Veterinary medicine
Effect of a combined iodine and selenium supplementation on I and Se status of cows and their calves

https://doi.org/10.1016/j.jtemb.2011.02.003Get rights and content

Abstract

Iodine (I) and selenium (Se) deficiencies are commonly reported in cattle, however, there are also studies regarding a very high iodine supply. The aim of the study was to determine the long-term effect of I and Se supplementation on non-pregnant cows, pregnant cows and their calves. The hypothalamus pituitary axis was investigated (TSH, T4, T3 assays) during a TRH challenge on non-pregnant cows. Twenty-four cows, half of them pregnant, were assigned into 2 diet-groups, one group with a low I (0.45 ppm) and Se (0.15 ppm) diet (LISe), the other with a high I (5.45 ppm) and Se (0.45 ppm) diet (HISe), for a period of 120 days. Nutritional (plasma iodide, urinary I, plasma Se, I content in colostrum and foetal fluids) and functional (thyrotropin, thyroid hormones, glutathione-peroxidase activity in erythrocytes) markers of I and Se status were assayed in dams at regular intervals for 120 days and in their calves at birth. A TRH challenge was performed on 8 non-pregnant cows at day 110 of the trial. At the end of the study, I and Se nutritional markers were higher in dams in the HISe group, compared to the LISe group, except for plasma Se. At birth, I nutritional markers in calves in the HISe group were higher compared to the LISe group. Reactivity of the pituitary–thyroid-axis was not influenced by I and Se supplementation. I and Se supplementation is efficient in improving newborn status.

Introduction

Iodine (I) deficiency is recognised as an international public health problem [1]. Recently, individual country and European regulations have increased the specified I requirements for people and animals [2], [3]. I deficiency during pregnancy may impair the growth and neurodevelopment of offspring and increase infant mortality. I deficiencies are commonly reported in cattle around the world [4], [5] and are associated with abortion and stillbirth and with weak calves [6]. However, to date, few studies have investigated placental transfer of trace elements in cattle [7]. As most of the symptoms involve the offspring of deficient dams [6], it is important to obtain an evaluation of the Se and I status of the dams before calving.

Selenoenzymes of the deiodinase family regulate the levels of thyroid hormones. Consequently, as Se is required for the biosynthesis of selenocysteine-containing proteins, there is an interplay between Se and I in thyroid function [8]. However, apart from considerations of the role of these trace elements in thyroid function, this interplay has been poorly investigated, both in cattle and humans.

To assess I intake in cattle, the commonly used methods are plasma iodide (PI) assays [4], urinary I or I content in milk [9]. Changes in thyroid hormone concentration are related to thyroid function and cannot be used to assess a nutritional factor such as I [9], [10], except in extremely low and too high I supply. An increase in thyrotropin (TSH) levels has been proven to be sensitive enough in mammalian species to be useful in evaluating thyroid function. Recently, reference values for TSH and T4 have been defined in cattle [11].

For assessing Se status, plasma Se, a short-term marker [12] and glutathione-peroxidase activity in erythrocytes (GPX), a long-term marker, are used and are correlated [13], [14].

The purpose of the study was to determine the long-term effect of I and Se supplementation on non-pregnant cows, pregnant cows and their calves. The interplay between I and Se was also investigated. Testing of TRH response was included in order to obtain information regarding the function of the hypothalamus pituitary axis.

Section snippets

Materials and methods

The study was divided into 3 parts. The first part consisted of a long-term trial (120 days) where the I and Se status of pregnant and non-pregnant cows, supplemented (HISe: High I and Se) or not (LISe: Low I and Se) with Se and I, was measured. The second part involved the assessment of the I and Se status of the calves of the pregnant supplemented and un-supplemented cows. At the end of the long-term trial, after calving, a TRH challenge was performed on these cows (3rd part).

Dams

At D0 and until delivery (D60), there was no significant difference (p > 0.1) observed between pregnant and non-pregnant cows regarding PI, TSH, T4 and T3, under the same diet (other markers not assayed at D30). Thus, the data of pregnant and non-pregnant cows were mixed within the HISe and LISe groups. The comparisons between the mean values of Se, GPX, PI, I urine, TSH, T4, T3, rT3 and T4/T3 in the 2 groups of cows as well as their statistical relevance are shown in Table 2. Nutritional I

Selenium and iodine status of the cows

In order to estimate the potential common action between Se and I, the trial was conceived with a simultaneous I and Se supplementation, as it was mostly carried out in the field. However, a larger number of cows and more groups (with or without Se and/or I) would be necessary to prove this interaction. The LISe group barely met the minimal National Research Council (NRC) requirements [17] for I and Se levels in non-lactating cattle (0.33 mg I/kg DM and 0.3 mg Se/kg DM). The HISe group received

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      The high level of iodine fed to the cows in the HI treatment group was reflected in the greater concentration of iodine in the plasma of calves of both the HI_HI and the HI_MI treatment groups when sampled at 0 h of age. Circulating iodine in the pregnant cow is readily transported to the bovine fetus (Aschbacher et al., 1966; Miller et al., 1967; Guyot et al., 2011), and thus the high level of PII in the HI_HI and the HI_MI calves is not surprising. Consistent with previous studies (Miller et al., 1967; Gilles et al., 2009), PII levels declined between 0 h and 24 h of age by 50, 50, 54, and 59% for calves in the MI_MI, SI_SI, HMI_HMI, and MI_HI treatment groups, respectively.

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