Overview of Conditions Affecting the Caprine UrinarySystem
Clinical disease of the urinary system is uncommon in goats, with the exception of obstructive urolithiasis. This condition occurs frequently in males, especially castrated males.
Urolithiasis is discussed in detail later in the chapter.Subclinical and Clinical Conditions
of the Kidney
Despite the low prevalence of clinical renal disease, pathologic lesions of the kidneys are not unusual in normal goats at slaughter. In an Indian study, 71% of all kidneys examined showed histologic abnormality, even when the kidneys were grossly normal. Nephrosis was the most common descriptive finding (Sankarappa and Rao 1982). In contrast, gross morphologic changes have been found in only 1.5-3% of kidneys examined at slaughter (Khanna and Iyer 1971b; Tomar 1984; Babu and Paliwal 1988; Baghban and Yaripour 2016). Interstitial nephritis of unknown etiology is the most common histologic lesion in these kidneys, followed by nephrocalcinosis. The most common gross abnormalities are congenital polycystic kidneys and white spots on the kidney surface. White spots are sometimes caused by leptospirosis infection (Kharole and Rao 1968; Khanna and Iyer 1971b), and in one case by Encephalitozoon (Nosema) cuniculi, a protozoal parasite uncommon in goats (Khanna and Iyer 1971a). Other conditions associated with grossly abnormal goat kidneys at slaughter include pyelonephritis, nephrosis, amyloidosis, hydatid cyst, infarction, and congestion (Baghban and Yaripour 2016).
Spontaneous glomerulonephritis occurs in goats, but is rarely recognized clinically. The glomerular lesion contains heavy deposition of immunoglobulin (Ig)G and complement, but the antibody is not directed against basement membrane. The inciting cause of the immune-mediated lesion is not known (Lerner et al. 1968). Glomerulonephritis has also been reported as an incidental necropsy finding in goats with a primary diagnosis of mycoplasma pneumonia.
Goat Medicine, Third Edition. Mary C. Smith and David M. Sherman. © 2023 John Wiley & Sons, Inc. Published 2023 by John Wiley & Sons, Inc.
A subclinical condition known first as symmetrical cortical siderosis and later as “cloisonne kidney” has been observed in goats in Iraq (Zahawi 1957) and India (Kharole 1967) and in castrated male Angora goats in Texas (Light 1960; Thompson et al. 1961; Grossman and Altman 1969). The condition has also been recorded in sheep (Oryan et al. 1993). The kidney cortices are diffusely pigmented dark brown to black, with the pigmentation stopping abruptly at the corticomedullary junction. The pigmentation is associated with thickening of the basement membranes of those portions of the proximal convoluted tubules present in the renal cortex. The lesion is frequently associated with renal hemosiderosis and the affected basement membranes stain variably for iron. While a number of explanations for the etiology of this subclinical condition have been offered, the actual cause remains unknown (Hatipoglu and Erer 2001).
Pyelonephritis is infrequently reported in goats and may be caused by organisms other than Corynebacterium renale, such as Trueperella (Arcanobacterium) pyogenes (Gajendragad et al. 1983). The relatively low prevalence of postpartum uterine infections in goats compared with cattle may in part account for the lower prevalence of this ascending kidney infection in goats.
The kidneys have filtering and excretory functions. As a result, toxins may concentrate in the kidneys, causing toxic nephropathy. A diverse group of metals, chemicals, plants, fungi, and drugs have been reported to produce renal lesions in the goat, either experimentally or in spontaneous cases. Despite this extensive documentation there is scant information on the antemortem effects of various toxins on renal function, clinicopathologic abnormalities, and relevant clinical signs.
The metals reported to cause toxic nephropathy include arsenic (Biswas et al.
2000), cadmium (Bose et al. 2001), copper (Humphries et al. 1987; Belford et al. 1989), iron (Ruhr et al. 1983), lead (Gouda et al. 1985), mercury (Pathak and Bhowmik 1998), and selenium (Hosseinion et al. 1972; Qin et al. 1994). Chemicals include aldrin (Singh et al. 1985), chlorpyrifos compounds (Mohamed et al. 1990), diesel fuel (Toofanian et al. 1979), ethylene glycol (Boermans et al. 1988), fenvalerate (Mohamed and Adam 1990), hexachloroethane (Vihan 1987), kerosene (Aslani et al. 2000), sevin (Wahbi et al. 1987), and uranyl nitrate (Dash and Joshi 1989).Plants causing toxic nephropathy in goats include Acanthospermum hispidum (Ali and Adam 1978), Agave Iechequilla (Mathews 1937), Amaranthus spp. (Gonzalez 1983), Aristolochia bracteata (El Dirdiri et al. 1987), Azadirachta indica (Ali 1987), Cadaba rotundi- folia (El Dirdiri et al. 1987), Capparis tomentosa (Ahmed and Adam 1980), Cestrum taurantiacum (Mugera and Nderito 1968), Citrullus colocynthis (Barri et al. 1983), Crotalaria saltiana (Barri et al. 1984), Gutierrezia micro- cephala (Mathews 1936), Heliotropium ovalifolium (Abu Damir et al. 1982), Indigofera hochstetteri (Suliman et al. 1983), Ipomoea carnea (Abu Damir et al. 1987), Jatrophia spp. (Barri et al. 1983), Lagenaria siceraria (Barri et al. 1983), Lantana camara (Ide and Tutt 1998), Narthecium ossifragum (Flaoyen et al. 1997), Nolina texana (Mathews 1940), Palicourea aenofusca (Dobereiner et al. 1987), Pennisetum clandestinum (Peet et al. 1990), Pieris japonica (Visser et al. 1988), Senecio jacobaea (Goeger et al. 1982), Solanum dubium (Barri et al. 1983), Tephrosia apollinea (Suliman et al. 1982), Tribulus terrestris (Jacob and Peet 1987), and Vestia foetida (McKeough et al. 2005).
Fungi causing nephropathy include Drechslera campan- ulata (Schneider et al. 1985) and Aspergillus flavus (Samarajeewa et al. 1975). Aspergillus and Penicillium fungi are frequent feed contaminants. Experimentally it was shown that ochratoxin, a metabolite of some species of these fungi, produced marked nephrotoxicity, especially in the proximal convoluted tubules when administered intravenously (Maryamma and Krishnan Nair 1990).
Ingestion of sawfly larvae also produced renal lesions in goats (Thamsborg et al. 1987).Halothane (O'Brien et al. 1986), imidocarb diproprion- ate (Corrier and Adams 1976), and furazolidone (Ali et al. 1984) are drugs documented to have caused lesions in the caprine kidney. The aminoglycosides are known to be nephrotoxic in various animals when used at high doses for prolonged periods of time, or if there are underlying conditions predisposing to renal damage such as dehydration. Gentamicin was shown to produce subclinical nephrotoxicity in goats, as evidenced by decreased urine specific gravity, proteinuria, presence of granular epithelial casts in urine, and increased urine alkaline phosphatase when the drug was given intramuscularly at a dose of 35 mg/kg bodyweight (bw) divided in two daily doses for 10 days (Kumar and Pandey 1994).
Several infectious diseases that affect primarily other organ systems also may produce renal lesions and severe kidney dysfunction. They are discussed in detail elsewhere in this book. Cowdriosis, or heartwater, discussed further in Chapter 8, produces renal ischemia that leads to tubular nephrosis (Prozesky and Du Plessis 1985). Chronic trypano- somosis, discussed further in Chapter 7, can produce mononuclear infiltrates and amyloid deposits in goat kidneys (Bungener and Mehlitz 1976). Leptospirosis, discussed in Chapters 7 and 13, may cause interstitial nephritis.
Renal failure can occur as a result of massive hemolysis or muscle necrosis because hemoglobin or myoglobin accumulates in the renal tubules. Therefore, parenteral fluid administration to promote diuresis is an important aspect of therapy for the hemolytic anemias and for nutritional muscular dystrophy. Pregnancy toxemia, a nutri- tional/metabolic disease, can produce fatty infiltration of the kidney proximal tubular epithelium (Tontis and Zwahlen 1987).
Conditions ofthe UrinarySystem Distal to the Kidney
Pathologic conditions of the ureters and bladder are infrequent in goats, including cystitis, a comparatively common disease in cows.
There are two reports of multiple leiomyomas in the bladder wall seen at necropsy. No clinical signs attributable to the tumors were reported (Jackson 1936; Lairmore et al. 1987). There are two additional reports of leiomyoma of the urinary bladder in goats, as well as a transitional cell papilloma of the urinary bladder identified during abattoir inspections (Timurkaan et al. 2001; Raoofi et al. 2007).The principal condition affecting the urethra is obstructive urolithiasis in male goats. Ulcerative posthitis affecting the preputial opening and causing dysuria is more common in sheep, but also occurs in bucks and especially wethers. It is discussed in detail in this chapter.
Malformations of the urethra also occur and are most commonly reported in newborn and young kids that present with dysuria. Abnormalities may include atresia, hypospadias, diverticulum, and/or dilatation of the urethra, usually at or near the prepuce (Karras et al. 1992; Kiliς et al. 2005). These abnormalities are often associated with the intersex condition in goats. Vaginitis in does and bala- noposthitis in bucks are caused by herpesvirus infection and are spread venereally, as discussed in this chapter. Mycoplasma infections are also associated with vaginitis. goat kidneys were weighed and measured in a slaughterhouse study in Pakistan (Khan et al. 2003). Mean kidney weight for right and left kidneys in male and female goats ranged between 65.4 and 66.7 g. Mean length ranged between 6.1 and 6.3 cm and mean thickness ranged between 2.0 and 2.9 cm. Breeds were not specified, but kidney weight and measurements will vary with the breed and size of the goats.
The right ureter follows the vena cava dorsal to the left kidney. The left ureter begins to the right of the median plane, courses ventral to the right ureter, and then crosses back to the left to enter the bladder. The ureters pass obliquely through the bladder wall and enter the dorsum of the bladder in the trigone region.
The ureteral openings are 1-1.5 cm apart. The urinary bladder is ovoid and extends into the abdominal cavity when full. It lies ventral to the uterus in the doe. Cystocentesis is difficult, even when the bladder is full, because of the depth of the caudal abdomen.The penis is fibroelastic in character, as in other ruminants, and similarly possesses a sigmoid flexure. Paired retractor penis muscles run laterally to the penis and attach proximal to the sigmoid flexure. The action of these muscles makes exteriorization of the penis from the prepuce for clinical examination difficult.
As is the case in sheep, the pars spongiosa of the penile urethra extends well beyond the glans penis for a length of approximately 2.5 cm, forming a vermiform appendage with erectile capacity known as the urethral process (Ghoshal and Bal 1976) (Figure 12.1). While the urethral process in sheep is attached to the left side of the glans, it is median in position in the goat. The process is folded back inside the prepuce when the penis is flaccid, but becomes rigid and extended when the penis is erect. During ejaculation, the process rotates spirally and is believed to spray semen on the external uterine orifice or possibly even enter the external os of the cervix. At birth, the urethral process is adhered to the preputial mucosa and gradually separates under the influence of testosterone.