Subacute ruminal acidosis is a common disease in captive non-domesticated ruminants and is mainly diagnosed by rumen fluid pH and rumen histology. Furthermore, differences in ruminant gastrointestinal histology have been hypothesized to correlate with the browser-grazer continuum. Twelve surplus addax antelope (Addax nasomaculatus) were divided into two groups, fed either their usual diet, consisting of a concentrate feed with a limited amount of hay, or a diet of unlimited hay only, for 3 months. After culling, descriptive and morphometric histology and pH measurements were compared between groups. Significant variations in cellular subpopulations were noted between groups, with roughage-fed individuals presenting primarily with balloon cells of the Stratum corneum and living layer cell vacuolization, whereas parakeratosis and intermediate-type cells were more frequent in the concentrate-fed group. Lesions typical of subacute ruminal acidosis were significantly more pronounced in concentrate-fed individuals. Ruminal pH measurements did not differ significantly, but were more consistent in forage-fed individuals, indicating a more stable reticuloruminal environment. The results indicate that ruminal histology may be more appropriate in assessing ruminal health compared to a single post-mortem pH measurement. It is proposed that Stratum corneum balloon cells may indicate cell maturation and not, as previously assumed, hyperfunction. Concentrate-fed individuals scored higher on the presence of inflammatory cells on hoof corium histology. The study further emphasizes the adaptability of ruminant digestive tract microanatomy in adult animals even after a short period of time and the positive effects an increased roughage diet may have in populations of captive grazing ruminants.