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Comparative digestion of food among wildlife in Texas: implications for competition.

Success in competition for food is determined in part by how efficiently a species can harvest and digest food. Intake of food, time of passage, and use by different species are influenced by several factors, including ability of individuals to find and consume the resource, composition of fiber in the diet (Demment and Van Soest, 1985; Baker and Hobbs, 1987; Robbins, 1993; Klasing, 1998), and physiological and morphological features that regulate intake and digestion, such as body size (Hanley, 1982; Demment and Van Soest, 1985; Illius and Gordon, 1991; Hume et al., 1993), shape of muzzle (Janis and Ehrhardt, 1988), structure and function of teeth (Bezzobs and Sanson, 1997), and anatomy and physiology of digestive system (e.g., ruminant, nonruminating foregut fermenter, hindgut fermenter; Stevens, 1988; Alexander, 1994; Chivers and Langer, 1994).

Because of the arid environment and unpredictable rainfall in Texas, high-quality foods such as mast often are variable, which may accentuate competition for these important foods among a wide variety of species. It is reasonable to predict that a species with superior digestive capability could obtain more nutrients from the resources it harvests, which in turn supports higher rates of survival and reproduction, leading to a competitive advantage over time. The white-tailed deer (Odocoileus virginianus), collared peccary (Pecari tajacu), wild turkey (Meleagris gallopavo), raccoon (Procyon lotor), and southern plains woodrat (Neotoma micropus) form a guild of mast-consuming species native to southern Texas. These species range in size (i.e., mass) and vary in their form and function of digestive system (major sites of microbial fermentation and absorption of nutrients), which may determine how effectively they can compete when foods are limited.

White-tailed deer are ruminants, classified as concentrate selectors (Hofmann, 1989) that feed selectively on foods that are low in fiber and highly digestible (Strey and Brown, 1989; Van Soest, 1996). Collared peccaries have a complex gastric anatomy and microbial fermentation in the foregut, although they do not ruminate (Langer, 1978, 1979; Carl and Brown, 1983; Stevens, 1988). The stomach of collared peccaries has a large capacity for storage, and folds in the stomach slow passage of food, which may aid in digestion of fiber (Langer, 1978; Comizzoli et al., 1997). Wild turkeys have a flexible crop that can accommodate a considerable volume of food (Korschgen, 1967) and they possess paired ceca where some microbial fermentation of fiber can occur (Klasing, 1998). Raccoons and southern plains woodrats are small, hindgut fermenters. Raccoons have a simple stomach and short intestinal tract (Clemens and Stevens, 1979; Stevens, 1988), and although they lack a cecum, some digestion of fiber occurs in the large intestine (Clemens and Stevens, 1979). Southern plains woodrats have a sectioned stomach (Stevens, 1988) and functional cecum where microbial fermentation of fiber can occur (Alderton, 1996). Additionally, woodrats can benefit from re-ingestion of soft fecal pellets (e.g., coprophagy; Alderton, 1996).

Wild boars (Sus scrofa) are an invasive exotic species that were first introduced to North America in the 1500s and subsequently were translocated throughout much of the southern and coastal portions of the united States for both food and hunting (Hanson and Karstad, 1959; Mayer and Brisbin, 1991). Nearly 1,000,000 wild boars exist in Texas (Mayer and Brisbin, 1991) and their populations are increasing in the central United States (Gipson et al., 1998). Wild boars have several advantages that may enable them to effectively compete with other species for food, which in turn may be harmful to native wildlife (wood and Barrett, 1979). Wild boars are large, enabling them to consume large amounts of food (Abrams, 1990) and they dominate discrete food patches by displacing smaller animals (Berger, 1985). Wild boars are generalists, able to consume a more variable diet (both plant and animal material) when compared to more specialized species such as the collared peccary (Ilse and Hellgren, 1995a). wild boars are hindgut fermenters, which may enable them to extract more nutrients per day from forage because they are able to consume large amounts of food without being limited by rate of passage (Reece, 1990) to the same extent as forgut fermenters such as white-tailed deer. wild boars are not limited by acidosis or other digestive problems arising from fermentation in the foregut. Additionally, as hindgut fermenters, wild boars can digest and absorb available carbohydrates and protein directly without intervening microbial metabolism, and they are not subject to loss of energy to microbes in the foregut (Hintz et al., 1978; Demment and Van Soest, 1985; Van Soest, 1994). Wild boars also can store large amounts of fat, allowing them to make greater use of high-quality, but ephemeral foods, such as mast. These high rates of consumption support high reproductive rates of 1.57 litters/year (Taylor et al., 1998), with an average of 5-7 young/litter (Sweeney et al., 1979; Taylor et al., 1998). In comparison, native ungulates, such as white-tailed deer and collared peccaries, have litters of 1-3/year (Packard et al., 1987; Demarais et al., 2000; Hellgren and Lochmiller, 2000).

The destructive nature of wild boars on native vegetation and landscapes has been documented (Wood and Barrett, 1979; Singer, 1984; Kotanen, 1995), but studies on direct competition with native wildlife are limited. Most studies have concentrated on sympatric relationships between wild boars and collared peccaries (Ilse and Hellgren, 1995a, 1995b; Gabor and Hellgren, 2000). Elston et al. (2005) reported similarities in digestive performance between wild boars and collared peccaries of comparable body size; however, as adults, wild boars weigh three times more than peccaries (Ilse and Hellgren, 1995a; Sowls, 1997) and, thus, can consume larger amounts of food.

In Texas, wild boars and white-tailed deer inhabit the same areas and some dietary overlap occurs (Yarrow, 1987; Mayer and Brisbin, 1991; Taylor and Hellgren, 1997). Additionally, white-tailed deer often will retreat when confronted by wild boars (Barrett, 1982). Where white-tailed deer, turkeys, raccoons, and wild boars exist together, they consume many of the same foods (Korschgen, 1967). Wild boars may compete extensively with white-tailed deer, turkeys, and raccoons for acorns during low-production years (Hanson and Karstad, 1959; Henry and Conley, 1972). Competition may be particularly important in semi-arid southern Texas where live oak (Quercus virginiana) forest occurs in patches with extensive rangelands, such that acorns are a high-quality, but discrete and ephemeral resource. Other mast resources in southern Texas, such as that produced by honey mesquite (Prosopis glandulosa), prickly pear cactus (Opuntia engelmannii), and persimmon (Diospyros texana) are less patchy, but still ephemeral and highly variable. During years of low production of mast, competition among mast-consuming species occurs (wood and Barrett, 1979; wood and Roark, 1980; McShea and Schwede, 1993; McShea, 2000). During years of high production of mast, direct competition may not be as important as ability of a species to consume large amounts of mast and digest it fully. Species with such abilities will benefit more from these high-quality, but ephemeral foods.

Our objective was to compare digestive performance by the introduced wild boar and native wildlife in southern Texas. We tested the hypothesis that because of the relatively large body size of wild boars, intake of dry matter and digestible energy and digestibility of dry matter, fiber, and energy by wild boars would be greater than smaller foregut-fermenting and hindgut-fermenting species. We also predicted that allometric relationships would exist between body size, digestibility of fiber, and rate of passage among species tested. This study provides insight into digestive performance of coexisting species of wildlife with distinctly different anatomy and physiology of digestive system and varying body size.

MATERIALS AND METHODS--Feeding trials were performed at the Caesar Kleberg Wildlife Research Institute Wildlife Research Facility at Texas A&M University-Kingsville, during 2000-2001. Protocols for the study were reviewed and approved by the Texas A&M University-Kingsville Animal Care and Use Committee (99-5-3). Four, non-reproductive adults from each of the following species were used: wild boar (four females), white-tailed deer (four females), collared peccary (two males, two females), wild turkey (two males, two females), raccoon (four females), and southern plains woodrat (four females). Three wild boars were trapped near Encinal, La Salle County, Texas, when <4 months of age and one was the captive-born offspring of wild-caught adults. White-tailed deer were captive raised from stock native to southern Texas. Collared peccaries were obtained as young orphans (< 4 months of age) and were raised by researchers for this study. Wild turkeys were purchased as 1-day-old poults from a commercial game-bird farm (QuailCo, Portales, New Mexico). Raccoons and southern plains woodrats were trapped in the vicinity of Kingsville, Kleberg County, Texas.

Experimental diet consisted of a combination of commercial pellets: 50% MoorMans Deer Pellets (MoorMans, Inc., Quincey, Illinois) and 50% Ranch Hand Beef Builder (Purina Mills, LLC, Saint Louis, Missouri) on a dry matter basis. Digestion trials were conducted with wild boars, white-tailed deer, and southern plains woodrats during November-December 2000, and collared peccaries, wild turkeys, and raccoons during October-December 2001. Each trial was preceded by a period of acclimation to diet during which the diet was offered ad libitum. For wild boars and white-tailed deer, animals were brought under a barn, weighed, and placed individually in 4 by 3-m stalls. The period of acclimation to diet was 4 days for wild boars and 6 days for white-tailed deer. After the period of acclimation to diet, animals were weighed and placed individually in metabolism crates to allow measurement of all feed consumed and collection of all feces and urine produced during feeding trials. Crates for wild boars were plywood, 1.2 by 1.5 by 1.2 m, with expanded metal flooring. Crates for white-tailed deer were plywood, 1.2 by 1.2 by 1.5 m, with expanded metal flooring. Crates were equipped with side doors to allow presentation of the diet and removal of orts, a funnel system for separation of urine, and a pull-out tray for fecal collection. Due to difficulty in handling and transferring collared peccaries, the 4-day period of acclimation to diet occurred within their home pens after animals had been separated from each other with fencing. After the period of acclimation to diet, collared peccaries were transported to the barn, weighed, and placed singularly in metabolism crates (the crates previously used by wild boars) for their feeding trials. Turkeys resided in an aviary, and for the trials birds were collected, weighed, and placed individually within metabolism cages for a 4-day period of acclimation to diet, after which the feeding trial began. Metabolism cages for turkeys were 1.2 by 1.2 by 1.2 m with 2.56 by 1.3-cm welded-wire sides and top and 1.3 by 1.3-cm welded-wire flooring and equipped with a pull-out tray for fecal collection. Raccoons resided in metabolism cages for the duration of their captivity. Metabolism cages for raccoons were 1.2 by 1.2 by 1.2 m with 2.56 by 1.3-cm welded-wire sides and top and 1.3 by 0.64-cm welded-wire flooring and equipped with a pull-out tray for fecal collection and a funnel system for separation of urine. Raccoons underwent a period of acclimation to diet of 4 days and were weighed at the beginning of feeding trials. Southern plains woodrats were moved from their home cages and placed individually in metabolism cages (37.2-cm diameter, 47.4-cm high) for their period of acclimation to diet. Metal cone-shaped shelters (ca. 12.7-cm wide, 12.7-cm high) were provided for hiding cover. Southern plains woodrats underwent a period of acclimation to diet of 4 days and were weighed at the beginning of feeding trials. To facilitate collection of feed, feces, and urine of southern plains woodrats during feeding trials, each cage was placed in a large plastic bowl (37.2-cm diameter) and a 1-mm wire-mesh screen was placed between cage and bowl to allow urine to pass through to the bowl and the feed and feces to fall on the screen for collection.

All feeding trials lasted 8 days. Diet and water were provided ad libitum. The first 3 days of each trial served to acclimate animals to the crates-cages and procedures. During the last 5 days of each trial, daily intake of feed was measured and all orts and feces were collected.

Samples of fiber from the diet were marked with chromium (Cr) and used to determine rate of passage (Uden et al., 1980). The Cr-marked fiber was offered to wild boars, white-tailed deer, and collared peccaries with a small amount of whole corn and honey to encourage consumption. Turkeys were fed the Cr-marked fiber via a gelatin capsule. Samples of Cr-marked fiber were offered to raccoons along with small amounts of canned cat food and to southern plains woodrats with a small amount of peanut butter (Hume et al., 1993) and sunflower seeds (without shells). Feces were collected every 4 h during the first 2 days after feeding the Cr-marked fiber (feces of southern plains woodrats were collected every 2 h during the first 12 h), every 6 h during day 3, every 8 h during day 4, and twice on day 5. After the final collection period, animals were removed from crates, weighed, and returned to their home pens. Body mass was determined by averaging pre-trial and post-trial weight for each animal.

Samples of diet, orts, and feces were frozen until laboratory analyses began. Samples of diet were dried at 100[degrees]C for 24 h for determination of dry matter. Additional samples of diet, orts, and feces were dried at 50[degrees]C for [greater than or equal to]48 h, then ground through a centrifuge grinder with a 1-mm screen to prepare samples for analysis. Because amount of feces collected from southern plains woodrats during each collection period was small, feces were crushed manually in a ceramic crucible to minimize loss of sample. A percentage (25%) of dried feces from each collection period was compiled for analysis. The remaining fecal sample from each collection period was kept separate for Cr-concentration analysis. Samples of diet, orts, and feces were analyzed for neutral-detergent fiber and acid-detergent fiber with an ANKOM fiber analyzer (ANKOM Technology, Fairport, New York; Goering and Van Soest, 1970). Additionally, samples of diet were analyzed for acid-detergent lignin using a 72% solution of sulfuric acid (Goering and Van Soest, 1970). Percentage values for acid-detergent lignin were corrected for ash content. Percentage of nitrogen (%N) was determined via the Kjeldahl procedure using a Tecator Kjeltec digester and distiller (Tecator, Hoganas, Sweden). Crude protein was determined by multiplying %N by 6.25. Gross energy was determined via a bomb calorimeter (Parr Instrument Co., Moline, Illinois). Intake of dry matter, intake of digestible energy, and digestibility of dry matter, detergent fiber, crude protein, and gross energy were calculated. Values for mammals are reported in apparent percentage of digestibility; however, urinary and fecal excreta of turkeys were not separated, thus, their data are reported as apparent percentage of metabolizability. Comparisons between turkeys and other species are discussed in this context. Metabolizability of crude protein by turkeys was not determined.

Chromium was extracted from fecal samples (Williams et al., 1962) and sent to the Texas A&M Agricultural Experiment Station in Uvalde for atomic-absorption determination (Perkin Elmer Life and Analytical Sciences, Inc., Wellesley, Massachusetts). Total excretion (100%) of marker was assumed to be the sum of all Cr-marker recovered over the collection period. Rate of passage was determined using the time after feeding the marked fiber when 50 (mean time of retention) and 95% of the marker was recovered in feces. When recovery of 50 and 95% of the marker did not occur during a specific fecal collection, recovery of 50 and 95% of the marker were calculated by a linear interpolation.

Data for digestion were analyzed by a one-way analysis of variance (ANOVA), with species as the factor, using least-squares means and Tukey's Studentized Range for separation of means (SAS Institute, Inc., Cary, North Carolina). To determine allometric relationships between body mass, digestion of fiber, and rate of passage, and relationships between rate of passage and digestion of fiber, linear regressions were performed. To reduce risk of making a Type II error, which can be associated with small samples (Johnson, 1999), effects of species were considered significant when P < 0.10. This approach allows for presentation of differences among species without limitations that can be incurred in biological studies when using the arbitrary alpha-value of 0.05 (Cherry, 1998).

RESULTS--In comparing composition of the diet offered in our study to mast consumed by wildlife in southern Texas, diet in our study was similar to mesquite pods in fiber, protein, and gross energy, and similar to acorns of Shumard oak (Quercus shumardii) in concentrations of fiber (Table 1). Diet in our study was higher in crude protein and lower in gross energy than acorns of Shumard oak and live oak.

Percentage change in body mass during trials varied among species ([F.sub.5,18] = 2.31, P = 0.09), with wild turkeys, which lost weight, differing from raccoons, which gained weight (Table 2). Intake of dry matter ([F.sub.5,18] = 2.29, P = 0.09) and intake of digestible energy ([F.sub.5,18] = 3.21, P = 0.03) also varied among species. Wild boars had nearly three times greater intakes of dry matter and digestible energy than collared peccaries (Table 2).

Digestibility of dry matter varied among species ([F.sub.5,18] = 25.76, P < 0.01; Table 3). Wild boars, white-tailed deer, collared peccaries, and southern plains woodrats had 10-25% higher digestibility of dry matter than turkeys and raccoons. Raccoons had higher digestibilities of dry matter than turkeys. Digestibility of neutral-detergent fiber and acid-detergent fiber also varied among species ([F.sub.5,18] = 38.95, P < 0.01 and [F.sub.5,18] = 9.73, P < 0.01, respectively; Table 3). White-tailed deer, wild boars, and collared peccaries had digestibilities of neutral-detergent fiber similar to one another and more than two times greater than turkeys, raccoons, and southern plains woodrats. Turkeys showed essentially no ability to digest acid-detergent fiber. White-tailed deer and collared peccaries had more than five times greater digestibility of acid-detergent fiber than turkeys, raccoons, and southern plains woodrats. Wild boars did not differ from raccoons and southern plains woodrats in digestion of acid-detergent fiber, in part because of high variation among wild boars.

There was some evidence of variation among species in digestibility of crude protein ([F.sub.4,15] = 2.73, P = 0.07), with collared peccaries having 10% greater digestibility of crude protein than raccoons. Variation among species also occurred for gross-energy digestion ([F.sub.5,18] = 22.52, P < 0.01; Table 3). Wild boars, white-tailed deer, collared peccaries, and southern plains woodrats had gross-energy digestibilities that were similar to one another but 12-18% higher than turkeys and raccoons.

Mean time of retention and time of passage of 95% of marked fiber varied among species ([F.sub.5,18] = 9.94, P < 0.01 and [F.sub.5,18] = 5.57, P < 0.01, respectively; Table 4). Wild boars, white-tailed deer, and collared peccaries had 2.4-3.5 times longer mean times of retention than turkeys and raccoons. Southern plains woodrats did not differ from any species and had essentially the same mean time of retention as wild boars and white-tailed deer. Wild boars and turkeys retained 95% of marked fiber more than two times longer than southern plains woodrats with all other species being intermediate.

Digestion of neutral-detergent fiber was related to body mass ([F.sub.1,22] = 6.43, P = 0.02, [r.sup.2] = 0.23; Fig. 1a), but digestion of acid-detergent fiber was not. Relationships also occurred between mean time of retention and body mass ([F.sub.1,22] = 3.35, P = 0.08, [r.sup.2] = 0.13; Fig. 1b) and time of passage of 95% of marked fiber and body mass ([F.sub.1,22] = 10.22, P < 0.01, [r.sup.2] = 0.32; Fig. 1c). Additionally, digestion of neutral-detergent fiber and acid-detergent fiber were related to mean time of retention ([F.sub.1,22] = 16.45, P < 0.01, [r.sup.2] = 0.43 and [F.sub.1,22] = 10.86, P < 0.01, [r.sup.2] = 0.33, respectively; Figs. 2a and 2b), but neither were related to time of passage of 95% of marked fiber.

[FIGURE 1 OMITTED]

DISCUSSION--There was evidence to support our hypothesis that wild boars have digestibilities similar to foregut-fermenting species and higher than smaller hindgut fermenters. Digestion of dry matter, fiber, and gross energy by wild boars was comparable to white-tailed deer and collared peccaries, which provides evidence of similar capability of digestion between foregut fermenters and large hindgut fermenters. As predicted, digestion of dry matter and gross energy by wild boars was higher than turkeys and raccoons. However, digestibility of dry matter and gross energy by wild boars was similar to that of southern plains woodrats, which was unexpected, given the extreme difference in size between species. Digestion of neutral-detergent fiber by wild boars was higher than turkeys, raccoons, and southern plains woodrats, illustrating an efficient capacity for digestion of fiber by wild boars compared to smaller hindgut fermenters. Digestion of acid-detergent fiber by wild boars was relatively high compared to other hindgut fermenters, although they were only significantly higher than turkeys. Effective digestion of dry matter, fiber, and gross energy by wild boars was likely related to their large body mass, long time of retention, and fermentation in the colon. Wild boars retained 50% of digesta longer than turkeys and raccoons; however, mean time of retention between wild boars and southern plains woodrats did not differ. This finding was unexpected because of the large difference in body size; however, wild boars did have a longer time of passage of 95% of marked fiber than southern plains woodrats. Although time of passage of 95% of marked fiber did not differ significantly between wild boars, turkeys, and raccoons, the latter two species were less effective than wild boars for digestibility of nutritional components of the diet. Rate of passage for wild boars was similar to the foregut-fermenting species; again, likely because of their large body size and large colon, which promoted an increased time of retention and enabled fermentation of fiber.

[FIGURE 2 OMITTED]

Greater intake of dry matter and subsequent greater intake of digestible energy by wild boars compared to collared peccaries may have been influenced by the stress of confinement, which resulted in lower intake of feed by collared peccaries and loss in body mass. Intake of digestible energy by collated peccaries during the trial was only 60.8 kcal/[kg.sup.0.75]/day, which is lower than the estimated basal-metabolic energy requirement for collared peccaries (67.4 kcal/ [kg.sup.0.75]/day during summer and 81.4 kcal/[kg.sup.0.75]/ day during winter; Zervanos and Hadley, 1973). However, collared peccaries maintained high levels of digestion of neutral-detergent fiber and acid-detergent fiber. Compared to a large hindgut fermenter (wild boar) and a ruminant (white-tailed deer), collared peccaries appeared to have a similar capacity for digesting fiber. Carl and Brown (1986) and Comizzoli et al. (1997) also concluded that collared peccaries have digestive capabilities similar to ruminants. Additionally, digestion of fiber by collared peccaries was higher than smaller hindgut-fermenting species. The high capacity for digestion of fiber by collared peccaries was likely a function of their large, complex forestomach (Langer, 1978) and relatively long retention of digesta. During this study, digestion of acid-detergent fiber by collared peccaries was similar to a deer ration (36.1%; Carl and Brown, 1986) and two swine diets varying in fiber components (35.4 and 25.6%, respectively; Comizzoli et al., 1997), and was somewhat higher than a commercial swine diet fed by Shively et al. (1985; 21.9%). Mean time of retention by collared peccaries was similar to a concentrated swine diet (39.3 h; Comizzoli et al., 1997).

As the only ruminant in this study, white-tailed deer were superior to small hindgut-fermenting species at digesting fiber, and were similar to a large hindgut fermenter (wild boar) and also the smaller foregut-fermenting collared peccary. White-tailed deer also maintained high levels of gross-energy digestion, likely a function of their capacity for digestion of fiber, which can be an important advantage when high-quality foods are limited. Mean time of retention of digesta by white-tailed deer on our commercial diet was similar to mean rate of passage for deer consuming a natural diet of aspen leaves (25 h; Mautz and Petrides, 1971).

Turkeys and raccoons had shorter mean time of retention of digesta than the other species, which was expected given that birds generally have fast rates of passage (Stevens, 1988; Blankenship, 1992; Klasing, 1998), and raccoons are relatively small and have a short gastrointestinal tract, with no cecum to delay passage. The comparative retention of 95% of the marked fiber by turkeys probably occurred because of small particles of digesta being retained in the ceca (Remington, 1989). Digestion of dry matter, fiber, and gross energy by turkeys and raccoons was low and likely a function of their short times of retention, and in the case of raccoons, gastrointestinal simplicity. Additionally, low digestibility of dry matter for turkeys could be explained in part by the fact that urine was excreted with feces. Raccoons may have compensated for low gross-energy digestibility by a relatively high intake of dry matter; thus, maintaining reasonable intakes of digestible energy.

Theoretically, as body size decreases, metabolic requirements per unit of body mass rise, leading to shorter times of retention of food in the fermentation chamber (Justice and Smith, 1992). Given their size, we expected southern plains woodrats to have faster rates of passage; however, they only defecated during the night, so after the first night when the Cr-marker was given, passage was delayed throughout the following day until the next night. Additionally, it is possible that southern plains woodrats were re-ingesting fecal material directly from the anus. Although coprophagy was not observed, if this practice occurred it could have increased time of retention. Metabolism cages for southern plains woodrats were designed so their feces fell through the floor onto a screen for collection, so feces became inaccessible to the woodrats. If southern plains woodrats were not ingesting feces directly from the anus, digestion of fiber could have been inhibited by their inability to practice coprophagy. Justice and Smith (1992) noted that woodrats were able to maintain body weight even on a high-fiber diet. Loss of body mass by southern plains woodrats during our study was inconsequential despite their relatively low digestion of fiber.

As expected, relationships occurred between digestion of fiber and body mass, digestion of fiber and time of retention, and time of retention and body mass. Additionally, our results suggest that over the range of body sizes and with the species we tested, structure of digestive system also has an impact on digestion of fiber and mean time of retention. A digestive system structured to delay passage of digesta and support gastrointestinal microflora will have capability for digestion of fiber. In our study, structures that served this function varied from a rumen to a large sacculated colon. Long mean time of retention by southern plains woodrats gave this species some capability to digest fiber. Presence of paired ceca in wild turkeys did not increase mean time of retention, but did result in a slow time of passage of 95% of marked fiber, most likely due to small fiber particles that entered the ceca. Because relatively small amounts of material generally enter the ceca (Remington, 1989), delay of passage as a result of the ceca did not allow for any appreciable digestion of fiber.

Digestive capability of wild boars was similar to, or greater than, other species. As foregut fermenters, white-tailed deer and collared peccaries did not appear to have a digestive advantage over wild boars. Wild boars and collared peccaries of comparable body mass also were reported to have similar digestive capabilities during another study (Elston et al., 2005). Documentation of direct competition between wild boars and native species in southern Texas was beyond the scope of this work; however, it appears that wild boars have a high capacity for efficient digestion, which may make them effective competitors with native species when foods are limited. Diets of wild boars are dominated by grasses when mast or other nutritious foods are unavailable (Everitt and Alaniz, 1980; Wood and Roark, 1980; Taylor and Hellgren, 1997); thus, wild boars likely can maintain themselves on poor-quality foods during lean periods. When high-quality foods become available, wild boars are likely to consume large amounts and digest it efficiently, while accumulating large stores of body fat. Additionally, wild boars have the potential to displace other species from foraging patches (Barrett, 1982; Berger, 1985). Thus, wild boars may be able to compete effectively with other species for food and benefit to a greater extent when nutritious foods are available. It is likely that because of their large size and effective digestive capability, wild boars will be successful animals even in highly variable environments.

The Caesar Kleberg Wildlife Research Institute and Texas A&M University-Kingsville provided funding for this work. We thank C. Hensarling for completing chromium-concentration analyses at the Texas A&M Agricultural Research and Extension Center in Uvalde. We also thank J. Arredondo, R. Coiner, L. Cooksey, J. Felderhoff, E. Klinksiek, and B. Mason for assistance with animals and facilities. Thanks are extended to E. Monaco and S. Copeland for laboratory support, R. Bingham for statistical guidance, Y. Ballard for administrative support, and the staff at the Chaparral Wildlife Management Area. Finally, we thank H. Giraldo and P. Ortega for Spanish translation and E. Valdes for comments on earlier drafts of this manuscript. This is manuscript 07-102 from the Caesar Kleberg Wildlife Research institute.

Submitted 10 April 2008. Accepted 23 May 2009. Associate Editor was Troy A. Ladine.

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JENNIFER J. ELSTON * AND DAVID G. HEWITT

Caesar Kleberg Wildlife Research Institute, MSC 218, Texas A&M University-Kingsville, Kingsville, TX 78363 Present address of JJE: Fort Worth Zoo, Fort Worth, TX 76110

* Correspondent: jelston@fortworthzoo.org
TABLE 1--Composition (percentage for all components, except gross
energy, which was kcal/g; n = 6) of commercial pellets on a dry
matter basis fed to wild boars (Sus scrofa), white-tailed deer
(Odocoileus virginianus), collared peccaries (Pecari tajacu),
turkeys (Meleagris gallopavo), raccoons (Procyon lotor), and
southern plains woodrats (Neotoma micropus) during digestion trials
in 2000 and 2001, Kingsville, Kleberg County, Texas, and values
from three species of mast in Texas (Elston, 2003).

                              Commercial diet

   Component of diet         Mean          SE

Dry matter                   92.6         0.3
Neutral-detergent fiber      38.0         0.5
Acid-detergent fiber         23.4         0.3
Crude protein                15.9         0.1
Gross energy                  4.1         0.0

                              Pods of mesquite
                           (Prosopis glandulosa)

   Component of diet         Mean          SE

Dry matter                   87.5         0.7
Neutral-detergent fiber      35.8         1.2
Acid-detergent fiber         24.2         0.4
Crude protein                13.7         0.6
Gross energy                  4.3         0.1

                             Acorns of live oak
                            (Quercus virginiana)

   Component of diet         Mean          SE

Dry matter                   61.0         0.8
Neutral-detergent fiber      26.8         1.7
Acid-detergent fiber         15.4         0.9
Crude protein                 5.8         0.0
Gross energy                  4.8         0.0

                           Acorns of Shumard oak
                            (Quercus shumardii)

   Component of diet         Mean          SE

Dry matter                   52.0         0.9
Neutral-detergent fiber      36.5         1.7
Acid-detergent fiber         26.9         0.7
Crude protein                 5.8         0.1
Gross energy                  5.2         0.1

TABLE 2--Body mass (kg), change in body mass (%), intake of dry
matter (g/[kg.sup.0.75]/day), and intake of digestible energy (kcal
digestible energy/[kg.sup.0.75]/day) (a) of six species of wildlife
(n = 4 animals/species) consuming a commercial diet during
2000-2001 in Kingsville, Kleberg County, Texas. Means in a column
that do not share a common letter are different at P < 0.10.

                                           Body mass

             Species                   Mean          SE

Wild boar (Sus scrofa)                 99.9         9.6
White-tailed deer (Odocoileus
  virginianus)                         45.0         1.6
Collared peccary (Pecari tajacu)       24.7         1.4
Wild turkey (Meleagris gallopavo)       6.3         1.8
Raccoon (Procyon lotor)                 5.0         0.5
Southern plains woodrat
  (Neotoma micropus)                    0.3         0.0

                                      Change in body mass

             Species                   Mean          SE

Wild boar (Sus scrofa)                  2.5ab        2.1
White-tailed deer (Odocoileus
  virginianus)                         -0.1ab        1.3
Collared peccary (Pecari tajacu)       -7.9ab        2.6
Wild turkey (Meleagris gallopavo)     -13.9a        12.3
Raccoon (Procyon lotor)                 8.8b         0.5
Southern plains woodrat
  (Neotoma micropus)                   -0.0ab        1.4

                                      Intake of dry matter

             Species                   Mean          SE

Wild boar (Sus scrofa)                75.8a         10.0
White-tailed deer (Odocoileus
  virginianus)                        54.4ab         5.2
Collared peccary (Pecari tajacu)      25.1b          3.8
Wild turkey (Meleagris gallopavo)     54.6ab         7.4
Raccoon (Procyon lotor)               71.6ab        25.0
Southern plains woodrat
  (Neotoma micropus)                  60.6ab         4.7

                                     Intake of digestible
                                             energy

             Species                   Mean          SE

Wild boar (Sus scrofa)                178.2a        25.3
White-tailed deer (Odocoileus
  virginianus)                        133.5ab        9.8
Collared peccary (Pecari tajacu)       60.8b         9.8
Wild turkey (Meleagris gallopavo)      93.3ab       13.0
Raccoon (Procyon lotor)               118.9ab       43.1
Southern plains woodrat
  (Neotoma micropus)                  138.2ab       13.5

(a) Values for wild turkeys are for metabolizability.

TABLE 3--Apparent digestibility (a) (%) of dietary components by
six species (n = 4 animals/species) consuming a commercial diet
during 2000-2001 in Kingsville, Kleberg County, Texas. Means in a
column that do not share a common letter are different at P < 0.10.

                                           Dry matter

             Species                   Mean          SE

Wild boar (Sus scrofa)                57.2a         1.4
White-tailed deer
  (Odocoileus virginianus)            59.7a         2.0
Collared peccary (Pecari tajacu)      61.3a         1.3
Wild turkey (Meleagris gallopavo)     35.9c         0.3
Raccoon (Procyon lotor)               45.6b         3.8
Southern plains woodrat
  (Neotoma micropus)                  54.0a         0.3

                                            Neutral-
                                           detergent
                                              fiber

             Species                   Mean          SE

Wild boar (Sus scrofa)                35.5a         2.2
White-tailed deer
  (Odocoileus virginianus)            38.6a         3.5
Collared peccary (Pecari tajacu)      39.2a         1.8
Wild turkey (Meleagris gallopavo)      2.0c         2.7
Raccoon (Procyon lotor)               15.6b         3.1
Southern plains woodrat
  (Neotoma micropus)                  13.6b         1.3

                                             Acid-
                                           detergent
                                             fiber

             Species                   Mean          SE

Wild boar (Sus scrofa)                20.4ab        10.6
White-tailed deer
  (Odocoileus virginianus)            32.2a          3.6
Collared peccary (Pecari tajacu)      33.3a          3.0
Wild turkey (Meleagris gallopavo)     -6.9c          3.6
Raccoon (Procyon lotor)                5.9bc         4.5
Southern plains woodrat
  (Neotoma micropus)                   1.9bc         1.9

                                             Crude
                                            protein

             Species                   Mean          SE

Wild boar (Sus scrofa)                67.4ab        1.4
White-tailed deer
  (Odocoileus virginianus)            69.6ab        2.9
Collared peccary (Pecari tajacu)      72.7a         0.9
Wild turkey (Meleagris gallopavo)       --           --
Raccoon (Procyon lotor)               66.0b         0.9
Southern plains woodrat
  (Neotoma micropus)                  70.0ab        0.6

                                          Gross energy

             Species                   Mean          SE

Wild boar (Sus scrofa)                57.5a         1.8
White-tailed deer
  (Odocoileus virginianus)            60.7a         2.2
Collared peccary (Pecari tajacu)      60.1a         1.3
Wild turkey (Meleagris gallopavo)     42.6b         1.2
Raccoon (Procyon lotor)               42.5b         2.7
Southern plains woodrat
  (Neotoma micropus)                  54.8a         0.9

(a) Values for wild turkeys are percentage metabolizability.

TABLE 4--Rates of passage (hours necessary to recover 50 and 95% of
chromium-marked fiber in the feces) of six species (n = 4
animals/species) consuming a commercial diet during 2000-2001 in
Kingsville, Kleberg County, Texas. Means in a column that do not
share a common letter are different at P < 0.10.

                                             Recovery time for 50% of
                                                   marked fiber

Species                                         Mean          SE

Wild boar (Sus scrofa)                         24.9a         3.4
White-tailed deer (Odocoileus virginianus)     24.6a         2.2
Collared peccary (Pecari tajacu)               35.6a         3.7
Wild turkey (Meleagris gallopavo)              10.4b         5.1
Raccoon (Procyon lotor)                         9.8b         0.9
Southern plains woodrat (Neotoma micropus)     23.2ab        1.3

                                             Recovery time for 95% of
                                                   marked fiber

Species                                         Mean          SE

Wild boar (Sus scrofa)                         100.0a        4.1
White-tailed deer (Odocoileus virginianus)      72.1ab        1.2
Collared peccary (Pecari tajacu)                70.0ab        5.2
Wild turkey (Meleagris gallopavo)               83.5a        11.6
Raccoon (Procyon lotor)                         67.0ab       14.9
Southern plains woodrat (Neotoma micropus)      41.0b         3.2
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Publication:Southwestern Naturalist
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Geographic Code:1U7TX
Date:Mar 1, 2010
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