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Agnieszka Kurosad, Pawel Jonkisz, Agnieszka Sikorska-Kopylowicz ©
Department of Internal Diseases with Clinic for Horses, Dogs and Cats, Faculty of Veterinary Medicine, Wroclaw University of Environmental and Life Sciences,
Poland
INFLUENCE OF IODINE CONTENTS IN FOOD ON ITS CONSUMPTION,
URINARY IODINE EXCRETION AND CONCENTRATION OF THYROID HORMONES IN CAT BLOOD SERUM
Abstract
The main aim of this study was to identify how iodine contents in cat food and Kalium iodide supplement influence food consumption, urinary iodine excretion and thyroid hormone concentration in cat s blood serum. The experiment was performed on 48 adult cats, divided into two groups no. I and no. II. The group no. I was composed of 30 European cats and the group no. II - of 18 Pure-bred cats (Persian and Exotic). Kalium iodide supplement was introduced into 3 subgroups: B, C, D in doses: 50, 100, 200 jug iodine/cat/d., respectively and it was given twice for 14-day-test terms. In group no. I no adverse effects on food consumption were observed. Urinary iodine excretion was proportional to iodine ingestion, but in cat blood serum from group no I the thyroid hormone levels were decreased. The iodine-creatinine ratio was in reference range in properly nourished cat. According to our observation: iodine consumption, iodine excretion and thyroid hormone levels in cats blood serum from group no. I and II, we may confirm that the iodine requirement proposed by Kraft, equals: 100-150 ug iodine/cat/d was optimal.
Key words: iodine, Kalium iodide, thyroid hormones, cat
Introduction
Iodine was discovered in France, in 1804, by Bernard Courtois. It is the main constituent of thyroid hormones. The main natural source of iodine for human are: algaes, fishes, milk and dairy products and eggs. However, for cats the main source of iodine is a commercial cat foods. Abnormal iodine level in cats diet can produce thyroid dysfunction (hyperthyroidism, hypothyroidism). Giving cats many various products with very high and very low level of iodine we may create the feline hyperthyroidism.
The aim of the experiment
The main aim of the experiment was to evaluate the influence of iodine content in food and Kalium iodide supplementation on its consumption, amount of iodine excretion in urine and serum concentration of thyroid hormones in cats.
© Agnieszka Kurosad, Pawel Jonkisz, Agnieszka Sikorska-Kopylowicz, 2009
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Material and methods
48 adult, healthy cats were divided into 2 groups. The first was consisted of 30 European cats (14 females, 16 males - neuter), in the age from 3 to 6 years old, weighted from 4 to 5 kg, living in the cats kennel in Department of Internal Diseases in Wroclaw. 7 days before the trial started, the thyroid hormones concentration (T4, T3, FT4) in blood serum was evaluated. Clinical examination, weighing and blood samples for haematological and biochemical analysis was taken from all cats on the first day of the experiment. The creatinine and iodine concentration was evaluated in urine. Cats were classified into the groups according to the results of clinical examination and laboratory analysis.
30 cats were divided into 5 subgroups, marked by capital letters from A to E. Subgroups A and E were set as the control for testing groups: B, C and D. Cats from subgroups A, B, C and D consumed the commercial cat food with beef and vegetables, marked as product K. Iodine content in cats food was evaluated in laboratory by modify Sandell-Kolthoff s methods.
The experiment lasted 49 days. The first 6 days were treated as pre-trials period, but for the next 14 days cats from subgroups: B, C and D were given the iodine in form of commercial therapeutic preparation named Jodid, produced by Merck. The animals from subgroups B, C and D obtained iodine in daily doses of 50, 100 and 200 ^g/cat/day, respectively. After 1 week-break of giving Jodid 100, the whole cycle of iodine administration was repeated in cats from subgroups B, C and D. The last 7 days of the experiment was lasting without giving Jodid 100. Each weeks, during the test, 24h urine collection was taken into the analysis for iodine concentration. The thyroid hormones concentration in cats blood serum was evaluated on 21 and 42 day of the test and on 7 day after its ending. Every day, the food consumption was noted and every week, cats were weighted.
The group no. II was consisted of 18 adult Persian and Exotic cats (9 females, 9 males), from the age of 2 to 9 years old, which were lived in houses of private owners from Poland. All cats were divided into 3 subgroups (marked by capital letters: R-1, R-2, R-3) consisted of 6 animals. These experiment lasted 14 days and during those time the urine and blood samples from cats were taken twice, e.g. on the first and 14 day of these test.
Haematological and biochemical analysis, general analysis of urine and creatinine concentration in urine were evaluated in the Laboratory of the Department of the Internal Diseases in Wroclaw. The estimation of iodine concentration in urine was done by modify Sandell-Kolthoff method in Diagnostic Laboratory of Jagiellonsky University in Cracow. The concentration of serum thyroid hormones was evaluated by RIA in the Isotopic Laboratory of the Medicine Academy in Wroclaw.
Results of researches
The estimation of testing foods. The quality analysis of the composition of cat foods was based on pet food label. The content of the product K, in descending order, was: cereals, meat-by product, vegetables, yogurt, animals fat, vitamins, colorants, preservatives, antioxidants.
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Product R was enabled as Premium, the best quality pet-foods. Dry poultry meat was the basis of the product R. The other ingredients, in descending order, were: rice, corn, corn gluten, poultry fat, fibre, dry poultry liver, corn flour, beet pulp, brewer yeast, minerals, oils, cod-liver oil, eggs power, D- and L-methionine, taurine, vitamins.
The quantity analysis of the foods. The main aim of those analysis was estimation the nutritional values of both products R and K, designed for adult cats, that was very important for the proper estimation of iodine-creatinine ratio. The quantity composition of both K products: with beef and vegetables and with chicken and vegetables, was the same. The crude protein content in both K products was 26% as fed , crude fat: 9%, carbohydrate: 45,5%, ash: 8%, crude fibre: 1,5%, water: 10%. In product R, crude protein was: 32% as fed, crude fat: 13%, carbohydrate: 38%, ash: 6,5%, crude fibre: 2,5%, water: 8%.
The iodine content in testing foods was: 0,1 mg/kg DM (K with beef and vegetables); 1,6 mg/kg DM (K with chicken and vegetables) and 2,5 mg/kg DM (R), respectively. If only the owner nourishes his cat all these three products alternatively and if these food changing are taken very often in feeding periods, he will provide his cat a three different amount of iodine which may influence on the thyroid hormones concentration.
Food and iodine consumption. In cats from all subgroups, food and iodine consumption was estimated on the level of 50% of their daily doses. The mean value of actual food and iodine consumption increased from day no. 1 to day no. 28 with two - days decrease in day no. 21 (in subgroups B and E) and 28 (subgroup D). In day no. 35 the actual food and iodine consumption decreased in all subgroups and after day no. 35 it progressively increased up to day no. 49. In subgroups: B, C, D, supplemented by Jodid 100, the iodine consumption was very high, around from 50 up to 205 ^g/cat/day, respectively. In group no. II food and iodine consumption was estimated on the level from 94% to 95% of the general consumption. Cats ate nearly 60g of food per day and consumed from 134 to 154 ^g iodine/cat/day, respectively.
Additionally, in both groups the palatability value of the products K and R was evaluated. Product R was the best, according to its palatability. Lower palatability of the product K might have decreased the food and iodine consumption in group no. I. Those result indicates that food should be not only nutritionally adequate for the special species but also enough tasty for them.
In subgroups: B, C and D, supplemented by Jodid 100, we did not observed any adverse reaction on iodine suplementation. However, in pigs iodine supplementation resulted in increase in daily body weight and better utilization of food consumed.
Creatinine level in urine. Creatinine is the main product of the muscles metabolism, independent of the protein content in food. The proper creatinine concentration in cats urine was limited from 110 up to 280 mg/dl.
Nearly two-fold increase in urine creatinine concentration was observed in 70% cats from group no. I. Lower food consumption resulted in inadequate cats' organism nourishment led animals into the negative energy balance, body mass
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decrease and increase in creatinine concentration in urine. In group no. II, where the food consumption was constant, the variation of the urine creatinine concentration was described as an insignificant and more dependent on such factors as: day's time, age and sex.
Iodine concentration in urine. 24-h iodine excretion in urine was straight proportional to iodine consumption in cats from the group no. I. It was the most obvious in subgroups: B, C and D, which were supplemented by Jodid 100. Tartellin et al. on their own experiment, observed that iodine excretion was changing proportionally to iodine content in cats food. Kyle et al. in long - term test (5 months), concerning on giving the cats diets with very high and very low amount of iodine, observed significant differences in iodine excretion just after 2 weeks of the experiment started. But iodine excretion in urine was also, as in Tartllins experiment, straight proportional to iodine consumption by cats. The same results were observed in tests performed on cats and dogs in France and Germany.
To sum up it may be ascertained that despite of that how long the iodine was consumed (2 weeks, 6 weeks or 5 months), its excretion is straight proportional to its content in food consumed. However, iodine excess is removed by kidney without any special regulatory mechanisms and limited value. Such as mechanisms work either in healthy or sick animals with thyroid dysfunction.
Because of low food consumption (especially it concerns on product K with beef and vegetables) and high creatinine concentration in cats urine from group no. I, iodine - creatinine ratio was irrelevant in estimation of iodine excretion in urine. However, in cats form group no. II, which consumed proper amount of food, those index was adequate to evaluate iodine excretion in urine.
The conclusion is that the iodine - creatinine ratio should be evaluate based on the analysis of animals nutrition and physiological fluctuations of creatinine concentration in urine.
Thyroid hormones concentration. Thyroid hormones concentration depend on the time of day, season, reproduction period and minerals supplementation. High iodine concentration in blood serum decreases production and release of thyroid hormones. It was confirmed by those experiment, where the iodine supplementation (Jodid 100) was introduced into the subgroups: B, C and D. After 2 weeks of iodine supplementation in all subgroups T3 and T4 concentration decreased in blood serum but Ft4 concentration increased. All of the results were within the reference range, estimated by Kraft. After next 2 weeks-period of iodine supplementation, the mean values of T3 and T4 concentration were significant lower then the lowest range of the reference values for serum thyroid hormone levels. Serum Ft4 concentration was also decreased. 7 days after the experiment was ended serum thyroid hormones concentration came round to the normal range. Peterson and Scarlet in their experiments also observed decline in serum concentration of T3 and T4. However, Tartellin and Ford in the test, performed on cats consuming very high level of iodine for 2 weeks, observed decrease in FT4, suggested that high level of iodine may decline the FT4 serum concentration. Next, the same experiment was repeated in 5 months period of time and the authors did not observed continuing decrease in FT4
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concentration in cats blood serum. In all performed experiments, serum T4 concentration reacted the most sensitive due to changing level of iodine consumption.
In cats from group no. II the thyroid hormones concentration was stable for all period of the experiment and placed within the reference range.
The results of study may indicate the proper level of iodine daily doses for adult cats. When cats consumed food with very low amount of iodine (0,1 mg/kg DM - product K with beef and vegetables), the thyroid hormones level declined significantly what could have led cats into hypothyroidism. Animals, which consumed food with iodine content of 1,6 mg/kg DM and 2,5 mg/kg DM, obtained daily doses of iodine from 122 to 160 ^g iodine/cat. Those quantity of iodine had no adverse effects on serum thyroid hormones concentration and iodine excretion in urine. Summing up, the daily iodine requirement for adult cats proposed by Kraft is still more reliable than others.
In cats from subgroups: B, C, D, the thyroid function was blocked by Jodid 100 supplement. Thyroid hormones concentration was declined and excess of iodine was excreted in urine. It means that iodine supplementation in form of Kalium iodide (Jodid 100) strongly influenced thyroid function and its value as the iodine supplement is not efficient.
Conclusion
1. Iodine, consuming by cats, does not influence the daily food consumption
2. Excess of iodine is excreted in urine
3. Iodine - creatinine ratio in properly nourished cats may be useful for the estimation the amount of iodine excreted in urine
4. Iodine supplementation in form of Kalium iodide, in daily doses of: 50, 100 and 200 ^g iodine/cat blocked the thyroid function and as the indicator of those reaction serum T4 concentration can be considered
5. Daily iodine requirement for adult cats should be limited from 100 to 150 ^g iodine/cat/d.
References:
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Summary
Kurosad A., Jonkisz P., Sikorska-Kopylowicz A.
Department of Internal Diseases with Clinic for Horses, Dogs and Cats, Faculty of Veterinary Medicine, Wroclaw University of Environmental and Life Sciences,
Poland
INFLUENCE OF IODINE CONTENTS IN FOOD ON ITS CONSUMPTION, URINARY IODINE EXCRETION AND CONCENTRATION OF THYROID HORMONES IN CAT BLOOD SERUM
The article describes the study on cats concerns on the influence of iodine contents in food on its consumption, urinary iodine excretion and concentration of thyroid hormones in cat blood serum. Our research showed that excess of given iodine is excreted in urine, but we cannot use Kalium iodide in Jodid 100 specimen as a iodine supplement in cats, because it blocked the thyroid function. Based on our research and previous experiment of other scientists we may conclude that the daily iodine requirement, equals: 100-150/ug of iodine per cat per day, proposed by Kraft is still the most adequate value.
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