Animal Nutrition in Production Systems (Strand 2 — Animal Science)

Feedstuffs, additives, and byproducts: types, composition, quality, and compatibility

Feedstuffs are the ingredients you feed animals to supply nutrients and energy. Learning feed types matters because the “same” diet on paper can perform very differently depending on digestibility, contamination risk, moisture, and whether the animal’s digestive system can actually use the ingredient.

Traditional feedstuffs

Traditional feeds are widely used because their nutrient profiles and handling characteristics are well known.

• Forages (roughages)—pasture, hay, haylage/silage. They are typically higher in fiber and support rumen function in cattle, sheep, and goats. Forages often vary the most in quality because maturity at harvest, leaf-to-stem ratio, and storage conditions strongly affect digestibility.
• Concentrates—grains (corn/maize, barley, wheat, oats), and protein meals (soybean meal, canola meal). These are more nutrient-dense and usually lower in fiber.
• Mineral and vitamin supplements—salt blocks, mineral premixes, vitamin premixes.

A key compatibility idea: ruminants need fermentable fiber to keep the rumen stable, while many non-ruminants (poultry, pigs) can’t use high-fiber feeds efficiently and may lose performance when fiber is too high.

Alternative feedstuffs and feed byproducts

Alternative feeds are ingredients outside “standard” grain/forage programs, often used to reduce cost or improve sustainability.

• Byproducts from food and fuel industries: distillers grains (from ethanol), oilseed meals, citrus pulp, beet pulp, wheat middlings/bran, molasses, bakery waste.
• Novel proteins: insect meal, single-cell proteins, some algae-based ingredients (use depends on regulations and availability).

Byproducts can be excellent feeds, but quality can be inconsistent—nutrient variation is a frequent problem. Another compatibility issue is fat level: high-fat byproducts can depress fiber digestion in ruminants if total dietary fat becomes excessive.

Feed additives (what they are and why they matter)

Feed additives are products added in small amounts to improve performance, health, feed stability, or handling.

Common categories (functions vary by species and regulations):

• Preservatives and antioxidants (reduce spoilage and rancidity)
• Enzymes (e.g., to improve use of specific carbohydrates in non-ruminants)
• Probiotics/yeasts (support gut/rumen microbial balance)
• Buffers (help stabilize rumen pH when feeding high-grain diets)
• Ionophores (used in some ruminant systems to shift rumen fermentation and improve efficiency—where permitted)
• Coccidiostats (common in poultry systems for parasite control)

A frequent mistake is assuming an additive “fixes” a fundamentally unbalanced ration. Additives can help, but they do not replace meeting basic requirements for energy, protein, fiber, minerals, and water.

Evaluating composition and feed quality

When you say “quality,” you’re usually combining four ideas:

1. Nutrient density (energy, protein, minerals per kg)
2. Digestibility/bioavailability (how much the animal can use)
3. Safety (contaminants, spoilage, toxins)
4. Consistency and handling (moisture, particle size, separation, storage stability)

Two feeds can have the same crude protein but different usable protein because heat damage, fiber binding, or anti-nutritional factors reduce availability.

Exam Focus

• Typical question patterns:
  • Classify ingredients as forage vs concentrate vs supplement, and match them to ruminant vs non-ruminant systems.
  • Interpret a scenario (e.g., inconsistent growth) and identify likely feed quality/compatibility issues.
  • Compare traditional vs alternative feeds with pros/cons (cost, variability, handling, nutrient limits).
• Common mistakes:
  • Treating “byproduct” as automatically low quality—many are excellent if tested and stored correctly.
  • Ignoring moisture: comparing feeds on an as-fed basis instead of dry matter.
  • Forgetting species differences (e.g., high-fiber feeds for pigs/poultry can reduce performance).

Nutrients and nutritional requirements across species and life processes

Nutrients are chemical substances animals need for maintenance, growth, reproduction, and production (milk, eggs, wool, work). Requirements vary because species digest differently and because life stage changes what the body is building.

The major nutrient classes (what they do)

Water is often the most limiting nutrient. It regulates temperature, transports nutrients, supports digestion, and is the medium for nearly all metabolic reactions. Restricting water quickly reduces feed intake and performance.

Carbohydrates are a major energy source. In ruminants, microbes ferment fiber and starch to volatile fatty acids (VFAs) that supply much of the animal’s energy. In non-ruminants, enzymes digest starch and sugars more directly.

Fats (lipids) are energy-dense and supply essential fatty acids. They can improve energy intake but can also cause problems—too much fat can reduce rumen fiber digestion or cause soft carcass fat in some species.

Proteins supply amino acids for muscle, enzymes, immune function, and (in lactation) milk protein. Ruminants can use non-protein nitrogen (NPN) (e.g., urea) because microbes convert nitrogen into microbial protein, but NPN must be matched with available energy to avoid toxicity.

Minerals support bones, nerves, muscles, and many enzymes.

• Macrominerals (needed in larger amounts): calcium, phosphorus, magnesium, sodium, potassium, chloride, sulfur.
• Trace minerals: copper, zinc, selenium, iodine, iron, manganese, cobalt, etc.

Vitamins are essential organic compounds.

• Fat-soluble: A, D, E, K (storage in body fat means deficiencies/toxicities behave differently).
• Water-soluble: B-complex and C (often less stored; ruminants can synthesize many B vitamins via rumen microbes).

Life processes that change requirements

Think of requirements as “priority budgeting.” The body prioritizes maintenance first (basic metabolism, temperature regulation), then allocates nutrients to growth, reproduction, and production.

• Maintenance: energy to keep organs running; protein to replace routine tissue turnover; minerals for basic function.
• Growth: higher energy and especially higher quality protein (essential amino acids) plus minerals for bone.
• Gestation: increased energy and protein—especially late gestation when fetal growth accelerates.
• Lactation/egg production: very high energy needs; high protein and specific minerals (e.g., calcium for eggshell formation).

Species differences that drive diet design

• Ruminants (cattle, sheep, goats): rely on microbial fermentation; need enough effective fiber to keep rumen pH stable. They can use fibrous forages well and can use NPN carefully.
• Hindgut fermenters (horses, rabbits): fermentation occurs after the small intestine; they need consistent forage intake and are sensitive to sudden starch increases.
• Monogastrics (pigs, poultry): require more precise amino acid balance and do poorly with high-fiber ingredients. Poultry layers have high calcium requirements.

A common misconception is that “protein percent” alone tells you whether a diet meets protein needs. In pigs and poultry, the amino acid profile (e.g., lysine, methionine) is often more important than crude protein.

Exam Focus

• Typical question patterns:
  • Match nutrient functions to symptoms or production outcomes (e.g., low energy intake causing low gain).
  • Compare requirements across life stages (maintenance vs lactation vs growth).
  • Explain why ruminants can use forages/NPN while monogastrics need higher-quality protein sources.
• Common mistakes:
  • Forgetting that water limitation reduces feed intake—students often diagnose “energy deficiency” without checking water.
  • Treating all carbohydrates the same—fiber vs starch affects rumen stability.
  • Assuming vitamin/mineral needs don’t change with production (they do).

Collecting feed samples and interpreting analysis to judge quality

Feed testing is how you replace guesswork with evidence. The lab can only analyze what you send—so sampling technique is often more important than the lab method.

How to collect a representative feed sample

A representative sample reflects the average of what animals actually eat.

• For hay: use a hay probe; sample many bales from the lot (different locations), then combine into a composite sample.
• For silage/haylage: take multiple grab samples across the face or during unloading, mix thoroughly, and seal quickly to limit moisture loss.
• For mixed rations: sample at the feed bunk soon after delivery and from multiple points.

Avoid “convenient” samples (top of a pile, one bale, one scoop). That is a classic reason results don’t match animal performance.

Common lab outputs (what they mean)

Labs report nutrients on either as-fed or dry matter (DM) basis. DM is preferred because it removes moisture differences.

Key measures you’ll often see:

• Dry matter (DM): percent of feed that isn’t water.
• Crude protein (CP): estimated from nitrogen content.
• Fiber measures (especially for forages): indicators of fill and digestibility.
• Ether extract (fat) and ash (total mineral content).
• Mineral profile: calcium, phosphorus, etc.
• Mycotoxin screening: for mold-related toxins when risk is high.

Interpreting data to determine quality (how to think)

Interpretation is about asking three questions:

1. Does it meet nutrient needs? Compare test results (on DM basis) to the animal’s required nutrient density.
2. Is it safe? Look for spoilage indicators and contaminant results.
3. Will animals actually eat it and perform? Consider palatability, particle size, and consistency.

Worked example: DM conversion and a quick quality check

Suppose a haylage test shows:

• DM = $40\%$
• CP (DM basis) = $18\%$

If you feed $10\,kg$ as-fed per animal per day, the DM intake from that haylage is:

$\text{DM intake} = 10\,kg \times 0.40 = 4\,kg\,DM$

The crude protein consumed from that haylage is:

$\text{CP intake} = 4\,kg\,DM \times 0.18 = 0.72\,kg\,CP$

This tells you how much protein the forage contributes—useful when deciding how much protein supplement is needed.

Exam Focus

• Typical question patterns:
  • Convert between as-fed and DM basis, then compute nutrient intake.
  • Identify why a lab result might not match performance (sampling error, spoilage, sorting).
  • Interpret a forage test qualitatively (high moisture, low protein, fiber concerns) and propose adjustments.
• Common mistakes:
  • Mixing as-fed and DM numbers in the same calculation.
  • Sampling only one location/bale and treating it as the whole lot.
  • Ignoring storage effects (heated hay can reduce protein availability even if CP looks normal).

Nutrient deficiencies and toxicities: recognizing symptoms and responding correctly

A deficiency happens when intake or absorption is too low for needs; a toxicity happens when an excess harms the animal. Both can look like “poor performance,” so you diagnose by combining symptoms, diet history, and sometimes lab tests.

General patterns of deficiency

Deficiencies often show up as:

• Reduced appetite and growth
• Weight loss or poor body condition
• Reproductive failures (low conception, weak offspring)
• Poor immune function (more disease)
• Coat/skin problems

Energy deficiency typically leads to weight loss and poor gain; protein deficiency often shows as poor growth, reduced milk/egg production, and poor muscle development.

Common mineral/vitamin issues (examples you should recognize)

• Calcium and phosphorus imbalance: bone problems in growing animals; in layers, poor shell quality. The balance matters, not just the absolute values.
• Copper: essential but can be toxic to sheep at levels tolerated by some other species. Species-specific mineral mixes matter.
• Selenium: required in small amounts; deficiency can contribute to muscle/weakness issues, but excess can be toxic. This is why supplementation is carefully controlled.
• Vitamin A: deficiency can cause poor growth and reproductive issues; risk increases when animals rely on old/damaged forage without green plant material.

Toxicities and “too much of a good thing”

Toxicities can come from:

• Over-supplementation (minerals, vitamins)
• Contaminated feeds (mycotoxins, heavy metals)
• Misuse of NPN in ruminants

For ruminants, urea/NPN toxicity risk increases when animals consume too much NPN too quickly or when there isn’t enough readily available energy for microbes to capture the ammonia.

How to address suspected deficiencies/toxicities

You generally respond in a controlled sequence:

1. Stop the suspected source (remove a new feed or supplement, isolate a batch).
2. Check water (quality and access), because dehydration mimics many nutrition problems.
3. Verify with evidence: feed test, ration review (DM basis), and veterinary/diagnostic support when animals show severe signs.
4. Correct gradually: sudden diet changes can create new problems (acidosis, digestive upset).

Exam Focus

• Typical question patterns:
  • Given symptoms + feeding history, identify the most likely deficiency or toxicity and the first management step.
  • Explain why a mineral mix safe for one species can harm another.
  • Propose a correction plan that avoids abrupt diet changes.
• Common mistakes:
  • Treating vague symptoms as a single-nutrient problem without checking intake, water, and overall ration balance.
  • “More supplement” as the default fix—over-supplementation can cause toxicity.
  • Forgetting species sensitivity (especially sheep with copper).

Feed contaminants: biological and non-biological hazards and their impacts

A contaminant is anything in feed that should not be there or is present at harmful levels. Contaminants reduce performance directly (toxicity) and indirectly (reduced intake, disease risk), and they can create food safety issues.

Physical contaminants

Physical contaminants include metal, glass, plastic, stones, and twine.

• Impact: choking, digestive tract injury, hardware disease in cattle, reduced intake.
• Control: good processing, magnets in feed systems, clean storage, careful bale twine management.

Chemical contaminants

Chemical contaminants include pesticide residues, cleaning chemicals, heavy metals, and excessive salt or minerals from mixing errors.

• Impact: acute poisoning, chronic organ damage, reproductive issues, reduced growth.
• Control: follow label directions, prevent cross-contamination, calibrate mixers, store chemicals away from feed.

Biological contaminants

Biological contaminants include molds, bacteria, and the toxins some molds produce.

• Molds and mycotoxins: not all moldy feed contains dangerous toxin levels, but mycotoxins can cause serious health and reproduction problems and reduce intake.
• Bacterial contamination (e.g., Salmonella risk in some contexts): can cause illness and may have public health implications.

Spoilage is both a quality and safety issue—hot spots in stored feed, poor silage fermentation, or wet storage can increase microbial growth.

Radiological contaminants

Radiological contaminants are uncommon but can occur from environmental contamination events. The main concern is uptake into animal products and long-term health risks.

Risk-based thinking (how to manage intelligently)

Not every feed needs every test. You choose testing and controls based on:

• Ingredient risk (e.g., damp grain has higher mold risk)
• Storage conditions
• Animal sensitivity (young animals are often more vulnerable)
• History (previous contamination events)

Exam Focus

• Typical question patterns:
  • Categorize contaminants as physical/chemical/biological/radiological and describe likely effects.
  • Given a storage scenario (wet grain, damaged silo), predict contamination risks and prevention steps.
  • Identify immediate actions during a suspected contamination event.
• Common mistakes:
  • Confusing “spoilage” with “low nutrients” only—spoilage can be a safety hazard.
  • Assuming contaminants only affect health, not performance—intake depression alone can cut gain.
  • Ignoring prevention: many questions reward storage and handling controls.

Formulating and preparing rations for life stages

A ration is the amount of feed offered over a given time (often per day). A diet is the combination of ingredients that makes up that ration. Formulation is the process of choosing ingredients and proportions to meet requirements safely and cost-effectively.

The logic of ration formulation (step-by-step)

A good formulation workflow is:

1. Define the animal and goal: species, weight, age, production stage (growth, finishing, lactation), desired gain or output.
2. Know what’s available: list feedstuffs, prices, moisture, and any limits (maximum inclusion due to fiber, fat, anti-nutritional factors).
3. Use requirements from an approved standard or your program’s tables: energy, protein/amino acids, minerals, vitamins, and water.
4. Balance on a DM basis first: then convert to as-fed for mixing/feeding.
5. Check constraints: fiber adequacy (especially ruminants), palatability, maximum supplement levels, and safety.
6. Plan mixing and delivery: consistent particle size, prevent separation, correct bunk management.

Protein balancing with the Pearson square (concept + example)

The Pearson square is a simple method to mix two ingredients to reach a target concentration of one nutrient (commonly crude protein). It doesn’t ensure the whole diet is balanced—so you use it as a starting tool.

Worked example: formulate a 16% CP mix from corn and soybean meal

Assume (DM basis):

• Corn = $9\%$ CP
• Soybean meal = $48\%$ CP
• Target mix = $16\%$ CP

Compute parts:

• Parts of corn = $48 - 16 = 32$
• Parts of soybean meal = $16 - 9 = 7$

Total parts = $32 + 7 = 39$

Proportions:

$\text{Corn fraction} = \frac{32}{39} \approx 0.821$

$\text{Soybean meal fraction} = \frac{7}{39} \approx 0.179$

So, for $100\,kg$ of the mix (DM basis):

• Corn: $82.1\,kg$
• Soybean meal: $17.9\,kg$

What can go wrong: students often stop here. But real diets also need minerals, vitamins, and (for ruminants) adequate effective fiber. For pigs/poultry you’d also check essential amino acids, not just CP.

Converting DM formulation to as-fed for preparation

If the corn is $88\%$ DM and soybean meal is $90\%$ DM, the as-fed amounts to supply the DM above are:

$\text{Corn as-fed} = \frac{82.1}{0.88} \approx 93.3\,kg$

$\text{SBM as-fed} = \frac{17.9}{0.90} \approx 19.9\,kg$

Total as-fed mix is $113.2\,kg$ because you’re including water weight.

Diet changes across life stages (how formulation shifts)

• Young/growing animals: higher protein quality and energy density; careful mineral balance for bone development.
• Finishing: higher energy density; manage digestive health (acidosis risk in ruminants).
• Late gestation and lactation: increased energy and protein density; higher mineral needs (species-dependent).
• Maintenance (non-producing): lower nutrient density is acceptable, but deficiencies still matter.

Exam Focus

• Typical question patterns:
  • Use Pearson square or simple balancing to hit a target protein level.
  • Convert DM to as-fed for mixing or daily feeding.
  • Choose ration changes for a given stage (starter vs grower vs finisher; dry vs lactating).
• Common mistakes:
  • Balancing one nutrient (protein) and assuming the ration is complete.
  • Forgetting DM conversion when feeds differ in moisture.
  • Making abrupt changes that create digestive disorders.

Performance indicators and feed-cost decisions

Performance indicators connect nutrition to measurable outcomes. They also let you compare feeds fairly when prices or availability change.

Average daily gain (ADG)

Average daily gain measures growth rate.

$ADG = \frac{\text{Final weight} - \text{Initial weight}}{\text{Days}}$

• Weights must be in the same units.
• Days is the time between measurements.

Worked example

An animal goes from $250\,kg$ to $310\,kg$ in $40$ days.

$ADG = \frac{310 - 250}{40} = \frac{60}{40} = 1.5\,kg\,day^{-1}$

Feed efficiency (and its inverse, feed conversion)

Two related metrics are used in practice:

• Feed efficiency (FE): gain per unit of feed.

$FE = \frac{\text{Weight gain}}{\text{Feed intake}}$

• Feed conversion ratio (FCR): feed per unit of gain.

$FCR = \frac{\text{Feed intake}}{\text{Weight gain}}$

Lower FCR means better efficiency, while higher FE means better efficiency—students often mix up which direction is “good.”

Worked example

Over a period, an animal eats $120\,kg$ of feed (DM) and gains $30\,kg$.

$FE = \frac{30}{120} = 0.25\,kg\,gain\,kg^{-1}\,feed$

$FCR = \frac{120}{30} = 4.0\,kg\,feed\,kg^{-1}\,gain$

Minimum energy required (conceptual model)

Animals require energy for multiple functions. A common way to express this is:

$E_{\text{total}} = E_{\text{maintenance}} + E_{\text{growth}} + E_{\text{production}} + E_{\text{activity}}$

The minimum energy required for a given situation is the total needed to meet the goal (e.g., maintain weight, achieve a target gain, produce milk/eggs). In many systems, maintenance is related to metabolic body weight:

$\text{Metabolic body weight} = BW^{0.75}$

The constant that converts $BW^{0.75}$ into an actual energy requirement depends on species, temperature, and the energy system used (digestible, metabolizable, net energy). In exam problems, you typically use the coefficient or requirement table provided.

Worked example using provided requirement values

If you are told:

• Maintenance energy = $50\,MJ\,day^{-1}$
• Growth energy = $20\,MJ\,day^{-1}$

Then:

$E_{\text{minimum}} = 50 + 20 = 70\,MJ\,day^{-1}$

Linking performance to cost, quality, and availability

Nutrition decisions are economic decisions:

• Cost per unit of nutrient (e.g., cost per kg of protein or per unit of energy) is more useful than cost per tonne of feed.
• Cost of gain links price to performance:

$\text{Cost of gain} = \text{FCR} \times \text{Feed cost per kg}$

If feed quality drops (lower digestibility, contamination, poor palatability), animals may eat less or convert less efficiently—raising cost of gain even if the feed is cheaper.

Worked example

If $FCR = 4.0$ and feed costs $0.30\,\text{currency}\,kg^{-1}$:

$\text{Cost of gain} = 4.0 \times 0.30 = 1.20\,\text{currency}\,kg^{-1}\,gain$

Exam Focus

• Typical question patterns:
  • Compute ADG, FE, and FCR from intake and weight data.
  • Compare two feeds using cost of gain rather than price per kg.
  • Use provided energy requirements to calculate minimum energy needed.
• Common mistakes:
  • Using as-fed intake when the question expects DM intake (or vice versa).
  • Reversing FE and FCR and misinterpreting “better.”
  • Ignoring that cheaper feed can increase cost of gain if performance drops.

Feeding and watering practices and systems

Feeding systems are the “delivery mechanism” for your nutrition plan. The best ration on paper fails if animals can’t access it consistently or if water supply limits intake.

Feeding practices and systems (how to choose)

You choose a system based on animal number, production goal, labor, and facilities.

• Grazing systems: low feed handling, but nutrient intake varies with pasture growth stage and weather. Often requires supplementation.
• Bunk or trough feeding: common in confinement; allows control of intake but requires good bunk management to reduce waste.
• Total mixed ration (TMR): mixes forages and concentrates together to reduce sorting and stabilize intake—especially useful in ruminants.
• Phase feeding (pigs/poultry): changes diet formulation as animals grow to match shifting amino acid and energy needs.
• Limit feeding: restricts intake of a high-energy ration to reduce waste and control body condition; must be managed carefully to avoid competition and uneven intake.

Key idea: animals eat in social environments. If bunk space is limited, timid animals may under-eat even when the ration is “correct.”

Watering practices and water quality

Watering systems include troughs, automatic drinkers, nipple systems (common in pigs), and pasture tanks. Water quality and access determine feed intake.

Important management points:

• Provide enough access points to reduce competition.
• Keep systems clean to limit microbial growth.
• Monitor for leaks or flow restrictions—reduced flow can quietly reduce intake.

Water contaminants (microbial, high dissolved solids, nitrates, some minerals) can reduce intake and health. In many course questions, the most testable concept is simply that poor water access/quality reduces feed intake and performance, and fixing water issues is often a first step.

Matching practices to purpose and requirements

• Growing groups: consistent feeding times and uniform ration mixing reduce variation in gain.
• Breeding stock: manage body condition—overfeeding can reduce fertility, underfeeding reduces conception and offspring vigor.
• High-producing animals: prioritize consistent access to a nutrient-dense diet and abundant clean water.

Exam Focus

• Typical question patterns:
  • Choose an appropriate feeding system for a scenario (large herd, limited labor, grazing vs confinement).
  • Diagnose performance problems tied to feeding management (sorting, insufficient bunk space, irregular feeding).
  • Identify how water system failures show up in animal performance and what to check first.
• Common mistakes:
  • Treating feeding as only “what” is fed, not “how” it is delivered (access and consistency matter).
  • Overlooking social competition and uneven intake within a group.
  • Neglecting water—students often troubleshoot feed first when water is the limiting nutrient.