ANSC 464 LECTURE 6

Lifecycle Nutrition of Cats - Growth

Overview of Feline Life Stages and Development (Page 1)

Cats undergo several developmental stages from kitten to adulthood, with specific milestones for physical and social maturity:

• Ten days old: Very young, highly dependent.
• Three weeks old: Beginning to explore surroundings.
• Five weeks old: More active and curious.
• Eight weeks old: Learns how to socialize with littermates and other pets.
• Fourteen weeks old: Continued growth and social development.
• Five months old: Sexual maturity may be attained around this age.
• Adult Cat: Full size and maturity are typically reached at about one year of age.

Introduction to Key Nutritional Factors (Page 2)

Understanding specific nutritional factors is critical for managing a cat's health throughout its life.
Key considerations include:

• Energy requirement
• Protein
• Palatability of food
• Digestibility
• Fiber

The concept of metabolic body weight is used to calculate energy needs and is expressed as $\text{kg}^{0.67}$. The Metabolizable Energy Requirement (MER) for adult cats guides dietary planning.

Objectives for Lifecycle Nutrition (Page 3)

The primary objectives are to understand nutritional needs during the growth phase, covering the first 12 months of a cat's life, divided into three periods:

1. Nursing period: From birth until weaning begins.
2. Weaning period: Transition from milk to solid food.
3. Post-weaning period: From full weaning to adulthood.

Additionally, the presentation aims to cover feline feeding behavior.

Nursing Kittens: Early Life and Dependency (Page 4)

Kittens are born immature and are entirely dependent on their queen for survival and development. They rely on the queen for:

• Food: Milk is their sole source of nutrition.
• Antibodies: Crucial for developing their immune system.
• Warmth: They cannot regulate their own body temperature initially.
• Hygiene: The queen stimulates urination and defecation.

Kittens exhibit a strong suckling reflex soon after parturition. They communicate their needs (hunger, cold, heat, discomfort) by crying. Poor interaction between the queen and kittens can unfortunately lead to severe outcomes like cannibalism or neglect.

Nursing Kittens: Body Temperature Regulation (Page 5)

Body temperature regulation is poorly developed during the first 4 weeks of a kitten's life, making them vulnerable to environmental temperatures.

• At birth: Body temperature is around $36.0^{\circ}\text{C}$.
• At 1 week of age: Body temperature rises to approximately $37.5^{\circ}\text{C}$.
• The queen plays a vital role in maintaining the temperature and humidity of the nest box.
• Both hyperthermia (overheating) and hypothermia (underheating) are equally detrimental to kittens.
• Maintaining a humidity level of $50\%$ in the nest box is recommended to reduce water loss from the kittens.

Nursing Kittens: Colostrum - The First Milk (Page 6)

Colostrum, the queen's first milk, is produced during the first 24 to 72 hours after parturition and is critical for neonatal health. Its unique composition includes:

• High Dry Matter (DM) content.
• Low lactose level: Approximately $29.9 \text{ g/L}$ or $23 \text{ mg/kcal}$, which is roughly $3\%$. The lactose level gradually increases as lactation continues.
• Protein and lipid levels initially decline from day 1 to day 3. This is largely a reflection of the initial change in water content. However, nutrient levels rebound after day 3 as the milk transitions to mature form.

Timely consumption of colostrum is essential for kitten survival.

Nursing Kittens: Colostrum and Immune System Development (Page 7)

Kittens are born with a naïve immune system and are highly susceptible to infections. Colostrum provides crucial passive immunity.

• It is essential for kittens to receive colostrum within 12 hours after birth.
• Passive immunoglobulin transfer significantly slows and eventually stops around 16 hours after birth, due to 'gut closure' where the intestinal lining can no longer efficiently absorb large protein molecules like antibodies.

Consequences of failure to consume colostrum: Kittens will have a compromised immune system, leading to increased susceptibility to infections, higher morbidity, and higher mortality rates. The term for discontinued passive transfer is Failure of Passive Transfer (FPT).

Nursing Kittens: Correcting Failure of Passive Transfer (Page 8)

Research has explored methods to correct FPT. A study by Levy et al. (2001, JAMVA 10:1401-1405) investigated different approaches:

• Study Design: 43 kittens were removed at birth and assigned to one of four groups:
  1. Colostrum deprived.
  2. Colostrum fed.
  3. Colostrum-deprived and administered pooled cat serum Intraperitoneally (IP).
  4. Colostrum-deprived and administered pooled cat serum Subcutaneously (SC).
• Measurements: Serum IgG concentrations were measured at birth, day 2, and weekly from week 1 to 8.
• Findings:
  • Both IP and SC administration of pooled cat serum resulted in IgG concentrations comparable to those in suckling kittens.
  • Colostrum-deprived kittens, without serum administration, took approximately 6 weeks to achieve 'normal' IgG concentrations, highlighting their prolonged vulnerability.

Nursing Kittens: Milk as Complete Nutrition (Page 9)

Queen's milk provides complete nutrition for nursing kittens, supporting normal growth and development.

• Key Components: Water, protein, fat, lactose, minerals, and vitamins.
• Essential Amino Acids: High levels of arginine and taurine are critical. Kittens require arginine for urea synthesis and growth, and taurine for retinal and cardiac health, as they cannot synthesize sufficient amounts themselves.
• Essential Fatty Acids: Crucial for neurological development.
• Docosahexaenoic Acid (DHA): The concentration of DHA in milk directly reflects the queen's dietary intake. DHA is a vital Omega-3 fatty acid for brain and retinal development. Sources include fish oil and certain algae.

Nursing Kittens: Milk Limitations for Optimal Growth (Page 10)

While queen's milk is complete, it may not always be sufficient to maximize growth rate, particularly concerning skeletal development.

• There is evidence that milk may be insufficient for skeletal calcification in some cases.
• The Calcium:Nitrogen (Ca:N) ratio, an index of unmineralized bone, has been observed to reduce during suckling, suggesting potential limitations for bone mineralization.

Nursing Kittens: Milk - Growth Factors and Immunoglobulins (Page 11)

Beyond basic nutrients, milk contains crucial non-nutritive factors that support neonatal health and development:

• Growth factors: These biological molecules, though poorly described for cats specifically (analogy from calves exists), are known to:
  • Increase food digestion efficiency.
  • Enhance neonatal development across various systems.
  • Provide increased immune protection.
• Immunoglobulins: Milk provides local immunoglobulins, particularly IgA, directly to the gut of the kitten, offering localized immune defense.

As lactation progresses, the milk's nutrient profile changes:

• Increases: Milk energy, protein, lactose, Calcium (Ca), and Phosphorus (P) levels.
• Decreases: Copper (Cu), Iron (Fe), and Magnesium (Mg) levels.
• Remains Constant: Zinc (Zn) levels.

Nutrient Comparison Across Milk Types (Page 12)

(Hand et al., 2000) provides a comparison of major nutrients in queen's colostrum, queen's milk, and the milk of other species:

Differences in Milk Metabolizable Energy (ME) content reflect the varying energy density for growth. Queen's milk is significantly more energy-dense and protein-rich compared to cow's or goat's milk, aligning with the rapid growth rate of feline neonates.

Composition of Mammal Milk and Growth Rate (Page 13)

(Hand et al., 2000) illustrates a clear relationship between milk composition and the growth rate of the young animal:

Relation between milk protein and growth rate: Generally, species with higher milk protein content have a faster growth rate, meaning fewer days are required for their young to double their birth weight. Cats, similar to dogs, show a high protein content in their milk, correlating with their rapid early growth.

Nursing Kittens: Monitoring Body Weight (Page 14)

Monitoring body weight is crucial for evaluating milk intake and overall kitten health (Hendriks and Wamberg, 2000).

• Birth weights: Typically range from $85 \text{ to } 120 \text{ g}$, with an average of $100 \text{ g}$.
• High Mortality Risk: Kittens born with a birth weight less than $75 \text{ g}$ have a very high mortality rate.
• Weekly Weight Gain: Nursing kittens should ideally gain approximately $100 \text{ g}$ per week.
• Minimal Daily Weight Gain: A minimal daily weight gain of greater than $7 \text{ g}$ indicates adequate nutrition and healthy growth.

Nursing Kittens: Energy Requirement (Page 15)

The energy requirements for nursing kittens are high to support their rapid growth and development.

• NRC (2006) Recommendation: $20-25 \text{ kcal/100 g BW}$.
• Lactation Progression: The energy content of the queen's milk increases as lactation progresses, adapting to the growing needs of the litter.
• Milk Energy Density: Queen's milk typically contains between $0.85 \text{ and } 1.6 \text{ kcal/mL}$.

Factors that can influence energy requirements: These include litter size, activity level of the kittens, environmental temperature, individual kitten metabolic rate, and the overall quality and quantity of the queen's milk production.

Nursing Kittens: Carbohydrate Requirement (Page 16)

• No established carbohydrate requirement: Kittens, being carnivores, primarily derive energy from fat and protein.
• Intestinal lactase activity: This enzyme is high during the nursing period to efficiently digest lactose, the primary carbohydrate in milk.
• Overfeeding with cow's milk: Can be detrimental. Cow's milk differs significantly from queen's milk in its nutritional profile, having lower energy and protein and a higher lactose content. Excessive lactose can overwhelm a kitten's lactase activity, leading to osmotic diarrhea, dehydration, and potentially nutrient deficiencies.

Orphan Kittens (Page 17)

For orphan kittens, proper nutritional management is critical (Debraekeleer 1998, Jacobsen 2004).

• Milk as Minimum Requirement: Cow's milk (or goat's milk) should be considered a minimum requirement and not a complete substitute without modification.
• Milk Replacer Preparation: Formulating a milk replacer is essential. Suitable ingredients can include a base of modified whole cow's milk or goat's milk, supplemented with egg yolk (for additional fat and protein), cream (for higher fat content), and finely ground sources of protein to more closely mimic the queen's milk composition in terms of protein, fat, and lactose levels.

Kittens: Weaning Process (Page 18)

Weaning is a crucial and gradual transition period in a kitten's life, typically starting around 3 to 4 weeks of age and completed by 6 to 10 weeks of age.

• Initiation: The queen naturally starts to avoid the kittens, prompting them to seek solid food.
• Progression: By 6 weeks of age, kittens should derive approximately $30\%$ of their caloric requirement from solid food.
• Stress of Forced Weaning: If weaning is forced or occurs too early, it can be a highly stressful event. This results in:
  • No maternal antibodies: Reduced immune defense due to the cessation of passive transfer from the queen's milk.
  • Increased morbidity and mortality in the post-weaning period.
• Benefits of Late Weaning: Allowing for a slightly later weaning period provides more time for the kitten's immune system to mature, leading to reduced kitten mortality in the post-weaning phase.
• Meeting Energy Requirements with Small Stomach Volume: To address the small stomach volume of kittens during weaning, it is recommended to offer highly digestible, energy-dense foods in small, frequent meals throughout the day.

Kittens: Introducing Weaning Food (Page 19)

Introducing solid food requires a careful approach to ensure proper acceptance and digestion.

• Initial Food: First, offer moist food, typically softened with water or a milk replacer, to make it easier to consume.
• Transition to Dry Food: By 6 to 8 weeks of age, kittens should begin learning to eat dry food.
• Semi-moist Foods Caution: Semi-moist foods can promote a highly acidic urinary pH, potentially leading to metabolic acidosis and impaired bone mineralization. Therefore, these should be given in limited amounts as occasional treats rather than as a primary diet.

Growing Kittens: Post-Weaning to Adulthood (Page 20)

This period spans from around 8 weeks of age until 10 to 12 months, marking the transition from kittenhood to full adult size and maturity.

• Nutrient Requirements: During this phase, nutrient requirements are a summation of those for maintenance (daily bodily functions) plus those for growth (tissue accretion).
• Impact of Deficiencies: Growth can be significantly slowed or stunted if nutritional deficiencies occur during this critical period.

Daily Metabolizable Energy Requirements for Growth (Page 21)

For growing kittens after weaning, the Metabolizable Energy Requirement (MER) for growth (NRC, 2006) follows a specific formula:

$\text{ME (kcal)} = \text{maintenance amount} \times 6.732 \times [e^{(-0.189p)} - 0.66]$

For kittens, this simplifies to:
$\text{ME (kcal)} = 100 \times \text{BW}_\text{a}^{0.67} \times 6.732 \times [e^{(-0.189p)} - 0.66]$

Where:

• $\text{P} = \text{BW}<em>\text{a} / \text{BW}</em>\text{m}$
• $\text{BW}_\text{a}$ = actual body weight at the time of evaluation (in kg).
• $\text{BW}_\text{m}$ = expected mature body weight (in kg).
• $e$ = the base of the natural logarithm, approximately $2.718$.

Example: For a kitten with an actual body weight of $1 \text{ kg}$ and an expected mature weight of $4 \text{ kg}$.
$\text{ME (kcal)} = 100 \times 1^{0.67} \times 6.732 \times [e^{(-0.189 \times 1/4)} - 0.66]$
$\text{ME (kcal)} = 100 \times 1 \times 6.732 \times [e^{(-0.04725)} - 0.66]$
$\text{ME (kcal)} \approx 673.2 \times [0.9538 - 0.66]$
$\text{ME (kcal)} \approx 673.2 \times 0.2938 \approx 198 \text{ kcal}$

Growing Kittens: Protein Requirement (Page 22)

Protein requirements for growing kittens are exceptionally high, particularly during the weaning phase, and then gradually decrease as they approach adulthood.

• Sulfur Amino Acids: Kittens have a notably higher requirement for sulfur amino acids (methionine and cystine) compared to many other species.
• Recommended Allowances (NRC, 2006) per 1000 kcal ME:
  • Total Protein: $56.3 \text{ g}$
  • Arginine: $2.4 \text{ g}$
  • Methionine + Cystine: $2.2 \text{ g}$
  • Taurine: $0.10 \text{ g}$

Growing Kittens: Fat Requirement (Page 23)

Growing kittens have higher fat requirements than adult cats due to their intense energy needs for growth and development.

• Docosahexaenoic Acid (DHA): This Omega-3 fatty acid is especially important for the proper neural development of young kittens.
• Recommendations: These are often based on the composition of queen's milk, which typically has around $9\%$ dry matter fat content.
• Recommended Allowance (RA) per 1000 kcal ME:
  • Total Fat: $22.5 \text{ g}$
  • Linoleic Acid: $1.4 \text{ g}$
  • $\alpha$ -Linolenic Acid: $0.05 \text{ g}$
  • Arachidonic Acid: $0.05 \text{ g}$
  • EPA + DHA: $0.025 \text{ g}$

Ingredients containing DHA: Primarily found in marine sources such as fish oil (e.g., from salmon, tuna) and certain types of algae, as well as some specialized animal fats.

Growing Kittens: Fat Digestibility (Page 24)

Fat digestibility in kittens increases significantly with age.

• Age-Dependent Improvement: As kittens mature, their digestive systems become more efficient at processing fats. The Attainable Total Tract Digestibility (ATTD) of fat can increase from around $80\%$ at birth to over $90\%$ by 15-20 weeks, continuing to improve up to 25-30 weeks of age.
• Between 9-17 weeks of age: This period shows a notable increase in fat digestibility, moving from the low 80s into the low 90s percentage-wise.

Ameliorating low fat digestibility using ingredients: To improve fat digestibility in young kittens, use highly digestible fat sources (e.g., high-quality purified animal fats or certain vegetable oils) and consider incorporating emulsifiers into the diet, which can help break down fat into smaller globules for easier enzymatic action.

Growing Kittens: Calcium (Ca) and Phosphorus (P) Requirement (Page 25)

Maintaining the correct balance of Calcium and Phosphorus is vital for skeletal development in growing kittens.

• Recommended Allowance (NRC, 2006):
  • Ca: $440 \text{ mg/kg BW per day}$
  • P: $400 \text{ mg/kg BW per day}$

Consequences of Imbalance: An imbalance, particularly a diet with reduced Calcium and increased Phosphorus, can lead to Nutritional Secondary Hyperparathyroidism (NSHP). NSHP causes the parathyroid glands to become overactive in an attempt to raise blood calcium levels, resulting in bone demineralization and a condition known as Osteitis Fibrosa, where bones become weak and fibrous.

Carbohydrates: Growing Kittens (Page 26)

• No Known Requirements: There are no officially established carbohydrate requirements for cats, as their carnivorous metabolism is primarily adapted to utilize protein and fat for energy.
• Gluconeogenic Amino Acids: An adequate supply of gluconeogenic amino acids (from protein) is important for maintaining glucose homeostasis, as cats can synthesize glucose from these amino acids.
• Starch Digestion: Growing kittens can readily digest some starch found in cereal grains.

Potential benefits or consequences of Carbohydrates (CHO) or fiber:

• Benefits: Digestible carbohydrates can serve as an energy source, sparing protein for tissue growth. Fiber can contribute to gut health, aid in stool formation, and help in regulating transit time.
• Consequences: Excessive intake of fermentable fiber can lead to digestive upset (gas, diarrhea). High levels of highly glycemic carbohydrates are generally not ideal for cats, given their metabolic adaptations, and can potentially contribute to metabolic issues if energy intake is not balanced.

Current Research: Kitten Microbiota (Page 27)

Recent research (Hooda et al., 2013; Deusch et al., 2014) highlights the impact of dietary protein-to-carbohydrate ratios during weaning on the kitten's gut microbiota.

• Recommended Protein Allowance: The recommended allowance for crude protein (CP) is around $22.5\%$.
• Common Diet Observation: Many commercial kitten diets exceed this minimal requirement, sometimes containing up to $40\%$ CP.
• High Protein Diet Impact: Studies showed that high protein diets (e.g., $53\%$ CP compared to $34\%$ CP) resulted in a reduction of 'healthy' beneficial bacteria such as Bifidobacterium, Megasphaera, and Lactobacillus.
• Mucin Degradation: Higher expression of mucin degradation genes was observed with high protein diets, suggesting a potential impact on the gut barrier.

Potential Implications: Alterations in the gut microbiota can have significant long-term effects on gut health, nutrient absorption efficiency, immune system development, and overall well-being. A reduction in beneficial bacteria might increase susceptibility to pathogens or digestive disturbances.

Key Nutritional Factors for Growing Kittens After Weaning (NRC, 2006) (Page 28)

To support optimal growth, the following factors are recommended for kitten diets:

Summary of Nutrient Requirements Across Life Stages (Page 29)

Nutritional needs vary significantly throughout a cat's life cycle:

• Nursing Kitten: Milk is essential, providing more than just nutrients, including critical antibodies and growth factors.
• Growing Kitten: Requires significantly increased energy, protein, and other nutrients (such as fats, essential amino acids, specific minerals like Ca and P) to support rapid development.
• Adult Cat: Requires maintenance levels of energy. Protein and fat requirements are typically high compared to many other species, phosphorus may be decreased relative to growth, and fiber intake is generally moderate.
• Senior Cat: Often requires increased protein to combat muscle loss, potentially higher fat for energy, and typically decreased phosphorus to support kidney health. Energy needs may be stable or slightly decreased with reduced activity.

Eating Behaviour of Cats (Page 30)

Cats exhibit unique eating behaviors rooted in their evolutionary history as solitary carnivores.

• Strictly Carnivorous: Cats are obligate carnivores, meaning their diet must primarily consist of animal material.
• Solitary Hunters: Unlike lions, most cats hunt solitarily, which influences their feeding patterns.
• Assessment Difficulty: Assessing normal feeding behavior can be challenging due to domestication and varying owner practices.
• Meal Frequency: When fed ad libitum, cats typically consume 12-20 small meals per day, evenly spaced over 24 hours.
• Activity Cycle: They hunt and sleep interchangeably during both day and night.
• Prey Energy: An average mouse provides approximately $30 \text{ kcal}$, which accounts for about $8\%$ of a cat's daily energy requirement.
• Energy Density Adjustment: Cats are adept at adjusting their food intake to match the energy density of their diet. They will eat more of a low-energy-dense food and less of a high-energy-dense food to meet their caloric needs.
• Obesity Risk: High energy diets combined with insufficient exercise can easily lead to obesity.
• Water Requirements: Cats are adapted to periods of water unavailability, reflecting their evolutionary origin in arid environments. However, they still require adequate hydration, needing approximately $2 \text{ mL}$ of water per $1 \text{ g}$ of dry matter food consumed.

Eating Behaviour of Cats (continued) (Page 31)

• Strong Predatory Drive: Cats retain a strong innate predatory drive. This instinct means a cat may stop eating to pursue a kill, which owners might mistakenly interpret as hunger.
• Sensory Preferences: Cats are highly sensitive to the physical form (including texture), odor, and taste of their food.
• Learned and Inherited Preferences: There is some evidence to suggest that food preferences can be both learned during kittenhood and potentially inherited from their parents.

Eating Behaviour of Cats (continued): Flavor Preferences (Page 32)

Cats' flavor preferences are closely tied to the nutritional characteristics of their natural carnivorous diet.

• Animal Product Attraction: They are strongly attracted to flavors derived from animal products, which signal high fat and protein content.
  • Examples include fat, protein hydrolysates, enzyme digests, meat extracts, and certain free amino acids abundant in muscle tissue (e.g., alanine, proline, lysine, histidine).
• Indifference to Sugars: Cats are generally not attracted to the taste of sugars because they lack the specific sweet taste receptors that many other mammals possess.
• Aversion to Plant-derived Flavors: They can be averse to some flavors derived from plant products, such as glutamic acid and medium-chain triglycerides.
• Texture Aversion: Cats typically reject foods with undesirable textures, such as powdery, sticky, or excessively greasy consistencies.

Eating Behaviour of Cats (continued): Odd Behaviours (Page 33)

Cats can exhibit certain behaviors that might seem unusual but are often rooted in instinct or specific needs.

• Coprophagia: This behavior, the ingestion of feces, is sometimes observed in queens with kittens less than $30 \text{ days}$ of age. It is considered normal for maternal hygiene and to stimulate defecation in neonates.
• Plant or Grass Eating: This is a natural behavior in cats.
  • Grass is typically not digested by cats.
  • It can act as a local irritant in the digestive tract, sometimes stimulating vomiting, which may help eliminate hairballs or other indigestible material.
  • It may also be a response to nutritional deficiencies, boredom, or simply a taste preference.

Eating Behaviour of Cats (continued): Anorexia and Learned Taste Aversion (Page 34)

• Anorexia: A few days of inappetence are usually not detrimental to an otherwise healthy cat. However, prolonged anorexia can lead to serious health issues:
  • Malnutrition
  • Reduced immune function
  • Increased risk for hepatic lipidosis: This severe liver condition occurs when, due to insufficient caloric intake, the body mobilizes large amounts of fat reserves. The liver becomes overwhelmed and cannot process all the fat, leading to excessive fat accumulation within hepatocytes.
  • Causes: Stress, unacceptable foods, or concurrent disease.
  • Correction: Often involves changing to a highly palatable food to stimulate appetite.
• Learned Taste Aversion: This is an adaptive response where cats develop an aversion to a specific food if its consumption is linked to a negative digestive tract experience (e.g., vomiting, nausea). This aversion can persist for up to $40 \text{ days}$.

Eating Behaviour of Cats (continued): Polyphagia and Fixed-Food Preferences (Page 35)

• Polyphagia: Excessive food consumption can be caused by various factors:
  • Disease: Certain medical conditions (e.g., hyperthyroidism, diabetes).
  • Drugs: Some medications can increase appetite.
  • Stress: Behavioral responses to stress.
  • Underfeeding: Insufficient caloric intake can lead to compensatory overeating.
  • Diagnostic Importance: The presence of concurrent weight loss or gain is a key diagnostic indicator to determine the underlying cause of polyphagia.
  • Control: Ultimately, while cats have innate drives, the owner plays a significant role in controlling food availability, type, and amount.
• Fixed-Food Preferences: These strong preferences develop early in a cat's life:
  • Foods consumed during the first $6 \text{ months}$ of a kitten's life profoundly influence their adult food preferences.
  • Feeding a limited number of foods during this critical period can lead to fixed-food preferences, making it difficult to introduce new diets later.
  • Maternal Influence: The queen's food preferences can also significantly influence the food preferences of her kittens, even before solid food is introduced directly to the kittens (Wyrwicka 1978, Pavlov J Biol Sci. 13:55-72).

Summary of Eating Behaviour (Page 36)

• Predatory Drive: Despite domestication, cats retain a strong predatory drive, influencing their meal patterns and sensory preferences.
• Carnivorous Metabolism: Their taste preferences are intrinsically tied to their carnivorous metabolism, favoring animal-derived flavors.
• Odd Behaviours: Certain seemingly odd behaviors, such as coprophagia (in queens) and grass eating, are natural and serve specific functions.
• Obesity Risk: Due to their ability to adjust intake based on energy density and the availability of palatable, energy-dense foods, excess energy intake leading to obesity is a common and easily possible issue in domestic cats.