No abstract

Scaling relationships between body mass and gut capacity are valuable to predicting digestive efficiency. Interspecific scaling relationships between body mass and gut capacity have consistently estimated a slope of 1.0; however, intraspecific scaling relationships between body mass and gut capacity have been highly variable. We examined the influence of demands of growth and production on scaling relationships of body mass and rumen–reticulum characteristics in white-tailed deer ( Odocoileus virginianus (Zimmermann, 1780)) because little is known about how juvenile and subadult ruminants accommodate increased digesta masses. We sampled 108 animals over a 2-year period and assessed the influence of body mass, time of kill, crude protein (%), and acid detergent fiber (%) in the rumen, lactation, sex, and back fat on rumen–reticulum organ mass, rumen–reticulum capacity, wet mass of the digesta, and the dry mass of the digesta. Juvenile and subadult white-tailed deer had rumen–reticulum organ masses, capacity, and digesta masses that were similar to adults because body mass and rumen–reticulum scaling relationships all had scalars similar to 1.0. Thus, under the confines of our study, ontogeny plays only a minor role in the physiological characteristics of the rumen–reticulum and the scaling relationships of body mass and rumen–reticulum capacity.

Intraspecific competition is one of the major factors that can have an effect on the resources utilized within a habitat. Differences in diet quality of selected forage have been noted in size-dimorphic ungulates. However, on an intraspecific basis, data demonstrating a body size influence on diet quality are lacking. We examined diet quality across a range of body masses (14–76 kg) in white-tailed deer Odocoileus virginianus (n  =  108) in a 2,628-ha enclosure at Kerr Wildlife Management Area, Kerr County, Texas, USA. The quality of the diet consumed was determined by crude protein, acid detergent fiber, and neutral detergent fiber content of digesta in the rumen–reticulum. Results indicated that in relation to body mass, the ratio of crude protein to acid detergent fiber was greater for smaller bodied white-tailed deer. By consuming a diet higher in crude protein than did large bodied individuals, small-bodied individuals should meet their high mass-specific metabolic demands more efficiently. Furthermore, selective foraging by different-sized individuals might also reduce intraspecific competition. Information presented herein is relevant to wildlife managers in that by increasing available high-quality forage, small-bodied individuals will more efficiently meet their metabolic demands, which could have ramifications on recruitment within that population.

Previous research into the liver has mainly examined liver function and liver response to energy restriction. There have been few investigations into how liver mass is coupled to body mass, body condition, age, and reproductive events like lactation. Therefore, we examined the scaling relationship between body mass and liver mass and the influences of age, sex, body condition (back fat), and lactation on liver mass to gain insight into liver-mass variation in white-tailed deer (Odocoileus virginianus (Zimmermann, 1780)). Deer from two sites in Texas (89 males, 70 females) were sampled; one site was sampled before the mating season (premating) and the other site was sampled during the mating season. There was an allometric relationship between body mass and liver mass (scalars 0.59–0.80) at both sites. Also, sex and age were predictors of liver mass at one site, whereas lactation was influential at the other location. Controlling for body mass, males had heavier livers than females during the mating but not the premating season and age was positively related to liver mass. Our findings indicate that sex and lactation status were coupled to liver masses, but the effect of these two factors differed between premating and mating seasons. It appears that animals in situations where metabolic demands might be higher than current nutrient intake, such as mature males during the rut or lactating females, have heavier liver masses when body mass is controlled.

No abstract