Supplementation of soybean meal and canola meal with ethylenediamine dihydroiodide and Ascophyllum nodosum on iodine metabolism, production performance, and nutrient utilization in dairy cows

Canola meal (CM) contains glucosinolates, which are metabolites known to inhibit the transfer of I from feed to milk. Therefore, we aimed to compare the effects of diets containing soybean meal (SBM) or CM, each supplemented with ethylenediamine dihydroiodide (EDDI) and the I-rich brown seaweed Ascophyllum nodosum (ASCO), on I metabolism, production performance, and nutrient utilization in dairy cows. Sixteen multiparous Jersey cows averaging (mean ± SD) 138 ± 58 DIM and 456 ± 62.1 kg of BW at the beginning of the study were used in a replicated 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments. Each experimental period lasted 21 d, with 14 d for diet adaptation and 7 d for data and sample collection. Diets were formulated to yield similar concentrations of CP and I. Cows were fed (DM basis) the following experimental diets as TMR: (1) 10% SBM plus 110 mg/d of EDDI (SB+I), (2) 10% SBM plus 113 g/d of the brown seaweed ASCO (SB+SWD), (3) 12.5% CM plus 110 mg/d of EDDI (CAN+I), and (4) 12.5% CM plus 113 g/d of the brown seaweed ASCO (CAN+SWD). The I sources EDDI and ASCO meal were mixed with ground corn, placed inside rubber tubs, and offered to cows immediately before the delivery of the TMR. We observed a protein source by I source interaction for milk I concentration, which was similar between diets containing EDDI (SB+I and CAN+I), but it decreased by 27.8% when feeding CAN+SWD versus SB+SWD. We also detected a protein source by I source interaction for the serum concentration of free thyroxin, with cows fed CAN+I showing a tendency to have greater free thyroxin levels than those fed SB+I. Iodine intake, milk I yield, serum I concentration, and urinary excretion of I were lower in cows fed CAN+SWD and CAN+SWD than SB+I and CAN+I. In addition, milk I yield, milk I transfer efficiency (milk I yield/I intake), and the serum concentrations of thyroid-stimulating hormone and total triiodothyronine were lower in diets containing CM than SBM. Contrarily, the serum concentration of I and the urinary excretion of I increased in cows receiving CAN+I and CAN+SWD versus SB+I and SB+SWD. Whereas DMI and total glucosinolate intake were greater with feeding CAN+I and CAN+SWD versus SB+I and SB+SWD, milk yield, milk N efficiency, and the apparent total-tract digestibility of nutrients were lower in cows fed diets containing CM than SBM. The CM used in our study was likely overheated based on the high concentrations of neutral detergent insoluble CP (23.6%) and acid detergent insoluble CP (17.5%), possibly explaining the reduction in milk yield and nutrient utilization in cows fed CAN+I and CAN+SWD compared with SB+I and SB+SWD. In brief, our results revealed that feeding CM reduced milk I concentration, milk I yield, and milk I transfer efficiency, particularly when supplemented with ASCO meal.