The digestive tract in horses is a complex system responsible for the breakdown and absorption of nutrients essential for maintaining equine health. It includes several key components: the mouth, esophagus, stomach, small intestine, cecum, large colon, small colon, and rectum. Each segment of the digestive tract performs specific functions, from the mechanical breakdown of feed to the enzymatic digestion and absorption of nutrients. The horse's digestive system is uniquely adapted to process fibrous plant material, relying heavily on microbial fermentation, particularly in the hindgut. This page compiles peer-reviewed research studies and scholarly articles that explore the anatomy, physiology, and function of the equine digestive tract, as well as common disorders and their management.
Roberts MC, Kidder DE, Hill FW.Two enzymes having lactase activity are present in the equine small intestine. The first, the digestive enzyme, neutral beta-galactosidase, declines in activity from birth to three years, disappearing completely between 3 and 4 years of age. The other, the soluble lysosomal enzyme, acid beta-galactosidase, having affinity for lactose and a synthetic beta-galactoside, shows a decrease in activity in the first three months of life and thereafter varies little in activity and represents the lactase enzyme in the adult horse. This pattern may parallel the development of lactase activity in many ot...
Schryver HF, Hintz HF, Craig PH, Hogue DE, Lowe JE.The site of phosphorus absorption was studied by comparing the absorption of 32P placed directly into the cecum of fistulated ponies, with that absorbed from an intragastric dose and by estimating apparent absorption in different areas of the intestinal tract of ponies using Cr2O3 as an unabsorbable marker. There was no difference in the absorption of 32P following gastric or cecal administration indicating that phosphorus may be absorbed from the large intestine. The Cr2O3/nutrient ratio technique indicated that phosphorus was secreted into the upper half of the small bowel and that a nearly ...
Hintz HF, Hogue DE, Walker EF, Lowe JE, Schryver HF.Eleven ponies were fed diets containing 1:0, 3:2 or 1:4 forage-grain ratios for 30 days. Animals were killed 4 hr. after feeding and the entire digestive tracts were removed and segments isolated. Digestion coefficients were calculated for dry matter, protein, available carbohydrate (ACHO) and neutral detergent fiber (NDF) by Cr2O3-nutrient ratio for seven segments of the gut.
The major site of ACHO and protein digestion was prececal; whereas, the major sites of NDF digestion were the colon and cecum regardless of the hay:grain ratio. Therefore the relative importance of digestion in the lo...
Slade LM, Hintz HF.A comparative digestion trial was conducted between horses, ponies, rabbits and guinea pigs. Alfalfa and alfalfa-grain diets were compared.
Although there was a trend for ponies to be more efficient than horses in digesting proximate principles of both diets, differences were not significant. Digestibility coefficients for crude fiber and energy were lowest in rabbits. The digestion of nitrogen-free extract (NFE) was greatest in guinea pigs, whereas digestion of crude protein was lowest.
Horses, ponies and rabbits digested organic matter, NFE and energy in the mixed ration more efficient...
Clayton HM, Duncan JL, Dargie JD.The mechanisms involved in the pathophysiological disturbances associated with the presence of mature Parascaris equorum in the small intestine were investigated with radioisotopic techniques. The results suggested that, compared with worm-free controls, infected foals had a reduction in gut motility, an increase in the body solids ratio, a lowering of the body pool of albumin and a decreased ability to incorporate dietary methionine into plasma protein.
La CelluleJanuary 1, 1977
Volume 72, Issue 1-2 5-25
Meuleman A, Latteur B.The topography of Cochliatoxum periachtum is studied. The cuticle is very thick. The digestive, nuclear and excretory systems are located in the ectoplasm, they are not surrounded by the mesoplasm. The endoplasm is very large, it contains vegetable inclusions. By the features of its topography, this species is similar to some species belonging to the Family Ophryoscolescidae and, especially, to Eudiplodinium giganteum.
van Dyk E, Neser S.The possible spread by horse faeces of plants that may become weeds in sensitive areas was investigated. It was found that the period 24-48 hours after ingestion of seeds included in rations was the retention time for seeds passing through the digestive system of the horse. The ability of seeds to germinate was not influenced by exposure to digestive fluids or sea-water. A feeding regime of compound feeds is suggested.
Sweeney RW.Malassimilation should be suspected in horses with weight loss in spite of a good appetite. Malassimilation is usually confirmed with oral glucose or D-xylose absorption tests, whereas the oral lactose tolerance test can be used to evaluate lactase deficiency in foals. Once malassimilation is confirmed, other diagnostic tests such as abdominocentesis, rectal mucosal biopsy, or exploratory laparotomy with intestinal biopsies may determine the etiology of malassimilation.
Hultgren BD.The congenital absence of myenteric ganglia in the terminal portion of the ileum, cecum, and entire colon of white foals with overo spotted parents was reported. Males as well as females were affected. The foals were generally normal at birth but did not defecate. Signs of colic were noticed between 5 and 24 hours after birth, with death occurring at 23 to 132 hours.
Hesta M, Costa M.Many horses are fed differently than their wild ancestors. They often have limited access to pasture and are fed conserved forage and concentrates rich in starch and sugars, in only 2 meals per day. Feeding practices in contrast to natural feeding behavior can lead to gastrointestinal issues. Standard nutritional evaluation is warranted because of its important role in prevention and in treatment and management of diseases. When medical and nutritional treatments are combined, success rates are higher. New techniques to characterize equine microbiota have been used, allowing for microbiota man...
Fischer AT, Yarbrough TY.A technique for retrograde contrast radiography of the distal portions of the intestinal tract of foals was developed and then performed in 25 foals (1 to 30 days old) with colic. Retrograde contrast radiography was shown to be sensitive (100%) and specific (100%) for evaluating obstruction of the small colon or transverse colon. It was slightly less sensitive (86%) and specific (83%) for evaluation of the entire large colon, particularly in older foals. Retrograde contrast radiography provided increased diagnostic capability, compared with that for noncontrast radiography. Retrograde contrast...
Simić V, Ilić A.The caecum in man as a part of the large colon (intestinum crassum) differs morphologically and topographically from the caecum of domestic mammals. The caecum in domestic mammals differs not only from the human caecum but also comparatively morphologically and topographically among the domestic mammals. The appendix vermiformis does not exist in domestic mammals, which represents the main difference between the human caecum and that of domestic mammals. There are certainly some differences in the physiological function of the caecum in man and the caecum in domestic mammals, which are carnivo...
Sellers AF, Lowe JE, Rendano VT.Transmission of intestinal content with respect to wall position and intraluminal pressure was studied using implanted catheters in portions of the haustrated left ventral colon and nonhaustrated pelvic flexure and left dorsal colon in 3 conscious, standing, and feeding ponies. Wall position and content movement was studied in 1 noncatheterized conscious pony that was standing and eating. When coordinated wall movements involving greater than or equal to 30 cm of adjacent colon were seen, point-to-point content movement accompanied intraluminal pressure peaks occurring in the same direction. N...
Brugère H, Castellani G, Boxebeld A, Wolter R.A re-entrant cannulation of the digestive tract was performed in Equidae (ponies and donkeys) between the distal extremity of the ileum and the base of the caecum. The operative technique was conceived to avoid risks of infection of the peritoneal cavity: the openings of the ileum and of the caecum were achieved only after the closure of the abdominal wall incision. Two donkeys were still alive ten months after the operation. This method can provide a convenient model for digestibility studies in Equidae, particularly for assessment of the pre-caecal digestibility.
Salloum RM, Duckworth D, Madison JB, Souba WW.The sodium-dependent transporter system responsible for L-glutamine uptake by brush border membrane vesicles prepared from equine jejunum was characterized. Vesicle purity was ascertained by a 14- to 17-fold increase in activity of the brush border enzyme markers. Glutamine uptake was found to occur into an osmotically active space with negligible membrane binding. The sodium-dependent velocity represented approximately 80% of total uptake and demonstrated overshoots. Kinetic studies of sodium-dependent glutamine transport at concentrations between 5 microM and 5 mM revealed a single saturable...
Simmons HA, Ford EJ.The rate of flow of fluid from the caecum and from the large colon was measured in four Shetland-type ponies fed a hay diet. In two ponies with cannulas in the caecum and at the origin of the right ventral colon, a continuous intracaecal infusion of a solution of chromium EDTA was used and samples were obtained from the cannula at the origin of the right ventral colon. Based on four determinations, the liquid flow from the caecum was 54.2 +/- 1.89 litres d-1. In the other two ponies with cannulas in the origin of the right ventral colon and near the end of the right dorsal colon, a continuous ...
Batt RM, Burgess D, Edwards GB, van de Waal S, Sørensen SH, Hart CA.To examine the postnatal development of equine small intestine, biopsy specimens of jejunal mucosa from 8 ponies, between 6 and 28 weeks old, were subjected to analytical subcellular fractionation and assay of organelle marker enzymes. Fractionation revealed a reduction in the particulate brush border component of beta-galactosidase (lactase) activity between 6 and 28 weeks, and a corresponding increase in soluble activity, although the reduction in mean specific activity was not significant. There also was a decrease in the proportion of brush border to soluble aminopeptidase N activity, a re...
Ochonski P, Drouillard JS, Douthit TL, Vahl C, Lattimer JM.Commercial horse feeds use cereal grains and by-products; however, their effects on the caecal environment remain poorly characterised. Objective: Characterise the effect of commonly used feed ingredients on caecal pH and volatile fatty acid (VFA) concentration. Methods: 6 × 6 Latin square. Methods: Two days prior to the start of the study, 6 caecally cannulated Quarter horses were moved into individual stalls where Smooth bromegrass hay (brome) was offered at 2.0% BW/d split between 2 feedings (0600 and 1800). On day 0, caecal digesta was collected every 2 h for 12 h relative to the 0600...
Bertone AL, VanSoest PJ, Johnson D, Ralston SL, Stashak TS.Fecal excretion of a particulate marker, ytterbium (Yb), was evaluated in 9 horses before surgery and 3 weeks, 3 months, and 6 months (4 trials) after sham-operation (group 1; n = 3) or extensive large colon resection (group 2; n = 6). Fecal excretion curves of total Yb excretion, loge Yb excretion, % Yb excretion, loge % Yb excretion, and cumulative % Yb excretion were evaluated, and kinetic analysis was performed on the loge Yb excretion curves to detect mixing pools and to calculate the fractional rate of particulate passage, turnover rate, and pool size. Calculations were performed to dete...
Davies JV, Gerring EL.Motility patterns in the equine small intestine were investigated in eight ponies. Muscular activity was assessed by means of extramural strain gauge transducers, bi-polar electrodes and in three of the animals, fitted with Thiry-Vella loops, the transit of fluid. Circular muscle contractions were preceded by spiking superimposed on the slow wave and fluid transit in the loops correlated with both these events.
Frape DL, Tuck MG, Sutcliffe NH, Jones DB.1. The rate of passage of chromic oxide (Cr) was similar in the pony and rhinoceros. 2. Higher apparent amounts digested were found using 4N-HCl-insoluble ash (AIA) than those determined by Cr, but overall digestibilities were similar for the two species. 3. An abrupt increase in the starch content of the horse diets increased the number of faecal ciliate protozoa. Only when the overall feed intake was increased in horses receiving a high dietary proportion of starch were the numbers depressed. 4. When the rhinoceros received 109 kJ apparent DE per kg bodyweight daily (716 kJ/W0.75 daily) it m...
Hansen TL, Bobel JM, Rankins EM, Sanchez LC, Warren LK.Digesta retention time within specific segments of the equine gastrointestinal tract (GIT) may be more relevant to scientific inquiries than total tract mean retention time (TTMRT); however, measuring retention time in individual segments requires access to the digestive tract. The objective of this study was to compare prececal, cecal, and colonic mean retention time (MRT) with model-derived compartment MRT. A cecally fistulated gelding was fed indigestible particulate and liquid markers to determine TTMRT and dosed with different pairs of particulate and liquid markers into the cecum (hindgu...
Wellard L, Medyk K, Pearson W.Feed additives that accelerate gastrointestinal transit time may help support normal gastrointestinal function in horses at risk for impaction colic. Previous research has demonstrated significant stimulatory effect of a hemp-based nutraceutical product (Gs Formula; GF) on contractility of gastric smooth muscle and gastrin production in vitro. Objective: To quantify effects of GF on indicators of GIT transit time and tight junction proteins. Methods: Randomized placebo-controlled cross-over study. Methods: Eight Standardbreds were administered 200 plastic beads by nasogastric tube before (base...
Bertone AL, Cockerell GL, Lee RE, Stashak TS.Light microscopy, morphometry, and scanning electron microscopy were used to examine the mucosal morphologic features of 7 intestinal specimens (3 from the small intestine; 4 from the large intestine) from each of 8 horses 1 year after sham operation (group 1; n = 3) or extensive large-colon resection (group 2; n = 5). Qualitative light microscopic examination did not reveal differences between groups, but morphometry revealed significantly (P less than 0.05) greater intercrypt area and distance in horses with colon resection and this was most pronounced in the cecum and remaining right ventra...
Earing JE, Lawrence LM, Hayes SH, Brummer M, Vanzant E.The ability of young and mature horses to digest DM, OM, and NDF was compared using 6 weanling colts and 6 mature (13.2 ± 3.0 yr) geldings. Each colt was paired with a gelding, and the pair was adapted to a diet containing 67% alfalfa cubes and 33% concentrate for 21 d. During the adaptation period, horses were accustomed to housing and all handling procedures. The adaptation period was also used to adjust the amount of feed offered to minimize orts and to maintain similar rates of intake within a pair. After the adaptation period, a 5-d fecal collection period using fecal collection harnesse...
Barlet JP, Davicco MJ, Coxam V.Intestinal absorption of inorganic phosphorus. In most mammalian species inorganic phosphorus (P) is absorbed at the duodenal and jejunal level. However in horses some P is absorbed from the large intestine, whereas in ruminant animals some absorption also takes place in the forestomachs. The structure of the putative phosphate-sodium carrier of the brush border from enterocytes still awaits identification. P absorption is modulated both by endocrine (calcitriol, triiodothyronine) and nutritional factors (minerals of the diet, chemical form of phosphorus). Regulation of salivary P secretion, i...
Ralston SL, Freeman DE, Baile CA.The roles of volatile fatty acids (VFA) and of the large intestine in the control of feeding in ponies were investigated. Ponies with cecal fistulas were adapted to ad libitum access to pelleted feed. Treatment solutions were given as a bolus 15 min before the animals were allowed free access to feed after a 4-h fast. Each dose of VFA solution was tested in a crossover design with a water control. When the ponies were permitted to eat after the treatments, the latency to eat, first meal size, and duration and first intermeal interval were recorded. Feed intakes were measured at 3 and 18 h afte...
Bertone AL, Toofanian F, Stashak TS.Lactase, maltase, sucrase, and alkaline phosphatase activities were determined in the intestinal mucosa from 3 locations in the small intestine and 4 locations in the large intestine 1 year after extensive large-colon resection (group 1; n = 5) and 1 year after sham operation (group 2; n = 3) in horses. Lactase, maltase, and sucrase activities were similar (P greater than 0.05) between group-1 and group-2 horses in all locations measured in the intestinal tract. Alkaline phosphatase activity in the remaining large colon of group-1 horses was significantly (P less than 0.05) greater than the ac...
Mobarak MS, Ryan MF.Light, scanning, and transmission electron microscopy were employed to provide further data on the putative origins of the immunogenic secretory-excretory product (ESP) of Strongylus vulgaris (Looss 1900). The sharply delineated but superficial attachment to the equine caecum by the mouth leaves behind an oval area devoid of epithelial cells. Attachment does not extend deeply enough to reach the muscularis mucosa layer of the equine intestine. The progressive digestion of the ingested plug of tissue (epithelial cells, blood cells and mucous) was visualized. The coelomocytes, floating cells and...
Williams TL, Mochal-King C, Rude BJ, Weed BC, Nicodemus MC.Cecal and ileal cannulations have previously been used to determine equine digestibility and define gastrointestinal physiology. However, research has been limited to specific portions of the equine digestive tract lacking utilization of dual cannulations. The purpose of this study was to develop and implement surgical and preoperative and postoperative procedures for cannulation of dual sections, ileum and cecum, of the equine digestive tract including development of recommendations for addressing postsurgery complications. A total of 8 ponies went through surgical procedures for the placemen...
Wawrzeńska M.In this paper, the effect of ascorbic acid on motoric activity of the intestines of rabbits, pigs, cows, sheep and horses has been determined, and a possible participation of the adrenogenic system in this mechanism has been shown. In experiments in vitro the motility of the duodeum, jejunum, caecum and colon in the animals mentioned abowe was recorded by the method of Magnus after administration of ascorbic acid. Diastolic reactions were observed in all animals, which were much greater in small intestines than in large ones. To elucidate the diastolic mechanism under the influence of ascorbic...
