Introduction to Nutrients
Introduction to Nutrients and Digestion
Learning Objectives
Describe differences in nutritional requirements among common domestic species.
Describe the basic nutrients in food.
Describe macronutrients, including common sources and uses of proteins, carbohydrates, and lipids.
Describe micronutrients, including common sources and uses of minerals and vitamins.
Describe methods of mineral supplementation.
Describe non-protein nitrogen (NPN) sources and their usefulness to ruminants.
Be able to calculate energy needs.
Eating Patterns
Herbivore: Diet is comprised of plant tissue.
Omnivore: Diet is comprised of both plant and animal tissue.
Carnivore: Diet is comprised of animal tissue.
Obligate carnivore: MUST eat animal tissue (e.g., cats).
Hypercarnivore: More than 70\% of diet is animal tissue.
Mesocarnivore: 50-70\% of the diet is animal tissue.
Hypocarnivore: Less than 30\% of the diet is animal tissue.
Digestion Types
Herbivore Digestion (Ruminants & Hind-Gut Fermentors)
Host (Cow, Sheep, Horse):
Finds forage.
Provides a fermentation vat (Rumen/cecum, Large intestine).
Buffers fluid via saliva and intestinal secretions.
Removes end products.
Controls temperature.
Microbes (Bacteria, Fungi, Protozoa):
Perform extracellular digestion.
Convert carbohydrates to volatile fatty acids (VFAs): Acetate (2-carbon), Butyrate (4-carbon), Propionate (3-carbon).
Degrade and synthesize amino acids.
Synthesize B vitamins.
Ruminant Digestion
Forestomachs (relative capacities):
Rumen: 52\% of capacity.
Reticulum: 2.5\% of capacity (often grouped within Rumen).
Omasum: 6\% of capacity.
Abomasum: 8\% of capacity.
Lower Digestive Tract (relative capacities):
Small Intestine: 28\% of capacity.
Cecum, Colon (Large Intestine): 14\% of capacity.
Nutrient Breakdown and Absorption:
Fibre, Starches, and Sugars are converted by microbes into VFAs.
VFAs (acetate, butyrate, propionate) are absorbed directly through the rumen wall.
Propionate is converted by the liver to glucose, providing an important energy source.
VFA formation varies depending on diet and microbe population.
VFAs provide 60-80\% of the cow's energy.
A healthy microbial flora is essential for this process.
Protein is degraded to ammonia, which then goes through the urea cycle to be turned into protein for the cow.
Efficient Digestors:
Fermentation occurs towards the start of the digestive tract.
More tolerant of poor-quality diets.
Do not require a dietary source of essential amino acids or essential fatty acids.
Do not routinely require B vitamin supplementation, as microbes synthesize them.
Hind Gut Fermentors (e.g., Horses)
Anatomy (relative capacities):
Stomach: 8\% of capacity.
Small Intestine: 24\% of capacity.
Large Intestine (Cecum, Large Colon, Small Colon, Rectum): 78\% of capacity.
Digestion Characteristics:
Fermentation occurs primarily in the large intestine.
Only VFAs, minerals, and water are absorbed in the large intestine.
Dependent on the diet to supply essential amino acids and vitamins, as microbial synthesis occurs too late in the tract for host absorption.
Large intestine fermentation allows capture of energy from plant cellulose and other plant fibers.
Omnivore Digestion (e.g., Pigs)
Anatomy (relative capacities):
Stomach: 29\% of capacity.
Small Intestine: 24\% of capacity.
Cecum, Colon (Large Intestine): 37\% of capacity.
Digestion Characteristics:
Require dietary B vitamins.
Require dietary essential fatty acids (alpha-linolenic, linoleic).
Require essential amino acids (methionine, cysteine, lysine are often limiting).
Dietary carbohydrates are the important blood glucose source.
Have limited ability to digest fiber.
Carnivore Digestion (e.g., Cats)
Specific dietary requirements.
Essential dietary nutrients include:
B vitamins.
Alpha-linolenic, linoleic, and arachidonic acid (arachidonic acid is found in animal fats).
Essential amino acids.
Taurine (a sulfonic amino acid, synthesized in other species from cysteine, but essential in cats).
Protein is a major source of blood glucose.
Very limited fiber digestion.
Species-Specific Nutrient Needs
Most specific nutrient needs: Carnivores (especially obligate carnivores like cats).
Least specific nutrient needs: Ruminants, due to microbial synthesis of many essential nutrients.
What are Nutrients?
Nutrients are substances that provide nourishment essential for the maintenance of life and for growth.
Six main classes of Nutrients:
Water
Minerals
Vitamins
Proteins
Fats (Lipids)
Carbohydrates
Dietary Sources of Energy:
Carbohydrates are digested into Glucose.
Fats are digested into Fatty Acids.
Proteins are digested into Amino Acids.
Carbohydrates
Energy Source: Provide approximately 3.5 \text{ kcal/g}.
Essentiality: Can be completely replaced by protein and lipid as an energy source for maintenance, meaning they are not strictly essential for adult maintenance.
Conditional Essentiality: However, during growth, gestation, and lactation, dietary carbohydrates are required for dogs and cats.
It takes too much energy to synthesize glucose from alternate sources (proteins or lipids).
Normal protein intake may be inadequate to support gluconeogenesis (synthesis of glucose from non-carbohydrate sources).
Therefore, carbohydrates are considered conditionally essential in these physiological states.
Types of Carbohydrates
Sugars (Non-Structural Carbohydrates):
Lactose: Most common mammalian disaccharide.
Sucrose: Most common plant disaccharide.
Fructose.
Starches (Non-Structural Carbohydrates):
Highly digestible.
Storage polymer of glucose.
Often the primary source of energy in foods.
Inexpensive.
Fibre (Structural Carbohydrates):
Structural glucose polymer (cellulose).
Polymers of other saccharides (gums, lignin).
Fiber is not digestible for monogastrics.
Lignin (found in wood) is difficult even for ruminant microbes to digest.
Starches and Digestibility
Common Sources: Grains and potatoes.
Small Animals: Usually cooked and ground to improve digestibility.
Example: Grinding corn into a meal increases its digestibility from 79\% to 94\%.
Uncooked Starch: Ferments in the large intestine, generating increased water intake, which can lead to complications like diarrhea.
Digestion Process: Starch is broken down into glucose by pancreatic enzymes (amylase) and digestive cells of the small intestine.
Starches and Food Texture
Extruded Pet Food Diets (Dry Foods):
Ground, heated with steam, forced through holes, and cut into shapes.
Gelatinized starch helps hold the food together and gives it texture.
Gravies and Sauces (Wet Foods):
Dextrins, corn syrup, and starches are used.
Dextrins are polymers of glucose, used to thicken gravy.
Fibre Types
Ability to be fermented by bacteria:
Fermentable
Non-fermentable
Ability to dissolve in water:
Soluble
Insoluble
Fibre Measurement
Different methods measure different components of fiber:
Crude Fibre (CF):
Measures insoluble fiber.
Mainly lignin and cellulose; can underestimate hemicellulose.
Historically used on labels only provides a partial picture of fiber content.
Neutral Detergent Fibre (NDF):
Measures lignin, cellulose, and hemicellulose.
Acid Detergent Fibre (ADF):
Measures lignin and cellulose.
Hemicellulose can be calculated as \text{NDF} - \text{ADF}.
Nitrogen Free Extract (NFE):
Digestible starches and soluble fibers.
Calculated as 100\% - (\text{Crude Protein} + \text{Crude Fat} + \text{Crude Fibre} + \text{Moisture} + \text{Ash}).
Total Dietary Fibre (TDF):
Measures all fiber (soluble and insoluble).
Importance of Fiber
Energy Source for Herbivores: Major energy source only in herbivores, where it is fermented to VFAs (acetate and butyrate primarily). Propionate also produced, but its absorption and utilization vary.
Pathogen Control: VFAs stop the growth of some pathogens.
Colon Health: Butyrate is the preferred energy source for colon epithelial cells.
GI Function: Required for normal gastrointestinal (GI) function in all species; both physical properties and VFA production are important.
Fecal Consistency: Helps maintain normal fecal consistency.
Fiber speeds intestinal transit in dogs with slow or normal transit.
Fiber slows transit in dogs with rapid intestinal transit.
Maintains stool quality (size and consistency).
General Health: A low level (typically < 5\% fiber on a dry matter basis) is often included in pet foods to promote GI health.
Disease Management:
In dogs, an increase in fiber is used to treat colitis.
In cats, fiber can be used to help manage constipation.
Fiber as Prebiotics
Prebiotics: Substances that selectively promote the growth of beneficial bacteria.
Many prebiotics are types of dietary fiber made from oligosaccharides (e.g., fructooligosaccharides, pectic oligosaccharides).
These are not digested by mammalian enzymes.
Preferentially fermented by beneficial microbes.
Bacterial fermentation of fiber creates short-chained fatty acids.
These provide 70\% of the energy needed by enterocytes (intestinal cells).
May be added to foods to promote gut health.
Lipids
Fats: Solid at room temperature, generally composed of saturated fatty acids.
Oils: Liquid at room temperature, mostly composed of unsaturated fatty acids.
Many lipids are triglycerides.
Energy Dense: Lipids are very energy-dense, providing approximately 8.5 \text{ kcal/g}.
Compare to carbohydrates (3.5 \text{ kcal/g}) and proteins (3.5 \text{ kcal/g}.)
Types of Lipids
By Chain Length
Long Chain Triglycerides (LCTs):
Most common lipid in the diet.
Sources: Canola or soybean oil, animal fats.
Transported from the small intestine in the lymphatics.
Medium Chain Triglycerides (MCTs):
More rapidly hydrolyzed (broken down) in the small intestine than LCTs.
Transported in the portal vein (directly to the liver).
A small component of common diets.
Source: Coconut oil is a good source.
Therapeutic Uses in Monogastrics:
When there are problems digesting LCTs.
To boost brain function.
By Carbon Bonds
Saturated:
No double bonds in their carbon chains.
Source: Tallow (animal fat) is about 40\% saturated.
Unsaturated:
Mono-unsaturated (MUFA): One double bond.
Sources: Olive, avocado, safflower, canola, sunflower oils (often > 50\% monounsaturated).
Poly-unsaturated (PUFA): Several double bonds.
Sources: Many plant oils. Fish oil is rich in omega-3 fatty acids.
Trans Saturated:
Artificial fats made when plant fats are hydrogenated (hydrogen atoms added in an unnatural manner).
Can block normal metabolism in the body.
Function of Lipids
Energy Source: More than twice the energy density of carbohydrates or proteins.
Supplies 60\% of the body's energy needs at rest.
Stored as adipose (fat) tissue.
Insulation and Protection: Adipose tissue provides thermal insulation and protects organs.
Structural: A key component of cell membranes.
Precursors: Precursors of eicosanoids and prostaglandins, which are signaling molecules important in cell regulation and inflammation.
Vitamin Carriers: Carry fat-soluble vitamins (A, D, E, K).
Palatability: Contribute flavor, aroma, and texture to food.
Essential Fatty Acids (EFAs)
Mammals cannot interconvert or synthesize omega-3 and omega-6 series fatty acids from simpler precursors; therefore, they need a dietary source of each.
Omegas: Polyunsaturated fatty acids, named for the carbon location of the first double bond (e.g., omega-6 vs. omega-3).
Ruminants: Have no dietary essential fatty acid requirement because EFAs are synthesized in the rumen by microbes.
Omega 3 Fatty Acids
Alpha-linolenic acid (ALA) is the essential source in the diet.
Precursor of anti-inflammatory mediators (eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)).
Sources: Fish oil, canola oil, flax (linseed oil), marine microalgae.
Omega 6 Fatty Acids
Linoleic acid is the essential dietary source.
Required to make inflammatory mediators.
Cats also require arachidonic acid, as they cannot elongate linoleic acid sufficiently.
Sources: Chicken fat, sunflower oil.
Conversion of ALA to EPA/DHA
Dogs: Can convert ALA to EPA and DHA, but conversion rates are relatively low.
Cats: Have very limited ability to convert ALA to EPA and DHA.
Anti-inflammatory Benefits: If the goal is to provide anti-inflammatory benefits from omega-3 fatty acids, ingredient sources already containing EPA and DHA (e.g., fish oil or marine microalgae) would be chosen over ALA sources, especially for cats.
Proteins
Proteins are groups of amino acids joined together by peptide links in different quantities and sequences.
Protein quality is affected by the types and balance of amino acids they supply.
Digestion: Breaks proteins into their constituent amino acids, which are then used by the body for various functions.
Excess Protein: If protein intake exceeds requirements, it is deaminated (amino group removed).
The ammonia produced is converted to urea and excreted, primarily by the kidneys.
The remaining carbon skeleton is utilized for energy or converted to fat for storage.
Function of Proteins
Structural Components: Build or replace body tissue; integral part of body organs, tissues, hair, nails, and cartilage.
Enzymes: Function as biological catalysts (e.g., digestive enzymes).
Hormones: Act as signaling molecules (e.g., insulin).
Carriers: Act as transport molecules (e.g., hemoglobin carrying oxygen and CO2).
Immune System: Part of the immune system (e.g., immunoglobins, antibodies).
Energy Source: Provide approximately 3.5 \text{ kcal/g}.
Essential Amino Acids (EAAs)
Dietary Essential Amino Acids: Cannot be synthesized by the mammal in sufficient quantities and must be supplied by the diet.
The specific essential amino acids vary with the species.
Cats have the greatest number of dietary essential amino acid requirements (11).
Dietary Non-Essential Amino Acids: Do not need to be supplied by the diet as they can be synthesized by the body from precursors.
Conditionally Essential Amino Acids: Required in certain physiological states (e.g., growth, disease, specific metabolic demands) when synthesis may not meet increased demand.
Measuring Protein
Crude Protein (CP):
Labels are required to report the crude protein content of the diet.
Calculated by measuring the total nitrogen content of the diet (\text{Protein} \approx \text{Nitrogen} \times 6.25).
Includes both true protein and non-protein nitrogen (NPN) sources (ammonia, nitrates, urea).
Infamously, melamine was added to protein meals to falsely inflate nitrogen content.
Melamine Scandal
Melamine is a plastic containing nitrogen.
Waste plastic was ground and added to protein meals in China to artificially increase the measured protein content.
These contaminated protein meals were used in baby food and pet food.
Melamine breaks down to produce cyanuric acid.
The combination of melamine and cyanuric acid is highly toxic to the kidneys, leading to renal failure.
This scandal led to improved feed testing, moving beyond just testing for common toxins.
Reputable pet food companies now test feed using spectroscopy and other advanced methods to ensure ingredients are normal and safe.
Protein Digestibility
Apparent Digestible Protein:
Calculated as (\text{Crude Protein Eaten} - \text{Crude Protein in Feces}) / \text{Crude Protein Eaten}.
Confounded by protein fermentation in the large intestine, as changes in amino acids in the large intestine affect apparent digestibility but are not available to the animal.
Ileal Digestible Protein (aka, True Digestible Protein):
Calculated as (\text{Crude Protein Eaten} - \text{Crude Protein at Ileum}) / \text{Crude Protein Eaten}.
Highly accurate because it is not confounded by protein fermentation in the large intestine, thus representing the amino acids absorbed and available to the animal.
However, it is a highly invasive measurement to obtain.
Biological Value (BV) of Protein
Definition: The usefulness of absorbed protein in building new tissue.
Determinant: Determined by the amino acid composition relative to the animal's needs.
High BV: If the amino acid composition of dietary protein is similar to that of the animal's tissue, it has a high biological value.
Examples: Protein from meat (not bone), liver, heart, milk (casein and whey) have an amino acid composition that parallels an animal's needs and are readily converted to tissue protein.
Zero BV: If a protein is completely missing an essential amino acid, it cannot be used to make body protein, resulting in zero biological value.
Mixing Sources: Protein sources may be mixed to balance amino acid deficiencies in one protein with amino acids from another, increasing the overall biological value of the diet.
Ruminants and Protein
Overall Nitrogen Requirement:
Comprised of Protein (from diet) and Non-Protein Nitrogen (NPN) (from diet and saliva).
Ruminants also have a sulfur requirement so that sulfur-containing amino acids can be synthesized by microbes.
Ruminal Microbes Functions:
Digest dietary proteins, with the amount depending on the protein's structure (e.g., availability).
Degrade and interconvert amino acids.
Can synthesize amino acids using:
A non-protein nitrogen (NPN) source (e.g., urea, ammonia).
A carbohydrate skeleton.
Dietary energy (typically from grain or molasses).
Crucially, no amino acid is essential in the diet for ruminants due to microbial synthesis.
Limitations on Feeding NPN
Microbes and undigested dietary protein leave the rumen and are digested in the small intestine, making amino acids available to the host.
General Rule for Ruminants: Typically need at least two-thirds of their nitrogen intake as dietary protein.
This is because there may not be enough dietary energy to synthesize all the necessary amino acids solely from NPN.
High-producing ruminants (e.g., lactating dairy cows) have higher protein requirements, as microbes alone cannot make enough to meet their needs.
Remainder as NPN: The remaining portion of the nitrogen requirement can be met by non-protein nitrogen (NPN).
Common NPN Sources: Ammonia and urea.
Ammoniated feeds: Can be highly toxic if poorly mixed or if too much ammonia is injected into feed (e.g., hay) without proper incorporation.
NPN Toxicosis (Ammonia Toxicity)
Ammonia in the rumen is generally absorbed into systemic circulation and detoxified by the liver via the urea cycle.
Mechanism of Toxicity: If the rate of ammonia production exceeds the ability of rumen microbes to utilize it, ammonia builds up in the rumen.
This overwhelms the liver's detoxification capacity.
Leads to elevated blood ammonia levels, which are toxic.
Urea Toxicity
Urea is widely used as an NPN source and is generally considered safer than ammonia.
Minor Excesses: Can lead to decreased production.
Major Urea Excess: Highly toxic, leading to clinical signs such as:
Muscle tremors.
Salivation.
Bellowing.
Bruxism (teeth grinding).
Incoordination and weakness.
Rapid death, often occurring close to the urea feeder due to rapid consumption.
Monogastrics and Protein
Species: Horses, omnivores (e.g., pigs, dogs), and carnivores (e.g., cats).
Dietary Requirement: Require a dietary source of certain amino acids because they cannot synthesize them (or not enough).
Tryptophan, lysine, and methionine are often of major concern as they can be limiting in diets.
Bacterial Fermentation: While bacterial fermentation occurs in the large intestine, any amino acids produced by these microbes cannot be digested or absorbed by the host because amino acid absorption primarily occurs in the small intestine.
Common Essential Amino Acids for Monogastrics: Arginine, Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine.
Specific Essential Amino Acids
Methionine: A sulfur amino acid (also cystine).
Essential in hair protein (keratin) synthesis.
Richly present in animal protein sources, eggs, and fish.
Arginine: Key role in the immune system and urea excretion.
Beneficial in heart and kidney disease.
Richly present in animal tissues and gelatin.
Lysine: Major role in protein synthesis.
Deficiency slows growth in puppies and kittens.
Meat and milk are good sources.
Cats and Taurine
Essential Amino Acid: Taurine is a dietary essential amino acid in cats (vs. conditionally essential in some other species).
Physiological Basis:
Cats have an obligatory loss of taurine in bile for conjugation, which other species can use glycine for as well.
Taurine is not synthesized in sufficient quantities in cats. Most species synthesize taurine from methionine via cysteine.
Taurine Functions:
Required for retina, heart, and brain health.
Important for reproduction functions.
Acts as an antioxidant.
Deficiencies: Can lead to serious health issues:
Reproductive failure.
Retinal degeneration (causing blindness).
Dilated cardiomyopathy (DCM), a severe heart condition.
Common Occurrence: Often seen when cats are fed dog food, which is typically deficient in taurine for felines.
Taurine and Dilated Cardiomyopathy (DCM) in Dogs
Conditionally Essential?: Taurine can be conditionally essential in some dogs.
Breed Connection: A connection exists between certain breeds of dogs (e.g., Golden Retrievers, American Cocker Spaniels) and the development of DCM, which may respond to taurine supplementation in some cases.
Dietary Concerns: Recent concern links certain types of diets (e.g., boutique, exotic ingredient, grain-free) to the development of DCM.
While many dogs on these diets did not have low taurine levels, clinical signs of DCM often improved after a diet change.
This suggests potential issues with ingredient processing, digestibility, or interaction with other nutrients affecting taurine availability or metabolism, even if taurine levels appear normal.
Protein Deficiency
Cause: Inadequate protein intake or a lack of essential amino acids in the diet.
Impact: Protein is required for all aspects of growth, production, and maintenance.
Susceptibility:
Growing animals are most susceptible due to their higher protein requirements and often less successful at competing for food, leading to reduced growth.
Heavily lactating dairy cows can experience severe deficiency due to very high dietary protein requirements that microbes alone cannot meet, resulting in poor milk production and possibly excessive weight loss.
Assessment: Muscle condition score (MCS), as advocated by WSAVA Global Nutrition Committee, helps assess muscle loss independent of body fat, noting that animals can have significant muscle loss even if overweight.
Minerals
Definition: Minerals are micronutrients, meaning they are only required in small quantities in the diet (usually less than 5\%).
Energy: They are not a significant source of energy.
Role: All minerals have some structural role, and many act as co-enzymes.
Essentiality: Despite being present in small amounts, they are essential to physiological function.
Types of Minerals
Macrominerals (required in larger quantities):
Requirements are often expressed as a percentage of the diet.
Includes: Calcium (Ca), Phosphorus (P), Potassium (K), Sodium (Na), Magnesium (Mg).
Microminerals (Trace Minerals) (required in smaller quantities):
Requirements are often expressed as parts per million (ppm) or milligrams per kilogram (mg/kg).
Includes: Iron (Fe), Zinc (Zn), Manganese (Mn), Copper (Cu), Iodine (I), Selenium (Se).
Individual Minerals and Their Importance
Potassium (K)
Role:
Maintains cell shape.
Major role in cardiac function.
Involved in nerve conduction and muscle contraction.
The majority of potassium in the body is found inside cells.
Source:
Widely distributed in foods.
Leafy plants are rich sources, particularly roughages like grasses and alfalfa.
Grains may be inadequate.
Supplementation:
Rarely a nutritional problem in herbivores when on pasture or fed good quality forage.
May need to be supplemented in pet foods, often as potassium salts.
Problems:
Commonly deficient in sick animals that are off feed.
Deficiency signs: Muscle weakness, cardiac rhythm disturbances, pica (craving for non-food items).
Diarrhea in small animals can lead to high potassium losses.
Some heart or kidney diseases demand modification of food-supplied amounts due to altered metabolism or excretion.
Excessive acidification of urine can also be related to potassium balance.
Sodium (Na)
Role:
Major contributor to the osmotic pressure of extracellular fluid, controlling blood volume.
Major role in cell's energy metabolism.
Source:
Sodium chloride (NaCl, common salt) of mineral or marine origin.
Fish, eggs, poultry by-product meal, and soy isolates.
Supplementation:
Sodium is the only mineral for which there is a clearly defined appetite; animals actively seek it out when deficient.
Added directly to food or offered as part of a mineral block.
Increases palatability of feed.
Deficiency:
In cases of deficiency, animals typically seek out salt.
After months of deficiency: Reduced feed intake, reduced growth/lactation, polyuria/polydipsia (PU/PD - increased urination/drinking).
Toxicity:
More than 2\% salt in the diet can be toxic.
Toxicity is significantly affected by water availability; limited or intermittent access to water exacerbates the risk.
Pigs are particularly susceptible.
Signs: Diarrhea, PU/PD, decreased production.
Salt Toxicity (Hypernatremia and CNS Disease):
Occurs with excess salt and/or limited/intermittent water.
Neurological signs: Wandering, blindness, deafness, head-pressing, dog-sitting posture.
At least 2 days are typically required for signs to develop.
Chlorine (Cl)
Closely associated with sodium in maintaining osmotic pressure, regulating acid-base equilibrium, and cell metabolism.
Usually present in sufficient amounts if the sodium requirement is being met, as they are often consumed together as NaCl.
Calcium (Ca)
Role:
Most important in the formation of bones (99\% of the body's calcium is retained in bones and teeth).
Essential for muscle function and nerve transmission.
Crucial for blood clotting.
Source:
Bone meals, milk, dairy products.
Grains and meat are generally poor sources.
Supplementation:
Calcium supplementation is often provided for high-risk individuals (e.g., growing animals, pregnant/lactating animals).
Vitamin D is important in regulating calcium absorption and metabolism.
Maintaining a proper balance of Ca and P is essential.
Calcium Homeostasis
Serum calcium levels are tightly regulated by feedback mechanisms involving:
Parathyroid Hormone (PTH): Secreted by the parathyroid gland, increases serum calcium.
Vitamin D: Facilitates calcium absorption from the small intestine and affects bone remodeling.
Acute Calcium Deficiency (Hypocalcemia)
Timing: Usually seen in late pregnancy and early lactation, periods of high physiological demand.
Late pregnancy: Particularly in sheep and small dogs with large litters (many fetuses).
Early or rapidly rising lactation: Dairy cows after parturition (known as