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 increments over eight weeks. A ration balancer was added during the 7th week of transition to ensure proper mineral and nutrient balance of the overall diet. Behavioral data, saliva, serum and fecal samples were collected during the eight weeks preceding and following the diet change. Behavioral data were collected approximately daily using instantaneous focal sampling. Serum was collected biweekly for insulin-to-glucose and calcium-to-phosphorus ratio analysis. Fecal samples were collected weekly to examine changes in microflora community structure. After the diet change, giraffe spent significantly more time feeding and significantly less time performing tongue and mouth stereotypies and people-directed and alert behaviors. The giraffe also experienced a significant decrease in salivary and serum insulin and serum insulin-to-glucose ratio. The diet manipulation did not result in a change in the serum calcium-to-phosphorus ratio, which remained >1:1 throughout the study. A significant shift in fecal microflora community structure was observed with effects from treatment and individual animal; further studies are needed to elucidate the nature of the change in fecal microbial community structure. We believe these changes represent an overall improvement in health from feeding a higher proportion of forage in the diet, and the reduced stereotypic behaviors may indicate an improvement in the welfare of these animals.