Basic Caprine Gastroenterology

Several atlases of topographic anatomy and dissection guides of the goat are available (Cihalelain 1987; Constantinescu 2001; Popesko 2008), but most anatomic texts focus on cattle or sheep, with goats mentioned com­paratively, if at all.

Goat Medicine, Third Edition. Mary C. Smith and David M. Sherman. © 2023 John Wiley & Sons, Inc. Published 2023 by John Wiley & Sons, Inc.

Clinical Anatomy

Oral Cavity

The upper lip of the goat is complete and muscular and lacks the dividing philtrum of the sheep. This favors the grasping and tearing of browse, while the philtrum in the sheep favors consumption of grasses close to the ground. The tongue of the goat is not used for prehension of feed, as it is in cattle. It is shorter and smoother and not as easily extracted or displaced from the oral cavity during oral examination. Taste buds on the tongue can discriminate bitter, sweet, salty, and sour tastes, and the tolerance for bitter taste exceeds that of cattle and sheep. This favors the browsing of a wider range of plant species.

There are four main pairs of salivary glands: the parotids, mandibulars, sublinguals, and buccals. The latter are divided into dorsal, middle, and ventral portions. The his­tology of these glands has been described (Nawar 1980). The parotid and ventral buccal glands are serous, the dor­sal and middle buccal glands are mucous, and the man­dibular and sublingual glands are mixed.

The dental formula of the goat is 0033/4033. The upper incisors are replaced by a dental pad that facilitates the tearing of forage. The lower incisors must properly appose the dental pad for efficient acquisition of feed during graz­ing or browsing. Brachygnathism and prognathism both occur in goats and adversely affect feeding behavior under range conditions. Deciduous lower incisors, or milk teeth, occur in young goats. The central pair may be present at birth or appear within the first week of life. The second pair generally appears at 1-2 weeks, the third pair at 2-3 weeks, and the lateral pair at 3-4 weeks of age.

Permanent incisors generally appear according to the following schedule: central incisors usually are present by 1 year of age, but appear as late as 1.5 years of age; second pair, 1.5-2 years of age; third pair, 2.5-3 years of age; and lateral or fourth pair, 3.5-4 years of age. Occasionally there is a failure of eruption of the permanent incisors. Aged goats with persistent deciduous central incisors have been observed. Aging of older goats using teeth is difficult. Incisors continue to wear over time and the teeth become rounded rather than rectangular. The speed of this process varies considerably with type of feed and management.

Anodontia, or absence of the mandibular incisor teeth, has been reported in a West African Dwarf goat (Emele- Nwaubani and Ihemelandu 1984). Congenital absence of the first cheek tooth (P2) has been noted in feral goats (Rudge 1970).

Molars are present at birth and elongate throughout life, but are continuously worn down by the grinding action of mastication. Shortened molars may be expelled altogether in older goats, leading to accumulation of feed in empty sockets and excessive growth of the unopposed molar.

The lower dental arcades are closer together than the upper arcades. Because the goat chews with a strong lateral grinding motion, extremely sharp dental points may develop on the lateral aspect of the upper molars and the medial aspect of the lower molars, and care must be taken in carry­ing out an oral examination so that fingers are not injured.

Cleft palate occurs in goats as a congenital malformation. Usually the cause is unknown. However, plants containing piperidine alkaloids, notably Lupinus formosus, can pro­duce teratogenic effects, including cleft palate and multiple tendon contractures, when consumed by dams between 30 and 60 days of gestation (Panter et al. 1990, 1994). The orhthobunyaviruses are a potential cause too, as cleft palate has been reported in stillborn lambs affected by the Schmallenberg virus (Endalew et al. 2019). Cleft palate has also been reported in fetal monsters, associated with dupli­cation of the pelvis and hindlimbs (monocephalus dipygus) in one case (Corbera et al. 2005), and with two faces (dipros- opus) in another (Mukaratirwa and Sayi 2006).

Esophagus

The embryonic development of the caprine esophagus has been described (Jung et al. 1994). In adult dairy goats of the European breeds, the esophagus is approximately 1 m in length, so at least that length of tube should be used to reach the rumen for relief of bloat or administration of medications. A speculum should be used to avoid the goat chewing the tube. The movement of swallowed boluses, eructated gas and cud, and correctly placed stomach tubes may be seen in the esophagus along the left jugular furrow.

An esophageal or reticular groove is present in the goat and reflexively closes in response to suckling in the neo­nate, allowing milk to bypass the rumenoreticulum and directly enter the abomasum via the omasal groove. This reflex wanes after weaning and is vestigial in adults, although it can be stimulated by drinking after severe, pro­longed water deprivation.

The surgical establishment and maintenance of esopha­geal fistulae for collection of dietary samples in goats have been described (Pfister et al. 1990). An apparatus for the remote-control collection of esophageal fistulae samples and its long-term performance have also been reported (Raats and Clarke 1992; Raats et al. 1996).

Forestomachs and Abomasum

The structure of the forestomachs is quite similar in goats and sheep (Gueltekin 1953; Horowitz and Venzke 1966; Bhattacharya 1980; Chungath et al. 1985). The reticuloru- men occupies most of the left half of the abdomen, and extends cranially to the eighth intercostal space and cau- dally to the tuber coxae, in contact with the left body wall. The cardia occurs at the eighth intercostal space.

The omasum of the goat is much smaller than the reticu­lum. In small ruminants, the omasum is proportionately smaller and lighter than in the cow. Internally, the longitudi­nal folds, or leaves of the omasum, produce Laminae omasi of four different lengths in sheep, but only three in goats; the fourth or shortest lamina is absent. The average number of laminae in the goat is around 35, compared with 169 in cat­tle (McSweeney 1988). The omasum is situated deep to the eighth and ninth intercostal spaces on the right-hand side of the abdomen, and does not contact the body wall.

The abomasum in small ruminants is proportionately larger and longer than in the cow. The abomasum of the goat is situated on the abdominal floor in the right anterior abdomen and runs caudally along the costal arch.

A wide variety of stomach volumes have been reported for mature goats. Much of the variation is probably caused by breed differences, rations fed, and the method of meas­urement. The range for rumen volume is 12-28 L, although in most cases the upper limit is around 20 L. For the reticu­lum, the range is 1.6-2.3 L; for the omasum, 0.75-1.2 L; and for the abomasum, 2.1-4 L.

The goat is born with an undeveloped rumen and a pro­portionately larger abomasum (Tamate 1956; Benzie and Phillipson 1957). During the first three weeks of life, the body of the abomasum is located mainly on the left side of the abdomen, adjacent to the diaphragm, with the pyloric antrum to the right of the midline. It gradually moves to its adult position in the right abdomen as the forestomachs enlarge on the left. At birth, the ratio of reticulorumen capacity to abomasal capacity is 1 : 4, with a reticulorumen volume of 70 mL and an abomasal volume of 290 mL. Omasal volume is negligible. In kids given access to roughage, the ratio at 6 weeks has become 5.7 : 1. Full rumen capacity is usually reached by 12 weeks of age. Acceleration of rumen development can be achieved by early introduction of roughage and concentrate into the diet of the suckling kid (Tamate 1957).

Small Intestine and Cecum

The small intestine accounts for approximately 77% of the length of the alimentary tract distal to the forestomachs, and the cecum an additional 2%.

Colon and Rectum

The structure of the caprine colon is typical of the rumi­nants, in that there is a proportionately elongated ascend­ing colon that is spirally coiled, followed by shorter transverse and descending colon segments leading to the rectum and anus. In the goat and sheep, there are usually three centripetal and three centrifugal turns in the spiral segment. The colon and rectum account for approximately 21% of the length of the alimentary canal distal to the fores­tomachs, and the mean length is 5 m in most breeds. The diameter is approximately 8 cm at the cecum and 2 cm at the rectum. The colon also is largely displaced to the right abdomen by the reticulorumen. The spiral colon lies medial to the small intestine and cecum.

Omentum and Mesentery

The goat shows a marked predilection for the deposition of fat in omentum and mesentery compared with cattle and sheep. This undoubtedly has adaptive value when goats inhabit environments with scarce feed supplies. It also may be significant in the pathogenesis of pregnancy toxemia, because overfeeding in early pregnancy can result in con­siderable deposition of intra-abdominal fat. This space­occupying fat can reduce feed capacity throughout the digestive tract, leading to decreased feed intake, negative energy balance, and ketosis. Intra-abdominal fat can also be misleading when assessing body condition. Goats that appear underconditioned, with little palpable subcutane­ous fat, may have considerable intra-abdominal fat stores. Goats with little mesenteric fat at necropsy have been severely malnourished for an extended period of time.

Digestive Physiology

Feeding Behavior

With regard to diet selection, the goat has been character­ized as intermediate between the true grazers, such as the domesticated cow and buffalo, and the true browsers or concentrate selectors, exemplified by wild ruminants such as the moose and whitetail deer (Demment and Longhurst 1987; Hofmann 1988). This means that the goat can exploit a range of plant materials to meet nutrient requirements. This diversity accounts in large part for the growing interest in goats as a desirable livestock species where intensive cropping or maintenance of abundant grassland is not possible. The goat is also being exploited in mixed farming systems, where stocking of goats along with sheep and cattle reduces weeds and shrubs. This improves grass quality and availability for the grazing species, and increases overall yields of animal products per acre.

The typical feeding behavior of goats also has a negative side. They are so successful at exploiting limited feed resources that when overstocking occurs in environments with marginal plant growth, permanent destruction of the flora with desertification of the environment can occur. Traditionally, the goat has been blamed for instances of desertification that are as much a result of failure of live­stock population management by stock owners as of the goat's superior foraging ability (Dunbar 1984; El Aich and Waterhouse 1999). The ecology of feeding behavior and its impact on animal productivity and environmental quality have been reviewed (Merrill and Taylor 1981; Owen-Smith and Cooper 1987; Van Soest 1987; Devendra 1987).

Nutrient Use

It has long been suggested that the goat has more digestive efficiency than cattle or sheep. Many studies have been car­ried out regarding comparative digestive efficiency and the results have not been consistent in identifying a distinct advantage for the goat. In general, goats and sheep show equal efficiency on high-quality, low-fiber diets. When fed low-quality, high-fiber diets, however, the two species show different compensatory advantages. Sheep digest fiber more completely than goats, but have a decreased rate of intake, while goats have a greater rate of intake and a faster rate of removal of non-digested fiber from the rumen (i.e., shorter rumen retention time; Brown and Johnson 1984). The subject of comparative digestive effi­ciency in domestic ruminants with emphasis on the goat has been reviewed (Morand-Fehr 1981; Devendra and Burns 1983; Brown and Johnson 1984).

Digestive Activities

Goats eat more frequently and rapidly than sheep (Geoffroy 1974). In the process, they produce more abun­dant saliva. Goats produced parotid saliva at the rate of 110 mL/hour compared with 40 mL/hour in sheep when eating the same diet of fresh-cut Egyptian clover (Seth et al. 1976). In addition to the known functions of bolus lubrication, urea recycling, and rumen buffering, copious saliva may have adaptive significance for goats regarding diversity of diet. Goat saliva contains as yet unspecified proteins that have a high tannin-binding affinity, enabling binding of potentially toxic tannins found in many of the tree and shrub species browsed by goats (Schmitt et al. 2020). The rumen flora of feral goats may also contain streptococcal bacteria that can degrade tannins (Brooker et al. 1994; Sly et al. 1997).

The rumination cycle of goats averages 63 seconds, or once per minute. The cycle is fairly constant, but may be slightly shorter on silage rather than hay diets. The motility pattern of rumenoreticular contraction of the goat is simi­lar to that of sheep and differs in similar ways from the bovine pattern (Dziuk and McCauley 1965). Involuntary rumen contraction in goats is under vagal control (Iggo 1956). In confinement, on a hay and concentrate ration, goats were observed to actively ruminate approxi­mately 7.75 hours per day, with 75% of cud chewing activity occurring at night (Bell and Lawn 1957).

Descriptions of normal caprine rumen fluid composition are limited, but it is known that certain properties of rumen fluid can vary markedly with changes in water intake. In desert breeds that may have access to drinking water only every three to four days, the rumen plays a vital role as a fluid reservoir. Desert goats are able to maintain a constant serum osmolarity in the face of severe dehydration and subsequent overhydration by pooling fluid in the rumen. After four days without water, the average rumen osmotic concentration in black Bedouin goats is 360 mOsm/kg, but only 82 mOsm/kg immediately after drinking as much as 32% of their original bodyweight. The sudden hypo-osmotic effect reduces rumen protozoa numbers presumably by rupture, but causes no decrease in bacterial numbers or fermentation activity (Brosh et al. 1983).

An interesting aspect of the caprine rumen microflora has to do with the ability to detoxify the feedstuff Leucaena Ieucocephala. This leguminous shrub or low tree is widely distributed throughout the tropics and subtropics. It can contribute considerably to improved animal nutrition and productivity when used as a protein-rich feed for rumi­nants (Jones 1979). However, when the plant comprises more than 30% of the diet, cattle, sheep, and goats in cer­tain countries develop a variety of clinical abnormalities including alopecia, wool loss, excessive salivation, poor appetite, hypothyroidism, cataracts, poor reproductive per­formance, weight loss, and death. Goats are reported to show hypothyroidism and erosions of the esophageal mucosa and rumen papillae (Jones and Megarrity 1983).

Some of these toxic effects are directly caused by the amino acid mimosine, which is present in the leaves of L. Ieucoceph- ala, at levels of 2-5%. The thyroid effects are caused by a breakdown product of mimosine, 3,4-dihydroxypyridine (DHP), a potent goitrogen. The DHP is produced during mas­tication and subsequent rumen bacterial degradation. In ani­mals not suffering ill effects from Leucaena consumption, DHP is additionally degraded in the rumen to harmless break­down products by specific anaerobic rumen bacteria (Allison et al. 1990). It has been demonstrated that cultures of rumen bacteria from goats in Hawaii, where clinical Leucaena toxico­sis is not observed, can prevent clinical signs when inoculated into the rumens of goats and cattle in Australia, where Leucaena toxicosis is widespread (Jones and Megamty 1986). This inoculum is now available commercially in Australia (Queensland Government 2019). The probiotic product con­tains a rumen bacterium (Synergistes jonesii) designed to break down mimosine to harmless byproducts.

Studies on the rate of passage of foodstuffs through the gastrointestinal tract of goats have been carried out using stained markers (Castle 1956a, b, c). Stained particles first appear in goat feces from 11 to 15 hours after ingestion, and have disappeared by 6-7 days. The maximum appearance of stained particles is at approximately 30 hours after inges­tion. The majority of the time spent by ingesta traversing the alimentary canal occurs in the forestomachs. Passage of ingesta through the entire small intestine takes an aver­age of three hours.

Approximately 58% of the total dry matter digested by the goat is digested in the forestomachs, as is 93% of the crude fiber, 11% of the crude protein, and 80% of the solu­ble carbohydrate (Ridges and Singleton 1962). Most of the soluble carbohydrate digested in the forestomachs is absorbed from the rumen after fermentation as volatile fatty acids. Some carbohydrate absorption and most pro­tein absorption occur in the intestine.

Extensive removal of water from intestinal contents occurs in the large intestine of goats and sheep. This serves as an adaptation for water conservation. The average time for passage of ingesta through the large intestine is 18 hours, compared with 3 hours in the small intestine, despite the fact that the small intestine is at least three times as long. This delayed transit accounts for the dry con­sistency of goat and sheep feces. The dry matter content of normal goat feces is usually between 50% and 60%, com­pared with 15-30% for cattle.

Clinical Pathology and Diagnostic Aids

Clinical Chemistry

Normal values for clinical chemistry parameters associated with the organs of digestion are given in Table 10.1

Serum electrolyte levels may change dramatically in digestive disease. Hypokalemia and especially hypochlo­remia are associated with gastrointestinal stasis. In obstruc­tive diseases such as intussusception and blockage by phytobezoars or foreign bodies, hypochloremia and hypokalemia may be marked (Sherman 1981). Metabolic alkalosis may also occur in these conditions, but if surgical obstructions are severe enough to cause shock, acidosis may prevail. Displacements of the abomasum, the most common cause of hypochloremic, hypokalemic, metabolic alkalosis in dairy cattle, rarely occur in goats. Experimental goats with surgically induced right abomasal displace­ment, left abomasal displacement, or abomasal torsion were hypochloremic, hyponatremic, and hypokalemic fol­lowing induction of these abnormalities, and also had increased chloride ion levels in rumen fluid (Kwon et al. 1997).

The major chemical abnormalities associated with diar­rhea are metabolic acidosis, with decreased serum bicarbo­nate, and hyponatremia, caused by sodium and bicarbonate loss in the diarrheic feces. Marked acidosis is also com­monly seen in d-lactic acidosis due to grain overload or engorgement toxemia. In this condition, serum lactate lev­els are also markedly increased.

Abdominocentesis

The examination of peritoneal fluid may help in the diag­nosis of digestive disease, particularly when lack of fores­tomach motility and abdominal distension are prominent clinical signs. The most common use of abdominocentesis in goats is to differentiate gastrointestinal causes of abdom­inal distension from non-alimentary causes. In male goats, ruptured bladder secondary to obstructive urolithiasis is common and leads to accumulation of urine in the abdo­men. Hydrops conditions associated with abnormal preg­nancy in the female must also be ruled out.

Table 10.1 Normal values for blood constituents used in the assessment of diarrheal and other gastrointestinal diseases.

sample can be collected. The fluid/gas interface of the rumen content can be estimated by ballotment or percus­sion of the left flank and a point selected below the fluid line. After aseptic preparation, a 3 in. (7.6 cm) 18-gauge needle can be passed through the abdominal and adjacent rumen wall and a fluid sample aspirated by syringe. This procedure presents no more risk of inducing peritonitis than does routine abdominocentesis. In outbreaks of acci­dental grain overload involving numerous animals, this method allows for rapid determinations of rumen pH in affected goats to establish treatment priorities.

Fecal Examination

The gross and microscopic examinations of feces are indis­pensable aids to the diagnosis of diseases of the digestive system. Normal goat feces is usually voided in piles of indi­vidual pellets 0.5-1.5 cm in diameter, although it is not nec­essarily abnormal if the pellets are sometimes caked together. Feces less well formed may be seen from animals grazing lush pasture. Feces similar to that normally produced by the dog, with poorly discernible pellets, should be considered abnormal. This is most often seen associated with gastroin­testinal parasitism and sometimes paratuberculosis.

Whole kernels or identifiable portions of grain are rarely observed in goat feces unless the goat is on a very high level of grain feeding, because the goat normally produces a consistently fine particle size of ingesta during mastication and regurgitation. Grain in the feces on a low-grain diet suggests dental disease or rumen disease.

Small, stony, darker pellets suggest constipation, most commonly caused by dehydration, and the cause should be pursued. Mucus coating the feces suggests prolonged tran­sit through the alimentary tract and possible dehydration.

Fresh blood is uncommon in normal-appearing goat feces, but may be seen mixed in diarrheic feces in a number of conditions, including Nairobi sheep disease, rinderpest, enterotoxemia, coccidiosis, nodular worm infection, chabertiosis, and Japanese pieris poisoning. Dark, tarry stools (melena) can be seen in coccidiosis. Diarrhea is dis­cussed in detail below.

Microscopic examination of goat feces, using direct smear or fecal flotation techniques, is valuable in the diag­nosis and monitoring of most gastrointestinal parasitic infections. Samples for analysis should be fresh, because ova will hatch rapidly and larvae will be undetectable using fecal flotation methods. Interpretation of results is dis­cussed under the various specific parasitic diseases.

Imaging Techniques

Because of the goat's small size, radiographic studies can be readily performed and can be helpful in diagnosing intestinal obstruction, congenital atresia, foreign-body penetrations, and mass lesions. The radiographic anatomy of the caprine digestive tract and contrast studies have been described (Cegarra and Lewis 1977; Chhadha and Gahlot 2006). Adult goats are fasted for 48 hours and given 600 mL of barium sulfate via stomach tube. The first film should be taken within one hour, because in some cases the media may rapidly leave the rumen and already be in the abomasum. If the media is still in the rumen, the next film can be taken six to eight hours later and then at four-hour intervals until 24 hours, when most of the gastrointestinal tract will have been visualized. The use of transabdominal ultrasonography in goats for diagnostic purposes has also been reported (Tharwat et al. 2012).