Monogastric Digestion Overview

Study Notes

A nutrient is a substance essential for life, found in feed. Feed components include ash, water, carbohydrates (nitrogen-free extract and cellulose), crude protein, and ether extracts. Nutrient proportion analysis is determined via proximate analysis.
Growth involves accumulation of lean tissue and fat. Lean growth requires energy and amino acids, while fat growth solely requires energy.
Feed formulation depends on animal nutritional needs and feed composition, aiming for the cheapest option.
Digestion begins in the mouth with chewing, increasing surface area for enzymatic breakdown. Saliva initiates carbohydrate digestion in pigs due to amylase.
The stomach maintains a pH <4, achieved by HCl produced by parietal cells. This acidic environment kills pathogenic bacteria like Escherichia coli. Pepsinogen, produced by chief cells, requires a pH of 1.5-3.5 to be activated into pepsin, thus initiating protein digestion.
The stomach also performs mechanical digestion through churning. Goblet cells in the stomach lining produce mucus. Regions include the cardiac (mucus production), fundic (HCl, mucus, and pepsinogen secretion), and pyloric (mucus secretion) regions.
H. pylori colonizes the stomach, converting urea into ammonia and carbon dioxide, neutralizing its immediate environment. Piglets may require added acidity in their diets.

Starch is composed primarily of alpha 1-4 linkages with some alpha 1-6 linkages. Monogastrics have endogenous enzymes (amylase) for starch degradation.
Cellulose is composed of beta 1-4 linkages. Monogastrics lack the enzyme cellulase, making cellulose degradation problematic.

Proteins are broken down into polypeptides by pepsin in the stomach. Peptidases further degrade polypeptides into amino acids, which are then absorbed.
Proteins that escape digestion in the small intestine enter the large intestine. Microbial deamination in the large intestine leads to the formation of toxic metabolites.
Ileal amino acid digestibility (apparent digestibility) overestimates protein utilization by not accounting for microbial activity, fermentation, and endogenously produced and fermented proteins. True ileal digestibility considers basal and feed-specific losses.

Energy is derived from carbohydrates, fats, and proteins. Degradable carbohydrates are converted into glucose and short-chain fatty acids (SCFA/VFA).
Energy is required for physical and mental tasks and is measured in Joules or calories, with 1 calorie being equivalent to 4.14 Joules.
Factors affecting feedstuff energy content include age, degree of saturation, free fatty acids, and chain length.

Minerals are inorganic elements essential for body functions. Bioavailability of minerals varies, potentially impacted by factors like oxalate or phytate.
Calcium (Ca++) is the most abundant mineral, primarily found in bones and teeth. Other relevant macro-minerals include potassium, phosphorus, chloride, sodium, sulphur, and magnesium. Micro-minerals such as iron, iodine, and selenium also play crucial roles.
Adequate Ca++ and P ratios (e.g. 2:1.5 for Mg and P) are essential for optimal absorption and utilization. Deficiency symptoms include problems like osteomalacia.
Several factors influence mineral absorption, such as the form of the mineral, pH, and the presence of other nutrients.

Feed formulation considers energy and nutritional needs of the animal. Knowledge of feed composition is utilized to formulate a balanced diet with lowest possible cost.
Methods like Near Infrared Spectrophotometry (NIR) analyze feed composition for efficient formulation.

Chick digestion: Food is consumed via the beak and transported to the crop for moistening before undergoing chemical breakdown in the proventriculus (glandular stomach), followed by mechanical breakdown in the gizzard. The cloaca is a common opening for the digestive, reproductive, and urinary tracts.
Hind-gut fermentors (e.g., the horse) have enlarged large intestines for microbial breakdown of cellulose into volatile fatty acids, which the animal utilizes. Microbial protein is not utilized fully as in ruminant species.