metabolism, composition of animal body & plants, nutritional characteristics of food

metabolism

sequence/succession of chemical reactions that take place in the living organism

catabolic and anabolic reactions

2 reactions in metabolism

catabolic reaction

involve the degradation of complex compounds to simpler materials

anabolic reaction

involve the synthesis of more complex compounds from simpler substances

substances absorbed after digestion

starting points of metabolism; absorbed into the portal blood & carried to the liver

energy

• capacity to do work

• various forms: chemical, thermal, electrical, & radiant

• amount of heat produced when completely oxidized in the body/loss of energy from the body

various systems

• based on the quantity needed, energy is required in the highest amounts in an animal’s diet

• partition of dietary energy

feeding standards for formulating diets

based on some form/measure of energy & additional needs for protein/AA, essential FA, vitamins, & minerals

1 calorie

heat required to raise the temperature of 1g of H2O 1°C (=4.1855 joules)

Gross Energy

heat generated when a feed is completely oxidized/burnt

digestible energy

• amount of energy apparently absorbed from a feed

• obtained by substracting fecal energy from GE

• can be determined relatively easily by a digestion trial

metabolizable energy

determined by substracting energy losses in urine & combustible gases from DE consumed - must collect feces, urine, & gaseous losses

net energy

• determined by subtracting energy losses due to rumen fermentation & tissue metabolism from ME

• most accurately predicts the available energy for the animal

• widely used in formulating diets for various ruminant species

total digestible nutrients

method used for many years for estimating the energy content of a feed - sums all the fractions that are digestible

digestible crude protein + digestible crude fiber + digestible nitrogen-free extract (starch & sugars) + 2.25 digestible ether extract (fat)

TDN formula

decreases

water _______ with age

accumulates

fat _______ with age

73%, 22%, 5.3%, 1%

on fat free basis, the body composition is _____ water; ______ protein & _____ Ash while carbs form less than ____.

CHO

formed & broken down in metabolism

90-92%

percentage of water present in blood

72-78%

percentage of water present in muscle

5%

percentage of water present in tooth enamel

protein

basic nutrient present in all cells, organs, & soft tissues

fats

basic nutrient localized in adipose tissues

carbohydrates

basic nutrient found in the liver, muscles, & blood

minerals

basic nutrient found in bones, teeth, & other organs

age and nutrition

factors that affect the gross composition of the animal body

functions of animal food

• plants & other feeds supply nutrients to:

  • build & renew body components

  • form new products

  • reproduction

  • furnish energy for these processes

25, 20, 13, 16, 16-20

nutrients in animal food should be at least ____ carbohydrates, at least _____ AA in its free form/as protein, at least ____ FA in the form of fat, ____ minerals, & ___-___ vitamins

composition of animal food - plants

• water

• dry matter (carbohydrates)

water

principal constituent of plant tissues

plant carbohydrates

• structural (cellulose)

• reserve material (sugars & starches)

leaves

has higher protein than stem

fat

nutrient that is high on leaves than in stem but highest in seeds as reserve energy for germination

legumes

plant that is high in Ca

by-product feeds

• seed coats

• endosperm

• embryo

• oil seed meal

seed coats

by-product feeds that are cellulosic but rich in fats

endosperm

by-product feeds that are mostly sugar & starch with very little cellulose

embryo

by-product feeds that is rich in protein & fat & very low in fiber

oil seed meals

by-product feeds that have high nutritive value, being high in protein & carbs

alpha linolenic acid

most abundant FA of grasses which comprises about 50% of the total

green herbage

exceptionally rich source of β-carotene (precursor of vit. A), & the dry matter of the young green crop may contain as much as 550 mg/kg

factors influencing the nutritive value of herbage

• stage of growth

• soils, fertilizers, & weather

• grazing system

• nutrient balance

stage of growth

most important factor influencing the composition & nutritive value of pasture herbage

soil type

may influence the composition of pasture especially its mineral content

most common mineral deficiencies of grass herbage

• phosphorus

• magnesium

• copper

• cobalt

acidity of soil

an important factor that can influence the uptake of many trace elements by plants

continuous grazing

traditional grazing systems, animals are kept on the same area of pasture throughout the year

rotational grazing systems

animals harvest most of the herbage on offer, & the pastures are then rested for longer periods of recovery

nutrient balance

balance of the 3 major groups of nutrients in grasses (protein, fiber, soluble carbs)

fiber

high ____ levels reduce digestibility & energy value

water-soluble carbohydrates

high contents of ______ ______ are rapidly fermented in the rumen & may depress the pH & so reduce fiber digestion

pasture and field crop legumes

• clover (Trifolium spp.)

• lucerne/alfalfa (Medicago sativa)

• sainfoin (Onobrychis viciifolia)

• peas (Pisum sativum)

• beans (Vicia faba)

• vetches (Vicia sativa)

clover

superior to grasses in protein & mineral content (Ca, P, Mg, Cu, & Co) & their nutritive value falls less with age

lucerne/alfalfa

• protein content is comparatively high & declines only slowly with maturity

• tends to be high in fiber (the stem), & at the late flowering stage crude fiber may be as high as 500 g/kg DM

sainfoin

• leaf is richer than the stem in crude protein, ether extract & minerals, especially Ca

• crude protein: 240 g/kg (early flowering stage) to 140 g/kg (full flower)

green fodder crops

peas, beans, & vetches are sometimes grown as ____ ______ ____

browse

collective term applied to food obtained by grazing mature grass pastures to supplement diet by consuming foliage of trees & shrubs

foliage of leguminous trees

high in protein (200-300 g/kg DM) & minerals , but also high in fiber (500-600 g neutral-detergent fiber per kilogram of DM)

tannins

reduces the palatability of browse possibly along with other constituents

Leucaena/ipil-ipil

• Leucaena leucocephala, one of the best known browse species

• valuable source of protein & minerals & is also rich in β-carotene

• also contains toxic AA mimosine

mimosine

toxic AA found in ipil-ipil

other legume forages

• gliricidia (Gliricidia sepium)

• sesbania (Sesbania sesban)

• acacia (Acacia angustissima)

cereals

• grown as green forage crops, either alone/mixed with legumes

• forage is rich in carbs & low in protein, its nutritive value depending mainly on the stage of growth when harvested

sugarcane/sugarcane mollases

Saccharum officinarum; high-energy, low-protein food similar in composition to the molasses obtained as a by-product from sugar beet

kales

Brassica oleracea; low in dry matter content (about 140 g/kg), which is rich in protein (about 150 g/kg), water-soluble carbs (200-250 g/kg) & Ca (10-20 g/kg), & their digestibility is generally high

other forages

• brassicas

• rapes

• cabbages (B. oleracea, var. capitata)

silage

material produced by the controlled fermentation of a crop of high moisture content

ensilage

name given to the process of producing silage

silo

container of silage

1st essential objective in preserving crops

• natural fermentation is the achievement of anaerobic conditions

  • done by chopping the crop during harvesting, by rapid filling of the silo, and by adequate consolidation and sealing

  • to prevent re-entry and circulation of air during storage

2nd essential objective in preserving crops

to discourage the activities of undesirable micro organisms such as clostridia and enterobacteria, which produce objectionable fermentation products.

lactic acid bacteria

ferments the naturally occurring sugars (glucose & fructose) in the crop to a mixture of acids, but predominantly lactic acid

respiration and proteolysis

important in influencing the nutritional value of the final product

proteolysis

hydrolysis of peptide bonds

carbohydrates

major respiratory source & the substrate for oxidation is usually a hexose sugar, which undergoes glycolysis and subsequent oxidation via the tricarboxylic acid cycle to CO2 and water.

protein

in fresh herbage, 75-90% of the total nitrogen is present as ________

aerobic fungi and bacteria

dominant microorganisms on fresh herbage but are replaced by bacteria that are able to grow in the absence of O2 as anaerobic conditions develop

anaerobic bacteria

lactic acid bacteria, clostridia, enterobacteria

lactic acid bacteria

• present on growing crops in small numbers but usually multiply rapidly after harvesting, particularly if the crop is chopped/lacerated

• when the crop is ensiled, these continue to increase, fermenting the water-soluble carbs in the crop to organic acids, mainly LA, which reduce the pH value

2 categories of lactic acid bacteria

• Homofermentative bacteria: (e.g. Lactobacillus plantarum, Pediococcus pentosaceus and Enterococcus faecalis)

• Heterofermentative bacteria: (e.g. Lactobacillus brevis and Leuconostoc mesenteroides)

homofermentative bacteria

lactic acid bacteria which are more efficient at producing LA from hexose sugars

clostridia

• present on crops, but the main source in silage is soil contamination

• occurs in the form of spores & grow only under strict anaerobic condition

• has 2 major groups:

  • Saccharolytic clostridia: (e.g. Clostridium butyricum and Clostridium tyrobutyricum)

  • Proteolytic clostridia: (e.g. Clostridium bifer mentans and Clostridium sporogenes)

saccharolytic clostridia

clostridia that ferments LA & residual water-soluble carbs to butyric acid, resulting in a rise in the pH

proteolytic clostridia

clostridia that ferments mainly AAs to a variety of products, including acetic & butyric acids, amines, & ammonia

enterobacteria

• associated with silage, sometimes describes as ‘acetic acid bacteria’ or ‘coliform bacteria’, usually present in very low numbers on crops

• facultative anaerobes, & consequently compete with the lactic acid bacteria for the water-soluble carbohydrates.

• can decarboxylate and deaminate AAs, with consequent production of large concentrations of ammonia.

• optimum pH for the growth of these organisms is about 7.0, and they are usually active only in the early stages of fermentation, when the pH is favorable for their growth.

• Examples of species commonly found in silage: Escherichia coli & Erwinia herbicola.

2 main categories of silages

• naturally fermented silages

  • well-preserved

    • unwilted

    • wilted

  • badly preserved

• additive treated silage

  • stimulants

    • sugars

    • LA bacteria

    • enzymes

  • inhibitors

    • formic acid

    • sulphuric acid

    • formaldehyde

haymaking

traditional method of conserving green crops; entirely dependent upon the chance selection of a period of fine weather

aim of haymaking

reduce the moisture content of the green drop to a level low enough to inhibit the action of plant & microbial enzymes

150-200 g/kg

In order that a green crop may be stored satisfactorily in a stack or bale, the moisture content must be reduced to _________

drying process

Chemical changes resulting in losses of valuable nutrients inevitably arise during the _________

actions that cause loss of nutrients during haymaking

• plant & microbial enzymes

• chemical oxidation

• leaching

• mechanical damage

mouldy hay

unpalatable & may be harmful to farm animals & man because of the presence of mycotoxins

farmer’s lung

allergic disease affecting man that is caused by actinomycetes from mouldy hay

leaching

causes a loss of soluble minerals, sugars, & nitrogenous constituents, & hence a concentration of cell wall components, which is reflected in a higher fiber content

artificial drying

a very efficient, though expensive, method of conserving forage crops

high-temperature drying

may reduce the digestibility of forage proteins, but is has the advantage of increasing the proportion of protein that escapes rumen fermentation to about 0.4 (rumen protein degradability 0.6)

straws and related by-products

• barley & oat straw

• maize straw

• rice straw

• wheat & rye straws

• legume straws

straws

consist of the stems & leaves of plants after the removal of the ripe seeds by threshing, & are produced from most cereal crops & from some legumes

chaff

consists of the husk/glumes of the seed, which are separated from the grain during threshing