Effects of monoterpenoid exposure on ability of rumen inocula to digest a set of forages.

Nagy et al. (1964) using in vitro techniques found that the monoterpenoids (essential or volatile oils) of big sagebrush (Artemisia tridentata) suppressed the growth of mule deer rumen microorganisms, decreased the rate of cellulose digestion and the production of gas and volatile fatty acids by the microorganisms. Oh et al. (I 967, 1968) found that the monoterpenoid hydrocarbons (the monoterpenes) of Douglas-fir needles actually enhanced in vitro microbial fermentation in sheep and deer inoculum. Sesquiterpenes were also found to be stimulatory. Microbial fermentation, however, was suppressed in the presence of the oxygenated monoterpenoids (alcohols, esters, aldehydes) of Douglas-fir (Oh et al. 1967, 1968; Longhurst et al. 1969). After a review of the literature, Welch and McArthur (1979) concluded that the results of in vitro and in vivo digestibility trials of big sagebrush did not support the contention that monoterpenoids suppressed digestion in mule deer. It was suggested by Nagy et al. (1964), Welch and McArthur (1979), and Van Soest (1981) that microorganisms in the rumen may be able to adapt to big sagebrush monoterpenoids. Observations made by Oh et al. (1967) support the adaptation idea. They found that citonellal (aldehyde), an oxygenated monoterpenoid, inhibited rumen microorganisms from sheep and deer that had no access to Douglas-fir needles (a monoterpenoid source), but produced no effect upon rumen microorganisms from deer that had access to Douglas-fir. Rumen inoculum collected from wild mule deer on summer, fall, winter, and spring ranges in central Utah was equally effective in If adaptation is important, the inoculum with unadapted rumen digesting alfalfa hay, orchardgrass hay, big sagebrush, curlleaf microorganisms should digest big sagebrush forage less readily mahogany, antelope bitterbrush, and hips of sweetbrier rose. than inoculum with adapted microorganisms. Therefore, we undertook this study to test the hypothesis that rumen inoculum Alfalfa hay was the forage most easily digested. Inocula from deer that had not been exposed to big sagebrush and juniper monotercollected from mule deer not consuming big sagebrush (summer penoids (essential oils) digested all test forages, including big sagerange) would digest significantly less dry matter of winter samples of big sagebrush forage than inoculum collected from mule deer brush equally as well as inoculum from deer that had been exposed consuming big sagebrush (winter range). to big sagebrush monoterpenoids. We concluded that rumen microorganisms do not have to adjust to the presence of the Materials and Methods monoterpenoids or other dietary changes. During 1979-1980, we collected rumen inoculum from 13 wild mule deer at seven points in time: July 18, September 7, October 29, December 3, January 14, February 25, and April 17. Two mule deer were sacrificed for each time period, with the exception of October 29 when one deer was taken. Deer were obtained from native ranges in central Utah. The method we used to collect rumen inoculum was described by Nagy et al. (1964). The collections of rumen inocula were tested against four native forages and two dry roughages collected from one site in central Utah and at one point in time. Native forages included the current year’s growth of big sagebrush, curlleaf mahogany (Cercocarpus ledifolius), antelope bitterbrush (Purshia tridentata), and the hips from sweetbrier rose (Rosa eglanteria). These forages were collected during midwinter and ground with a motorized steel mortar and pestle to a fine powder in liquid nitrogen (Welch and Pederson 1982). During the early spring of 1979, samples of alfalfa (Medicage sativa) and orchardgrass (Dactylis glomerata) were collected, dried, and ground in a Wiley mill (1 mm). All forages were stored in a freezer (-35” C). Welch and Pederson (1982) through in vitro means, found big sagebrush to be a highly digestible browse for wintering mule deer. They collected rumen inoculum from wild mule deer that had been feeding on big sagebrush for about 3 weeks. This was to ensure that the rumen microorganisms had fully adapted to the presence of big sagebrush monoterpenoids. Although that study (Welch and Pederson 1982) demonstrated that rumen inoculum readily digested big sagebrush, it did not furnish evidence concerning the ability of rumen microorganisms to adapt to the presence of monoterpenoids. We used the in vitro digestion procedure outlined by Pearson ( 1970), except that 1 . O g of fresh tissue was used for the four native forages. The dry matter content was determined for all forage samples digested. Rumen inoculum for each deer was tested separately. Burbank et al. (1979) reported that the pH of the bufferrumen inoculum can significantly affect the digestive ability of the inoculum. We found that the pH of the rumen fluid collected from the 13 deer varied from 6.5 to 6.8, therefore, the pH of the bufferrumen inoculum was adjusted to a pH of 6.8. Data were expressed as percent of digestible dry matter. Percentages were transformed (arcsin) for statistical analysis. Analysis of variance for a completely randomized design was used to evaluate differences in treatment effects. Treatment effects were measured by the ability of the various inoculum sources to digest each forage. Hartley’s range test was used to compare inoculum collection dates-the treatment means (Snedecor and Cochran 1967). Authors are regional game manager, Utah State Division of Wildlife Resources, Rumen contents of all 13 deer were saved to determine the Springville, 84663; principal research plant physiologist, Intermountain Forest and amount of big sagebrush and Utah juniper (Juniperus osteosRange Exp. Sta., Shrub Sciences, Laboratory, Provo, Utah 84601. The authors extend thanks to the Utah Division of Wildlife Resources personnel perma) in the diet (Cluff et al. 1982). who gave so freely of their time and talent: Harold Blackburn, Kevin Cherry, Dale Gurley, Norman Hancock, Robert Hasenyager, Rodney John, Leonard Newlin, and Results Ken Tuttle. Manuscrrpt received January 7, 198 I. Amount of big sagebrush and juniper in the diet of the mule deer JOURNAL OF RANGE MANAGEMENT 35(4), July 1982 Table 1. Percent of big sagebrush and juniper in the diets of wild mule deer collected during 1979-1980. Two deer per date, except for October.