Effects of diets containing organic and inorganic zinc sources on hair characteristics, zinc concentration in blood and hair, and the immune response of dogs

Abstract

Background: There are two commercial forms of zinc, organic and inorganic, and its form may infl uence absorption and utilization by the animals. The inorganic form dissociates to Zn2+ in the gastrointestinal tract and can interact with other substances that the animal cannot absorb. The interest in using organic minerals has increased because of the reported potential of higher bioavailability compared to inorganic sources. In dogs, little research has been done concerning the bioavailability of organic and inorganic mineral sources. This study compared the effects of diets containing organic and inorganic zinc on hair characteristics, zinc concentration in blood and hair, and the infl uence of organic minerals on the immune response of dogs. Materials, Methods & Results: Eighteen healthy adult dogs of different breeds (Labrador, German Shepherd, Malinois Shepherd, and Rottweiler) were separated into two groups of nine animals per treatment and fed diets for 30 days. Two diets were used: an inorganic mineral source diet (IMSD) and an organic mineral source diet (OMSD). Four parameters were evaluated (days -14, 0, 10, 20, 30) to determine the hair characteristics: brightness, texture, looseness, and greasiness. On days 0 and 30, two blood samples were taken and two hair samples were collected to measure zinc concentrations. On the 10th day of the trial period, the animals received an injection of 4 mL of a 10% solution of sheep red blood cells (SRBC) subcutaneously as a stimulus to assess the humoral response. Blood samples were taken prior to injection as well as on days 10 and 20 post-injection for antibody titer. All dogs consumed adequate amount of the diets and body weight did not change during the experiment. The daily dry matter, energy, and zinc consumption did not differ between groups The zinc concentration in the blood remained stable throughout the experiment in animals fed the OMSD but decreased signifi cantly in the animals fed the IMSD (P = 0.0145). The zinc concentration in hair increased (P = 0.0075) in dogs fed the OMSD, while the dogs fed the IMSD had no difference. The consumption of the OMSD resulted in higher brightness in the hair of the face, muzzle, armpit, back, abdomen, and tail compared with the IMSD. The animals fed the chelated mineral-supplemented diet also showed better texture in hair of the abdomen (P = 0.0327), chest (P = 0.0335), and tail (P = 0.0291). The parameters looseness and greasiness showed no signifi cant differences. No differences were observed in the production of antibodies against SRBC between groups; however, the antibody concentration was maintained throughout the experiment in the animals supplemented with OMSD, in contrast to the animals supplemented with IMSD, which reduced their antibody concentration. Discussion: There is controversy in the literature regarding the benefi ts of organic over inorganic zinc source. This may be due to two factors: the time of zinc supplementation, and the levels of zinc included in the diets, which varies in each experiment. In the present study, both criteria were adequate for the responses evaluated and the results suggest that organic zinc is suitable for supplementation into the commercial dog foods and could enhance the hair characteristics of adult dogs. Moreover, the improvement in immune status, although subtle, must be taken into account. It should be noted that the diets were formulated with high levels of minerals, especially calcium, which increases the possibility of interactions and competition in the absorptive process, increasing the challenge and impairing absorption of divalent minerals.