Antilope Cervicapra) and the Arabian Sand Gazelle (Gazella Subgutturosa Marica) Cathrine Sauer1,2*, Mads F
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Anatomia, Histologia, Embryologia ORIGINAL ARTICLE Macroscopic digestive tract anatomy of two small antelopes, the blackbuck (Antilope cervicapra) and the Arabian sand gazelle (Gazella subgutturosa marica) Cathrine Sauer1,2*, Mads F. Bertelsen2, Sven Hammer3,4, Peter Lund1, Martin R. Weisbjerg1 and Marcus Clauss5 Addresses of authors: 1 Department of Animal Science, Aarhus University, AU Foulum, Blichers Alle 20, PO Box 50, DK-8830 Tjele, Denmark; 2 Center for Zoo and Wild Animal Health, Copenhagen Zoo, Roskildevej 38, DK-2000 Frederiksberg, Denmark; 3 Al Wabra Wildlife Preservation, P.O. Box 44069, Doha, Qatar; 4 Present address: Naturschutz-Tierpark Gorlitz,€ Zittauerstr. 43, D-02826 Gorlitz,€ Germany; 5 Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Winterthurerstr. 260, CH-8057 Zurich, Switzerland *Correspondence: Summary Tel.: +45 6171 6000; fax: +45 72 200 264; The digestive tract anatomy of 14 blackbucks (Antilope cervicapra) and seven e-mail: [email protected] Arabian sand gazelles (Gazella subgutturosa marica) was quantified by dimen- sions, area and weight. Data from the two small-sized antilopinae were evalu- With 5 figures and 2 tables ated against a larger comparative data set from other ruminants classified as having either a ‘cattle-type’ or ‘moose-type’ digestive system. The digestive Received June 2015; accepted for publication anatomy of the blackbuck resembled that of ‘cattle-type’ ruminants, which cor- September 2015 responds to their feeding ecology and previous studies of solute and particle doi: 10.1111/ahe.12214 retention time; however, a surprising exception was the remarkably small oma- sum in this species, which makes the blackbuck stand out from the general rule of a relatively large omasum in grazing ruminants. Sand gazelles had morpho- logical features that corresponded more to the ‘moose type’ or an intermediate position, although previous studies of solute and particle retention time had led to the expectation of a more ‘cattle-type’ anatomy. The results show that outliers to general morphological trends exist, that findings on physiology and anatomy do not always match completely and that differences in the digestive morphology among ruminant species are more difficult to demonstrate at the lower end of the body mass range. Dittmann et al., 2015), though with large seasonal varia- Introduction tion in forage type preference (Cunningham, 2013). Most ruminant species of small body size are classified as The classification of ruminants into feeding types has ‘concentrate selectors’ or ‘browsers’ (Hofmann, 1989). Of traditionally been based on either observations of feeding the exceptions, the majority are classified as ‘intermediate ecology, morphophysiological traits of the gastrointestinal feeders’ (e.g. many species of deer and gazelles), while a tract, or a combination of the two. However, recent stud- few are ‘bulk and roughage eaters’ or ‘grazers’ (e.g. the ies indicate that digestive anatomy is not necessarily a oribi (Ourebia ourebi) and the mountain reedbuck (Re- reliable proxy for the diet of a species, though some traits dunca fulvorufula)). With a body mass (BM) of 20–55 kg appear to be more common among browsing than graz- (males being larger than females), the blackbuck is one of ing species and vice versa. Instead, it has been suggested the few small ruminants considered to be a strict grazer, to classify ruminants as either ‘cattle type’ or ‘moose type’ including approximately 80% grass in their diet (reviewed according to their digestive strategy (Clauss et al., 2010b), by Dittmann et al., 2015). Arabian sand gazelles, another with ‘cattle types’ having a stratified rumen content, a fast member of the Antilopinae subfamily with a small BM flow of fluid through the reticulorumen (RR) and an (15–30 kg), are considered intermediate feeders including uneven pattern of ruminal papillation. In contrast, an average of around 40% grass in their diet (reviewed by ‘moose-type’ ruminants have a homogenous rumen © 2015 Blackwell Verlag GmbH 392 Anat. Histol. Embryol. 45 (2016) 392–398 C. Sauer et al. Blackbuck and sand gazelle GI anatomy content, a relatively slower RR fluid flow and an evenly ach anatomy and salivary gland weight of other ruminant papillated ruminal mucosa. species, classified as having either a ‘moose-type’ or ‘cat- Fluid throughput and retention of particles in the RR tle-type’ digestive tract [for species and literature sources, can be measured using indigestible markers, for example see Sauer et al. (in press), with additional data from Cr- or Co-EDTA as solute marker and Cr-mordanted Short (1964), Hofmann and Geiger (1974), Nagy and fibres as particle marker. Using this marker system, the Regelin (1975), Weston and Cantle (1983), Stafford and mean retention time of both fluid and solid material has Stafford (1993), Staaland et al. (1997) and Wang et al. been determined in many ruminant species including (2014)]. blackbucks (Hummel et al., 2015) and sand gazelles (Ditt- To determine the relation between BM and anatomical mann et al., 2015). Given the results of these studies, measurements, data were ln-transformed and allometric where a clear separation of solute and particle marker regression analysis was used to determine the coefficients excretion was found in both species, we expected both of the model: species to have a ‘cattle-type’ digestive anatomy, for lnðYÞ¼a þ b  lnðBMÞ example having high reticular crests, thick rumen pillars where Y = the anatomical measurement and BM = body and a relatively large omasum. In particular, the omasum mass in kilogram. The hypothesis of isometric scaling was of the blackbuck was expected to be large, to reabsorb the accepted if 0.33, 0.67 and 1.00 was included in the 95% high amount of fluid passing from the RR of this species, confidence interval of the BM exponent (b) of linear as documented by Hummel et al. (2015). The aim of this dimensions, areas and weights, respectively. Anova was study was to provide quantitative data on the gross gas- used for step-wise model reduction. All statistical analyses trointestinal anatomy of blackbucks and sand gazelles and were performed using the statistical software R (version to determine whether predictions regarding digestive tract 3.1.0, R Foundation for Statistical Computing, Vienna, morphology based on their feeding ecology and previous Austria). Significance was accepted at P ≤ 0.05 with retention time studies could be confirmed. values below 0.1 considered as trends. Materials and Methods Results and Discussion Data were collected from 14 blackbucks (five males and nine females, BM range 20.1–30.0 kg) and seven sand The stomach of both blackbuck and sand gazelle was com- gazelles (all males, BM range 16.1–19.2 kg). Four of the prised of a rumen, reticulum, omasum and abomasum as blackbucks and all sand gazelles were kept at Al Wabra in all other true ruminants (Fig. 1). The rumen was the Wildlife Preservation (AWWP), State of Qatar, on a diet largest compartment followed by the abomasum, then the of grass hay ad libitum and limited amounts of fresh reticulum and the omasum. When dissecting the black- lucerne for 4 weeks prior to culling. In addition, black- buck omasa for laminar surface area determination, only bucks were fed a small amount of pellets. The remaining the first, most of the second and a few of the third-order ten blackbucks were kept on a diet of ad libitum grass leaves were dissectable, i.e., more than just a small ridge hay, limited amounts of grass haylage and free access to on the basal layer of the omasum. On average, the black- Æ pasture during the day time at Ree Safari Park, Denmark. buck omasum had 9.7 1.1 leaves of first order, Æ Æ Pellets had been gradually removed from the diet at days 9.4 1.4 leaves of second order, 14.4 5.3 leaves of Æ 5–4 prior to culling and completely withheld on days 3– third order, 3.0 2.1 leaves that were positively identified Æ 0. All animals were culled for management reasons except as fourth order and 4.0 0.7 leaves where order could for one blackbuck that died from trauma. Dissections fol- not be determined. The size and position of the parotid lowed a previously described protocol (Sauer et al., in and mandibular salivary glands of blackbuck are shown on press). Not all measures were obtained from each individ- Fig. 2, while the average anatomical measurements of both ual animal due to practical limitations or time con- species are presented in Tables 1 and 2. straints; in particular, no measurements of omasal In blackbucks, all RR and omasum size measures corre- ≥ laminar surface area and salivary glands of sand gazelles lated poorly to BM (all P-values 0.1), while abomasum were made. Heads of the blackbucks from Ree Park were tissue weight and greater curvature length tended to = = frozen prior to dissection of the salivary glands, while increase with BM (P 0.096 and P 0.052, respectively). salivary gland weight was determined in fresh heads from The length of the lesser abomasal curvature was not = AWWP blackbucks. related to BM (P 0.203). Small intestine (SI) length did = For a comparative evaluation of the anatomical mea- not correlate to BM (P 0.733), while SI tissue weight = sures of blackbucks and sand gazelles, measurements increased with BM (P 0.019). Caecum length and tissue = obtained were plotted against literature data on forestom- weight tended to increase with BM (P 0.057 and © 2015 Blackwell Verlag GmbH Anat. Histol. Embryol. 45 (2016) 392–398 393 Blackbuck and sand gazelle GI anatomy C. Sauer et al. (a) (b) Fig. 1. Digestive tract of the blackbuck. DR, dorsal rumen; VR, ventral rumen; RE, reticulum; OM, omasum; A, abomasum; SI, small intestine; CE, caecum; LI, large intestine.