Animal Nutrition - Chapter 1 Notes

Course context and announcements

• Biology 346: Animal Nutrition

• Chapter 1: Introduction to Nutrition

• Welcome back lunch announcements appear on pages 2 and 35 (date: Friday, Aug. 29, 2025; time 12:15 p.m. – 1:10 p.m.; location: Science Center - 2nd Floor entrance). Divisions of Biology/Biochemistry, Environmental Studies/Geology, Physics/Astronomy will provide food; attendees provide appetite.

What is animal nutrition?

• Definition: Study of nutrients in feed and how they support growth, health, and performance of animals.

• Nutrients are chemical elements or compounds found in feed, including water, carbohydrates, protein, fat, vitamins, and minerals.

• Complete ration concept: A planned combination of feeds designed to meet all nutritional needs.

Tree of Life / taxonomy context (big picture from the slide)

• Diagram/slide shows broad relationships among organisms labeled as:

  • Eukaryotes, Archaea, Bacteria, and the major kingdoms/groups (e.g., Plants, Green algae, Red algae, Diatoms, Dinoflagellates, Alveolates, Excavates, Heterokonts, Amoebas, Choanoflagellates, Fungi, Animals, etc.).

  • Emphasis on evolutionary relationships and organelles:

  • Mitochondria originating from α-proteobacteria

  • Plastids from cyanobacteria (in photosynthetic lineages)

• The slide positions Animals within Opisthokonts, close to Fungi and certain protists (e.g., choanoflagellates, nucleariids).

• Highlights how broad taxonomic groups connect to nutrition science (differing digestive strategies, symbioses, and nutrient requirements across life forms).

What is feed? and Forage definitions

• Feed: broad term for substances provided to animals, including:

  • Fodder, silage, hay, pellets, and other processed forms

  • Byproducts from food production

  • Names vary by animal species (e.g., scraps for pigs = slop; scraps for chickens = chicken scratch)

• Forage: grazing-based feeds for livestock, including pasture and grazing land

Reasons for animal nutrition (why we formulate feeds)

• Primary goals:

  • Growth

  • Health

  • Performance (production efficiency, e.g., egglaying, milk yield, body mass)

• Nutrient formulation is necessary to ensure these outcomes

What is animal nutrition? Complete ration and its components

• A complete ration is a combination of feeds that includes:

  • Vitamins

  • Chemically prepared inorganic salts

  • Biogenically synthesized amino acids

• Key aspect: the quantity and assortment of nutrients are critical for meeting needs

• Human ration analogy: MRE (Meal, Ready-to-Eat) used as a reference point for complete nutrition in humans

Animal feed making process (illustrative example)

• Raw material feeds into processing chain (illustrated by a generic flow: Raw material → processing steps → finished feed)

• Historical note: Geared Sweep Mill (1907 Griffith and Turner Co.) capable of grinding all grains, with a capacity of 10–15 bushels per hour for 2 horses; example of early feed milling technology

Economic and financial impact of animal nutrition

• Economic considerations:

  • Total feed cost in the U.S. around $73.1 billion in 2024

  • Feed represents roughly 15% of total farm expenditures

  • In swine or poultry production, feed accounts for about 65% of total production expenses

Environmental impact of animal nutrition

• Nutrient flows and environmental concerns:

  • Focus on total nitrogen, ammonium-nitrogen, and total phosphorus in waste streams

  • Manure and undigested waste nutrients can affect air, soil, and water quality

  • Higher digestibility of feed can minimize environmental pollution

• Source cited: University of Minnesota (conceptual reference in slides)

Impact on product nutrient quality

• Nutritional quality of animal-derived products (eggs, meat, milk) is directly influenced by the diet and nutrient balance

• Images/notes compare nutrient content in different production settings (e.g., Caged Chickens vs. Free-Range Chickens)

Nutrient classifications and analysis (overview)

• Classifications of nutrients are broad; used as approximate content indicators for analytical purposes

• Sub-categories used for analysis include fats, proteins, carbohydrates, minerals, vitamins, fiber, etc.

• Example: Oklahoma State University sources used for sub-category definitions

Proximate analysis of feed (Weende analysis) – overview

• Purpose: to characterize feed composition through a set of standard components

• The process involves:

  • Sampling as many times as possible

  • Drying the sample

  • Grinding the sample

  • Mixing for subsampling

• Proximate analysis components typically include:

  • Water (moisture)

  • Crude Protein (CP)

  • Ether Extract (EE; fat)

  • Ash (mineral content)

  • Crude Fiber (CF)

  • Nitrogen-free Extract (NFE; estimate of water-soluble carbohydrates and other soluble components)

• This framework partitions feed into meaningful categories for nutritional evaluation

Proximate analysis: drying (water content and dry matter)

• Water content determination:

  • Feed is dried usually around 105°C for a set period to reduce damage

  • Alternatives: lower temperature (e.g., 55°C) or freeze-drying

  • Mass before and after drying is used to determine water loss

• Outcome: Dry Matter (DM) = mass of dry matter / mass of fresh matter

• Example formula:

  • $ext{Dry Matter (\% DM)} = rac{ ext{dry weight}}{ ext{fresh weight}} imes 100$

• Conceptual note: DM excludes water and includes all other constituents

Proximate analysis components (dry matter basis framing)

• After drying, the feed is conceptually partitioned into:

  • Water / moisture

  • Carbohydrates

  • Fats (lipids)

  • Proteins

  • Organic vitamins

  • Minerals (inorganic) via ash

• The core categories are often tabulated as:

  • Water, DM, Carbohydrates, Fats, Proteins, Organic vitamins, Minerals (ash)

Kjeldahl method – crude protein (CP)

• Principle: estimate protein by measuring nitrogen content, with a conversion factor

• Assumptions:

  • Protein contains about 16% nitrogen (≈ 0.16 N)

  • Therefore, CP is approximated as $CP = N imes 6.25$

• Typical reasoning:

  • Since most amino acids contain nitrogen, the total nitrogen is used to estimate total protein

• Limitations:

  • Some nitrogen-containing compounds (e.g., urea, DNA, RNA) contribute nitrogen but are not true proteins

  • Not all proteins have exactly 16% nitrogen; thus CP can be biased in some feeds

Proximate analysis: ether extract (EE) – fat content

• Principle: extract dried matter with an organic solvent (ether)

• Process: weigh dry matter; extract with ether; re-weigh to determine fat content via mass loss

• Limitations:

  • Not all fats are soluble in ether; some non-fat substances (e.g., certain vitamins, pigments, citric acid) may also be extracted

  • May misestimate fat content in some feeds

Mineral content via ashing

• Ash definition: inorganic residue remaining after combustion; represents total minerals

• Method: ashing in furnace at 500–600°C for 2–4 hours

• Limitations:

  • Some minerals can be destroyed during high heat (e.g., chloride, zinc, selenium, iodine)

  • Soil contaminants can overestimate mineral content if present in sample

Crude Fiber (CF)

• CF = plant cell wall material; primarily insoluble carbohydrates (cellulose and lignin) and some hemicellulose

• Importance:

  • Associated with gut health in pigs and poultry

  • Ruminants can ferment CF more effectively

• Determination method:

  • Treat with weak acid (e.g., 1.25% H2SO4) and weak base (e.g., 1.25% NaOH) to isolate fibrous components

  • The residue is ashed; the loss on ashing estimates CF

• Limitations:

  • Tends to underestimate actual fiber content

Nitrogen-free extract (NFE)

• Purpose: estimate water-soluble carbohydrates and other readily soluble components not captured by CP, EE, ash, or CF

• Traditional equation (textbook):

  • ext{NFE} = ext{% DM} - ( ext{% EE} + ext{% CP} + ext{% Ash} + ext{% CF})

• Alternatively (for dry matter basis):

  • $ext{NFE} = ( ext{DM}) - ( ext{Fat} + ext{Protein} + ext{Minerals} + ext{Crude Fiber})$

• Note: Both forms rely on proximate components to estimate the remainder as NFE

Van Soest detergent fiber system (fiber analysis)

• Purpose: more refined analysis of plant fiber; separates plant cell wall components

• Key fractions:

  • Neutral Detergent Fiber (NDF): includes cellulose, hemicellulose, and lignin (cell wall components)

  • Acid Detergent Fiber (ADF): includes cellulose and lignin (cell wall, but excludes hemicellulose)

  • Hemicellulose = NDF − ADF

• Procedure concept:

  • Plant material subjected to detergent extraction (SLS, EDTA, etc.) at pH ~7.0; process involves boiling with detergents for about one hour

• Protoplast concept: non-cell wall components (e.g., starch, sugars, proteins) are removed by detergents, leaving fibrous fractions

• Practical outcome: NDF relates to total cell wall content (affects intake and digestibility), while ADF relates to digestibility (cellulose and lignin mainly)

Comparing NDF and ADF (fiber analysis methods)

• NDF = cellulose + hemicellulose + lignin

• ADF = cellulose + lignin

• Hemicellulose = NDF − ADF

• Interpretive takeaway:

  • Higher NDF generally reduces intake stability due to gut fill; higher ADF indicates lower digestibility (more lignin and cellulose content)

Proximate analysis recap (dry matter framing)

• Core components to measure in feed: water, CP, EE, ash, CF, NFE

• DM basis is used for comparison across feeds

• Remember the sequence: dry to measure DM, then partition into CP, EE, CF, ash; remaining material estimated as NFE

Math review: practical calculations for proximate analysis

• Dry Matter (DM):

  • Example: Dry weight = 50 g; Fresh weight = 100 g

  • ext{DM ( ext{%)} } = rac{50}{100} imes 100 = 50 ext{ ext{%}}

• Crude Protein (CP) calculation from nitrogen (N):

  • If Nitrogen content = 10 g, then

  • $CP = N imes 6.25 = 10 ext{ g} imes 6.25 = 62.5 ext{ g}$

• Nitrogen content example involving 20 mg N to CP:

  • $CP = 20 ext{ mg} imes 6.25 = 125 ext{ mg}$

• % Nitrogen-free Extract (

  • ext{NFE} = (100 ext{ ext{% DM}}) - ( ext{% EE} + ext{% CP} + ext{% Ash} + ext{% CF})

  • For a DM basis example: Fat = 10%, Protein = 20%, Minerals = 5%, Crude Fiber = 10%

  • ext{NFE} = 100 ext{% DM} - (10 ext{%} + 20 ext{%} + 5 ext{%} + 10 ext{%}) = 55 ext{% DM}

Discussion prompts (for Section 2 classroom activities)

• Discussion 1: Nutrient ranking

  • Rank the six classes of nutrients by importance for survival; defend reasoning; groups of 3; write answers on notecards with names

• Discussion 2: Nutrition & Society Reflection

  • Based on Ch. 1, why should consumers (not just farmers or vets) care about animal nutrition?

• Discussion 3: Clarity of Chapter 1 topics

  • What topics were unclear? What topics are most interesting?

  • Groups of 3; write answers on notecards with names

Additional course notes and reminders

• The slides include a recap of the welcome back lunch as a recurring element (same notice appears on multiple pages)

• The content encompasses historical context, environmental considerations, and product quality implications for animal nutrition

• Subtle emphasis on the link between feed composition, digestibility, and environmental outcomes

Quick reference formulas and constants

• Dry Matter (DM) fraction:

  • $ext{DM} = rac{ ext{dry weight}}{ ext{fresh weight}} imes 100$

• Crude Protein (CP) from Nitrogen:

  • $CP = N imes 6.25$

• Nitrogen-free Extract (NFE) on DM basis:

  • ext{NFE} = ext{%DM} - ( ext{%EE} + ext{%CP} + ext{%ash} + ext{%CF})

• Hemicellulose from NDF and ADF:

  • $ext{Hemicellulose} = ext{NDF} - ext{ADF}$

• Fiber definitions (conceptual):

  • NDF = Cellulose + Hemicellulose + Lignin

  • ADF = Cellulose + Lignin

Summary takeaways

• Animal nutrition focuses on providing a complete ration that meets all nutrient needs via a mix of feeds, considering both growth and production efficiency while accounting for economic and environmental impacts.

• Proximate analysis (Weende) provides a practical framework to quantify major feed components (water, CP, EE, ash, CF, NFE) and forms the basis for more detailed fiber analyses (Van Soest system: NDF/ADF).

• The Kjeldahl method offers a widely used, but imperfect, proxy for protein content via nitrogen; fat content is measured by ether extraction; minerals by ash; fiber by CF and NFE by difference.

• Fiber analysis refinements (NDF/ADF) better reflect plant cell wall components and their impact on intake and digestibility, influencing feed formulation decisions.

• Calculations for DM, CP, and NFE are essential practical skills for evaluating feeds and formulating rations.