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Effect of different levels of Ascophyllum nodosum meal on iodine metabolism in Jersey cows.

M. Ghelichkhan



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Effect of different levels of Ascophyllum nodosum meal on iodine metabolism in Jersey cows.
M. Ghelichkhan*2, L. H. P. Silva2, R. C. R. Tinini1, J. G. Dessbesell1, M. A. Zambom1, A. F. Brito2. 1Universidade Estadual do Oeste do Paran� Marechal C�ndido Rondon, Brazil, 2University of New Hampshire Durham, NH.

Previous research showed that over 50% of organic dairies in the Northeast and upper Midwest US feed Ascophyllum nodosum meal (ASCO) known to be a rich source of iodine (I). Thus, ASCO supplementation is challenging because excess I intake may increase milk I above the 500-�g/L threshold recommended for consumers. We aimed to investigate the effects of different levels of ASCO on I metabolism in lactating dairy cows. Twenty organic-certified Jersey cows (102 � 52 DIM) were paired by DIM or milk yield and assigned to treatments in a randomized complete block design. The experiment was conducted as follows: 400 g/d of ASCO was fed during 3 wk [elevated-phase; period 1 (P1)] then dropped to 100 g/d for another 3 wk (stepdown-phase; P2) and completely removed from the diet during the last 3 wk of the trial (withdraw-phase; P3). Cows were fed (DM basis) 60% alfalfa hay (19.6% CP, 43.6% NDF) and 40% concentrate (13.3% CP, 50% starch). Control (CON) cows received no ASCO. Milk, blood, and urine samples were collected on wk 3, 6, and 9. Additional milk samples were taken at 24, 48, 72, 96, and 168 h after ASCO supplementation was discontinued in the end of P2. Data were analyzed with repeated measures in SAS using MIXED procedure. Rate of milk I decline was estimated by regressing the natural log of milk I concentration on time of sampling using a nonlinear method for determining the slope in SAS. Diet by period interactions were observed for milk, plasma, and urine I concentrations, with cows fed ASCO showing greater values in P1 and P2 and no difference in P3 (Table 1). The slope of milk I decline over time was calculated as 0.76%/h according to the equation Y = 6.26 (�0.13) — 0.0076x (�0.0013). Overall, feeding 100—400 g/d of ASCO elevated milk I above recommended levels for humans, and about 48 h are needed to bring milk I below 500 �g/L.Table 1. Iodine metabolism

Milk I, �g/L198b854a265b578a18621857.0<0.01<0.01
Milk I, mg/d4.89b20.50a6.44b14.13a4.515.241.70<0.01<0.01
Plasma I, �g/L146b719a135b282a15917321.3<0.01<0.01
Urine I, �g/L88.5b412a88.8a125a52.862.327.3<0.01<0.01

Keywords: iodine, organic, seaweed.