Animal Nutrition, Feedstuffs, and Digestive Physiology

Comprehensive review flashcards covering animal nutrition, nutrient biochemistry, proximate feed analysis, feedstuff classifications, and comparative digestive tract anatomy and physiology across monogastrics, ruminants, hindgut fermenters, and poultry.

What is a nutrient, and what are the six essential nutrient classes in animal nutrition?

A nutrient is a substance that provides nourishment for growth and maintenance of life. The six essential nutrient classes are carbohydrates, lipids, proteins, vitamins, minerals, and water.

What chemical elements compose carbohydrates, and how do structural carbohydrates differ from non-structural carbohydrates in plants?

Carbohydrates are composed of carbon, hydrogen, and oxygen ($C_n H_{2n} O_n$). Structural carbohydrates reside within the plant cell wall, where lignin (a non-carbohydrate polymer) binds together cellulose and hemicellulose. Non-structural carbohydrates consist of readily available sugars and starches.

How are non-structural carbohydrates classified according to saccharide units, and what is an example of each?

They are classified as monosaccharides (simple sugars that cannot be hydrolyzed into simpler compounds, e.g., glucose, fructose, galactose); disaccharides (two monosaccharides joined by a glycosidic bond, e.g., lactose = glucose + galactose, sucrose = glucose + fructose); oligosaccharides ($3$ to $15$ monosaccharide units, e.g., raffinose); and polysaccharides (long complex chains, e.g., starch, the most common form in animal feed).

What are the three structural classifications of lipids, and which fatty acids are essential?

Lipids are classified into triacylglycerols (glycerol backbone plus $3$ fatty acids; the most common dietary lipid), cholesterol (hormone precursors), and phospholipids (cellular membranes). The essential fatty acids are linoleic, linolenic, and arachidonic acids.

How do saturated, unsaturated, and polyunsaturated lipids differ in chemical structure and room-temperature physical state?

Saturated lipids have no carbon-carbon double bonds and are solid at room temperature. Unsaturated lipids possess double bonds. Polyunsaturated lipids contain more than two double bonds and are liquid at room temperature.

What chemical elements compose proteins, how are peptide chains classified by length, and how do essential amino acids differ from nonessential amino acids?

Proteins are composed of C, H, O, and N, consisting of amino acids linked by peptide bonds. They are classified as dipeptides ($2$ amino acids), tripeptides ($3$ amino acids), or polypeptides (more than $10$ amino acids). Essential amino acids cannot be synthesized by the animal body and must be supplied in the diet, whereas nonessential amino acids can be produced internally.

How are dietary minerals classified, and what specific physiological roles do the $\text{Ca:P}$ ratio, $\text{NaCl}$, iodine, and selenium fulfill?

Minerals are divided into macrominerals (required in large dietary quantities) and microminerals or trace minerals (required in smaller quantities). The $\text{Ca:P}$ ratio regulates skeletal growth; $\text{NaCl}$ maintains fundamental biological functions; iodine is essential for thyroid function; and selenium is essential for reproductive functions.

How do fat-soluble and water-soluble vitamins differ in tissue storage, and which vitamins are synthesized by ruminant microbes?

Fat-soluble vitamins (A, D, E, K) are stored in adipose tissue with fat and must be supplied in the diet. Water-soluble vitamins (C and B-complex) are not stored and require regular supplementation in monogastrics. Ruminant rumen microbiota synthesize B-complex vitamins (e.g., $\text{Vitamin B}_7$ / biotin for hooves and hair coat, and $\text{Vitamin B}_9$ / folic acid for milk production) and Vitamin K.

What primary analytical fractions are separated during the proximate analysis of feedstuffs?

Feed is first dried to remove moisture and yield Dry Matter. Dry Matter is separated into Inorganic Matter (Ash) and Organic Matter. Organic Matter is partitioned into Crude Protein, Fat (Ether Extract), and Carbohydrates (which divide into Structural carbohydrates / Crude Fiber and Non-structural carbohydrates).

What is the mathematical definition of feed digestibility, and what does Total Digestible Nutrients ($\text{TDN}$) measure?

Digestibility is calculated as: $\text{Digestibility} = \text{Nutrients consumed} - \text{Nutrients extracted via feces}$. Total Digestible Nutrients ($\text{TDN}$) represents the total calculated amount of digestible energy available to an animal for work, movement, muscle deposition, body temperature maintenance, and production.

According to the guaranteed analysis on the Super Horse 14 tag, what are the minimum and maximum percentages of crude protein, crude fat, crude fiber, and calcium?

Crude Protein is Min. $14.00\%$, Crude Fat is Min. $2.50\%$, Crude Fiber is Max. $10.00\%$, and Calcium is Min. $0.55\%$ / Max. $1.05\%$.

What mechanical and chemical digestive processes take place in the oral cavity and stomach of a monogastric animal?

In the oral cavity, mastication mechanically reduces particle size, and saliva containing salivary amylase initiates carbohydrate digestion. In the stomach, $\text{HCl}$ denatures proteins, mucus shields the epithelial wall, proteases break proteins into polypeptides, and gastric lipase continues hydrolyzing triacylglycerols (TAG) into diglycerides and free fatty acids.

What are the five anatomical regions of the monogastric stomach shown in this diagram?

Cardia (esophageal entrance), Fundus, Body, Pyloric antrum, and Pylorus (exit sphincter into the duodenum).

Which three major salivary glands are illustrated in this diagram of a pig's head?

Parotid gland, Sublingual gland, and Mandibular gland.

What specific enzymatic and chemical components are present in pancreatic juice and bile delivered to the duodenum?

Pancreatic juice contains $\text{HCO}_3^-$ (buffers acidic gastric chyme), trypsin and other proteases (hydrolyze polypeptides and peptides into amino acids), pancreatic amylase (hydrolyzes polysaccharides into disaccharides and monosaccharides), and pancreatic lipase (hydrolyzes TAGs into monoglycerides and free fatty acids). Gallbladder bile supplies bile salts, which emulsify dietary lipids.

How do enterocytes absorb and package monosaccharides, amino acids, small peptides, and lipids across intestinal villi?

Monosaccharides are absorbed via facilitated diffusion into blood; amino acids are absorbed via sodium-dependent active transport into blood; dipeptides and tripeptides enter via peptide transporters and are hydrolyzed into amino acids. Micelle-derived fatty acids, monoacylglycerols, cholesterol, and vitamins ADEK enter enterocytes, are synthesized back into triacylglycerols, re-packaged into chylomicrons, and released into the lymph.

What pre-gastric enzymatic characteristics distinguish ruminants from monogastrics, and what are the primary mechanical functions of the four stomach compartments?

Ruminants lack salivary amylase, and lingual lipase is present only in young animals. The four compartments function as follows: the reticulum selects and sorts large particles to be regurgitated and rechewed; the rumen provides an anaerobic microbial fermentation vat; the omasum absorbs water; and the abomasum acts as the true glandular stomach performing acid and enzymatic breakdown of bypass nutrients.

Identify the two ruminant stomach compartments shown here and describe how their mucosal surfaces correspond to their digestive roles.

The reticulum (left) features a honeycomb mucosal pattern that traps dense particles and coordinates regurgitation for rumination. The rumen (right) is lined with carpet-like papillae designed to absorb volatile fatty acids ($\text{VFAs}$) and ammonia ($\text{NH}_3$).

What specific digestive activities are performed by bacteria, protozoa, and fungi in the rumen, and what are the primary end-products of ruminal fermentation?

Bacteria ferment starch and structural carbohydrates (cellulose and hemicellulose); fungi break down lignin to expose cellulose and hemicellulose; protozoa engulf and digest bacteria to yield amino acids. Ruminal fermentation produces volatile fatty acids ($\text{VFAs}$: acetate, propionate, butyrate), amino acids, ammonia ($\text{NH}_3$), and gases ($\text{CH}_4$ and $\text{CO}_2$).

Where are volatile fatty acids, ammonia, and amino acids absorbed along the ruminant digestive tract?

Volatile fatty acids ($\text{VFAs}$) and ammonia ($\text{NH}_3$) are absorbed across the rumen papillae into the bloodstream. Amino acids (derived from microbial protein and rumen-undegradable bypass protein) are absorbed across the enterocytes of the small intestine.

Identify the gross digestive organs visible in this equine anatomical dissection and summarize the trade-offs of hindgut fermentation.

Visible organs include the stomach, small intestine, cecum, and large intestine. Hindgut fermenters ferment fiber post-gastrically, making them more efficient at using simple dietary carbohydrates and reducing methane and $\text{CO}_2$ losses. However, they exhibit lower utilization of microbial protein because microbial bodies synthesized in the hindgut cannot be digested or absorbed upstream in the stomach and small intestine.

What organ is highlighted by the blue circle in this diagram of the equine digestive tract, and what is its specific physiological function?

The cecum, which serves as an expansive microbial fermentation vat where anaerobic microorganisms break down structural carbohydrates.

What are the specialized organs of the avian digestive tract, and how do the crop, proventriculus, and gizzard function?

Poultry possess a beak (no teeth), esophagus, crop (storage and moistening controlled by a sphincter responding to proventriculus fullness), proventriculus (chemical stomach secreting $\text{HCl}$ and digestive enzymes), gizzard/ventriculus (muscular organ for mechanical grinding), duodenum loop with pancreas, jejunum, ileum, two ceca, colon, and cloaca. Ingesta moves back and forth between the proventriculus and gizzard.

What is the biological function of the avian cloaca and the process of antiperistalsis?

The cloaca is the common terminal opening for the digestive, reproductive, and urinary systems, eliminating both feces and urine. Antiperistalsis moves excreted urine retrogradely from the cloaca back into the colon and two ceca to reabsorb additional water.

How are domestic animals classified by natural diet (carnivore, herbivore, omnivore) and digestive anatomy (monogastric, ruminant, pseudoruminant, hindgut fermenter)?

By diet: carnivores consume animal tissue (cats); herbivores consume plant tissue (sheep, cattle, horses); omnivores consume both plant and animal tissues (dogs, pigs). By anatomy: monogastrics have a single stomach chamber (pigs, poultry); ruminants have four chambers with foregut fermentation (cattle, sheep, goats); pseudoruminants have three chambers (llamas, camels, rhinos); hindgut fermenters rely on an enlarged cecum/colon (horses, rabbits).

What defines a feedstuff, and what are the six recognized classes of feedstuffs?

A feedstuff is any material made into or used as feed by an animal (with over $2000$ products characterized). The six classes are: 1. Roughages, 2. Energy concentrates, 3. Protein supplements, 4. Mineral supplements, 5. Vitamin supplements, and 6. Feed additives.

What are the distinct technical definitions of forage, roughage, and herbage?

Forage is the total plant material available to be consumed by an animal (term commonly used in wildlife management). Roughage refers to bulky dietary components high in structural fiber / cellulose (term commonly used by livestock nutritionists). Herbage refers to vegetative plant material that excludes seeds or roots.

What two chemical composition thresholds classify a feedstuff as roughage, and what fraction of U.S. livestock feed do roughages represent?

A feedstuff must contain $>18\%$ crude fiber ($\text{CF}$) and $<70\%$ total digestible nutrients ($\text{TDN}$). Roughages account for over $50\%$ of all livestock feed fed in the U.S. ($36\%$ from pastures and rangelands, and $8\%$ harvested as hay).

How do cool-season and warm-season forages differ in optimal growing temperature and representative species?

Cool-season plants thrive between $15^\circ\text{C}$ and $18^\circ\text{C}$ ($60^\circ\text{F} - 65^\circ\text{F}$); examples include cheatgrass, kochia, triticale, and alfalfa. Warm-season plants thrive between $18^\circ\text{C}$ and $30^\circ\text{C}$ ($65^\circ\text{F} - 86^\circ\text{F}$) and are sensitive to frost; examples include bermudagrass, sagebrush, and indiangrass.

How do perennial and annual plants differ in life cycle and seasonal availability?

Perennials persist over multiple growing seasons, regrowing annually from an established root system to provide long-term availability (e.g., alfalfa, orchardgrass, tall fescue). Annuals complete their entire life cycle within a single growing season, germinating from seeds and growing rapidly (e.g., sorghum, ryegrass, corn).

What botanical and nutritional characteristics distinguish grasses from legumes?

Grasses (Gramineae) produce long, narrow leaves, hollow stems, and a single leaf sprout from seeds, typically providing $5\% - 9\%$ crude protein ($\text{CP}$) (e.g., cheatgrass, blue grama). Legumes have broader compound leaves (often trifoliate), fix atmospheric nitrogen into the soil, and are protein-rich, providing up to $25\%$ $\text{CP}$ (e.g., alfalfa, white clover).

What is the ranking hierarchy of forage nutritive value from highest to lowest?

Legumes possess higher nutritive value than grasses. The full ranking from highest to lowest is: 1. Cool season Annual, 2. Cool season Perennial, 3. Warm season Annual, and 4. Warm season Perennial.

What percentage of the Earth's land surface is rangeland, and what are the specific rangeland characteristics of Nevada?

Rangeland comprises $40\%$ of Earth's land surface. Nevada is a rangeland state with approximately $57.5\text{ million acres}$, of which approximately $86\%$ is public land. Prominent species include Wyoming sagebrush, Big Basin sagebrush, Mountain sage, and cheatgrass (an invasive species).

What is browse, which livestock consume it, and what are the anti-nutritional effects of secondary plant compounds and silica?

Browse consists of woody plant material consumed primarily by sheep, deer, and goats (and to some extent cattle and horses). Secondary plant compounds (tannins, saponins, alkaloids, terpenes) decrease digestibility or cause toxicity. Silica is a plant defense mechanism that increases tooth wear, decreases voluntary intake, and reduces digestibility.

How do hay, silage, and haylage differ in target moisture levels and preservation methods?

Hay is dried down to $\le 15\%$ moisture to prevent microbial spoilage. Silage is preserved at $30\% - 35\%$ Dry Matter via controlled anaerobic fermentation of carbohydrates into organic acids (commonly whole corn or sorghum). Haylage is a low-moisture silage ($40\% - 55\%$ moisture) and a type of wilted silage requiring high compaction for anaerobic storage.

What materials are categorized as crop residues, and what is their typical protein content?

Crop residues are low-quality forages that include cereal straws and chaff (rice, wheat, barley), grass straws, stover (leaves and stalks of corn and sorghum), corncobs, cottonseed hulls, and standing winter forages (e.g., tall fescue, orchardgrass). Straws typically contain only $2\% - 4\%$ crude protein ($\text{CP}$).

What chemical composition defines energy concentrates, and what common grains, byproducts, and fats belong to this category?

Energy concentrates contain $>70\%$ $\text{TDN}$ and $<20\%$ crude protein ($\text{CP}$), supplying energy via non-structural starches, sugars, fats, and oils. Examples include cereal grains (corn, wheat, rice, barley, oats, sorghum), milling byproducts (bran, germ meal, distillers grains, brewers grains), liquid sources (molasses, whey with $13\% - 17\%$ $\text{CP}$ on a DM basis), and rumen-protected fats (e.g., Megalac, Magnapac).

What chemical criterion defines protein supplements, and what rule governs the use of animal-origin proteins in ruminant diets?

Protein supplements must contain $>20\%$ crude protein ($\text{CP}$). Animal-origin protein sources (e.g., meat meal, meat and bone meal, dried blood plasma for weaned piglets, feather meal at $85\%$ $\text{CP}$, fish meal, seafood meal) are legally banned from ruminant rations due to the threat of Bovine Spongiform Encephalopathy (BSE).

What are the primary commercial plant protein sources, and how do rumen microbes utilize Non-Protein Nitrogen ($\text{NPN}$)?

The most important commercial plant protein sources are oilseed meals, primarily soybean meal and cottonseed meal. Non-Protein Nitrogen ($\text{NPN}$) contains nitrogen without peptide bonds (e.g., urea, biuret, ammonia). Ruminal microorganisms utilize dietary carbohydrates ($\text{CHO}$) and $\text{NPN}$ to synthesize microbial amino acids and proteins: $\text{NPN} + \text{CHO} \rightarrow \text{amino acids}$.

What is a commercial vitamin-mineral premix, and what delivery methods provide free-choice supplementation to range livestock?

A premix is a highly concentrated commercial blend of minerals and vitamins sold to feed mills and large livestock operations, requiring precise scale weighing and pre-dilution prior to mixing. Range livestock are supplemented free-choice ($24\text{ hours/day}$, $365\text{ days/year}$) via loose meal, liquid molasses mixes, pressed blocks, or tubs.

What is a feed additive, and where should a growth hormone implant be positioned in the bovine ear as illustrated?

Feed additives are non-nutritive ingredients that stimulate growth, improve feed utilization efficiency, or support animal health (e.g., ionophores like Rumensin 90, direct-fed microbials like probiotics and postbiotics, and antifungal agents). As illustrated, hormone implants must be inserted $3.8\,\text{cm}$ under the skin into the middle third of the ear between the skin and cartilage.

What are the primary physiological roles of the liver, gallbladder, and pancreas in digestion?

The liver synthesizes bile and bile salts and metabolizes nutrients. The gallbladder stores bile. The pancreas performs endocrine functions (regulating blood glucose) and exocrine functions ($84\%$ of its tissue mass is devoted to producing digestive enzymes including trypsin, amylase, lipase, and bicarbonate buffer).