We hypothesized that switching to a diet that provides a higher hay-to-grain ratio offered to four Masai giraffe (Giraffa camelopardalis tippelskirchi) at the Cleveland Metroparks Zoo would reduce oral stereotypies and increase time spent performing feeding behaviors, maintain or increase serum calcium-to-phosphorus ratio, decrease serum insulin-to-glucose ratio, and alter fecal microbiome community structure. The diet change consisted of transitioning the male from a 50:50 hay-to-grain ratio and the females from a 70:30 hay-to-grain ratio to a 90:10 ratio in even