A potential case of copper-related sand eating behaviour in Grevy zebras Equus grevyi at Kolmården Wildlife Park

Abstract

In the spring of 2023, a zebra Equus grevyi at Kolmården Zoo was euthanized due to colic. During the autopsy, over 20 kg of sand was found in her intestines. During the summer of 2023, it was noted that the black stripes of the rest of the zebra group appeared less dark than usual. Two mares were observed actively eating sand at a specific location for the first time in August; when moved, they were not seen eating sand in other enclosures. When moved back to the original enclosure, they returned to eating sand from the same spot. Analysis of the sand from that specific location, compared to sand from other areas in the enclosure, showed markedly higher levels of copper (Cu), a mineral suggested to be associated with geophagia in horses Equus caballus when deficient. This, together with the coat coloring, strengthened suspicions of a Cu deficiency. The total diet had previously contained 9 ppm Cu in dry matter. First, the pellet feed was increased to raise this to 12 ppm; then, the pellet recipe was adjusted so that the diet increased to 14 ppm without further increasing the pellet amount. 30% of the Cu sulfate was replaced with copper chelate to putatively enhance absorption. In the spring of 2024, the amount of pellets was reduced while a Cu and zink chelate supplement was added, so that the total diet contained about 15 ppm Cu, with most of the Cu coming from bioavailable sources. During the summer of 2024, the zebras were not seen eating sand, except for one occasion after the introduction of a new stallion, during which the mares exercised intensively for many days. The results suggests Cu as the underlying cause of the observed behavior, which in turn may indicate nutritional wisdom.