Abstract/Summary

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 four diets used in a replicated 4×4 Latin square design experiment: (i) control diet (CON), (ii) a pelleted rapeseed supplement (RSS; 2,550 g/d), (iii) a mixture of rapeseed and Spirulina platensis (RSAL; 1,280 g RSS + 570 g S. platensis/day), and (iv) S. platensis (ALG; 1130 g S. platensis/day). In each of the four experimental periods, a 2-week adaptation to the experimental diets was followed by a 7-day sampling and measurement period. Feed samples were composited per measurement period, milk, and feed samples (4 consecutive days; day 17-20) and blood plasma samples (day 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 to 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 to 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 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.