Effects of protein source and seaweed supplementation on mineral intake, milk mineral concentrations, and iodine transfer efficiency from feed to milk in lactating dairy cows

The objective of this experiment was to study the effects of protein source and seaweed supplementation on intake, milk concentration, and transfer efficiency of minerals from feed to cow milk. Twelve multiparous Nordic Red cows were used in a cyclic change-over study with a 2 × 3 factorial arrangement of treatments. The cows were divided into block 1 (DIM 151 ± 12.7 d, milk yield 29.7 ± 4.08 kg/d) and block 2 (DIM 115 ± 15.1 d, milk yield 39.5 ± 3.45 kg/d). The study consisted of three 17-d periods with an 18-d washout between periods. Cows were randomly assigned to treatments which included rapeseed cake (RSC) or pea (MFP) as protein feed without (CON) or with seaweed supplementation (Ascophyllum nodosum [AN; 57 g DM/d] or Laminaria digitata [LD; 7.8 g DM/d]). Cows were offered a concentrate mix of seaweed, sugar beet pulp, mineral supplement, and molasses, and ad libitum partial mixed ration consisting of grass silage, barley, and protein feed. Diets had I concentration (mg/kg DM) of 4.1 for RSC-CON, 6.8 for RSC-AN and RSC-LD, 1.9 for MFP-CON, and 4.7 for MFP-AN and MFP-LD. Despite decreased I intake, I transfer efficiency and concentration in milk were increased when rapeseed was substituted with pea. Seaweeds increased the intake, transfer efficiency, and milk concentration of I. Seaweeds increased the intake of As, but highly toxic trace elements (As, Cd, Cr, Hg, Pb) were not found in milk on any treatment. Milk I concentration was very low, especially in RSC-CON (38 µg/kg), possibly due to the unexpectedly high glucosinolate concentration (48 mmol/kg DM) of rapeseed. Milk I concentration on MFP-CON and I transfer efficiency on all pea diets were also lower than usual. In conclusion, pea diets resulted in more favorable milk I concentration for human consumers than rapeseed high in glucosinolates.