Farm Animal Metabolism and Nutrition

serous saliva containing -amylase from
the parotid salivary glands. Swine, like
most farm species, do not have an
abundant supply of salivary amylase (Vonk
and Western, 1984). The ingesta is formed
into a bolus by the tongue and swallowed.
The importance of salivary amylase in
those species that posses it is poorly
defined and probably under-appreciated.
Typically, it is assumed that salivary
amylase is inactivated rapidly by the acid
environment in the stomach. It requires a
measurable time for boli entering the
stomach to be disrupted by the churning
action of the stomach and, hence, stomach
acid slowly penetrates the boli. In humans
consuming a starchy meal, 40% of the
starch is digested in the stomach (Vonk and
Western, 1984). Salivary amylase activity
eventually is overpowered by pancreatic
amylase in terms of starch digestion per se.

The extent of salivary amylase activity

expressed in the stomach, however, would

be expected to affect the viscosity of

digesta in animals consuming starchy

feeds. Viscosity is a factor in rates of

passage and digestion. Thus salivary

amylase could affect practical factors as the

glycaemic index and feed intake.

There are no other carbohydrases added

to the ingesta until the digesta enters the

small intestine. Thus the acidic material

entering the small intestine from the

stomach will contain native starch, dextrins

resulting from partial digestion of starch and

other saccharides contained in the feeds, e.g.

sucrose, lactose, mannose, fructose, glucose,

trehalose, chitin and cellulose. The carbo-

hydrates must be digested to their mono-

saccharide units for absorption.

Continued processing of the carbo-

hydrates requires interaction of the digesta

Glucose Availability and Associated Metabolism 125

Extracellular Intermatrate

Dietary substrate enzymes products/substrates Intestinal mucosal enzymes Absorbed form

Carbohydrates

Amylose

Amylopectin

Glycogen

α-Amylase

(saliva, pancreas)

α-Amylase

(saliva, pancreas)

Maltose

Isomaltose

α1–4 Oligosaccharides

Maltose

Isomaltose

α-Limit dextrins

Maltose,

Maltotriose

α1–4 Oligosaccharides

Maltase

Isomaltase

Glucoamylase

Maltase

Isomaltase

Isomaltase

Glucose

Glucose

Glucose

Glucose

Glucose

Glucose

Glucose

Glucose

Fructose

Glucose

Galactose

Glucose

Glucosamine

N-acetyl-

glucosamine

Maltase

Glucoamylase

α-Limit dextrinase

Isomaltase

Sucrase

Lactase

Trehalase

Chitobiose Chitobiase

Isomaltose

Chitinase

(Gastric mucosa, microbial)

Chitobiase

(Microbial)

Sucrose

Lactose

Trehalose

Chitin

Table 6.2.Summary of carbohydrate digestion in direct absorbers.