Fundamentals of Animal Nutrition and Feedstuffs

Proximate Analysis of FeedstuffsThe proximate analysis system determines the major nutrient components of feeds. The concentration of these nutrients is fundamentally dependent on the dry matter (DM) content of the material. High dry matter, such as in corn, indicates a high nutrient density, whereas high water content indicates low nutrient density per unit of weight.## Categories of Dry MatterDry matter is divided into two primary categories: inorganic matter (ash) and organic matter.### 1. Water and Voluminous FeedsVoluminous feeds, such as green forage, hay, and silage, have high water content. For example, $1\,kg$ of feed might contain $20\%$ dry matter and $80\%$ water.### 2. Concentrated FeedsThese include cereal grains and have high energy levels within the dry matter. Storage quality is critical; feed exposed to hot sun or dry conditions loses palatability, while hot, humid conditions lead to molding and insect infestation. Storage should be in cool, dry locations.### 3. Ash (Inorganic Matter)Ash consists of minerals and inorganic contaminants (sand, soil). It is determined using a muffle furnace where the feed is burned; organic compounds burn away, leaving the inorganic residue. Ash provides no energy value.## Organic Matter ComponentsThe organic portion is further analyzed into four main fractions:### 1. Crude Protein (CP)Crude protein consists of true protein (chains of amino acids) and non-protein nitrogen (NPN). Proteins generally contain $16\%$ nitrogen. The nitrogen content is determined via the Kjeldahl method, which involves three steps:1. Degradation of nitrogenous compounds using $H_2SO_4$.2. Liberation of ammonia using an alkaline ($NaOH$).3. Back titration with acid.The final calculation is: $CP = N \times 6.25$.### 2. Ether Extract (EE)This fraction includes fats (saturated in animals) and oils (unsaturated in plants), as well as waxes, steroids, and glucolipids. It is measured using the Soxhlet procedure, where compounds are dissolved in petroleum ether.### 3. Crude Fiber (CF)Crude fiber represents the undigested structural part of the plant cell wall, including cellulose, hemicellulose, and lignin. Determination involves boiling the sample in acidic pH (simulating the stomach) followed by alkaline pH (simulating the small intestine) to calculate the residue.### 4. Nitrogen-Free Extract (NFE)NFE is a calculated value representing soluble carbohydrates, primarily starch and sugars. It serves as a major energy source.# Fiber Fractionation (Van Soest Analysis)While proximate analysis uses Crude Fiber, more precise methods separate cell wall components based on digestibility.1. Neutral Detergent Fiber (NDF): Includes hemicellulose, cellulose, and lignin. It is the residue left after boiling in a neutral detergent solution. NDF\% > CF\%.2. Acid Detergent Fiber (ADF): Includes cellulose and lignin. It is the residue after boiling in an acid detergent solution.3. Acid Detergent Lignin (ADL): Represents pure lignin, obtained by treating ADF with concentrated $H_2SO_4$.# Energetic Evaluation of FeedsEnergy is required for maintenance (basic life functions), growth (meat), lactation (milk), and reproduction.## Energy Terms and Flow1. Gross Energy (GE): Total energy released when feed is burned in a bomb calorimeter.2. Digestible Energy (DE): $DE = GE - \text{Fecal Energy Loss}$.3. Metabolizable Energy (ME): $ME = DE - (\text{Urinary Energy} + \text{Gaseous Energy Loss})$.4. Net Energy (NE): $NE = ME - \text{Heat Increment}$. NE is used for maintenance ($NE_m$), lactation ($NE_l$), and gain ($NE_g$).## Units and ConversionUnit of energy is the Joule ($J$). $\text{1 calorie} = 4.184\,J$.- $\text{1 kJ/g} = 1\,MJ/kg$.- Monogastrics: MJ/kg feed.- Ruminants: MJ/day.## Transformation Factors- Metabolizability (q): $\frac{ME}{GE} \times 100$.- Partial Transformation Factor (k): $\frac{NE}{ME} \times 100$. Higher feed quality increases both $q$ and $k$.- Feeding Level (i): $\frac{\text{Energy Intake}}{\text{Energy Required for Maintenance}}$. An $i$ value of $2$ means the animal is consuming twice its maintenance requirement for production.# Feed Intake RegulationRegulation is categorized into qualitative (taste, smell) and quantitative (short-term and long-term control).## Determinants1. Energy Content: Animals eat to meet calorie needs. Rabbits and poultry reduce intake as energy density increases.2. Taste and Smell: Swine and humans prioritize taste; cats prioritize smell.3. CNS Control: The hypothalamus releases anabolic peptides (Neuropeptide Y increases hunger) and catabolic peptides (CRH decreases hunger).4. Peripheral Signals:- Positive Feedback: Ghrelin (from empty stomach).- Negative Feedback: Cholecystokinin (CCK) (from full intestine) and Leptin (from adipose tissue).## Lipostatic ControlLeptin is produced by adipocytes. Greater fat mass increases leptin, which inhibits Neuropeptide Y to decrease feed intake. Fatty Cow Syndrome occurs when overfeeding leads to high fat mobilization and ketosis.# Protein Evaluation Systems## Monogastric AnimalsMonogastrics utilize true protein (amino acids).1. Chemical Score: Ratio of essential amino acids (EAA) in feed vs. a standard protein.2. Biological Value (BV): $\frac{\text{Retained N}}{\text{Absorbed N}}$.3. Net Protein Utilization (NPU): $\frac{\text{Retained N}}{\text{N Intake}}$.4. Protein Efficiency Ratio (PER): $\frac{\text{Body weight gain (g)}}{\text{Protein intake}}$.5. Limiting Amino Acids: Lysine is typically the first limiting AA in cereals.## Ruminant AnimalsRuminants utilize a system based on Metabolizable Protein (MP), which includes rumen-undegraded protein (UDP or bypass protein) and microbial protein synthesized in the rumen.- MPN: Nitrogen-dependent metabolizable protein.- MPE: Energy-dependent metabolizable protein (based on Fermentable Organic Matter, FOM).$1\,kg$ of FOM supplies energy for $160\,g$ of microbial protein.# Antinutritive Substances and Food Safety## Common Antinutrients1. Protease Inhibitors: (e.g., Trypsin inhibitors in raw soybeans) cause pancreatic hypertrophy and growth depression. Heat treatment inactivates them.2. Lectins: Glycoproteins that bind intestinal epithelium, reducing absorption.3. Saponins: Steroid glycosides that cause foaming (bloat) and reduce palatability.4. Tannins: Polyphenols that bind proteins and minerals. In ruminants, they can increase bypass protein in moderate amounts but are toxic at high levels.5. Phytic Acid: Stores phosphorus in plants; binds $Ca, Mg, Fe, Zn$, making them unabsorbable in monogastrics.6. Gossypol: Found in cottonseed; toxic to monogastrics, causes respiratory distress.## Deterioration- Hydrolytic Rancidity: Fungi/bacteria lipase convert TGs to FAs. Non-toxic but reduces palatability.- Oxidative Rancidity: Auto-oxidation creates free radicals. Destroys Vitamins A and E. Harmful if Peroxide Number > 20-30.## Mycotoxins- Zearalenone (ZEN): Estrogenic metabolite from Fusarium; causes infertility and abortion in swine.- Aflatoxin: From Aspergillus; carcinogenic and hepatotoxic. Found in humid climates.- Fumonisin: Causes Leukoencephalomalacia in horses and pulmonary edema in swine.# Minerals and Electrolyte Balance## Calcium ($Ca$) and Phosphorus ($P$)- Functions: Bone structure, blood clotting, muscle contraction.- Deficiency: Rickets (young), Osteomalacia (adult), Milk Fever (parturient cows).- Ca:P Ratio: Optimal is $2:1$ to $1.5:1$. High phosphorus can induce secondary hyperparathyroidism.## Magnesium ($Mg$)- Function: Enzyme cofactor. Deficiency causes Grass Tetany (hyper-excitability, convulsions) in ruminants grazing lush spring pasture high in potassium.## Electrolytes ($Na, K, Cl$)- SID (Strong Ion Difference): $[Na^+] + [K^+] - [Cl^-]$. Low SID causes metabolic acidosis.- DCAD (Dietary Cation-Anion Difference): $[(Na + K) - (Cl + S)] / 100\,g\,DM$.- Lactating Cows: Positive DCAD ($+25$ to $+40\,mEq/100\,g$) maximizes milk yield.- Dry Cows: Negative DCAD aids in preventing milk fever by mobilizing bone calcium.## Trace Minerals- Iron ($Fe$): Prevents anemia; sow milk is deficient, so piglets require injections.- Zinc ($Zn$): Requirement is $40-80\,mg/kg$. Deficiency causes Parakeratosis.- Copper ($Cu$): Essential for melanin and ligaments. Sheep are highly susceptible to toxicity.- Selenium ($Se$): Antioxidant (Glutathione peroxidase). Deficiency causes White Muscle Disease.# Vitamins## Fat-Soluble- Vitamin A: Essential for night vision and epithelial health. In deficiency: Xerophthalmia, night blindness.- Vitamin D: $\text{1000-3000 IU/day}$ for monogastrics. Regulates $Ca$ absorption.- Vitamin E: Antioxidant. Deficiency: Encephalomalacia (chicks), Mulberry Heart (pigs).- Vitamin K: Blood clotting. Antagonized by dicoumarol in moldy sweet clover.## Water-Soluble- $B_1$ (Thiamine): Deficiency causes Cerebrocortical Necrosis (CCN) and Chastek paralysis.- $B_2$ (Riboflavin): Deficiency causes Curled Toe Paralysis in chicks.- $B_{12}$ (Cobalamin): Contains Cobalt. Required for nucleic acid synthesis.- Vitamin C: Synthesized by most livestock except primates and guinea pigs (requires $5\,mg/kg$ LW/day). Prevents Scurvy.# Feedstuffs## Cereal Grains- Corn: Highest energy ($DE = 15\,MJ/kg$). Lowest CP ($10\%$).- Wheat: Highest CP ($14\%$). Contains pentosans (NSP).- Barley: Contains $\beta$-glucans. Improves lard hardness in swine.## Grain Legumes- Soybean: Highest biological value. Contains Trypsin Inhibitors. $EE = 20\%$.- Field Pea: Used for poultry fattening. Improves lard hardness.## Milling By-Products- Wheat Bran: High fiber ($10-12\%$), P source ($11\,g/kg$). Laxative effect.- Wheat Germ: Rich in Vitamin E and polyunsaturated fats.## Forage Preservation- Haymaking: Drying to $15\%$ moisture. Loss of carotene is significant.- Silage: Anaerobic fermentation. Optimal pH is $4.0-4.2$. Lactic acid is the primary acid.- Corn Silage: $\text{DM} = 30-35\%$, $\text{CP} = 9-10\%$. Palatable energy source for ruminants.## Non-Protein Nitrogen (NPN)- Urea: $1\,g$ urea = $2.32\,g$ CP equivalent. Feed only if protein balance ($MPN - MPE$) is negative. Max dose: $20-30\,g / 100\,kg$ Body Weight/day.