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Journal of Animal Science - Special Topics

COMPANION ANIMALS SYMPOSIUM: Dietary management of feline lower urinary tract symptoms12

 

This article in JAS

  1. Vol. 91 No. 6, p. 2965-2975
     
    Received: Oct 28, 2012
    Accepted: Jan 11, 2013
    Published: November 25, 2014


    3 Corresponding author(s): krkerr2@illinois.edu
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doi:10.2527/jas.2012-6035
  1. K. R. Kerr 3
  1. Division of Nutritional Sciences and Department of Animal Sciences, University of Illinois, Urbana 61801

Abstract

Experimental and clinical investigations have confirmed the importance of dietary modifications in medical protocols designed to treat and prevent feline lower urinary tract signs (LUTS). The objective of this review is to discuss common medical conditions contributing to feline LUTS and to present currently used and potential preventative dietary modifications. Feline LUTS are a set of clinical conditions with similar symptoms related to inappropriate urine elimination due to a combination of genetics, stress and frustration reactions, environment, and medical condition or conditions, for example, idiopathic cystitis, urolithiasis, urethral obstruction, and urinary tract infection. The main goals of dietary modifications to prevent LUTS are 1) promote large dilute volumes of urine, 2) decrease the relative supersaturation of urine for specific stone types, and 3) promote healthy bacterial populations in the gastrointestinal and urogenital tracts. The impact of dietary composition, including dietary moisture, protein concentration and digestibility, mineral concentrations (i.e., Na, Cl, Ca, P, and Mg), inclusion of acidifiers and alkalinizing agents, inclusion of vitamin B6, eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and γ-linolenic acid, fiber concentration and characteristics, and oxalate degrading probiotics, on these outcomes is discussed, and dietary guidelines for cats are provided. Because of the complex interaction of diet composition, environment, and animal physiology, there is a need for clinical research linking current recommendations or dietary options for the treatment and prevention of LUTS with physiological outcomes (i.e., decreased relative supersaturation and LUTS recurrence). Additionally, for many recommendations (e.g., probiotic administration, EPA, DHA), extrapolation from other species was necessary. Research is needed in feline patients with LUTS on these dietary components.



Introduction

Lower urinary tract signs (LUTS) are a set of clinical conditions with similar symptoms related to inappropriate urine elimination including anuria (i.e., no passage of urine), pollakiuria (i.e., frequent urination), stranguria (i.e., straining to urinate), dysuria (i.e., painful urination), hematauria (i.e., blood in the urine), and urination in inappropriate places. The underlying medical condition may be related to the urinary bladder, bladder sphincters, and urethra. A majority (i.e., 55 to 69%) of cats with LUTS have feline idiopathic cystitis (FIC; Kruger et al., 1991; Gerber et al., 2005). Some other causes discussed in this review are urolithiasis (13 to 28%), urethral obstruction (10 to 21%), and urinary tract infections (UTI; 1 to 8%).

The scientific literature often focuses on the underlying medical condition; however, LUTS are due to a combination of genetics, stress and frustration reactions, environment, and medical condition or conditions. As such, the thresholds for what is normal compared with abnormal and the ability to deal with and adapt to stressors will be different for each animal. It is not surprising when one considers the multifactorial nature of LUTS that reports of risk factors in cats vary by study and are commonly conflicting (Lekcharoensuk et al., 2001; Hostutler et al., 2005). Some common dietary factors that have been included as risk factors are water intake, use of dry foods, and intermittent feeding (Hostutler et al., 2005). Results of experimental and clinical investigation have confirmed the importance of dietary modifications in medical protocols designed to treat and prevent LUTS in at-risk cats (Forrester and Roudebush, 2007).

Because of the multifactorial contributors and individual responses of animals, the treatment of LUTS must be individualized to the patient. Medical conditions should be treated when necessary, including urinary tract obstruction, urinary tract infections, and urolith dissolution. In many cases, especially with FIC, individual episodes of LUTS are self-limiting. However, rate of LUTS recurrence within 1 yr can be as great as 40 to 50% in some feline populations (Barsanti et al., 1982; Markwell et al., 1999). The objective of this review is to discuss common medical conditions contributing to LUTS and to present currently used and potential preventative dietary modifications.

Contributing diseases

There can be overlaps in the etiology of the individual medical conditions suggested to contribute to LUTS. The factors contributing to LUTS may be single, multiple and interacting, or multiple and unrelated (Osborne et al., 1992). In the case of disease interaction, the signs and symptoms could be due to individual medical conditions concurrently acting to produce the same LUTS or 1 medical condition predisposing a cat to another medical condition. For example, inflammation from FIC or urolith formation may predispose animals to UTI (Osborne et al., 1992).

Feline Idiopathic Cystitis

Feline idiopathic cystitis is characterized as LUTS with no known or an unknown cause. Additionally, there is no widely accepted medical or dietary treatment. It is likely that FIC is not a single disease and may not be localized to the bladder. Some cats with severe FIC may have underlying neuroendocrine abnormalities (Westropp et al., 2006, 2007). These abnormalities may explain increased bladder permeability and serum catecholamine concentrations (i.e., dihydroxyphenylalanine and dihydroxyphenylglycol) as well as increased norepinephrine release in response to an 8-d moderate stress protocol for FIC cats when compared with healthy cats (Westropp et al., 2006, 2007).

Specifically, the stress response systems, the sympathetic nervous system (SNS), and the hypothalamic-pituitary-adrenal axis (HPA) may be altered. Cats with FIC compared with healthy cats have decreased adrenal gland size (3.2 vs. 6.5% of BW), and the cortisol release in response to adrenocorticotropic hormone (i.e., mimicking stress response) is decreased at 30 and 60 min after administration (7 vs. 13 μg/dL; Westropp et al., 2003). Therefore, the stimulation of the SNS in response to stress is unrestrained, and the lack of feedback inhibition at the HPA perpetuates the response (Westropp et al., 2006). The unrestrained SNS stimulates C-fibers and pain receptors of the bladder, resulting in submucosal edema, vasodilation, increased bladder permeability, smooth muscle contraction, and release of inflammatory mediators (Lavelle et al., 2000; Westropp et al., 2006; Wu et al., 2011). These nerve endings also can be stimulated by urine composition (i.e., K, Mg, and Ca concentrations) and acidic pH (Lavelle et al., 2000).

Although these differences have only been identified in a subset of FIC cats, the management of a cat with FIC includes decreasing animal stress through modifications of physical and social environment. Additionally, there may be some benefit to promoting larger volumes of dilute urine to decrease the concentration of irritants in the urine; however, this theory has not been adequately examined.

Urolithiasis

Urolithiasis is the formation of calculi within the urinary tract. The most common feline urolith types for cats are struvite (i.e., magnesium ammonium phosphate) and calcium oxalate (each >40% of uroliths; Osborne et al., 2009; Houston and Moore, 2009). When the urine becomes saturated with a solute or solutes, crystals may form, aggregate, and grow. Other substances (e.g., cell debris, bacteria, and foreign bodies) must be present to act as a nidus for crystal precipitation to occur (Kavanagh, 2006). Many factors contribute to the saturation of the urine with a given solute or solutes, including urine volume, pH, concentrations of the solute, and urolith promoters and inhibitors. Relative supersaturation (RSS) is a technique in which the saturation of minerals that may precipitate and form crystals is measured. It is used as an indicator of stone formation risk (Robertson et al., 2002). The technique requires knowledge of urine volume, pH, and inorganic and organic electrolyte concentrations (i.e., Ca, Mg, oxalate, citrate, phosphate, Na, K, ammonium, sulfate, and urate). Urolith formation may not only be impacted by urine composition; sufficient residence time of crystals may be required for aggregation to occur (Chew et al., 2010).

Prevention should be based specifically on crystalline types found within a given urolith; however, care should be taken not to increase risk of other urinary stones. Dietary alterations should focus on decreasing concentrations of urinary solutes and crystal promoters (i.e., decrease intake of solutes and substances that are metabolized to solutes and increased water intake) and increase inhibitors of urolithiasis (e.g., citrate inhibits calcium oxalate salt formation). Increased water intake paired with timely voiding also may decrease urinary retention and, thus, time for crystals to form. When necessary, dietary alterations also can be made to meet urine pH targets (i.e., inclusion of dietary acidifiers and alkalinizing agents).

Urethral Plug and Obstructions

Urethral obstruction can be deadly and recurs in approximately 20 to 40% of cats (Gerber et al., 2008; Segev et al., 2011). Urethral plugs account for approximately 20 to 60% of urethral obstructions whereas approximately 5 to 30% of cases are due to uroliths and approximately 30 to 55% are idiopathic (Kruger et al., 1991; Gerber et al., 2008). Urethral plugs are composed of varying combinations of a protein colloid matrix and crystalline matrix (Osborne et al., 1992, 1996). The most common crystalline aggregates are struvite (50 to 80%; Escolar and Bellanato, 2003; Houston et al., 2003). It is hypothesized that inflammation causing increased bladder permeability allows proteins and organic materials (e.g., mucoproteins, albumin, globulin, cells) to leak from the bladder wall and aggregate with mineral crystals (Osborne et al., 1992, 1996); however, the presence of crystals is not necessary for urethral plugs to form. Some cases of idiopathic urethral obstruction may be due to urethral spasm and edema secondary to FIC; however, this relationship has not been determined (Osborne et al., 1992).

The risk factors associated with crystalline components of urethral plugs are likely similar to those of classic uroliths. Prevention should be based on crystalline types found within a given urethral plug and would be similar to those of urolithiasis. Additionally, given the high percent of idiopathic obstruction cases, including stress reduction (internal and external) techniques, as in FIC, may be important.

Urinary Tract Infection

Uropathogenic microbes originate from the gastrointestinal tract of the host or other environmental exposures. For example, bacterial strain sharing is common within households, and pets may act as a reservoir for human uropathogens. Johnson et al. (2008) reported a 50% likelihood that when 1 household member (person or pet) had a UTI, the same uropathogenic clone would be identified in the feces of another household member. Bacteria ascend through the urethra, gaining access to the bladder. They adhere to the bladder wall, invade epithelial cells, and result in an inflammatory response (Litster et al., 2009). Untreated and or recurrent UTI can progress to include bladder thickening, upper urinary tract infection, and renal damage (Chew et al., 2010). Some bacterial UTI produce an alkaline urinary pH, predisposing animals to struvite urolithiasis or fungal infections (Pressler et al., 2003; Chew et al., 2010).

Multiple types of virulence genes (e.g., flagella, adhesins, toxins, invasins) contribute to colonization and severity of UTI (Yuri et al., 1998). The most common UTI-causing species, Escherichia coli (40 to 66% of UTI), often express several adhesins (e.g., P, S, F1C, type 1 fimbrae) that mediate binding to the uroepithelium with different receptor specificities (Yuri et al., 1998; Chew et al., 2010). Beneficial and commensal bacterial strains and dietary ingredients can interfere with pathogenic bacterial ascension and infection by decreasing bacterial adherence (Grieshop et al., 2004). Dietary and environmental management should focus on optimizing gut and urinary tract microbial species and promoting host immunity. Other areas that may be of importance include promoting acidic pH (<7.0) and maintaining a urine specific gravity >1.025 (Litster et al., 2009; Chew et al., 2010). However, data regarding these recommendations are limited and are specific to types and species of bacteria.

Dietary Modifications

The main goals of dietary modifications to prevent LUTS are to 1) promote large dilute volumes of urine, 2) decrease the relative supersaturation of urine for specific stone types, and 3) promote healthy bacterial populations of gastrointestinal and urogenital tracts. There is a need for clinical research linking current recommendations and dietary options for the treatment and prevention of LUTS with physiological outcomes (i.e., decreased RSS and LUTS recurrence). Due to the paucity of data, extrapolation from other species often is necessary to make recommendations.

Interaction of Environment and Dietary Modifications

Data reveal that a decreased ability to adapt to environmental and physiological stressors (e.g., moving, new family members, dehydration) may play an important role for some cats with LUTS (Westropp et al., 2006, 2007; Stella et al., 2011). For these animals, reducing environmental stressors may be an important aspect of treatment and prevention in at-risk cats (Buffington et al., 2006). Environmental modifications should be tailored to the specific cat and household. Five key resources that should be taken into consideration are water, food, litter boxes, resting sites, and stimulation resources (e.g., toys, human interactions). Buffington et al. (2006) reported decreases in LUTS, fearfulness, and nervousness over 10 mo for cats after an individualized environmental modification plan was put in place; however, research is needed linking stress reduction to the reduction of LUTS.

Environmental factors, such as the presentation of food and water, can impact physiological characteristics (i.e., water intake, urine volume and pH, and fecal water excretion), and these factors may complement nutritional changes (discussed subsequently in more detail). Additionally, environmental changes may be necessary for nutritional alterations to be truly beneficial. For example, the benefits of increasing water intake could be paired with environmental modifications that promote timely urination (e.g., more litter boxes).

Increasing Water Intake

Increased water intake has been recommended for cats with LUTS, with the main outcomes being dilution of the urine and promoting timely voiding. In cats with uroepithelium damage (i.e., FIC or urinary obstruction), urine dilution may decrease concentration of substances in the urine that are irritating to the bladder mucosa (Markwell et al., 1998). For prevention of urolith or obstruction recurrence, dilution of urine is associated with decreased concentrations of urolith-forming minerals in urine (Buffington et al., 1990; Buckley et al., 2011). Additionally, it has been proposed that there may be some benefit to the increased volume of urine produced. Increasing the volume of urine should increase frequency of urination, thus reducing retention time in the bladder and crystal growth potential (Markwell et al., 1998). Increased urine volume paired with timely urination may also result in hydrokinetic washout of small numbers of bacteria, adding to the defenses of the cat against UTI (Chew et al., 2010). Research linking increased water intake and its impacts on urine volume and relative supersaturation, and decreased risk or recurrence of LUTS is needed.

Dietary Water Intake.

Likely the most important method for altering water intake is increasing dietary water intake. This can be achieved by feeding a moist cat food or by wetting dry cat food directly before feeding. When energy density is diluted with water (i.e., 9 to 75% moisture), cats eat to maintain DM intake (∼55 g/d) and dietary water intake is increased (0 to 165 g/d dietary moisture; Castonguay, 1981). Additionally, when fed whole prey and raw meat diets with >67% water, cats were able to maintain water balance (i.e., required no external water source; Caldwell, 1931; Prentiss et al., 1959). Increasing dietary water intake or total water intake does not necessarily equate to increased urine volume or dilution. Dietary water intake must be increased over total water intake requirements for urine volume to be potentially increased (Gaskell, 1989; Buckley et al., 2011). Buckley et al. (2011) reported no differences in total water intake (99 to 105 mL/d), urine volume, or urine specific gravity (1.052 to 1.054) for cats fed the same diet with differing moisture concentrations (6, 25, and 53% moisture); however, when moisture was increased to 73%, total water intake (145 mL/d) and urine volume (87 mL/d) were increased, and urine specific gravity (1.036) was decreased. Unless water is being added directly to a diet, it is unlikely that other dietary factors will remain constant, and these should be considered. Changes in diet also may change the water requirement of the cat, urinary mineral excretion, fecal moisture excretion, and metabolic water production (Devois et al., 2000; Carciofi et al., 2005). For example, when cats were fed dry, canned, and ground whole chicken diets (i.e., 4, 87, and 105 mL dietary water intake, respectively), urine volumes were similar (52 to 54 mL/d); however, fecal moisture was greater in cats fed dry and canned diets (18 mL/d) compared with those fed ground whole chicken (6 mL/d; Kerr, 2012).

Diet Composition and Water Intake.

The feeding of dry diets has been implicated in the epidemiology of LUTS; however, there is little data to support this hypothesis (Buffington and Chew, 1998). The tendency of cats fed dry diets to produce smaller volumes of more concentrated urine may be a contributing factor to LUTS (Burger et al., 1980); however, nutrient composition may impact urine volume and concentration. Methods to increase water intake by altering dry diet composition also can be used. Dietary potential renal solute load (PRSL) may explain diet-induced changes in water intake (Markwell et al., 1998). The PRSL is estimated as the sum of dietary N (expressed as micromoles of urea, i.e., milligrams N divided by 28), Na, Cl, P, and K (i.e., milligrams N/28 + Na + Cl + K + P). When these factors are increased in the diet, hypothetically their renal excretion is increased and, concurrently, urine volume is increased due to osmotic pressure. Thirst may be stimulated to provide the volume necessary to excrete the excess solutes (Michell, 1991). The impacts of altering dietary protein and NaCl on water intake have been examined experimentally. Daily water intake increased (70 to 126 mL intake/d) with increasing dietary protein concentration (26 to 66% CP), and urine volume increased linearly (r = 0.88; y = 19.34 + 9.89 × x) with increasing N intakes (∼1.5 to 6.5 g/d) in adult cats (Hashimoto et al., 1995). Similar results have been reported for 0.5- to 12-mo-old kittens (Hashimoto et al., 1996). Anderson (1982) reported that cats fed diets with no or low NaCl compared with those with high NaCl (0 and 1.4 vs. 4.6% DM) had decreased (P < 0.001) water intakes (130 vs. 250 mL/d). Additionally, intake of diets with low (<7.3 g Na/MJ) Na vs. high (11.5 to 16.7 g Na/MJ) have been reported to increase urine volume (55 vs. 78 mL) and decrease urine calcium oxalate relative supersaturation (2.9 vs. 2.5) and specific gravity (1.051 vs. 1.045; Hawthorne and Markwell, 2004). There appears to be no implications regarding hypertension and bone metabolism for cats (Xu et al., 2009), indicating that for healthy cats, increased salt intake may be a viable option; however, long term studies are needed to confirm this suggestion.

Water Presentation.

Many aspects of water presentation can be altered to potentially impact water intake and urine volume. Aspects of cat preference (e.g., dish size, water freshness, flavoring) and interanimal interactions (i.e., 1 water dish per animal plus 1 additional water dish) should be addressed; however, individual results will vary based on pet and household. As the energetic costs increase to obtain commodities, such as water, cats and other animals will decrease the initiation of obtaining it but ingest more per bout (Kanarek, 1975). Increasing the ease of access to water may allow for decreased variation in water intake throughout the day.

Altering Urine Characteristics through Dietary Manipulation

Dietary ingredients and feeding patterns influence the volume, pH, and solute concentration of urine. The implications of dietary protein and mineral concentrations for water intake, urine volume, and dilution were discussed previously. In cats with uroepithelium damage (i.e., FIC or urinary obstruction), dietary manipulations should aim to decrease concentration of substances in the urine that may be irritating to the bladder mucosa (Markwell et al., 1998). When the goal is prevention of urolith or obstruction recurrence, dietary manipulations should aim to decrease the concentrations of stone-forming substances and increase their solubility, ultimately reducing the relative supersaturation for a given stone type (Robertson et al., 2002).

The interactions between dietary constituents in the body are complex. The impacts of dietary changes on urine characteristic should be monitored with the diet being evaluated as a whole. For example, decreasing dietary Ca may potentially increase the risk of calcium oxalate urolith formation (Stevenson et al., 2003). Dietary oxalate and Ca can interact in the lumen of the intestine to form nonsoluble calcium oxalate complexes with relatively low absorption, that is, approximately 7% in rats (Hanes et al., 1999). However, if dietary Ca is reduced without a concomitant reduction in oxalate, the oxalate available for intestinal absorption increases (Von Unruh et al., 2004) and, potentially, increases the urinary excretion of oxalate and calcium oxalate stone risk.

Because of these complex interactions, dietary mineral concentrations should be maintained at the recommended levels (i.e., Mg at 0.07 to 0.14% on DM basis, P at 0. 5 to 0.9% on DM basis, and Ca at 0.6 to 1.0% on DM basis), with both restriction and excesses avoided (Forrester et al., 2010). The implications of restriction and excess for urinary tract health are highlighted with Mg. Historically, struvite urolitiasis prevention diets were formulated to have low concentrations of Mg and promote urinary acidification (Taton et al., 1984; Tarttelin, 1987). These recommendations likely contributed to the reported increases in the proportion of feline urolithiasis that are composed of calcium oxalate (Dijcker et al., 2011). Urinary Mg forms complexes with oxalate, reducing the amount of oxalate available to form uroliths and thus acting as a calcium oxalate inhibitor.

Urinary tract diets should be chosen on a case by case basis. Forrester and Roudebush (2007) provide guidelines for therapeutic diet recommendations for FIC prevention, struvite urolithiasis dissolution, struvite urolithiasis prevention, and calcium oxalate urolithiasis prevention. In the case of urolith prevention, urinary relative supersaturation should be measured for a specific diet to monitor efficacy.

Diet and Urine pH.

Altering urine pH impacts urolith RSS. Acidification of the urine (i.e., to pH < 6.6) by altering diet composition has been used as a tool for decreasing struvite RSS and for dissolution and prevention of struvite urolithiasis in cats (Forrester and Roudebush, 2007); however, using dietary acid load to maintain urine pH below 6.0 can induce metabolic acidosis and may increase risk for calcium oxalate urolithiasis (Dow et al., 1990). For prevention of calcium oxalate urolithiasis recurrence, a range of higher pH (i.e., 6.8 to 7.5) has been proposed (Chew et al., 2010). For commercial diets, the relationship between urolith RSS and urine pH is not consistent, that is, low pH does not equal low struvite RSS, and high pH does not equal low calcium oxalate RSS (Smith et al., 1998; Stevenson et al., 2000). These data indicate a need to test in vivo the impacts of a diet as a whole.

Dietary contributors to the acid load are S-containing AA (i.e., methionine and cysteine), phospholipids, organic acids, and the balance of inorganic cations and anions. The correlation between the balance of these factors and urine pH can be great (i.e., r2 = 0.70 to 0.96) for a given experiment (Kienzle and Schuhknecht, 1993; Yamka et al., 2006); however, Yamka et al. (2006) reported that when a previous model by Kienzle and Schuhknecht (1993) was applied to urine pH data for cats (n = 40; average age = 8.5 yr) fed 60 wet and 90 dry foods, it accounted for considerably less variation (r2 = 0.25).

Ingredients such as corn gluten meal, animal proteins, and animal digests naturally promote acidic urine (Skoch et al., 1991; Funaba et al., 2003). Some common dietary acidifiers include DL-methionine, ammonium chloride, phosphoric acid, magnesium chloride, magnesium sulfate, and sodium bisulfate (Spears et al., 2003). Ingredients that act as alkalizing agents include calcium carbonate, magnesium carbonate, and potassium citrate (Pastoor et al., 1994; Buffington and Chew, 1998).

Vitamin B6and Calcium Oxalate Urolithiasis.

The endogenous production of oxalate from glyoxalate in the liver can be a significant contributor to urinary oxalate excretion. However, glyoxylate also can be transaminated to glycine by alanine glyoxylate aminotransferase 1, an enzyme that requires vitamin B6 as a co-factor (Dijcker et al., 2011). Kittens fed vitamin B6–free foods have increased urinary oxalate excretion (∼5 mg/kg BW) compared with those fed diets containing 8 mg/kg vitamin B6 (<1 mg/kg BW; Bai et al., 1989). An epidemiological study of women reported that intakes of ≥40 mg/d vitamin B6 were associated with less relative risk of urolith formation compared with intakes <3 mg/d (relative risk = 0.66; Curhan et al., 1999). Administering increased amounts of vitamin B6 could potentially increase the transamination of glyoxalate to glycine and reduce endogenous oxalate production. However, concentrations present in commercial diets are hypothesized to be adequate, and there have been no studies of vitamin B6 administration and calcium oxalate urolithiasis in cats (Dijcker et al., 2011).

Essential Fatty Acids and Calcium Oxalate Urolithiasis.

Altering dietary fatty acid composition can impact cell membrane composition, greatly influencing membrane fluidity, permeability, ion channels, and the behavior of membrane-associated receptors and enzymes. In humans, there is a relationship between dietary arachidonic acid intake and urinary oxalate excretion (R = 0.27; Naya et al., 2002). Thirty-day dietary administration of fish oil (850 mg, 3 times daily) containing 50% eicosapentaenoic acid (EPA) and 40% docosahexaenoic acid (DHA) to human stone formers decreased the proportion of plasma linoleic from 24.6 to 21.0% and arachidonic acid from 10.0 to 7.8% and increased the proportion of plasma EPA from 0.7 to 2.6% and DHA from 3.5 to 5.8% (Baggio et al., 2000). Additionally, daily calcium and oxalate urinary excretion decreased (Baggio et al., 2000). The changes in urinary oxalate concentration are likely related to an increased absorption of oxalate in the intestinal lumen and increased oxalate clearance in the kidney (Baggio et al., 2000). Phospholipid arachidonic acid content is correlated to 1,25-vitamin D3 and PGE2 values (Buck et al., 1983; Baggio et al., 2000), indicating that Ca metabolism may be modulated at the intestine, kidney, and bone.

The effects of omega-3 PUFA could potentially be enhanced by omega-6 PUFA derived from γ-linolenic acid (GLA). Dietary inclusion of 1000 mg evening primrose oil (i.e., 72% linolenic acid, 8% GLA, and 20 IU vitamin E) for 20 d to healthy subjects decreased urinary Ca excretion from 3.1 to 1.7 mmol/d and increased urinary citrate excretion from 2.2 to 3.6 mmol/d (Rodgers et al., 2009). The impact of omega-3 fatty acid and evening primrose oil for the prevention of calcium oxalate urolithiasis has not been examined in domestic cats. Given the unique fatty acid requirements of the domestic cat (Sinclair et al., 1979), research in this area is needed and may provide insight into the mechanism of essential fatty acids and the prevention of calcium oxalate urolithiasis.

Food Presentation.

Many aspects of food presentation can be altered to potentially impact urine characteristics. Diet transitions should be slow, with new diets being incrementally increased and the old diet decreased over time. Feeding a new diet can result in diarrhea when no adaptation time is allowed for the gastrointestinal tract and microbial populations. The increased fecal moisture may cause dehydration, decreased urine volume, and urine concentration if water intake is not increased to compensate for fecal losses (Hesta et al., 2001).

Feeding pattern also can be altered. Meal-fed cats show marked increases in urine pH after eating (i.e., 6.1 to 7.6) whereas those fed ad libitum showed only a small increase in urine pH over the course of the day (i.e., 6.4 to 6.9; Taton et al., 1984). Alkaline urine is produced by the kidneys to compensate for the secretion of gastric acids, and the postprandial rise in urine pH is a function of meal size (r = 0.80; Finke and Litzenberger, 1992). When fed ad libitum, cats choose to eat many (i.e., 8 to 18) small meals throughout the day (Kanarek, 1975; Kane et al., 1981). These data indicate that ad libitum or multiple small meal feeding patterns may reduce the magnitude of the pH shifts. Overfeeding and treats should be avoided, given the relationship between meal size and pH and the additional minerals of the excess food to be excreted in the urine. Food restriction (i.e., fasting) should also be avoided. Water and food intake are closely related in dogs; when food deprived, dogs decreased their water intake by 10 to 50% (Cizek, 1960). Food and water intake may also be linked for cats. When allowed access to food ad libitum and continuously (i.e., 24 h/d) vs. periodic (i.e., 1 h/d) food intake, water intake, and urinary outputs were increased (86 vs. 52 g/d, 178 vs. 127 mL/d, and 63 vs. 51 mL/d, respectively; Finco et al., 1986). The impact of food restriction on feline urine characteristics has not been examined, but if water intake was decreased to the point of dehydration, then small volumes of concentrated urine would be expected.

Promoting Healthy Bacterial Populations

The mucosal tissues of the digestive, respiratory, and urogenital tracts and the skin are colonized by a diverse microbiota. Most microbes are either harmless or of benefit to the host. When the microbial populations are predominantly composed of these commensal bacteria, the synbiotic relationship provides the host with many health benefits. The gastrointestinal microbiota, which provide essential vitamins, impact nutrient and energy metabolism, impact water balance, protect against enteropathogens, and contribute to normal immune function, are the most studied. However, microbial populations of the urinary tract may provide protective and immunologic benefits. Promoting healthy bacterial populations play obvious roles in preventing UTI; however, there are also implications for microbial populations and other LUTS conditions directly through impacts on water balance and nutrient metabolism (e.g., oxalate degradation) and indirectly through the benefits of gut health and immunity (Murphy et al., 2009; Prola et al., 2010). Dietary factors can impact the microbial populations, either promoting a healthful population or disturbing the microbial balance and favoring outgrowth of potentially pathogenic bacteria (Kanakupt et al., 2011; Hooda et al., 2013).

Protein.

Poorly digested dietary protein and increased dietary protein concentrations can contribute to proliferation of potentially pathogenic bacteria in the ileum and colon (Zentek et al., 1995; Hooda et al., 2013). Data from captive exotic and domestic cats indicate that interactions exist among diet formats (i.e., canned, extruded, raw meal, and whole-prey diets), dietary fiber characteristics, and dietary protein characteristics when fecal characteristics and microbial populations are considered (Vester et al., 2010; Kerr, 2012; Kerr et al., 2013). However, the impacts of protein fermentation on microbial populations for domestic cats have not been adequately studied. For commercial extruded and canned diets, high protein digestibility (i.e., >85%) and moderate protein concentrations are appropriate (i.e., ∼30% CP on DM basis). For high protein diets (≥35% CP), even with high digestibility, protein fermentation is inevitable and the importance of dietary fiber inclusion is increased.

Fiber, Fermentation, and Short-Chain Fatty Acid Production.

It is well recognized that dietary fibers and fiber-like (i.e., resistant starch) materials exert different physiological effects in the body depending on their characteristics. Less fermentable fibers can provide fecal bulk, decreasing transit time and enhancing fecal consistency and mass (Prola et al., 2010). Inclusion of fermentable fibers, prebiotic fibers, and resistant starches promote proliferation of beneficial bacteria and increased short-chain fatty acid (SCFA) production (Sunvold et al., 1995). Increases in SCFA concentrations decrease colonic pH, promoting mucosal barrier function and inhibiting the growth of pathogenic bacteria (Chawla and Patil, 2010). The absorption of SCFA is paired with Na, Cl, and water absorption and can beneficially impact fluid balance (Binder, 2010). However, excessive production of SCFA above the absorptive capacity of the gut can cause osmotic diarrhea, so fermentable fiber concentrations should not be excessive (Sunvold et al., 1995).

Prebiotic fibers are readily fermented by beneficial types of colonic microbiota and not extensively used by pathogenic bacterial species; therefore, the stimulation of health-promoting bacterial populations is selective. Some examples of prebiotics researched for use in companion animal diets are inulin, fructooligosaccharides (FOS), galactooligosaccharides (GOS), and mannan-oligosaccharides (MOS). Research relating the impact of economically plausible concentrations of prebiotics on the microbial populations of cats is lacking. Kanakupt et al. (2011) reported increased fecal Bifidobacterium spp. concentrations as measured by quantitative PCR for cats fed FOS or GOS at 0.5% of the diet or in combination (i.e., 1% total prebiotic) compared with those fed a cellulose control diet (9.9 to 10.3 vs. 9.4 cfu log10/g fecal DM). The impact of dietary MOS inclusion on fecal microbial populations has not been evaluated in the domestic cat; however, data from other species indicate that in addition to directly influencing the population of beneficial bacteria within the colon, MOS also may act by preventing binding of certain bacteria (Grieshop et al., 2004). Numerous E. coli strains, including common uropathogens, exhibit mannan-binding behavior (Yuri et al., 1998); thus, MOS reduces pathogenicity of these bacteria by interfering with type 1 fimbrae-mediated adhesion.

By combining multiple fibers, a range of fermentability (i.e., slow to rapidly fermentable) could be used to sustain SCFA production along the entire length of the colon. Furthermore, combinations of different fibers may result in synergistic beneficial health effects. Therefore, fiber blends have the potential to provide a number of advantages over the use of a single fiber source as they can allow achievement of a range of physiological effects. Fiber as measured by the total dietary fiber method should be approximately 7.5% of DM with a ratio of insoluble to soluble fiber of 70:30 to 80:20 being recommended.

Probiotics.

Probiotics are administered to cats with increasing frequency, and their use may have implications for prevention of UTI and calcium oxalate urolithiasis. Data regarding probiotic use for prevention of urogenital tract diseases in cats is lacking. Research has primarily examined the role of probiotic administrations for gastrointestinal diseases. The efficacy of probiotic administration depends on the bacterial species and strains administered and can vary among cats administered the same probiotic (Garcia-Mazcorro et al., 2011).

In humans, administration of Lactobacillus rhamnosus GR1 + Lactobacillus reuteri RC14 or B54 (109 cfu dose, oral or vaginal, 1 to 2 times per day) has shown promising results for the treatment and prevention of recurrent urogenital tract infections; however, the impact of oral administration on urinary tract infections specifically have not been thoroughly examined (Reid et al., 2001; Anukam et al., 2006). Interest in probiotic treatment to reduce calcium oxalate risk is based on the link between the reduced prevalence of Oxalobacter forminges, an oxalate-degrading bacterial species, in stone-forming populations (Troxel et al., 2003; Gnanandarajah et al., 2012). Oxalobacter forminges was detected by quantitative PCR in 25% of dogs with Ca oxalate uroliths compared with 50% of clinically healthy age-, breed-, and gender-matched dogs and 75% of non-stone-forming breeds (Gnanandarajah et al., 2012). These data indicate that the presence of O. forminges or other oxalate-degrading species may have a protective effect. Women that had received a probiotic supplement containing 800 billion live bacteria (Streptococcus thermophiles, Bifidobacterium breve, Bifidobacterium longum, Bifidobacterium infantis, Lactobacillus acidophilus, Lactobacillus plantarum, Lactobacillus paracasei, and Lactobacillus delbrueckii subsp. bulgaricus) for 4 wk had decreased urinary oxalate excretion (i.e., 32 mg oxalate) for 22 h after an 80-mg oxalate challenge when compared with their baseline excretion (i.e., 47 mg oxalate; Troxel et al., 2003). Many microbes that inhabit the gastrointestinal tract of healthy cats, including O. forminges and Lactobacillus spp., express enzymes for oxalate metabolism (Weese et al., 2004, 2009; Murphy et al., 2009); however, the link between microbial oxalate metabolism and feline calcium oxalate stone risk has never been examined. One study examined the administration of an oxalate-metabolizing bacterial species, Bacillus subtilis PTA 6737 (1010 dose), to healthy domestic cats; however, no alterations in urine characteristics were reported (Kerr et al., 2011). Examination of oxalate metabolizing species is needed in stone-forming cats. Although the data from other species indicate that probiotics can be used in the prevention of UTI and calcium oxalate urolithiasis, further research is needed to identify appropriate and efficacious strains for use in the cat.

summary and Conclusions

Many aspects of the diet can be modified to alter physiological characteristics related to feline LUTS. Experimental and clinical investigations have confirmed the importance of dietary modifications in medical protocols designed to treat and prevent LUTS. Environmental factors, such as the presentation of food and water, can impact physiological characteristics (i.e., water intake, urine volume and pH, and fecal water excretion) and considering these factors may complement nutritional changes. The main goals of dietary modifications to prevent LUTS are 1) promote large dilute volumes of urine, 2) decrease the relative supersaturation of urine for specific stone types, and 3) promote healthy bacterial populations in gastrointestinal and urogenital tracts.

To promote the production of large volumes of dilute urine and potentially limit stagnation, dietary moisture concentrations should be >70%. This can be achieved by feeding a moist cat food or by wetting dry cat food directly before feeding. Additionally, water intake can be promoted by increasing NaCl concentrations above the requirements (Na = 0.2 to 0.4% of DM and Cl = 0.3% of DM). Highly digestible protein should be included at moderate to high concentrations (30 to 40% of DM). Increased protein may promote water intake and act as a natural urine acidifier. High digestibility is important to limit the escape of protein into the colon, which can promote proliferation of pathogenic bacterial species.

The interaction between dietary mineral intakes and urinary concentrations is complex; therefore, dietary concentrations of Ca, P, and Mg should be maintained at the recommendation (Mg = 0.07 to 0.14% of DM, P = 0. 5 to 0.9% of DM, and Ca = 0.6 to 1.0% of DM) with both excess and restriction avoided (Forrester et al., 2010). Dietary ingredients high in oxalate should be avoided (e.g., spinach, kale). The final diet should be tested in vivo to determine the urinary saturation for common stone types. Dietary ingredients that act as urinary acidifiers (e.g., phosphoric acid, methionine, magnesium chloride) and alkalinizing agents (e.g., potassium citrate) should be used to target the appropriate urinary pH (6.2 to 6.5) as this can also impact urine saturation. Diets specifically targeting calcium oxalate urolithiasis should aim for a more alkaline pH (6.8 to 7.5). Vitamin B6, EPA, DHA, GLA, and oxalate-degrading probiotics positively impact the metabolism of calcium and oxalate in other species, and additional levels above requirements should be considered (B6 = 0.07 mg/kg DM, EPA + DHA = 0.5 to 1.0% DM, GLA = 0.3% DM, and oxalate-degrading probiotic = 1 to 2 × 109 cfu).

In addition to dietary supplementation with oxalate degrading probiotics, attention should be paid to maintaining healthy gastrointestinal and urogenital tract microbial populations. This can be accomplished by inclusion of dietary fiber or fiber-like materials. Total dietary fiber should be about 7.5% of DM with a ratio of insoluble to soluble fiber of 70:30 to 80:20. A fiber blend (i.e., slow to rapidly fermentable) should be used to sustain fermentation along the length of the colon and provide synergistic effects of multiple fiber types. Prebiotic fibers that selectively stimulate beneficial bacteria (i.e., FOS, GOS, and MOS) should be included in the fiber blend (at least 0.5 to 1.0% of diet, as fed).

Because of the complex interaction of diet composition, environment, and animal physiology, there is a need for clinical research linking current recommendations or dietary options for the treatment and prevention of LUTS with physiological outcomes (i.e., decreased RSS and LUTS recurrence). Additionally, for many recommendations (e.g., probiotic administration, EPA, DHA), extrapolation from other species was necessary. Research is needed in feline patients with LUTS on these dietary components.

 

References

Footnotes


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