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Disorders Related to Nutrition URINARY CALCULI Urinary calculi are occasionally a problem during the spring in pregnant and lactating female mink and during the summer in male kits (Leoschke et al., 1952; Nielsen, 1956) where losses have been reported to exceed 10 percent (Gorham et al., 1972~. The occurrence of the disorder is usually greater in the inland areas, where diets are composed primarily of meat products, than along coastal areas, where fish constitute the main component of the diet (Leoschke et al., 1952~. Mink urinary calculi consist primarily of magnesium am- monium phosphate hexahydrate (Leoschke et al., 1952), and their formation appears to be favored by the presence of alka- line urine. As these calculi are soluble in solutions below pH 6 (Leoschke and Elvehjem, 1954), substances are often added to mink diets to reduce urine pH levels and prevent urolithiasis. Leoschke and Elvehjem (1954' reported that the addition of 1 g of ammonium chloride per mink per day to the diet pre- vented formation of urinary calculi. Urolithiasis can also be prevented by the addition to the diet of 2.0 percent phosphoric acid (75 percent acid concentration) on a dry matter basis (Leoschke, 1956~. This is equivalent to 0.8 percent phosphoric acid (75 percent feed grade) with diets containing 15 to 20 per- cent fortified cereal and 80 to 85 percent fresh/frozen feedstuffs. Sulfuric acid is frequently used as a preservative for fish silage in the Scandinavian countries. This is also helpful in reducing urinary calculi. Three percent sulfuric acid by weight and 0.5 to 1.0 percent acetic or formic acid added to the fish produces a silage of plI 2.5 to 3.2 Jensen and Joergen- sen, 1975; Lund, 1975~. A diet containing 35 percent acid-preserved fish silage has been successfully fed to mink during the late growth period (Lund, 1975j; however, the use of silage-containing feeds of pH less than 5.5 Tiring reproduction and early kit growth has given unsatisfactory results Joergensen et al., 1976; Poulsen and ~oergensen, 1977, 1978; Poulsen' 1978) If too high levels of sulfuric acid-preserved fish silage are fed, the mineral balance of the diet (Hansen, 1977a) and rate of food passage through the digestive tract (tIansen, 1977b) are adversely af- fected. The recommended levels for feeding fish silage to mink ~, , are up to 10 percent during reproduction and early growth and up to 30 percent during the late growth and furring periods. WET-BELLY DISEASE Wet-belly disease occurs predominantly in male mink and i characterized in the live animal by intermittent soaking of the fur with urine around the urethral orifice (Figures 8 and 9~. This causes local irritation and interruption of normal fur maturation, resulting in a darkened discoloration due to melanin granules in the inguinal area on the leather side of the pelt. This disorder is most frequently encountered at the onset of cold weather prior to pelting and during the breeding sea- sor1 (Leoschke, 1957, 1962; Gunn, 1962; Schaible et al., 1962~. Many factors involving nutrition, genetics, physiology, and bacteriology have been implicated. Studies by Leoschke ~1959) and Evans et all (1961) have shown a positive relation- ship between the caloric density of the diet and the occurrence and severity of the disorder. Others have reported little or no problem with certain strains of animals receiving high levels of fat in the diet (Stout et al., 1964, 1965; Evans 1964b, 1967a). Roberts (1959), Schaible et al. (1962), and Aulerich et al. (1963) have noted greater incidence of the disorder on diets high in calcium or with wide calcium-to-phosphorus ratios. Gunn (1962) reported diets that contained high proportions of raw poultry waste, whole fish, and tripe were conducive to wet belly in females. He attributed the condition to infections by Proteus organisms in these feedstuffs and suggested that stress of cold weather may predispose the animals to the infec- tion (Gunn, 1966~. Studies by Leoschke (1961), Lauerman (1964), Stout et al. (1964, 1965), and Pastirnac (1977) have demonstrated that susceptibility to wet-belly disease appears to be controlled by genetics, with nutritional factors greatly influencing the extent and severity of the condition in geneti- cally susceptible strains. Restricting feed intake from mid- October to pelting may be helpful in reducing wet-belly in- cidence. Is 19
20 Nutrient Requirements of Mink and Foxes FIGURE 8 Typical symptoms of wet-belly disease of mink. SOURCE: W. L. Leoschke, Valparaiso University, Valparaiso, Indiana. .. . . . ............................. ........ ............... . ~. . ~, ..,. ~i . ~.~,~,~.: .,.,.,~,...,,..~,..,.,~,..... . ~ . ~. ..,.~...,..~,,,..,,,~.~, i,. ..~....~....... . ~.,.~.~ ~. .......... .... ......... : ...... ......... . i............... ........ ..~...~.~....~. .................. . FIGURE 9 Normal (left) and wet-belly pelts. SOURCE: J. E. Oldfield and J. Adair, Oregon State University, Corvallis.