Dairy and Swine Research and Development Centre, Agriculture and Agri-Food Canada, Sherbrooke, QC, Canada.
J Dairy Sci. 2011 Sep;94(9):4684-9. doi: 10.3168/jds.2010-3714.
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.
在之前的一项研究中，发现加拿大 501 个农场的牛奶碘浓度差异很大，似乎受到饲养方式的影响。从 200 个参与农场的亚群中选择了具有不同牛奶碘浓度的对照水平的农场，以确定牛奶碘浓度与不同饲料和给泌乳奶牛的全价日粮中这种矿物质的浓度之间的关系。选择了牛奶碘含量最低的 30 个农场（低组）和牛奶碘含量最高的 30 个农场（高组）。采集了批量奶样、所有饲料成分和水的样本。此外，每个农民都完成了一份调查问卷，提供有关饲养管理的信息。根据 Ration'L 软件（加拿大圣安妮德贝尔维尤的 Valacta）推荐的日粮中饲料量和用电感耦合等离子体质谱法分析的饲料样本中的碘浓度，估计了每个农场提供的碘量。低组的每日碘摄入量比高组低 33%；即，分别为 1.20±0.099 与 1.81±0.195mg/kg 干物质（DM）。低组的牛奶碘浓度平均为 146±13.9μg/kg，高组为 487±44.6μg/kg。发现日粮碘浓度与牛奶碘水平之间存在线性关系，如下所示：牛奶碘（μg/kg）=145（±66.9）+113（±39.4）日粮碘浓度（mg/kg DM）。然而，低的 R² 值（0.15）表明，其他因素，如挤奶管理和致甲状腺肿物质的存在，可能会影响牛奶中的碘浓度。饲草约占泌乳奶牛日粮中碘需求的 17%。因此，饲草中碘含量的变化不太可能导致碘过量喂养。相比之下，27%的矿物质混合物样本中的碘浓度超过 100,000μg/kg DM（高达 322,000μg/kg DM）。超过 85%的受测农场的给碘水平高于日粮碘推荐量（0.5mg 碘/kg DM）。在泌乳奶牛日粮中使用碘补充剂应谨慎。
