON; organic, ORG; channel island, CHA) and season would cause variation in the concentrations of macrominerals and trace elements in retail milk. On average, milk retained its status as an excellent source of Ca, P, I, and Mo across different demographics, and a very good source of K, Mg, and Zn for children. Compared with CON and ORG, CHA milk contained higher concentrations of Ca, Mg, P, Cu, Mn, and Zn; and lower concentrations of K and I. Macrominerals did not show a clear seasonal pattern but trace elements were all at lower concentrations during the typical grazing season. Variation in mineral concentrations can have implications to Ca and P supply in children, and I and Zn supply across different consumer demographics; while the seasonal variation was more pronounced than that associated with production system.

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Sixteen multiparous Holstein cows in four blocks of 4 × 4 Latin square over 4-week experimental periods were used to study the effects of seaweed (Saccharina latissima) supplement (with/without) and protein source (rapeseed meal (RSM)/wheat distiller's grain (WDG)) on milk mineral concentrations. Dietary treatments did not affect milk production and basic composition. Feeding seaweed slightly decreased milk Ca and Cu concentrations; whilst increased (by 3.3-fold) milk iodine (I) concentration, due to a higher dietary I supply. Substitution of WDG with RSM increased feed-to-milk transfer of Ca, Na, and Se and decreased that of Mg, P, Fe, and Mn; but only reduced milk Mn and I concentrations (the latter by 27 % as a potential result of increased glucosinolate intake). Seaweed supplement can improve milk I content when cows' I supply/availability is limited, but care should be taken to avoid excess milk I contents that may pose nutritional risks for young children.

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Given the lack of research regarding the effect of microalgal supplementation in dairy cows on milk mineral concentrations, this study investigated the effect of feeding different protein supplements in dairy cow diets on milk, feces, and blood plasma mineral concentrations, associated milk and blood plasma transfer efficiencies, and apparent digestibility. Lactating Finnish Ayrshire cows (n = 8) were allocated at the start of the trial to 4 diets used in a replicated 4 × 4 Latin square design experiment: (1) control diet (CON), (2) a pelleted rapeseed supplement (RSS; 2,550 g/d), (3) a mixture of rapeseed and Spirulina platensis (RSAL; 1,280 g of RSS + 570 g of S. platensis per day), and (4) S. platensis (ALG; 1,130 g of S. platensis per day). In each of the 4 experimental periods, a 2-wk adaptation to the experimental diets was followed by a 7-d sampling and measurement period. Feed samples were composited per measurement period, milk, and feed samples (4 consecutive days; d 17-20), and blood plasma samples (d 21) were composited for each cow period (n = 32). Data were statistically analyzed using a linear mixed effects model with diet, period within square, square and their interaction as fixed factors, and cow within square as a random factor. Cows fed ALG were not significantly different in their milk or blood plasma mineral concentrations compared with CON, although feeding ALG increased fecal concentrations of macrominerals (Ca and Mg) and trace elements (Co, Cu, Fe, I, Mn, and Zn), and reduced their apparent digestibility, compared with CON. When compared with CON and ALG, milk from cows fed RSAL and RSS had lower milk I concentrations (-69.6 and -102.7 µg/kg of milk, respectively), but total plasma I concentrations were not affected significantly. Feeding S. platensis to dairy cows did not affect mineral concentrations in cows' blood or milk, but care should be taken when rapeseed is fed to avoid reducing milk I concentrations which may in turn reduce consumers' I intake from milk and dairy products.

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Thirty conventional and twenty-four organic dairy farms were divided into equal numbers within system groups: high-pasture, standard-pasture, and low-pasture groups. Milk samples were collected monthly for 12 consecutive months. Milk from high-pasture organic farms contained less fat and protein than standard- and low-pasture organic farms, but more lactose than low-pasture organic farms. Grazing, concentrate feed intake and the contribution of non-Holstein breeds were the key drivers for these changes. Milk Ca and P concentrations were lower in standard-pasture conventional farms than the other conventional groups. Milk from low-pasture organic farms contained less Ca than high- and standard-pasture organic farms, while high-pasture organic farms produced milk with the highest Sn concentration. Differences in mineral concentrations were driven by the contribution of non-Holstein breeds, feeding practices, and grazing activity; but due to their relatively low numerical differences between groups, the subsequent impact on consumers' dietary mineral intakes would be minor.

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This study investigated the effect of seaweed supplementation in dairy cow diets on milk yield, basic composition, and mineral concentrations. Thirty-seven Icelandic cows were split into three diet treatments: control (CON, no seaweed), low seaweed (LSW, 0.75% concentrate dry matter (DM), 13-40 g/cow/day), and high seaweed (HSW, 1.5% concentrate DM, 26-158 g/cow/day). Cows were fed the same basal diet of grass silage and concentrate for a week, and then were introduced to the assigned experimental diets for 6 weeks. The seaweed mix of 91% Ascophyllum nodosum: 9% Laminaria digitata (DM basis), feed, and milk samples were collected weekly. Data were analyzed using a linear mixed effects model, with diet, week, and their interaction as fixed factors, cow ID as random factor, and the pre-treatment week data as a covariate. When compared with CON milk, LSW and HSW milk had, respectively, less Se (-1.4 and -3.1 µg/kg milk) and more I (+744 and +1649 µg/kg milk), while HSW milk also had less Cu (-11.6 µg/kg milk) and more As (+0.17 µg/kg milk) than CON milk. The minimal changes or concentrations in milk for Se, Cu, and As cannot be associated with any effects on consumer nutrition, but care should be taken when I-rich seaweed is fed to cows to avoid excessive animal I supply and milk I concentrations.

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To study the effects of dairy production system on milk macromineral and trace element concentrations, milk samples were collected monthly in 2019 from 43 conventional and 27 organic farms. Organic milk contained more Ca (1049.5 vs. 995.8 mg/kg), K (1383.6 vs. 1362.4 mg/kg), P (806.5 vs. 792.5 mg/kg) and Mo (73.3 vs. 60.6 µg/kg) but less Cu (52.4 vs. 60.6 µg/kg), Fe (0.66 vs 2.03 mg/kg), Mn (28.8 vs. 45.0 µg/kg), Zn (4.51 vs. 5.00 mg/kg) and Al (0.32 vs. 1.14 µg/kg) than conventional milk. Significant seasonal variation was observed in all determined minerals' concentrations. Milk I concentration was not consistently affected by production system, whereas organic milk contained less I in June and July than conventional milk. Dietary factors contributing to different milk mineral concentrations between production systems included intakes of maize silage, dry-straights and oils (higher in conventional diets), and pasture, clover and wholecrop (higher in organic diets).

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