Rumen–reticulum organ mass and rumen mucosa surface area of white-tailed deer (Odocoileus virginianus) consuming two energy diets

Abstract

Flexibility in gut morphology has fitness consequences in herbivores. To accommodate dietary variation in energy concentration, rumen-reticulum absorptive capacity and organ mass might also covary. We hypothesized that low energy diets result in greater food intake but lower volatile fatty acid concentrations. The consequence would be heavy rumen-reticulum organs and low absorptive capacity. We measured rumen-reticulum organ mass and absorptive capacity in captive white-tailed deer (Odocoileus virginianus Zimmermann, 1780) from central Texas, USA. Deer consumed a pelleted ration, ad libitum, of 1.77 (low) or 2.67 kcal/gm (standard) digestible energy from the time animals were weaned. In December, 4.5- and 5.5-year-old deer were euthanized, the rumen-reticulum was extracted, thoroughly rinsed, wrung out, and weighted. Four, 1 x 3 cm samples were extracted from four regions of the rumen and mucosal surface area was measured. Our surrogate of food intake and mastication intensity was first molar height. Molar height was lower in animals consuming the low energy diet. Analyses indicated sex-specific responses. Males eating the low energy diet had heavier rumen-reticulum organs but females did not. Females consuming the low energy diet had lower SEF but males did not. The processes driving variation in rumen-reticulum morphology from dietary variation require further examination.

Ontogenetic and static scaling of antler mass in White-tailed Deer (Odocoileus virginianus)

“…Diet and litter type were 2 reasons for body and antler mass variability in 1.5-year-old males. Dietary influences on growth trajectories of ungulates are well-studied (Ullrey 1982;McCulloch and Smith 1991;Jones et al 2010Jones et al , 2018Spilinek et al 2020). There has been less work examining the expression of maternal effects on antler size.…”

“…For each male, the following morphological data were collected annually in October after antlers had been removed: left main beam length, right main beam length, Boone and Crockett score, left antler mass, right antler mass, and body mass. Antlers were removed with a hand saw just above the pedicle (Spilinek et al 2020). Lengths were recorded to the nearest mm and masses to the nearest 0.1 kg.…”

“…Males were fed ad libitum 1 of 2 kinds of pelleted feed from the time they were weaned until they perished. The diets differed in digestible energy (DE)-low-energy pellets had 1.77 kcal/g of DE and standard-energy pellets had 2.65 kcal/g of DE (Spilinek et al 2020). Both diets had a protein content of 18%.…”

“…The impact of dietary nutrition on antler growth has been well-studied in cervids. Male deer fed a low-energy diet throughout life have reduced body and antler size compared with deer that are fed a higher-energy diet (Ullrey 1982;McCulloch and Smith 1991;Jones et al 2010Jones et al , 2018Spilinek et al 2020). What has been less studied is how antler growth, relative to body mass, might change with dietary nutrition and age (Demarais and Strickland 2011).…”

Influences on food supply from elk abundance and precipitation early in the growing season

“…If a study of ungulate grazing is not designed to detect herbivore optimization, which would include measuring aboveground net primary productivity, then it will be difficult to detect when only forage state is measured. Another possibility is that per capita food intake might have varied across years from carry over effects that occurred the previous summer and fall when forage quality was low, and it might have been low for an extended period [47][48][49]. Per capita food intake in such a setting might then increase when green feed becomes available in late fall [19,38].…”