International Animal Agriculture

Iodine (I) is an essential element for efficient dairy cow metabolism. Iodine status is however not well known on farms. The objective was to measure milk and plasma I concentrations in a selected group of commercial dairy herds in central Iranian province of Isfahan. During summer of 1999 and winter of 2000, 11 dairy farms were randomly chosen and a minimum of 10 cows were sampled from each farm. Tail veins blood and milk samples from a total of 135 lactating Holstein cows in summer and 162 cows in winter were obtained. Totally, 367 blood samples and 297 milk samples were collected. The dairy herds had comparable nutritional (e.g., feed and diet types), reproductive (e.g., artificial insemination), and vaccination programs. Milk was sampled after washing and cleaning teat tips in the milking parlor. Management data including feed ingredients, and average milk properties were recorded. Total plasma and milk I concentrations were assayed using the Sandell-Kolthoff reaction. Data were analyzed as mixed models with acquired fixed effects of season and herd. Correlations among Milk and plasma I with milk production were determined. Iodine in plasma ranged from 9.9 to 46.2 μg/L in winter vs. 17.9–56.2 μg/L in summer. The plasma I in all herds in summer (P < 0.01) and in all except one herd in winter (P < 0.05) was lower than the minimum critical range in dairy cows (i.e., 50–100 μg/L). Total plasma I was lower in winter than in summer (27.1 ± 12.3 vs. 42.4 ± 16.6 μg/L). Milk I concentrations varied considerably among cows (CV = 14–62%). Across seasons, a negative correlation was found between milk fat % and milk yield (r = −0.40, P < 0.01), as was a positive correlation between milk and plasma I (r = 0.22, P < 0.01). In winter but not in summer, milk I concentrations positively correlated with milk fat % (r = 0.31, P < 0.01). Results indicate prevalent hypo-iodinemia in selected Isfahan dairy herds, suggesting inadequate I supply via feeds and supplements to maintain blood I within normal ranges. It is recommended to provide sufficient edible or non-edible supplemental I to lactating cows in Isfahan.