Practical implications of comparative digestion in farm animals

Monogastric (non-ruminant) animals cannot digest fibrous feed (cellulose, hemicellulose) and depend on high quality, low-fiber concentrate diets. Among the monogastrics, horses and rabbits, due to their well developed caecum is less efficient than in the rumen. Therefore, horses should be fed good quality forages. On the other hand, ruminants, because of efficient microbial fermentation in the rumen, have acquired the ability to digest a wide range of roughages, including poor quality cereal straws and other crop residues. Ruminants can also utilize non protein nitrogen from sources such as urea as a dietary crude protein and convert it to a protein of high biological value (microbial protein).
The unique digestive features of ruminants enable them to utilize agro-industrial by products and wastes which cannot otherwise be used by monogastrics, including man. As ruminants depend largely on the fermentation products of the rumen (VFA's and microbial protein), conditions in the rumen should be optimal at all times to support efficient fermentation. This can easily be achieved by taking care of the nutrient requirements of rumen microbes. Recent developments in ruminants nutrition have emphasized that these animals should be fed in such a way that their capacity to utilize roughages and non-protein nitrogen is exploited to the greatest extent possible, and at the same time high quality feeds (such as good quality feeds and starches) should be protected from rumen fermentation so that they escape from the rumen and are efficiently digested and abosrbed in the small intestine. Unlike ruminants, monogastrics cannot synthesize amino acids and vitamins B and K. Therefore they depend on feed resources for these nutrients.

Functions of Various Parts of Digestive Tract: Large Intestine

The large intestine is the terminal part of the alimentary canal; it consists of the caecum (blind sac), colon, and rectum. The size of the large intestine varies considerably in farm animals. In horses it constitutes 46% of the total volume of the digestive tract. In ruminants, it represents only 10% of the total digestive tract capacity. The large intestine serves as a major site for the absorption of water, sodium, and chloride. Other salts such as potassium, phosphorus, and magnesium can also be absorbed from the large intestine. The large intestine has only mucous secretions and no enzymatic activity.
Undigested materials which escape the digestive processes in the stomach and small intestine are subjected to microbial digestion in the caecum. In monogastric animals, particularly horses and rabbits, the caecum serves as a major site for digestion of fibrous materials. This is accompanied by a variety of microflora. However, microbial digestion and absorption of end products in the caecum is not as efficient as it is in the rumen, and therefore does not nutritionally benefit the animal as much. The microbial protein synthesized in the caecum is mostly excreted in the faeces. The colon is part of the large intestine extending from caecum to rectum. The rectum is a dilatable tube serving as a storage place for feces until it is excreted.
The anus is the opening at the posterior end of the alimentary canal under the root of the animal's tail. The anal canal or lumen is normally closed by the contraction of sphincter muscles. During defecation, this canal is opened and undigested material (excreta) is passed through the anus.
Note: Next post on this blog will cover, "Practical Implications of Comparative Digestion in Farm Animals"

Functions of various parts of the digestive tract: Accessory Organs

Pancreas: The pancreas is a lobulated organ located in the deodenal loop. It has both endocrine and exocrine functions. Exocrine tissue produces pancreatic juice, which is composed of the digestive enzymes amylase, lipase, and trypsin and sodium bicarbonate. Other salts including potassium, chloride, calcium and magnesium are also present in relatively small quantities. The endocrine system consists of a vascular area called the Islet of Langerhans which secretes the hormones insulin and glucagon. Exocrine secretions drain directly into the duodenum through the pancreatic duct, while endocrine secretions are absorbed into the blood and circulated. Pancreatic enzymes require an optimum pH of 6.9 for their action in the small intestine, which is provided by pancreatic juice. Compared to monogastrics, the pancreatic juice of ruminants has a relatively low bicarbonate content, and therefore the pH of the acidic digesta entering the duodenum increases only slowly. Hence, the initiation of proeolytic activity does not take place immediately in the small intestine of ruminants.
Pancreatic enzymes are classified into three major groups: proteases, amylases and lipases. Among these, proteases are the major enzymes, representing about 72% of the total enzyme secretion. Pancreatic proteases are responsible for protein digestion, so they are also known as protelytic enzymes. Most of the proteolytic enzymes secreted from the pancreas are in inactive form and need to be activated by other enzymes present in the small intestine.
Pancreatic lipase causes hydrolysis of fats into carboxylic acids and glycerols, This action is facilitated by the prior emulsification of fat by the action of bilel salts. In other words, complete hydrolysis of fats in the small intestine is accomplished by the combined action of bile salts and pancreatic lipases. In adult animals, the activity of pancreatic llipase is increased when the animal consumes a high-grain diet. Pancreatic amylase activity is relatively low in ruminants compared to non-ruminants, because most of the starch is fermented in the rumen and little escapes to the small intestine. Pancreastic amylases convert starch into dextrin and maltose (disaccharides) and are of greater sifnificance in starch digestion than the salivary amylases.
Liver and gall bladder: Bile is continuously secreted by the liver. All domestic animals except horses have a gall bladder which serves as a storage organ for bile, which is spoured into the duodenum through the bile duct. In most farm animals, bile and pancreatic secretions are carried into the duodenum through a common duct. In cattle and buffaloes, pancreatic juice and bile are discharged into the duodenum through separate ducts.
Fats entering the small intestine are mostly in the dorm of large globules which cannot be hydrolysed by pancreatic lipases until emulsified by bile salts. Bile contains calcium and potassium salts of flycocholic and taurocholic acids which are required for maintaining alkaline pH and emulsification of fats. In addition to salts, bile also contains pigments (bilirubin and biliverdin), cholesterol, and mucin.
Note: Next Post will Cover The "Large Intestine" of domestic animals.