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THE DIGESTIVE SYSTEM OF VERTEBRATES

MAMMALS: Horse, Pony, domestic

Horse, mare with colt (photo by Biomedical Communication Department, College of Veterinary Medicine, N. C. State University, Raleigh, NC 27606)



Pony (Equus caballus) digestive tract (Stevens & Hume 1995)



Figure 2.1.  Relationship between mass-specific metabolic rate (ml O₂/g^.h) or metabolic intensity and log of body mass for eutherian mammals ranging from 6 g shrews to 1,300-kg elephants. Note the inverse relationship between mass-specific metabolic rate and body mass. (From Schmidt-Nielsen 1984).  (CD Figure 3.1)



Figure 3.3.  A longitudinal and cross section of the horse skull.  Most mammals have teeth and jaws that aid in the procurement and breakdown of food. The lower jaw or mandible is narrower than the upper jaw, and its lateral to and fro movements provide an extremely efficient mechanism for grinding of food. (From Norman and Weishampel, 1985.)  (CD Figure5.7a)



Figure 4.8. Horse stomach showing the region of stratified squamous epithelium.  (Modified from Stevens and Hume 1995)  (CD Figure 5.8)



Figure 4.10.  The large intestine of the horse.  (Modified from de Lahunta and Habel 1986.)  (CD Figure 5.10)


Table 6.4.  Mean digesta retention time for herbivorous colon fermenters  (CD Table 7.4)

Although digesta retention times are affected by differences in the diet, and in the body temperatures of the reptiles, marsupial, and eutherian mammals, colon fermenters retain particulate digesta as long or longer than fluid digesta. The effects of colonic retention of particles can be muted in animals with a relatively large cecum such as the chimpanzee, orangutan and gorilla.  (modified from Stevens and Hume 1995)


Table 7.5b.  (CD Table 8.6b)

Enzymatic activity is designated as + (present), trace or 0 (absent). Results in brackets indicate use of and alternate substrate. All data from adult specimens. (from Vonk and Western 1984 plus perissodactyla data from Roberts 1975)


Table 7.7.  (CD Table 8.10)

Enzyme activities expressed as the equivalent amount of bovine trypsin (casein or BAEE) or chymotrypsin (BTEE) under the same conditions. *A: 200-1,200 g RNase per gram pancreatic tissue; B: 20-100 g per gram pancreatic tissue; C: 0-20 µg RNase per gram pancreatic tissue. (from Vonk and Western 1984)


Table 7.8.  (CD Table 8.11)

0, no absorption or transfer; + to +++, degrees of absorption or transfer. (from Brambell 1970)


Table 8.3.  (CD Table 9.3)




Figure 8.6. Concentrations of VFA (SCFA) along the gastrointestinal tracts of mammalian carnivores, omnivores, and herbivores. Animals were fed a at 12 hour intervals.  Each value represents the mean (+/- SE) of 12 samples, consisting of three samples collected at two, four, eight, and 12 hours after a meal, from the oral (S1) and aboral (S2) segments of the stomach, three equal-length segments of the small intestine (SI1, SI2, SI3), the cecum (Ce), and two or three equal-length segments of the colon (C1, C2, C3).  (Modified from Argenzio et al. 1974; Clemens et al. 1975a; Clemens and Stevens 1979; Clemens 1980.)  (CD Figure 9.6)


Table 8.6.  (CD Table 9.6)

Dashes indicate absence of information. Contributions of SCFA to maintenance energy were estimated from the rate of SCFA production by in vitro isotope dilution or measurements of digesta flow. Total maintenance energy was either calculated as twice  the BMR or assumed to be equivalent to ad libitum digestible energy intake in captive, nonreproducing, adult animals. (From Stevens and Hume 1995)


Table 8.7a.  (CD Table 9.7a)

* Absorption from cecum (or ceca) alone.
Dashes indicate absence of information. Contributions of SCFA to maintenance energy were estimated from the rate of SCFA production by in vitro isotope dilution or measurements of digesta flow. Total maintenance energy was either calculated as twice the BMR or assumed to be equivalent to ad libitum digestible energy intake in captive, nonreproducing, and adult animals. (From Stevens and Hume 1995.)



Figure. 8.7.  Volume, net transmucosal flux of water, and net appearance and disappearance of VFA (SCFA) in the large intestine of ponies, with time after feeding. All values, other than volume, are corrected for exchanges between segments that resulted from digesta flow. (Modified from Argenzio et al. 1974 a,b.)   (CD Figure 9.7)



Figure 8.9.  Relationship between colonic water exchange, plasma renin activity, and aldosterone levels in ponies fed a pelleted hay-grain diet at 12-hour intervals. (From Clarke et al. 1990a.)  (CD Figure 9.9)


Table 9.1.  (CD Table 10.1)

(human data: Soergal & Hofmann 1972; sheep data: Denton 1957, Harrison 1962, Hill 1965, Kay 1960, Kay & Pfeffer 1970, MaGee 1961, Taylor 1961; pony data: Alexander & Hickson 1970, Argenzio et al. 1974)



Figure 9.3.  Mean digesta osmolality and concentrations of the major electrolytes along the gastrointestinal tract of the pony obtained from four measurements over a 12-h period after a meal. Segments represent the stomach (S), three equal segments of the small intestine (SI), the cecum (C), and the ventral (VC), dorsal (DC) and small (SC) colon. Hydrogen was omitted, because it is only a small component (1 mEq/L) of the cations, even in gastric contents. Concentrations of PO₄^-- were calculated on the basis of a pKa of 6.8 for NaH₂PO₄ and the mean pH of digesta in each segment.  The principal organic acids (OA) are SCFA and lactic acid. At the pH of intestinal contents, ammonia, SCFA and lactic acid exist principally in their ionized form. Concentrations of HCO₃^- were calculated as the difference in concentration of measured cations and anions. (Modified from Argenzio 1975).   (CD Figure 10.3)



Figure 9.4c.  Mean (+/- SE) values for digesta pH in the gastrointestinal tract of ponies 2 hours (closed triangle), 4 hours (open circle), 8 hours (x), and 12 hours (closed circle) after a meal. The segments of the tract are the cranial (S1) and caudal (S2) halves of the stomach, equal succeeding segments of small intestine (SI1, SI2, SI3), the cecum (Ce), and equal lengths of succeeding segments of colon (RVC, LVC, LDC, RDC, SC1, SC2). (Argenzio et al. 1974.)  (CD Figure 10.4c)