Short communication: Feed iodine concentrations on farms with contrasting levels of iodine in milk

Abstract

In a previous study, milk iodine concentration from 501 farms across Canada was found to vary considerably and appeared to be influenced by feeding practices. Farms with contrasting levels of milk iodine from a subset of 200 participating farms were used to determine the relationship between milk iodine concentration and the concentration of this mineral in different feeds and complete diets given to lactating dairy cows. The 30 farms with the lowest levels of iodine in milk (low group) and the 30 farms with the highest levels (high group) were selected. Samples of bulk tank milk, all feed ingredients, and water were collected. Additionally, each farmer completed a questionnaire providing information on feeding management. The iodine offered on each of the farms was estimated from the amount of the feed in the diet recommended by the Ration'L software (Valacta, Ste-Anne-de-Bellevue, QC, Canada) and the iodine concentration in the feed sampled and analyzed using inductively coupled plasma mass spectrometry. The dietary concentration of iodine offered daily was 33% lower for the low group compared with the high group; that is, 1.20±0.099 versus 1.81±0.195 mg/kg of dry matter (DM), respectively. Milk iodine concentrations averaged 146±13.9 μg/kg for the low group and 487±44.6 μg/kg for the high group. A linear relationship was found between dietary iodine concentration and milk iodine level, as follows: milk iodine (μg/kg)=145 (±66.9)+113 (±39.4) dietary iodine concentration (mg/kg DM). However, the low R(2) value (0.15) indicates that other factors, such as milking management and the presence of goitrogens, may have affected the concentrations of iodine in milk. Forages supplied approximately 17% of iodine requirements in the average lactating cow diet. Therefore, variations in the iodine content of forages are unlikely to cause iodine overfeeding. In contrast, 27% of the mineral mix samples presented iodine concentrations >100,000 μg/kg of DM (and up to 322,000 μg/kg of DM). More than 85% of the farms tested were feeding iodine levels higher than the dietary iodine recommendations (0.5 mg of iodine/kg of DM). Iodine supplements should be used with caution in lactating cow diets.

A model to secure a stable iodine concentration in milk

“…However, there are considerable differences in milk iodine levels when feeds with and without rapeseed products are offered ( 5 , 30 ). In contrast to previous models ( 5 , 24 – 26 ), the models in the present study included intake of GSL or rapeseed products in addition to iodine as variables in the same model. The model explains a large part of the variation in milk iodine concentration.…”

“…Models for a theoretical prediction of iodine concentration in milk have been introduced; however, these models have used iodine intake as the only variable ( 24 – 26 ) and do little to explain variations in iodine concentration. Moreover, they indicate that other factors, such as goitrogenic substances, considerably affect milk iodine concentration.…”

Large Variability of Iodine Content in Retail Cow’s Milk in the U.S.

“…Dairy products provide 49% of total estimated daily iodine intake from food in the U.S. [15], making milk one of the most common food sources of iodine [16,17]. The concentration of iodine in milk is affected by the iodine content of the cows' diet and iodine supplementation levels [18], presence or absence of goitrogens [19], sanitation practices that may or may not use iodine in different forms, levels, and modes of application [20], seasons and other factors [21][22][23].…”

Effects of different strategies of mineral supplementation (marine algae alone or combined with rumen boluses) in organic dairy systems

“…However, it is also possible that the low Se and I status of cattle under organic systems in Spain could lead to a lower production in these farms compared to other pastured‐based farms in this area, which can lead to reproductive disorders and other diseases (Cook and Green, , ; Spears and Weiss, ; Borucki‐Castro et al., ; Overton and Yasui, ).…”

“…All these studies have pointed out that the general mineral restrictions in organic farming leads to a significantly lower I content in organic milk, which could pose a problem for populations at risk including pregnant women and children (Bath et al, 2012). However, it is also possible that the low Se and I status of cattle under organic systems in Spain could lead to a lower production in these farms compared to other pastured-based farms in this area, which can lead to reproductive disorders and other diseases Green, 2007, 2010;Spears and Weiss, 2008;Borucki-Castro et al, 2011;Overton and Yasui, 2014).…”