🏋️ Lecture 10: Energy for Maintenance

Food Energy Requirements

Today’s Objectives

- Expand understanding of proximate analysis and metabolizable energy (ME) estimation

Uses of Food Energy

• Maintenance → sustaining metabolism and essential body functions (today’s lecture)

• Growth → building body tissues

• Reproduction → supporting reproductive functions

• Physical activity → providing energy for movement

Basal Metabolic Rate (BMR)

Definition

• Minimal amount of energy required by an endothermic animal each day to maintain homeostasis

• Measured in the absence of factors that affect energy expenditure (in kcal/day)

Essential Body Functions

• Respiration

• Circulation

• Nerve function

• Cellular maintenance

• Kidney and liver function

Thermoregulation: Endotherms vs. Ectotherms

Endotherms

- Body temperature primarily determined by heat generated through metabolic activity

Ectotherms

- Body temperature primarily determined by heat obtained from the environment

Basal Metabolic Rate (BMR)

Conditions for Measuring BMR

• At rest (but awake)

• In a post-absorptive state

• In a thermoneutral environment

• Without physical or psychological stress

Thermoneutral Zone (TNZ)

Definition

- Environmental temperature range where endotherms do not need to actively warm or cool themselves

Heat Balance

• Basal metabolic heat production = heat lost to the environment

• The body releases heat at the same rate it produces it to maintain a stable internal temperature

• Heat loss does not mean the animal loses all its warmth

• If heat were retained instead of released, body temperature would continuously rise to dangerous levels

Energy Expenditure: Basal Metabolic Rate (BMR)

Energy Expenditure

- Total energy an organism uses to maintain life, process food, and perform physical activity (represtented by BMR since BMR is the rate of metabolism, energy use)

Basal Metabolic Rate (BMR)

• Applies specifically to endotherms

• Minimum energy required to maintain vital, involuntary body functions under resting conditions

• Supports functions such as respiration, circulation, nerve function, and cellular maintenance

Basal Metabolic Rate (BMR): Lowest Metabolic Rate

When Metabolic Rate Falls Below BMR

• Sleeping → reduced energy expenditure

• Prolonged starvation and/or dehydration → metabolic rate may decrease

• Hibernation → reduced metabolism and body temperature

• Torpor → temporary reduction in metabolic rate and body temperature

Kleiber’s Equation: Estimating BMR

Purpose

• Developed by Kleiber (1947) to estimate BMR

• Based on metabolic body weight

• Used for mature (non-growing) endothermic mammals

Equation

- Y = 70 × BW^0.75

Variables

• Y = BMR (kcal/day)

• 70 = constant

• BW^0.75 = metabolic body weight (body weight in kg raised to the 0.75 power)

McNab’s Equations: Estimating Mammalian BMR

Purpose

- McNab (1988) introduced updated equations to estimate BMR in mammals

BMR Equations

• Placental mammals: Y = 57.2 × BW^0.716

• Marsupial mammals: Y = 46.6 × BW^0.737

Marsupial Characteristics

• Certain feeding habits associated with lower metabolic rates

• Less tolerant of cold temperatures

• Short gestation time

Variables

• Y = BMR (kcal/day)

• BW = body weight (kg)

BMR Equations: Feeding Habits

Vertebrate Eaters

• Equation: Y = 91.8 × BW^0.813

• Weight range: 0.05–175.0 kg

Variables

• Y = BMR (kcal/day)

• BW = body weight (kg)

BMR Equations: Mammalian Feeding Habits

Invertebrate Eaters

• Flying: Y = 47.3 × BW^0.797

  • Weight range: 0.01–0.06 kg

• Burrowing: Y = 31.7 × BW^0.738

  • Weight range: 0.40–4.00 kg

• Small: Y = 44.1 × BW^0.597

  • Weight range: 0.01–0.12 kg

• Large: Y = 43.5 × BW^0.719

  • Weight range: 0.20–7.70 kg

• Anteaters: Y = 19.7 × BW^0.753

  • Weight range: 1.20–30.6 kg

Variables

• Y = BMR (kcal/day)

• BW = body weight (kg)

BMR Equations: Frugivores

Flying Frugivores

• Equation: Y = 56.6 × BW^0.691

• Weight range: 0.01–0.60 kg

Arboreal Frugivores

• Equation: Y = 50.1 × BW^0.603

• Weight range: 0.30–14.30 kg

Terrestrial Frugivores

• Equation: Y = 60.9 × BW^0.744

• Weight range: 0.50–9.20 kg

Variables

• Y = BMR (kcal/day)

• BW = body weight (kg)

BMR Equation: Nectarivores

Nectarivores

• Equation: Y = 23.3 × BW^0.451

• Weight range: 0.01–0.05 kg

Variables

• Y = BMR (kcal/day)

• BW = body weight (kg)

BMR Equations: Grazers

Small Grazers

• Equation: Y = 62.5 × BW^0.617

• Weight range: 0.03–0.11 kg

Large Grazers

• Equation: Y = 69.1 × BW^0.808

• Weight range: 0.14–150.00 kg

Burrowing Grazers

• Equation: Y = 42.5 × BW^0.799

• Weight range: 0.17–6.80 kg

Variables

• Y = BMR (kcal/day)

• BW = body weight (kg)

BMR Equations: Folivores

Small Folivores

• Equation: Y = 42.7 × BW^0.545

• Weight range: 0.05–0.32 kg

Arboreal Folivores

• Equation: Y = 39.9 × BW^0.657

• Weight range: 0.86–7.00 kg

Terrestrial Folivores

• Equation: Y = 52.6 × BW^0.750

• Weight range: 0.80–400.00 kg

Variables

• Y = BMR (kcal/day)

• BW = body weight (kg)

BMR Equations: Birds

Passerine Birds

- Equation: Y = 114.7 × BW^0.73

Non-Passerine Birds

- Equation: Y = 73.6 × BW^0.73

Variables

• Y = BMR (kcal/day)

• BW = body weight (kg)

Estimating BMR from Oxygen Consumption

Alternative Method

- Thompson and Nicoll (1986) → estimate BMR by converting resting oxygen consumption into kcal/day

Conversion Formula

- BMR (kcal/day) = resting O₂ consumption (mL/hr) × 0.0048 (kcal/mL O₂) × 24 hr

Unit Conversion

- 1 cm³ of O₂ = 1 mL of O₂