ANSC 464 LECTURE 5

ANSC 464: Nutrient Requirements of Adult Cats

Summary of Nutritional Peculiarities (Page 2)

• The lecture addresses the nutritional peculiarities of cats.
• It emphasizes that none of the so-called metabolic "peculiarities" of cats are truly unique.
• A key question posed is: What nutritional evidence do we have that cats are carnivores?

Objectives (Page 3)

• To define adult cats.
• To discuss the nutrient requirements of adult and older cats, specifically covering:
  • Water
  • Energy
  • Carbohydrates
  • Protein
  • Fat
  • Vitamins
  • Minerals

Definition of Adult Cats (Page 4)

• Cats typically reach adulthood at approximately $12$ months of age.
• They have a potential lifespan of $\ge 20$ years.
• Cats are generally considered "older" when they are near $7$ years of age.
• Cats between $1$ to $7$ years of age are categorized as "young to middle-aged" cats.
• This age classification is important because it relates to their ability to tolerate metabolic and physiologic distresses.
• A fundamental question is: What are our feeding goals for cats at different life stages?

Water Requirement (Page 5)

• A finite, exact water requirement for cats has not been definitively established.
• Water intake needs to be adjusted based on diet composition, specifically:
  1. Dry matter (DM) content
  2. Protein content
  3. Sodium content
• Cats have an adaptation to conserve water by forming highly concentrated urine.
• The requirement for water varies significantly with physiological and environmental conditions.
• Three main ways cats at maintenance lose body water:
  1. Urine
  2. Feces
  3. Evaporation (respiratory/cutaneous)
• Potential consequence of water conservation adaptation: This adaptation can predispose cats to urinary problems, such as crystal formation or urinary tract disease, if water intake is insufficient or if fed primarily dry diets without adequate compensatory water intake.

Water Requirement Recommendations (Page 6)

• Recommended intake: $1 ext{ mL water per kcal ME}$.
• Cats should ideally be allowed to self-regulate their water intake.
• Adequate water intake is crucial for the prevention of urinary problems and crystal formation, highlighting the important relationship between nutrition and health for cats.
• Feeding moist foods versus dry foods: Feeding moist foods significantly increases both water intake and urine volume in cats.
• Sources of water for cats:
  • Drinking water (from bowls, fountains, etc.)
  • Moisture content of food
  • Metabolic water (produced during nutrient metabolism)
• Other factors influencing water requirement: Activity levels, ambient temperature, humidity, physiological state (e.g., lactation, illness), and certain medications.

Energy Requirements (Page 7)

• Factors influencing a cat's energy requirement include:
  • Activity levels
  • Age
  • Thermoregulation
  • Castrated male cats are more prone to becoming obese, indicating a potential reduction in energy need post-neutering or an increased propensity for weight gain due to altered metabolism and decreased activity.

Thermogenesis (Page 8)

• Cats' thermoneutral zone is between approximately $30$ and $38 ext{°C}$. This is the ambient temperature range where an animal does not need to expend extra energy to maintain its body temperature.
• Metabolic rate at room temperature: At typical room temperatures (e.g., $20-22 ext{°C}$), which are below their thermoneutral zone, cats will have a higher metabolic rate than their basal metabolic rate within their thermoneutral zone, as they need to generate heat to maintain body temperature (Scholander et al., 1951; NRC, 2012).
• Dietary thermogenesis (or specific dynamic action): This is the energy expended for the digestion, absorption, and metabolism of food, and it is similar in cats, dogs, and humans, accounting for approximately $10\%$ of metabolizable energy (ME).
• How protein catabolism affects thermogenesis: Protein catabolism typically has a higher thermogenic effect compared to fat or carbohydrate catabolism. The breakdown and synthesis of proteins require more energy, thus increasing heat production. This means a diet higher in protein could lead to a slightly higher thermogenesis.

Energy Requirement - Across Species (Page 9)

• The "mouse-to-elephant curve": This figure (Figure 6.1, adapted from Benedict, 1938, from Schmidt-Nielsen 1984) illustrates how metabolic rates for mammals and birds, when plotted against body mass on logarithmic coordinates, tend to fall along a single straight line.
• This demonstrates that the association between body mass and energy requirement (or metabolic rate) is not linear. Instead, metabolic rate scales allometrically with body mass, generally following a power law where metabolic rate is proportional to $BW^b$, where $b$ is typically around $0.75$.
• For instance, a mouse has a much higher metabolic rate per unit of body mass than an elephant, but an elephant has a much higher total metabolic rate.

Energy Requirement - Adult Cats (Page 10)

• Cats generally have a relatively uniform body shape; adult cats commonly range from $2 ext{ to } 7+ ext{ kg}$, with an average around $4-5 ext{ kg}$.
• Metabolic body weight: This is an important concept used to normalize energy requirements across animals of different sizes. It is calculated as body weight raised to a power (e.g., $BW^{0.75}$ or $BW^{0.67}$).
  • For cats, the most accurate interspecies metabolic body weight exponent has been found to be $BW^{0.67}$. This exponent helps to account for the non-linear relationship between body size and metabolic rate.
• The first measurements of animal energy requirements date back to the mid-1800s.
• Energy requirements can vary significantly, by up to $50\%$, among individual cats.
• Scientific literature reports a wide range of energy requirements, from $31-100 ext{ kcal/kg BW}$, compared to practical recommendations. This highlights the variability and the challenge in providing a single universal figure.
• Why metabolic body weight is important: It normalizes metabolic rate with body size, allowing for more accurate comparisons of energy needs between animals of different weights. Using a simple kilocalories per kilogram of body weight ($kcal/kg BW$) can be misleading for animals with significant size differences because smaller animals typically have higher metabolic rates per unit of body mass than larger animals. $BW^{0.75}$ or $BW^{0.67}$ attempts to correct for this.

Energy Requirement - Adult Cats at Maintenance (NRC, 2006) (Page 11)

• The National Research Council (NRC, 2006) provides specific maintenance energy requirements (MER) based on cat type:
  • Domestic cats, lean: $100 ext{ kcal ME }\times ext{ kg BW}^{0.67}$
  • Domestic cats, overweight: $130 ext{ kcal ME }\times ext{ kg BW}^{0.4}$ (Note the different exponent for overweight cats, reflecting altered metabolism)
  • Exotic cats: $55-260 ext{ kcal ME }\times ext{ kg BW}^{0.75}$
• Reasons for the wide range in exotic cats: This variability is likely due to several factors including:
  1. Species diversity: "Exotic cats" encompasses a broad range of species (e.g., serval, ocelot, tiger, lion) with vastly different sizes, metabolic rates, and natural activity levels.
  2. Environmental conditions: Varying captive environments (temperature, enclosure size, enrichment) can influence energy expenditure.
  3. Individual variability: Just like domestic cats, individual exotic cats will have different activity levels, age, and health status.

Body Condition Scoring System - Adult Cats (NRC, 2006) (Page 12)

• The Body Condition Score (BCS) system is a visual and tactile assessment method used to evaluate an animal's fat reserves and muscle mass.
• BCS Descriptions (on a $1-9$ scale, where $5$ is ideal):
  • BCS 1 (Emaciated): Ribs visible on shorthaired cats; no palpable fat; severe abdominal tuck; lumbar vertebrae and wing of ilia obvious and easily palpable.
  • BCS 3 (Thin): Ribs easily palpable with minimal fat covering; lumbar vertebrae obvious; obvious waist behind ribs; minimal abdominal fat.
  • BCS 5 (IDEAL): Well proportioned; waist observed behind ribs; ribs palpable with slight fat covering; abdominal fat pad minimal.
  • BCS 7 (Overweight): Ribs not easily palpable with moderate fat covering; waist poorly discernible; obvious rounding of abdomen; moderate abdominal fat pad.
  • BCS 9 (Obese): Ribs not palpable under heavy fat cover; heavy fat deposits over lumbar area, face, and limbs; distension of abdomen with no waist; extensive abdominal fat deposits.
• Why body condition scoring is important:
  • It's a practical and non-invasive tool to assess a cat's nutritional status.
  • It helps in identifying underweight or overweight/obese cats, allowing for dietary adjustments to prevent health problems associated with poor body condition.
  • It aids in monitoring the effectiveness of dietary interventions.
  • It is a better indicator of health risks than just body weight alone, as cats of the same breed and weight can have different body compositions.
• What might be even better? More precise methods like Dual-energy X-ray Absorptiometry (DEXA) scans could provide more accurate measurements of body composition (fat mass vs. lean mass), but these are not practical for routine use.

Digestible Carbohydrates (Page 13)

• Cats have a limited capacity to metabolize certain sugars.
• Toxicity with galactose: As little as $5.6 ext{ g galactose/kg BW/d}$ can be toxic to cats.
• They show low adaptation of disaccharidases at the brush border of the small intestine, meaning they are not very efficient at breaking down complex sugars.
• Despite this, they can effectively utilize some monosaccharides (simple sugars).
• Safe upper limits of selected carbohydrates (g/kg DM diet):
  • Glucose or sucrose: $50 - 150 ext{ g/kg DM}$ (dry matter)
  • Lactose or raffinose: $50 ext{ g/kg DM}$
  • Fructo-oligosaccharides (FOS): $7.5 ext{ g/kg DM}$
  • Cellulose: $100 ext{ g/kg DM}$
• There is no known optimal starch inclusion level for the cat diet, reflecting their carnivorous adaptation and lower reliance on carbohydrates.

Digestible Carbohydrates: Lactase Activity (Page 14)

• The table shows the lactase activity (in U/g SI protein) in cats at different ages:
  • <1 Week: $96 \pm 66a$
  • $3-5$ Weeks: $69 \pm 63a$
  • $6-12$ Weeks: $13 \pm 9b$
  • Adult: $7 \pm 8b$
  • (Values with different superscripts (a, b) are significantly different, meaning lactase activity declines significantly with age).
• Why the change? Lactase is an enzyme that breaks down lactose (milk sugar). Kittens (especially very young ones) consume milk, which is rich in lactose. Their bodies produce high levels of lactase to digest it. As they mature and are weaned from milk, their natural diet (carnivorous prey) contains little to no lactose. Consequently, the production of lactase decreases significantly. This is a common physiological adaptation in many mammals known as lactase non-persistence or adult-type hypolactasia.

Resistant Starch (Fiber) (Page 15)

• The specific requirement for resistant starch (fiber) in cats has not been determined.
• Cats have limited fermentation capacity due to their anatomy:
  1. Relatively short gastrointestinal tract.
  2. Small cecum and minimal large intestine for extensive microbial fermentation compared to herbivores or omnivores.
• A small amount of fiber is recommended for cats.
• Why? Even though they are carnivores, some fiber can be beneficial for:
  • Normal gut motility and stool formation.
  • Hairball control.
  • Satiety (in weight management).
  • As a source of prebiotics.
• Prebiotics: Fructooligosaccharides (FOS) are discussed as prebiotics. Supplementation has been shown to result in increased Lactobacillus and decreased E. coli in feces, indicating a beneficial shift in gut microbiota.
• The natural foods of cats (prey) typically contain $\le 1\%$ dietary fiber.
• For commercial diets, a recommended dietary fiber level is $\le 5\%$.

Resistant Starch (Fiber) in Commercial Diets (Page 16)

• Example Ingredients (Hills Metabolic RC Satiety): Chicken By-Product Meal, Brewers Rice, Corn Gluten Meal, Powdered Cellulose, Dried Tomato Pomace, Flaxseed, Dried Beet Pulp, Chicken Liver Flavor, Coconut Oil, Pork Fat, Lactic Acid, etc.
• Nutrient composition (% DM):
  • Protein: Hills Metabolic ($38.7$), RC Satiety ($33.9$)
  • Fat: Hills Metabolic ($13.3$), RC Satiety ($8.9$)
  • Carbohydrate: Hills Metabolic ($31.7$), RC Satiety (Not listed, but implicitly present)
  • Fiber: Hills Metabolic ($9.8$), RC Satiety ($14.3$)
• Fiber-containing ingredients identified from the list:
  • Powdered Cellulose (a common purified fiber source)
  • Dried Tomato Pomace (fiber-rich byproduct)
  • Flaxseed (source of soluble and insoluble fiber)
  • Dried Beet Pulp (excellent source of fermentable and insoluble fiber)

Protein (Page 17)

• Meeting minimal protein requirements is critical for cats.
• Cats have approximately $2x$ the protein requirement compared to adult non-carnivores (such as dogs or humans).
• Why do cats have such high protein requirements?
  1. Constitutive enzyme activity: Cats have unique liver enzymes (e.g., aminotransferases, urea cycle enzymes) that are constitutively active at high levels, constantly breaking down protein for energy regardless of dietary protein intake. This means they cannot easily downregulate protein catabolism to conserve nitrogen when on a low-protein diet.
  2. Gluconeogenesis: As true carnivores, cats rely heavily on amino acids for gluconeogenesis (glucose production), even when carbohydrates are available.
  3. Specific amino acid requirements: They have absolute requirements for certain amino acids (e.g., arginine, taurine) that other species can synthesize or have lower requirements for, which must be met by dietary protein.
• Protein in excess is rapidly catabolized for:
  1. Energy: Amino acids are deaminated, and the carbon skeletons are used for energy.
  2. Glucose: Via gluconeogenesis.
  3. Storage as fat: If energy intake exceeds immediate needs, carbon skeletons from amino acids can be converted to fatty acids and stored as fat.
• There is little benefit to feeding large excesses of protein beyond their requirements.
• Excess protein may potentially increase the risk for renal disease in susceptible or older cats, as the kidneys must excrete the nitrogenous waste products (e.g., urea).
• Protein should primarily derive from animal tissues.
• Why animal tissues? Animal tissues provide a highly bioavailable source of protein with an amino acid profile that naturally meets the specific and high requirements of a carnivore, including essential amino acids like arginine, taurine, methionine, and cysteine, which are often less abundant or less available in plant-based proteins.

Endogenous Urinary N Excretion of Animal Fed a Protein-Free Diet (NRC, 2006) (Page 18)

• This table illustrates the endogenous urinary nitrogen (N) excretion in different species when fed a protein-free diet, expressed as mg N/kg$^{0.75}$ /d (metabolic body weight):
  • Human: $62$
  • Rat: $128$
  • Pig: $163$
  • Dog: $210$
  • Cat: $360$
• The data clearly support a significantly higher nitrogen requirement for cats than for other species, as evidenced by their high endogenous nitrogen loss even on a protein-free diet. This implies a constant, unavoidable breakdown of body protein.
• However, the efficiency of protein utilization is lower in cats compared to other species. This is due to their inherent lack of ability to conserve nitrogen and certain essential amino acids, meaning a larger dietary intake is needed to compensate for this constant loss and meet requirements.

Protein - Requirements (Page 19)

• Nitrogen Balance: Unlike other species, cats do not show a clear plateau in nitrogen balance curves, making it difficult to define a precise minimum protein requirement by this method. Their high constitutive protein catabolism means they always excrete a significant amount of nitrogen.
• Recommended Allowance (RA) (NRC, 2006): These allowances are typically expressed per $1000 ext{ kcal ME}$ to relate nutrient intake to energy intake, ensuring a balanced diet regardless of the cat's total energy needs.
  • Total Crude Protein (CP): $50 ext{ g/1000 kcal ME}$
  • Arginine: $1.93 ext{ g/1000 kcal ME}$
  • Methionine + Cysteine: $0.85 ext{ g/1000 kcal ME}$
  • Taurine: $0.10 ext{ g/1000 kcal ME}$
• Why expressed per $1000 ext{ kcal ME}$? Expressing nutrient requirements per unit of metabolizable energy (e.g., $1000 ext{ kcal ME}$) is a common and practical way to formulate diets. It ensures that regardless of how much food a cat eats to meet its energy needs, it simultaneously receives the appropriate proportion of all other essential nutrients. This automatically adjusts for differences in caloric density of foods and individual energy requirements related to activity level, life stage, etc.

Fat (Page 20)

• Functions of dietary fat for cats:
  • Energy source: Fat is a concentrated source of energy, providing approximately $2.25$ times more energy per gram than protein or carbohydrates.
  • Fat-soluble vitamins: Dietary fat is necessary for the absorption and transport of fat-soluble vitamins (A, D, E, K).
  • Palatability: Fat significantly enhances the palatability and appeal of food for cats, making it more likely they will eat enough to meet their energy and nutrient needs.
• Essential Fatty Acids (EFAs): Cats have specific essential fatty acid requirements that they cannot synthesize or synthesize efficiently, including:
  • Linoleic Acid (an omega-6 EFA)
  • Arachidonic Acid (an omega-6 EFA, which cats cannot synthesize from linoleic acid like most other mammals due to a lack of $\Delta 6$-desaturase activity)
  • $\alpha$-Linolenic Acid (an omega-3 EFA)
  • Eicosapentaenoic acid (EPA) and Docosahexaenoic acid (DHA) (long-chain omega-3 EFAs, derived from $\alpha$-linolenic acid, though cats have limited conversion ability).
• Cats tolerate high amounts of dietary fat, consistent with their carnivorous diet.
• They are known as "high-density lipoprotein (HDL) mammals," meaning they primarily transport lipids as HDL, which is different from humans who transport more via LDL.
• Fat digestibility in cats is generally very high, ranging from $84$ to $99\%$.

Fat - Requirement (Page 21)

• Cats are susceptible to deleterious effects of lipid oxidation.
• Feline pansteatitis (Yellow Fat Disease): This condition occurs when the body fat (adipose tissue) becomes inflamed, often due to diets high in unsaturated fatty acids (especially polyunsaturated fatty acids or PUFAs) and insufficient Vitamin E. The fat takes on a yellow-brown discoloration.
• Due to the risk of lipid oxidation, high levels of PUFA in the diet necessitate high levels of vitamin E to prevent free-radical or oxidative damage.
• Recommended Allowance (RA) and Safe Upper Limit (SUL) (NRC, 2006) per $1000 ext{ kcal ME}$:
  • Total Fat:
    • RA: $22.5 ext{ g}$
    • SUL: $82.5 ext{ g}$
  • Linoleic Acid:
    • RA: $1.4 ext{ g}$
    • SUL: $18.8 ext{ g}$
  • $\alpha$-Linolenic Acid:
    • RA: Not specified with a value in the table from the slide
    • SUL: Not specified with a value in the table from the slide
  • Arachidonic Acid:
    • RA: $0.015 ext{ g/1000 kcal ME}$
    • SUL: $2 ext{ g/kg DM}$
  • EPA + DHA:
    • RA: $0.1 ext{ g/kg DM}$
    • SUL: Not specified with a value in the table from the slide

Vitamin - Requirement (Page 22)

• Cats have some unique vitamin requirements or metabolic pathways compared to other species.
• Vitamin A:
  • Cats are unable to convert $\beta$-carotene (a plant pigment) to active Vitamin A (retinol).
  • This is due to low activity of the enzyme $\beta$-carotene $15,15'$ '-dioxygenase.
  • Therefore, they require pre-formed Vitamin A from animal sources.
  • The liver is the main storage site for Vitamin A.
  • Recommended Allowance (RA): $24.7 ext{ µg retinol/kg BW}^{-0.67}$.
• Vitamin D:
  • Cats' skin has low concentrations of $7$-dehydrocholesterol, which is the precursor for Vitamin D synthesis upon UV exposure.
  • This precursor is rapidly converted to cholesterol rather than Vitamin D in cats.
  • Consequently, cats cannot synthesize sufficient Vitamin D from sunlight and require dietary pre-formed Vitamin D.
  • Recommended Allowance (RA): $0.17 ext{ µg cholecalciferol/kg BW}^{-0.67}$.
• Thiamin (Vitamin B1):
  • Cats require approximately $4$ times more thiamin than dogs.
  • Recommended Allowance (RA): $1.4 ext{ mg thiamin/kg BW}^{-0.67}$.
• Niacin (Vitamin B3):
  • Cats have high picolinic carboxylase activity, an enzyme that diverts tryptophan away from niacin synthesis.
  • This prevents them from converting tryptophan (an amino acid) into niacin efficiently, unlike many other mammals.
  • Therefore, cats have an absolute dietary requirement for pre-formed niacin.
  • Recommended Allowance (RA): $0.99 ext{ mg niacin/kg BW}^{-0.67}$.

Minerals - Ca and P - Requirement (Page 23)

• Calcium (Ca):
  • Calcium deficiency may occur in cats exclusively eating non-supplemented meat (e.g., a pure muscle meat diet without bone, which is a common source of calcium in a natural diet).
  • A balanced dietary calcium intake is essential for bone health and numerous metabolic functions.
• Phosphorus (P):
  • Phosphorus excess is often more problematic than deficiency in formulated diets.
  • High phosphorus levels are strongly implicated in the progression of lower urinary tract disease and renal disease in cats, particularly as they age.
  • Therefore, a lower dietary phosphorus level can be beneficial, especially for older or predisposed cats, to help manage kidney health.
• Recommended Allowance (RA) (NRC, 2006):
  • Ca: $45 ext{ mg/kg BW per day}$
  • P: $40 ext{ mg/kg BW per day}$
• Ca : P ratio: The ideal dietary calcium to phosphorus ratio is critical for proper mineral metabolism and bone health, recommended at $0.9 ext{ to } 1.1 : 1$ (or generally $1:1$ up to $1.2:1$ is often cited).

Key Nutritional Requirements for Adult Cats (NRC, 2006) (Page 24)

• This table summarizes the recommended allowances for adult cats based on the NRC (2006) guidelines, provided in three different units: per kg DM (dry matter), per $1,000 ext{ kcal ME}$ (metabolizable energy), and per kg BW$^{0.67}$ (metabolic body weight).
• Energy density: $4,000 ext{ kcal ME/g}$
• Crude protein:
  • $200 ext{ g/kg DM}$ (dry matter)
  • $50 ext{ g/1,000 kcal ME}$
  • $4.96 ext{ g/kg BW}^{0.67}$
• Arginine:
  • $7.7 ext{ g/kg DM}$
  • $1.93 ext{ g/1,000 kcal ME}$
  • $0.19 ext{ g/kg BW}^{0.67}$
• Methionine & Cysteine:
  • $3.4 ext{ g/kg DM}$ (combined)
  • $0.85 ext{ g/1,000 kcal ME}$
  • $0.084 ext{ g/kg BW}^{0.67}$
• Taurine:
  • $0.4 ext{ g/kg DM}$
  • $0.10 ext{ g/1,000 kcal ME}$
  • $0.0099 ext{ g/kg BW}^{0.67}$
• Crude fat:
  • $90 ext{ g/kg DM}$
  • $22.5 ext{ g/1,000 kcal ME}$
  • $2.2 ext{ g/kg BW}^{0.67}$
• Linoleic acid:
  • $5.5 ext{ g/kg DM}$
  • $1.4 ext{ g/1,000 kcal ME}$
  • $0.14 ext{ g/kg BW}^{0.67}$
• Arachidonic acid:
  • $0.06 ext{ g/kg DM}$
  • $0.015 ext{ g/1,000 kcal ME}$
  • $0.0015 ext{ g/kg BW}^{0.67}$
• Calcium (Ca):
  • $2.9 ext{ g/kg DM}$
  • $0.72 ext{ g/1,000 kcal ME}$
  • $0.071 ext{ g/kg BW}^{0.67}$
• Phosphorus (P):
  • $2.6 ext{ g/kg DM}$
  • $0.64 ext{ g/1,000 kcal ME}$
  • $0.063 ext{ g/kg BW}^{0.67}$
• Magnesium (Mg):
  • $400 ext{ mg/kg DM}$
  • $100 ext{ mg/1,000 kcal ME}$
  • $9.5 ext{ mg/kg BW}^{0.67}$
• Retinol (Vitamin A):
  • $1000 ext{ µg/kg DM}$
  • $250 ext{ µg/1,000 kcal ME}$
  • $24.7 ext{ µg/kg BW}^{0.67}$
• Cholecalciferol (Vitamin D):
  • $7 ext{ µg/kg DM}$
  • $1.75 ext{ µg/1,000 kcal ME}$
  • $0.17 ext{ µg/kg BW}^{0.67}$
• Niacin (Vitamin B3):
  • $40 ext{ mg/kg DM}$
  • $10 ext{ mg/1,000 kcal ME}$
  • $0.99 ext{ mg/kg BW}^{0.67}$

Lifecycle Nutrition - Older Cats (Page 25)

• Age classifications:
  • $7-8$ years of age are considered "old."
  • >10 to $12$ years of age are considered "very old."
• Older cats experience an increase in age-related diseases.
• They undergo gradual behavioral, physical, and metabolic changes:
  • Become less active.
  • Experience a decrease in lean body mass.
  • Effect on metabolic rate: A decrease in lean body mass generally leads to a decrease in basal metabolic rate since muscle is more metabolically active than fat.
  • Show decreased digestive function, immune response, glucose tolerance, and renal function.
  • May experience a decline in smell and taste perception, which can affect appetite.
  • Become less adaptable to metabolic and physiological perturbations (e.g., changes in diet, environment, or illness).

Older Cats - Nutritional Goals (Page 26)

• The primary goals of nutrition for older cats are:
  • To maintain an ideal body condition and weight.
  • To ensure adequate intake of nutritious food.
  • To promote good hydration.
  • To minimize the progression or occurrence of disease.
• Nutritional modifications to potentially slow down aging:
  • A common strategy is to moderately reduce caloric intake for weight management and to potentially extend lifespan (caloric restriction).
  • Ensure adequate amounts of all other essential nutrients, even with reduced caloric intake, which can be challenging to achieve.

Water Requirement - Older Cats (Page 27)

• Older cats often experience impaired thirst sensitivity, meaning they may not feel thirsty enough to drink adequate water.
• They typically have a decline in renal function, which leads to:
  • Increased water losses due to an incapability to concentrate urine effectively.
  • Predisposition to dehydration, as their kidneys are less efficient at conserving water.
• Older cats may also have a reduced ability to thermoregulate, making adequate hydration even more critical for heat dissipation.
• In healthy older cats without increased losses (e.g., from illness), a recommended daily water intake is $200 ext{ to } 250 ext{ mL/day}$.
• What could you do to increase water intake?
  • Feed moist or canned diets.
  • Provide multiple water bowls in different locations.
  • Use water fountains, as many cats prefer running water.
  • Add flavored broths (low sodium) to water or food.
  • Ensure water bowls are clean and fresh water is always available.

Energy Requirement - Older Cats (Page 28)

• The graph (Figure 1, Sparkes 2011, adapted from Laflamme, 2005) illustrates the effect of age on the maintenance energy requirement (MER) of adult cats.
• It suggests that MER may decrease initially in middle age but can then increase again in very old age, potentially due to decreased digestive efficiency or chronic disease processes.

Energy Requirement - Older Cats (Page 29)

• The energy requirement for cats tends to decrease in middle age but then may increase again in very old age (as shown in the previous figure).
• Fewer obese cats are observed in the very old age group, often due to age-related physiological changes or diseases that lead to weight loss.
• Very old cats often experience weight loss and may require energy-dense diets. This is because:
  • They may have significant reduction in fat digestibility.
  • They may have a slight reduction in protein digestibility.
  • There can be a decline in pancreatic enzyme secretion, further impairing nutrient digestion and absorption.
  • They may also have reduced appetite or dental issues.
• The text suggests this might be a function of high fat and protein diets, implying that the typical highly digestible fat and protein content of cat diets might become challenging for the diminished digestive capacities of very old cats.

Protein Requirement - Older Cats (Page 30)

• Older cats experience a decrease in lean body mass (sarcopenia).
• No restriction of dietary protein is recommended for healthy older cats. Instead, adequate protein is crucial for:
  • Maintaining lean body mass.
  • Supporting protein synthesis.
  • Maintaining immune function.
• Protein needs for older cats are often higher than for young to middle-aged cats, when expressed on a per-unit-of-energy basis, to counteract muscle loss and maintain overall health.
• Additional benefits of moderate protein amounts (in older cats):
  • Improved palatability, which can stimulate appetite.
  • Improved food intake and weight maintenance in very old cats who are prone to a decline in appetite and weight loss.
• It is crucial to feed high protein quality. High-quality protein provides all essential amino acids in appropriate proportions, which is vital for building and repairing tissues, especially when digestive efficiency may be compromised.

Fat Requirement - Older Cats (Page 31)

• The risk of death increases $3$-fold in obese cats, emphasizing the importance of weight management, especially as cats age.
• Moderate to low levels of fat may reduce the risk of obesity in older cats when energy requirements are generally lower for most of their senior years.
• Fat sources should be highly digestible because the ability to digest fat often decreases with age in cats.
• Dietary fat improves palatability, which is particularly important for very old cats who may have reduced appetite. Good palatability helps improve food and caloric intake, which is critical for preventing weight loss in these very frail animals.
• Fat is also essential for the absorption of fat-soluble vitamins (A, D, E, K), which may be compromised with reduced fat digestibility.

Aging and Fat Digestibility (Page 32)

• A reduction in fat digestibility is a known phenomenon in aging cats (Peachey et al., 1999).
• This reduction is a general phenomenon observed for all fatty acid groups:
  • Unsaturated fatty acids: Digestibility decreases from $95.2\%$ in young cats to $93.2\%$ in senior cats.
  • Monounsaturated fatty acids: Digestibility decreases from $98.2\%$ in young cats to $96.4\%$ in senior cats.
  • Polyunsaturated fatty acids (PUFA): Digestibility decreases from $98.7\%$ in young cats to $98.0\%$ in senior cats.
• Although the percentage drop might seem small, a consistent reduction across all types of fats contributes to overall decreased nutrient absorption, which can be critical for older cats.

Aging and Fat Digestibility - Pooled Data (Page 33)

• Figure 2 (Sparkes 2011, adapted from Patil, 2010) presents pooled data from four colonies ($n=188$ cats) on digestibility:
  • A) Proportion of cats with low fat digestibility ($< 80\%$): This graph would show an increase in the proportion of cats experiencing significantly reduced fat digestion as they age.
  • B) Proportion of cats with low protein digestibility ($< 80\%$): Similarly, this graph would likely show an increase in the proportion of cats with low protein digestibility as they age, although perhaps less pronounced than fat digestibility failures for most senior cats.
• The observation of low crude protein (CP) digestibility (< 80\%) in some older cats further highlights the physiological decline in digestive capabilities.

Fiber Requirement - Older Cats (Page 34)

• Constipation is a common problem in older cats, often attributed to:
  • Reduced water intake.
  • Limited physical activity.
  • Reduced colonic motility.
• Insoluble fiber ($< 5\%$ of the diet) can be beneficial in managing constipation by increasing fecal bulk and stimulating gut motility.
• Beyond constipation, fiber can contribute to:
  • Overall gut health.
  • Management of obesity, diabetes mellitus, and hyperlipidemia in some cases, by promoting satiety and slowing glucose absorption.
• High levels of fiber ($> 10\%$) in the diet should be used with caution (or avoided as a general rule) in older cats because it can:
  • Reduce overall nutrient digestibility (by diluting the diet or interfering with absorption).
  • Decrease the caloric density of the diet, which is undesirable for older cats predisposed to weight loss or with reduced appetite.

Ca and P Requirement - Older Cats (Page 35)

• Bone mass of cats declines after $7$ years of age. This is a natural aging process, though less bone mass may be needed for structural support in less active senior cats.
• Bone loss can also occur due to buffering elevation in metabolic acids. Older cats might have a greater metabolic acid load and potentially a lower urinary pH, leading to the mobilization of calcium from bone to buffer these acids.
• Moderate levels of available dietary Calcium (Ca) are recommended for the maintenance of bone mass in older cats.
• Reduction in dietary Phosphorus (P) levels is recommended for older cats, particularly because approximately $30\%$ of cats have kidney disease (or are predisposed to it). Lower phosphorus diets can help slow the progression of renal disease and mitigate its negative impacts.

Summary - Older Cats (Page 36)

• Energy requirement: Tends to decrease initially in middle age, then may increase in very old age due to decreased digestive efficiency or health issues.
• Palatability of food: Becomes especially critical (*indicated by an asterisk on the slide) for older cats, as their sense of smell and taste may decline, impacting appetite and food intake.
• Digestibility: Generally decreases with age (*indicated by an asterisk on the slide), particularly fat and to a lesser extent protein, necessitating highly digestible nutrient sources.
• Fiber: Moderate levels of insoluble fiber can help with constipation, but high levels should be avoided due to potential reduction in nutrient and caloric density.
• Urinary pH: Important to maintain appropriate urinary pH (acidic) to avoid crystal formation. Decreased renal function in older cats can impact urine concentration and pH.
• The humorous image of the cat suggests that despite the challenges of aging, cats maintain a calm demeanor, perhaps due to their inherent resilience or simply their nature.