Effects of dietary zinc chloride hydroxide and zinc methionine on the immune system and blood profile of healthy adult horses and ponies.

The effects of dietary zinc on the immune function of equines have not been evaluated in detail so far. In the present study, eight healthy adult ponies and two healthy adult horses were fed a diet supplemented with either zinc chloride hydroxide or zinc methionine in six feeding periods of four weeks each (according to maintenance zinc requirement, 120 mg zinc/kg dry matter, and 240 mg zinc/kg dry matter, for both dietary zinc supplements, respectively). All animals received the six diets, with increasing amounts of zinc chloride hydroxide in the feeding periods 1-3, and with increasing amounts of zinc methionine in the feeding periods 4-6. At the end of each feeding period, blood samples were collected for a blood profile and the measurement of selected immune variables. Increasing dietary zinc chloride hydroxide doses increased the glutathione concentrations in the erythrocyte concentrate and the glutathione peroxidase activity in the erythrocyte lysate, decreased the numbers of total leukocytes and granulocytes in the blood, and also decreased the interleukin-2 concentrations in the plasma of the animals. The dietary supplementation of increasing doses of zinc methionine enhanced the mitogen-stimulated proliferative activity of peripheral blood mononuclear cells, and decreased the glutathione concentrations in the erythrocyte concentrate and the glutathione peroxidase activity in the plasma of the animals. The percentage of blood monocytes with oxidative burst after in vitro stimulation with E. coli decreased with increasing dietary zinc concentrations, independently of the zinc compound used. The blood profile demonstrated effects of the zinc supplements on the red blood cells and the bilirubin metabolism of the horses and ponies, which require further investigation. Overall, high doses of dietary zinc modulate the equine immune system, for the most part also depending on the zinc compound used.

Zinc Status of Horses and Ponies: Relevance of Health, Horse Type, Sex, Age, and Test Material.

Little is known about the animal- and diet-related factors that could interfere with the plasma zinc (Zn) concentrations of equines. Additionally, the adequacy of plasma to reflect changes in the Zn intake is unclear. In the first part of this study, the plasma Zn concentrations of hospitalized horses and ponies (n = 538) were measured and evaluated for the impact of the age, sex, horse type, and internal diseases of the animals. In the second part, the effects of increasing dietary Zn chloride hydroxide and Zn methionine supplementations were assessed on the plasma and mane hair Zn concentrations of healthy horses (n = 2) and ponies (n = 8). Part 1: The age, sex, and horse type did not influence the plasma Zn concentrations. No effect of internal diseases was observed, with the exception of higher plasma Zn concentrations in animals with metabolic disorders compared to the control group (p < 0.05). Part 2: Both Zn supplements dose-dependently increased the Zn concentrations in the mane hair (p = 0.003), but not in the plasma of the horses and ponies. In conclusion, the plasma Zn concentrations were widely unaffected by nutritional and non-nutritional factors in equines, while mane hair samples better reflected the dietary Zn supply.

Impact of Dietary Zinc Chloride Hydroxide and Zinc Methionine on the Faecal Microbiota of Healthy Adult Horses and Ponies.

Zinc supplements are often used in equine nutrition to support skin and hoof quality or the immune function. However, no data on the effects of dietary zinc on the intestinal microbiota of horses and ponies are available so far. In the present study, varying dietary zinc concentrations (maintenance (4 mg/kg BW0.75/day), 120 mg/kg dry matter (DM)/day and 240 mg/kg DM/day) were achieved by the supplementation of either zinc chloride hydroxide or zinc methionine (six treatment periods of 4 weeks each). Eight healthy adult ponies and two healthy adult horses were included, and faecal samples were collected at the end of each treatment period to analyse the microbiota (16S rDNA sequencing) and microbial metabolites. With increasing dietary zinc concentrations, the richness of the faecal microbiota decreased, independently of the zinc compound used. In addition, a decrease of the relative abundance of Bacteroidetes and Fibrobacteres as well as of acetate and total short-chain fatty acids in the faeces of the animals was observed at high zinc intakes. Effects on the bacterial order, family and genus level were also detected, which were partly more pronounced for zinc chloride hydroxide. It can be concluded that high dietary zinc levels decrease the richness and fermentative activity of the faecal microbiota of horses and ponies. Although all animals were healthy throughout the study, the effects could be critical for gut health, and deserve more research. The detected differences between the zinc compounds used indicate differences in the bioavailability of organic and inorganic zinc sources in equines.