Abstract #M166

# M166
Interactions between iodine and protein sources: Effects on milk iodine and thyroid hormones in Jersey cows.
M. Ghelichkhan*1, D. Williams1, L. H. P. Silva1, A. F. Brito1, 1University of New Hampshire, Durham, NH.

Kelp meal (KM) is a supplement made from the brown seaweed Ascophyllum nodosum known to bioaccumulate iodine (I). However, feeding KM may result in milk I above the recommended concentration of 500 µg/L. Canola meal (CM) contain goitrogenic glucosinolates (GLS) that affect I distribution in tissues through competitive inhibition of iodide transportation by the Na-iodide symporter. Our goal was to assess the interactions between 2 sources of I and RDP on I metabolism in dairy cows. Sixteen multiparous Jersey cows (93 ± 58 DIM) were used in a factorial replicated 4 × 4 Latin square design (21-d periods). Diets were formulated to yield similar concentrations of CP and I and consisted (DM basis) of 55% baleage and 45% concentrate. Dietary CP and NDF concentrations averaged 18.5 and 35.6%, respectively. Experimental treatments were: 10% soybean meal (SBM) + 110 mg/d of ethylenediamine dihydroiodide (EDDI) or 114 g/d of KM and 12.5% CM + 110 mg/d of EDDI or 114 g/d of KM. Kelp contained 775 mg/kg of I. Data analysis included the main effects of RDP and I source and interaction. Although I intake was greatest in SBM and EDDI diets, the actual difference between treatments was small. The drop in the concentration and yield of milk I was more pronounced in cows fed CM plus KM than CM plus EDDI (RDP x I interaction). Cows fed CM had greater concentrations of plasma thyroid stimulating hormone (TSH), triiodothyronine (T3), and thyroxine (T4) than those fed SBM possibly in response to GLS found in CM. Milk I decreased below 500 µg/L only in CM plus KM diet, which was also linked to CM-GLS. The fact that milk I did not drop below 500 500 µg/L with feeding CM plus EDDI was unexpected and requires further investigations. Table 1 (Abstr. M166). Iodine metabolism in Jersey cows
I intake mg/d96.393.395.792.80.30<0.001<0.0010.83
Milk I, ng/ml78647179965256.530.009<0.0010.02
Milk I, mg/d16.710.217.815.10.58<0.001<0.001<0.001
Plasma TSH, µIU/mL0.3930.3880.3960.3960.0030.010.250.19
Plasma total T3, ng/mL1.070.981.
Plasma total T4, ng/mL40.537.946.

Key Words: iodine, protein, seaweed