Nutrition for Health Bioavailability of Zinc Propionate in Dogs

Supplementation with zinc improves overall health, productivity and performance of production animals such as poultry, swine and dairy animals as measured by body weight increase, final body weight or feed/gain ratios. Reports on beneficial effects of zinc supplementation are fewer for companion animals. Lowe et al. (1994 a) reported more hair growth with higher zinc content in dogs upon supplementation with zinc. Based largely on research conducted with production animals, the NRC recommends a minimum of 39 mg zinc/kg dry matter for companion animals. However, clinical signs of zinc deficiency have been observed even when dietary zinc was increased above the recommended minimum levels (Van den Broek and Thoday 1986). Similar results were obtained for the supplementation of dog diets with dietary copper (Morris and Rogers 1995). The apparent deficiency can be explained in part by reduced bioavailability resulting from dietary antagonists and interaction with other minerals. Dogs and cats may also experience a higher demand for zinc under circumstances of stress, during growth periods, levels of high activity, gestation, lactation or illness (Morris and Rogers 1994). In the light of these observations, absorption and bioavailability of the zinc source are critical for effective zinc supplementation and maintenance of health of companion animals. Organic zinc sources have been demonstrated to possess greater bioavailability in production animals and thus may meet the animal’s zinc requirements better than inorganic sources. Higher absorption of organic zinc sources allows lower inclusion rates for zinc supplementation and makes mineral balance in animals easier to maintain. The zinc demands of pets vary by breed, genetics, life stage, nutritional status and environmental stress. The organic zinc form is also more likely to satisfy these varying demands, especially when the demand is greatest. In production animals, organic zinc sources such as zinc methionine or zinc propionate have been clearly demonstrated to be significantly more bioavailable than inorganic zinc sources such as zinc oxide or zinc sulfate (Hahn and Baker 1993, Kemin Industries 1995, Wedekind et al. 1992). In companion animals, supplemental zinc from zinc amino acids resulted in dogs growing more hair of a higher zinc content compared with zinc oxide (Lowe et al. 1994 b). Furthermore, the negative effect of calcium on zinc absorption was overcome when zinc was supplied as a zinc amino acid compound. The objective of this study was to compare absorption and availability of an inorganic and an organic zinc source. The serum levels of zinc after oral administration of zinc oxide and zinc propionate were determined over a period of 6 h after intake. Material and methods. The experiment was conducted by Summit Ridge Farms, Susequehanna, PA. The protocol was reviewed by the Institutional Animal Care and Use Committee and was found to comply with the Animal Welfare Act. Ten adult beagles, 8.98–13.4 kg body weight, were used for this experiment. Food was withheld for a 24-h period before administering the zinc supplement and during the testing period. Before food restriction, the dogs were fed a diet according to Table 1. Water was freely available. Zinc was provided in gelatin capsules as either zinc oxide or zinc propionate. The zinc dosage administered was 5 mg zinc/kg body weight. Two groups (n 5 5/group) received either the zinc oxide or the zinc propionate treatment. Blood was drawn before dosing (time 0) and 30 min, 1, 2, 3 and 6 h after dosing. Samples were centrifuged at 6°C and 3000 3 g for 15 minutes and the plasma was stored at 220°C. Plasma samples were analyzed for zinc using atomic absorption spectrometry (Perkin-Elmer 460 AA). For the statistical analysis, a two-factor ANOVA test, utilizing a Duncan multiple range test to analyze the interaction of diet and time was used. Differences were considered significant at the 95% probability level. Results and discussion. Results of the study are summarized in Figure 1. Zinc plasma levels for the zinc propionate and zinc oxide treatments were significantly different (P , 0.05) for all measurements except for 0 and 2 h. A twofactor ANOVA test revealed that the effect of time on zinc absorption was significant (P 5 0.0132) and the interaction of time vs. zinc treatment was significant as well (P 5 0.025). Zinc levels in the blood plasma were significantly higher over the entire 6-h period measured when zinc propionate was fed compared with zinc oxide (Fig. 1). A pronounced peak in zinc 1 Presented as part of the Waltham International Symposium on Pet Nutrition and Health in the 21st Century, Orlando, FL, May 26–29, 1997. Guest editors for the symposium publication were Ivan Burger, Waltham Centre for Pet Nutrition, Leicestershire, UK and D’Ann Finley, University of California, Davis. 2 To whom correspondence should be addressed.