فسيولوجيا الهضم في المجترات

Study Notes

Agriculture production is divided into animal and plant production; these are complementary. Animal manure is essential for plant production.
Animal production is divided into animal husbandry, animal nutrition, and animal physiology.
Animal physiology studies the functioning of the animal's body and includes digestion, blood and body fluids, endocrine and nervous systems, reproduction and artificial insemination, milk production, and environmental adaptation.
Digestion is the process by which the digestive tract and its accessory glands prepare food for absorption and eliminate undigested matter.
The digestive system includes the alimentary canal (from mouth to anus) and accessory glands (salivary glands, liver, and pancreas).
The alimentary canal varies in length and complexity among different animal species. Animals are classified into three categories based on their diet.
Carnivores: Have a simple and relatively short digestive system (e.g., dogs, cats).
Herbivores: Have a longer and more complex digestive system than carnivores. Horse and rabbit stomachs are simple, similar to carnivores, but their intestines are more complex/larger (cecum). Cows, sheep, and goats have a four-compartment stomach (rumen, reticulum, omasum, and abomasum); these animals are called ruminants. Some herbivores have a three-chambered stomach (ruminant-like, e.g., camels, llamas).
Omnivores: Have a digestive system intermediate between carnivores and herbivores (e.g., humans, pigs).

The ruminant stomach takes up about three-quarters of the abdominal cavity, predominantly filling the left half.
It consists of four compartments: rumen, reticulum, omasum, and abomasum.
The rumen is the largest compartment, located above the median abdominal plane. It's further subdivided into sections.
The reticulum is the foremost compartment, shaped like a sac, located near the diaphragm and liver.
The omasum is a spherical structure, located to the right of the median plane. It has muscular folds with papillae.
The abomasum (true stomach) is an elongated sac situated in the abdominal cavity's floor.

The pharynx is a common passage between the digestive and respiratory systems. Food and air pass through the pharynx. The epiglottis regulates the flow to the trachea or esophagus.
The esophagus is a muscular tube connecting the pharynx and the stomach. Its muscular tissues change in structure from the skeletal to smooth muscles.

Digestion involves mechanical (chewing, vomiting), chemical, and microbial actions.
The esophagus empties directly into the rumen.
The ruminant stomach has a specialized groove called the esophageal groove (or reticulor groove). This groove permits milk from the mother's udder to bypass the rumen and reticulum, going directly to the abomasum.

Ruminants produce copious amounts of saliva with a neutral pH to counter the pH fluctuations during feed intake and rumination.
Salivary glands are classified into paired and unpaired glands. Paired glands include parotid, sub-maxillary, and ventral sub-linguals; unpaired include palatine, pharyngeal, and labial glands.
Saliva functions in chewing, swallowing, and dissolving food, stimulating taste buds, providing enzymes (salivary lipase), buffering the acidity from the rumen, maintaining oral hygiene, and providing nutrition to rumen microbes.
Salivary production increases during feed intake and is influenced by feed nature and palatability.
Saliva is regulated by a reflex response that activates salivary glands nerves.

At birth, the abomasum is the largest stomach compartment (approximately 50%).
The rumen and reticulum grow rapidly, particularly when animals ingest dry feeds.
The relative size of the abomasum decreases.
The omasum develops more gradually.
Rumen and reticulum growth is rapid before 8 weeks; they are fully developed by 12 weeks.
Omasum growth is more prolonged (36-38 weeks).
The reticulum in lambs reaches a mature size at 30 days, while the rumen expands between 7 and 30 days and matures by 8 weeks.
Factors affecting ruminant stomach growth include feed type and quality (e.g., liquid vs. solid feeds); fibrous feeds promote rumen growth, while concentrated feeds have less effect. Organic acids (e.g., volatile fatty acids) in the rumen support rumen papillae growth.

Methods for estimating the comparative volumes include measuring water in the stomach post-mortem, or by use of indicator dyes.
Various techniques are employed for ruminant stomach volume estimations depending on animal type and age.