Scaling Relationships between Body Weight and Fermentation Gut Capacity in Cervus axis and Cervus elaphus nannodes

Abstract

The scaling relationship between body weight and fermentation gut capacity impacts dietary patterns of ruminants. Interspecific scaling relationships between body weight and fermentation gut capacity were reported to have a slope of 1.0 (isometric scaler) when body weights ranged between 3-5 orders of magnitude. The implications of an isometric scaling relationship between body weight and fermentation gut capacity have been extended to explain dietary patterns within species. Whether or not scaling relationships are isometric within a single species or when body weight differences between species are small is unresolved. The goals of my study were to determine if the intraspecific scaling relationship between body weight and fermentation gut capacity was isometric, assess any potential influence from reproductive status of females on the scaling relationship, and determine if the interspecific scaling relationship between two species differing in weight by roughly 200 kg was isometric. I collected 29 adult male (n = 8) and female (n = 21) axis deer (Cervus axis) from January 2004 to April 2005 at a private ranch in Bastrop County, Texas. Capacity of the rumen-reticulum, cecum, and colon, organs where fermentation occurs, was estimated by calculating wet weight and volume capacity. Forage samples were taken from the rumen-reticulum of each specimen to assess variation in forage quality across the collection period. Forage quality and gender did not influence scaling relationships for axis deer. Regressions for axis deer had isometric scalers for fermentation gut capacity. Female axis deer were analyzed for a relationship between reproductive status and fermentation gut capacity. A trend was identified with pregnant females having lowest fermentation gut capacity. Tule elk (C. elaphus) data (n = 25), collected using methods identical to mine, was combined with axis deer data to conduct an interspecific comparison between body weight and rumenreticulum capacity. Regression analysis estimated scalers that were similar for both axis deer and Tule elk but the scalers were not isometric. The scaling relationship between body weight and fermentation gut capacity is isometric for axis deer. However, scaling relationships between body weight and fermentation gut capacity are stronger between species than within a single species.