water and energy requirements

Daily water requirement: adult dog

60-100 ml/kg BW per day

Daily water requirement: adult cat

60-100 ml/kg BW per day

Daily water requirement: idle adult horse

~60 ml/kg BW per day (idle adult or yearling at 20°C consuming 1.5-2.0% BW in dry matter)

Gallon to liter conversion

1 gallon = 3.8 liters

Factors that influence water requirements

Losses (sweating, urine, stool/manure, milk, disease such as diarrhea); environment (temperature, humidity); diet (dry matter, protein, sodium)

Sources of water

Drinking water; water in food; metabolic body water

Water content of foods

~10% in kibble and hay; ~80% in canned food and fresh forage

Metabolic body water

Water produced as a byproduct of metabolism: glucose + oxygen → ATP + carbon dioxide + water (e.g., camel)

Pasture moisture content

26-82% moisture as fed (AF); average 46% AF

Why does a pet food label say "moisture max"?

The guaranteed analysis lists the maximum moisture, meaning the food contains no more than that percentage of water (data are on an as fed basis)

Water quality target

Total dissolved solids (TDS) < 1,000 mg/L is ideal

Water presentation

Influences accessibility, palatability, and monitoring (bowl, fountain, trough, bucket, automatic waterer); keep fresh and prevent freezing

Dry matter (DM)

Feed with zero water (e.g., dried in an oven until there is no further change in weight); food is not fed on a DM basis

As fed (AF)

Food with water, as it is in its packaging; food is fed on an AF basis

Water content varies by feed type

Pasture > hay; canned > kibble

Why use dry matter basis

Eliminates the variable of water to compare nutrient concentrations across foods; used to calculate dry matter intake (DMI) in herbivores

Convert nutrient % from AF to DM

Divide the nutrient % AF by the DM % (as a decimal); nutrient concentration is higher on a DM basis

Calculate DM % of a food

100% - moisture % (e.g., 12% moisture = 88% DM; 80% moisture = 20% DM)

Example: food with 16% crude fat AF and 12% moisture

DM = 88%; 16 / 0.88 = 18.2% crude fat DM

Example: food with 3.5% crude fat AF and 80% moisture

DM = 20%; 3.5 / 0.20 = 17.5% crude fat DM (similar fat content to the 18.2% food)

When do you not need to convert to DM to compare foods

If the moisture content of the foods is the same

Target daily DMI for herbivores

Generally 2% of body weight (BW); voluntary dry matter intake (VDMI) varies

Why DMI matters in herbivores

Calories are important, but so is dry matter (bulk) because of their GI physiology

Convert AF weight to DM weight

Multiply AF weight by DM % (decimal); feed weight is lower when you eliminate moisture

Convert DM weight to AF weight

Divide DM weight by DM % (decimal); feed weight is higher when you add in moisture

Example: 950 lb horse fed 25 lb AF hay (90% DM)

25 x 0.9 = 22.5 lb DM; 22.5 / 950 = 2.4% BW

Example: how much 90% DM hay for a 1,100 lb adult maintenance horse

DM target = 1,100 x 0.02 = 22 lb DM; 22 / 0.9 = 24 lb AF

Three uses of AF/DM conversion

AF → DM for nutrient concentration; AF → DM to check whether the current amount provides enough DM; DM → AF to determine how much to feed using the daily DM target

Anaerobic metabolism

Oxygen not available; fast energy; occurs in the cytosol; substrate is carbohydrate (glucose) only

Anaerobic byproduct

Lactate (build-up associated with fatigue); recycled by gluconeogenesis via the Cori cycle

Aerobic metabolism

Oxygen available; slow energy; TCA/CA cycle in the mitochondria; more energy produced

Aerobic substrates

Amino acids, fatty acids, or glucose (glucose can generate ATP anaerobically or aerobically)

Why energy requirements are not linear

Energy needs scale with metabolic body weight (BW^0.75), which relates to surface area; the mouse needs ~18x more energy per unit BW than the elephant

Metabolic body weight

BW^0.75 (BW in kg)

Resting energy requirement (RER) equation

RER = 70 x BW(kg)^0.75; units are kcal/day

How to calculate RER on a phone calculator

Enter BW in kg (pounds / 2.2); press x^y; enter 0.75; press multiply; enter 70; press equals

RER

Energy requirement at rest; the foundation to which a life stage factor is multiplied; expressed as kcal metabolizable energy (ME) per day

Daily energy requirement (DER)

DER = RER x life stage factor (DER factor); expressed as kcal ME per day; the estimated total daily energy need

DER for adult maintenance

Also called maintenance energy requirement (MER)

RER vs DER

RER is energy at rest (70 x BW^0.75); DER is RER multiplied by a life stage factor to account for lifestage, activity, and status (adult maintenance, growth, work, etc.)

Which life stage factors to memorize

Neutered adult factors for cats and dogs for most calculations

Example: adult neutered 25 kg dog, BCS 5/9, normal MCS

RER = 783 kcal; DER = 1,096-1,253 kcal (RER x 1.4-1.6)

Why energy calculations are only a starting point

Life stage factors only estimate DER and there is lots of individual variation

How to determine if the calculated DER is appropriate

Use the nutrition assessment, especially BCS (the "calorie-meter") and MCS, body weight, and appetite

Gross energy (GE)

Total food energy (burnt in a bomb calorimeter)

Digestible energy (DE)

Gross energy - fecal energy

Metabolizable energy (ME)

Digestible energy - urinary energy and gas energy

Net energy (NE)

Metabolizable energy - heat increment (energy lost as heat)

Energy value used by species: horse

Digestible energy (DE)

Energy value used by species: dog and cat

Metabolizable energy (ME)

Energy value used by species: cattle

Net energy (NE)

How is ME of pet food determined

By feeding test or by calculation (most common) using modified Atwater factors

Atwater factors: human food

Fat ~9 kcal ME/g; protein ~4 kcal ME/g; carbohydrate ~4 kcal ME/g

Modified Atwater factors: pet food

Fat 8.5 kcal ME/g; protein 3.5 kcal ME/g; carbohydrate 3.5 kcal ME/g

Most energy dense macronutrient

Lipid/fat

How is DE of horse feed and NE of cattle feed determined

Different calculations are used than for ME of pet food

Is energy provided adequate

Assess BCS (and MCS, body weight) to determine if the energy provided is adequate