Milk Production Management & Dairy Development

Module 9. Feeding of dairy animals

Lesson 14
DIGESTIVE SYSTEM AND ROLE OF NUTRIENTS IN DAIRY CATTLE

14.1 Introduction

Feeding is the important factor influencing productive function of the dairy animal and milk production in particular. The feed that the animal consumes, after undergoing digestion, releases the nutrients for the synthesis of milk. For maximum production, sufficient nutrients are to be provided in the ration of the animal so that the animal utilizes them and high milk production can be achieved. Hence a balanced ration should be provided to the dairy animal in order to achieve maximum out put of milk. In this chapter digestive system of cattle, role of various nutrients and their requirements, various feed resources and their nutritive values are discussed.

14.2. Digestion of the Ruminants

Fig. 14.1 Digestive system of Cattle

14.2.1 Digestive system of ruminants

The digestive organs of ruminants consists of mouth, oesophagus, rumen, reticulum, omasum and abomasum, small intestine, and large intestine.

The cow takes food into the mouth. The food taken in by the animal after mixing with saliva enters into the rumen through oesophagus.

Cattle stomach has four compartments such as:

Rumen: In the rumen the feed is subjected to microbial fermentation. Esophagus leads the food into the rumen which is a large receptacle divided into four areas by muscular bands or pillars. The four areas are dorsal, ventral and two posterior sacs. The feed inside the rumen is agitated in a rotary fashion by the contraction of the muscular bands .This helps in mixing feed well with the rumen fluid. Unlike non ruminant’s stomach, the rumen is the major area for a absorption of nutrients. The finger like papillae lining the rumen greatly increases the surface area for absorption.

The herbivores generally have an expanded part of digestive system so as to hold the bulky fibrous feeds and delay their passage to undergo microbial fermentation. In ruminants this enlarged part is represented by the rumen which is the biggest compartment in their four-chambered stomach.

The micro- organisms are benefited as follows:

Ingestion of feed by the animal ensures a sure and steady supply of nutrients to the micro-organisms.
The temperature of rumen is 38- 40°C. This is ideal for the growth of micro-organisms and they flourish as if grown in an incubator.

The important differences in carbohydrate digestion in ruminants from that of non-ruminants is that: (i) cellulose is utilized, (ii) the diges­tion is mainly microbial and, (iii) the end-products are volatile fatty acids such as acetic acid, propionic acid, butyric acid and not glucose.

Proteins are attacked by bacteria and the end-products are usually ammonia and short chain fatty acids. A considerable proportion of the protein needs of the animals are met through such microbial protein. These micro-organisms ultimately pass from the rumen to the lower stomach and intestines, where digestion of the microbial protein takes place in the same way as protein is digested in non-ruminants.

Vitamins belonging to the B-complex, group is dietary essen­tials for non-ruminants. But in the ruminants they are synthesized by the rumen micro flora in sufficient quantities to meet all the dietary needs. In other herbivores a' similar synthesis to a lesser degree takes place in the large intestine.

Reticulum: It is a smaller sac partially separated from rumen. This organ has a thick wall resembling honeycomb. The contents of rumen and reticulum mix freely. Reticulum is connected to omasum, the third compartment of stomach through an opening on the right side of reticulum.

Omasum: This organ has many layers of muscular leaves giving it the resemblance to a book. After fermentation the ingesta passes through the reticulo-omasal orifice into the omasum. With the help of the muscular leaves having horny papillae the ingesta is squeezed out. Water and fatty acids so squeezed out are absorbed.

Abomasum: it is the true stomach in the ruminant. From this organ onwards the digestion taking place in ruminants is similar to that of non-ruminants.
Small Intestine: Duodenum is the first loop of small intestine. It is an important area because pancreatic duct and bile duct join.
Large Intestine: Absorption of water takes place from large intestine.

14.3 Role of Nutrients in Dairy Cattle

A nutrient is defined by Morrison as “any food constituent or group of food constituents of the same general chemical composition that aids in the support of life.” Nutrients are essential for the preservation of life.

E.g.: water, proteins, carbohydrates, fats, minerals and vitamins are the well recognized feed nutrients.

14.3.1 Water

Functions of water: Animals require water for the formation of their bodies. Water acts as a medium and universal solvent in almost all vital processes like digestion absorption, intermediary metabolism, excretion and even in reproduction. Water can absorb large quantity of heat with limited temperature change, besides animals get rid of a major portion of excess body heat evolved in metabolic processes through evaporating body water. It also helps in maintaining the pH of body fluids with in normal range. Water content of the body varies considerably between species of animals. Factors like age, sex, degree of fatness and physiological status of animals and environmental factors like climate also influence the concentration of water in the animal body. Adult cattle require 3.5-5.5 liters of water for every / kg DM intake. Calves require 6.5 L/kg DM intake.

14.3.2 Carbohydrates

In plants 50-80% of dry matter is usually carbohydrates. Thus animals which consume plant materials, consume large quantities of carbohydrates. The main function of carbohydrates is to provide energy. These are important as these are chief source of energy for the animal for its maintenance, growth, production and work.

Carbohydrates include sugars, starch, cellulose, hemi cellulose, peptones, gums and mucilage. These carbohydrates are classified into monosaccharide, (glucose, galactose, fructose etc,) disaccharides (sucrose, lactose, maltose) and polysaccharides (starch, cellulose and glycogen) depending on number of sugar molecular present in them.

Plants store excess food nutrients as starch (cereal grains, fruits, tubers etc). Starch is not soluble in water but easily digested into sugar. Therefore the food value is high. Cellulose is a more complex and less soluble and digestible carbohydrate. No known enzyme of animals can digest cellulose. The fermentation of cellulose in the rumen results in formation of volatile fatty acids like acetic, propionic, butyric and Valeric acids. These constitute major source of energy for ruminants. For ruminants cellulose has same energy value as starch.

Any carbohydrate absorbed in excess of the body’s need for energy is first converted into glycogen and stored in the liver. Any carbohydrate in excess of this is converted into fat and stored in different parts in the body.

14.3.3 Fats

Natural fats are complex mixtures of mixed triglycerides, a molecule of fat consisting of three fatty acids attached to a glycerol molecule. An unsaturated fatty acid has one or more double bonds depending on the degree of un-saturation. Fatty acids having two or more double bands are called Poly Unsaturated Fatty Acids (PUFA’s). Fats in the food serve as a source of energy. The oxygen content of fats is much less and therefore on oxidation, they liberate roughly 1.25 times more energy than carbohydrates. Apart from being a concentrated source of energy, fats aid in the absorption of vitamin ‘A’, carotene and calcium.

14.3.4 Proteins

Proteins are another group of nutrients that provide energy to the animals. The energy value of proteins is approximately similar to that of carbohydrates. But, they form structural com­ponents of cell walls and membranes. Some proteins function as hormones and enzymes. They play important role in acid-base balance, oxygen and other nutrient transport, muscle contraction, osmotic pressure, immunity (anti-bodies), blood coagulation.

Proteins molecule is composed of a considerable number of amino acids. A protein molecule contains one or more polypeptides. Each polypeptide chain consists of many amino acids varying in number from around 20 to several hundreds. The large-animal tissues cannot form certain amino acids from any other source. These are called essential amino acids, such as arginine valine histidine isoleucine, leucine, lysine, metheonine, phenylalanine, tryptophan and threonine. These amino acids are, therefore, necessary for life and must be supplied through feed in required quantities.

The micro-organisms in the rumen are able to synthesize all amino acids from other amino acids and even from non-protein nitrogenous compounds. The pattern of protein metabolism is modified in the ruminant by the synthesis of microbial protein in the rumen. Ruminants digest these microbial proteins of high biological value in the intestines and absorb amino acids.

14.3.5 Minerals

Animal body contains 3 to 5 percent mineral matter depending on factors like age, condition, species and physiological status of animals. Out of these, 21 elements have been recognized as essential. Minerals are usually classified into major and trace elements based on the vast difference in the amounts required in the diets and/or present in the animal body. Minerals play many a vital role in the animal system. As constitutes of the skeletal tissue minerals impart rigidity and strength to it. Minerals also form part of the soft tissues and body fluids in the body. Nucleoproteins, which form the continuity from generation to generation, have phosphorus as a constituent. Phospholipids are an essential part of cell protoplasm. They also exert either stimulative or depressive effect on response and tonicity of muscles and irritability of nerves. Blood contains minerals mostly responsible for maintaining proper osmotic pressure and acid base balance in the system. Hemoglobin contains iron useful in transport of oxygen.

14.3.5.1 Major elements

The dietary requirement of the essential major elements is more than 0.010% (100 ppm). The average tissue concentrations of these elements also exceed 100 ppm.

• Skeletal development in various species of farm animals is dependent on adequate calcium and phosphorus supply in the presence of vitamin D. Calcium deficiency in young animals is characterized by poor skeletal development and rickets. In adult animals chronic Ca deficiency leads to osteomalacia and osteoporosis. Dairy cows shortly after calving may develop milk fever, a condition characterized by low plasma Ca with symptoms of muscular spasms and paralysis.
• Phosphorus is the important element in the energy transformations of living cells involving formation and breaking of high energy P bonds. Pica or deprived appetite with tendency to chew objects like bones, wood .or leather is seen. Reproductive problems like anoestrus and low conception, rates are often seen in females having P deficiency.
• Sodium, Chlorine and Potassium are mainly concerned with main­tenance of acid-base balance and osmotic pressure in the animal body. Magnesium plays a vital role in many body processes especially as an activator in many enzymatic reactions.

14.3.5.2 Trace elements

The dietary needs and body concentrations of essential trace elements are always below 100 ppm. On the basis of present day knowledge, 14 trace elements appear to be essential.

• Iron is an essential part of the respiratory pigment hemoglobin.
• Presence of copper is necessary for the utilization of iron. Copper is also a constituent of some of the enzymes like cyto­chrome oxidize, catalase, tyrosine and ascorbic acid oxidize.
• Cobalt is a constituent of vitamin B12.
• Zinc plays an important role in keratinisation and calcification and, as a constituent of many important enzymes, it has an essential role.
• Iodine forms about 65 per cent of the hormone thyroxin of thyroid gland which regulates the development of the animal and the metabolic rate.
• Body contains comparatively larger quantities of sulphur, mostly in the organic form. The body can utilize mostly the organic sulphur which is part of the amino acids, methionine and cystine.
• Selenium in trace quantities is an essential nutrient in spite of its well-known toxic effect in larger doses which cause 'alkali disease' or blind staggers.
• Excess fluorine increases the incidence of dental caries and bone abonormalities

14.3.6 Vitamins

Vitamins are vital constituents required by the body. They are classified as water soluble and fat soluble. Members of the B-complex and vitamin C belong to the category of water soluble vitamins whereas vitamins A, D, E and K form the fat soluble group.

14.3.6.1 Water soluble vitamins

Vitamins B-complex group includes thiamine (B1), riboflavin (B2) and vitamin B6 (Pyridoxine, pyridoxamine and pyridoxaI), niacin, pantothenic acid, biotin, folic acid, Choline and cyanocobalamine (B12),

• Thiamin as a constituent of the coenzyme carboxylase and other­wise plays an important role in intermediary metabolism.
• Riboflavin required to form many lipoprotein enzymes and coenzymes, which act at important stages in the metabolic release of food energy in the body.
• Niacin (Nicotinamide) is essential metabolically for all species of animals as it forms part of two important co-enzymes co enzyme I (NAD) and co-enzyme II (NADP).
• Vitamin B6 (pyridoxine, pyridoxamine and pyridoxal) helps in efficient metabolism of tryptophan.
• Feeding of raw egg-white has been found to produce biotin deficiency in many species due to presence of avidin in raw egg-white which makes dietary biotin unavailable.
• Folic acid plays an important role in intermediary metabolism.
• Choline is essential for the formation of cell structure.
• Vitamin B12 (Cyanocobalamine) prevents and cures pernicious anemia in human beings.
• Vitamin C is essential in the diet of all species

14.3.6.2 Fat soluble vitamins

Fat soluble vitamins include Vitamin A, D, E and K

• Vitamin A has four distinct biological functions; namely, bone formation and growth, vision, reproduction and maintenance of healthy epithelial tissue. Vitamin A deficiency symptoms are watering from the eyes, night blindness, loss of appetite, exophthalmia and infected eyes. This is followed by retardation of growth and malformation of epithelial and skeletal structures. Excess of vitamin A can cause toxicity. However animals have some built-in mechanism to guard against hypervitaminosis.
• Vitamin D has a major role in calcium and phosphorus metabolism. Its main role is to increase the absorp­tion of calcium from the alimentary tract. Deficiency of the vitamin causes rickets in all species.
• Vitamin E (Tocopherols) is important for the health of reproductive system and act as antioxidants. Vitamin E has inter-relationships with selenium, sulphur containing amino acids, poly unsaturated fatty acids and antioxidants.
• Vitamin K is involved in the coagulation of blood. Cattle may develop deficiency of vitamin K when they consume large quantities of mouldy sweet clover hay.