General Livestock Nutrition - Lecture 148

General livestock nutrition - Lecture 148

1. Recognise the animal feeds that are given to livestock and identify the nutritional composition of common feedstuffs that are given to livestock

Nutrients: 

• Protein
• Carbohydrates
• Fat
• Minerals
• Vitamins

Also need Water and some water-soluble vitamins

Main nutrient in hay = Carbohydrate

main nutrient in grass = Water

Dry Matter: 

milk ~10% DM

wheat ~ 85% DM

hay ~85-90% DM

grass ~30-40% DM

banana ~60-70% DM

human ~60% DM

Sugars: 

Polysaccharides: 

• Most important for animal feed
• made of alpha-linked glucose molecules
• starch - storage in plants
• glycogen - storage in animals
• made of beta-linked glucose molecules
• cellulose - most abundant - only microbes can digest
• hemicellulose
• pectins
• gums
• fructins

Monosaccharides: glucose

• trioses, tetroses, pentroses, hexoses, glucose, galactose

Oligosaccharides:

• Disaccharides
•  sucrose: fructose + glucose
• most abundant disaccharide
• found in animal feeds high in sugar - sugar beet, sugar beet pulp, molasses
• Maltose = 2 glucose
• main sugar found when cereals germinated
• Lactose = glucose + galactose
• milk sugar
• Trisaccharides
• Tetrasaccharides

Lignin:

• Nature's cement 
• non-polysaccharide
• 3D structure gives it strength
• occurs in woody parts of plants, such as stems, trunks
• accumulates as plants mature - eg straw
• resists breakdown by any enzyme or micro-organism

Proteins:

Essential amino acids

• valine, leucine, isoleucine, threonine, methionine, phenylaline, tryptophan, lysine, histidine 
• cystine can replace methionine to a certain extent
• cats and growing dogs: arginine
• cats: taurine

Non-essential amino acids

• alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, proline, serine, tryosine

Limiting amino acid - essential in ruminant diets

• the amino acid that is used up first in protein synthesis
• will prevent further synthesis of protein
• malnutrition will occur
• in most cases it is methionine or lysine

Lipids: 

• Important for supplying energy
• added to animal feeds
•  essential fatty acids
• limitations in adding to diets

Feedstuff: 
Fresh:

• Grass – natural or cultivated
• Forage crops – legumes: clover Lucerne/alfalfa, Leucaena (Ipil-Ipil)
• Cereals – grown as forage crops: Sugar beet tops (sugar cane) 
• Brassicas – Kales, cabbage, rapes

Roots, tubers and by-products: 

• Swedes and turnips 
• Sugar beet 
• Sugar beet pulp 
• Molasses (beet and cane) 
• Potatoes
• Cassava Sweet potatoes

Cereal grains and by-products: 

• Oats 
• Wheat 
• Barley 
• Triticale 
• Maize 
• Sorgum 
• Rye 
• Millet 
• Rice
• Brewing industry – Brewers grains 
• Malt Culms – distilling industry 
• Spent hops 
• Dried brewer’s yeast
• Bran

Straw (in many parts of the world - poor source of nutrients)

• Wheat Straw
• Barley Straw
• Oat Straw 
• Legume Straw

Protein concentrates: CP ~ 25-50%- most expensive part of feed

• Fishmeal 
• Meat and bone meal 
• Blood meal
• Milk products
• Whole milk 
• Skim milk 
• Whey
• Oil seed cakes and meals
• Soya bean meal
   
• Rape seed meal 
• Linseed meal 
• Cottonseed meal 
• Groundnut meal 
• Palm kernel meal 
• Sunflower seed meal 
• Seasame seed meal
• Single cell protein

Non-Protein: 

• Urea
• poultry waste

2. Understand how the nutrient composition of feeds is evaluated using chemical methods

CP = the Nitrogen content of food x 6.25
(16% of food protein is Nitrogen)

Crude Fibre (CF) - Cellulose, hemicellulose, lignin (wood component, indigestible), pectin
Ash - Inorganic ash - minerals
Ether Extract (EE) - fats, oils, fat soluble vitamins

To calculate Carbs:
Nitrogen Free Extracts = 100 - (Water - Ash - CP - CF - EE)

This contains the sugar, starch, pectins, some cellulose

NDF - Natural Detergent Fibres 

• cell wall constituents
• hemicellulose, cellulose, lignin

ADF - Acid Detergent Fibres

• cellulose, lignin
• in all ruminant feed
• high ADF, digestibility is low
• low ADF, digestibility is high

3. Understand how the digestibility and protein quality of feeds are evaluated using in-vivo methods

Protein Quality: 

• Good quality proteins contain all essential amino acids in proportions capable of promoting growth (when only proteins in diet) 
• High BV score = good quality protein
• egg BV = 100 = perfect protein quality

Biological Value (BV):

BV = amount of Nitrogen retained in the body, thus protein quality

MFN - metabolic faecal N (N in cells excreted) 

EUN - Endogenous urinary N (N in cells excreted)

N secreted = mucous, urine, faeces, dead skin cells

Digestibility:

• some nutrients are better absorbed than others
• rate of passage matters - slower, more will be absorbed
• measured by the total food intake (DM) and total faecal output over a period of time

Example: 

Cow ate 10kg hay containing 90% DM

She excreted 3kg faeces DM

What is the digestibility of the hay? 

9kg - 3kg

------------   = .67 or 67%

    9kg

Measuring digestibility in-vivo: 

Example:
A sheep ate 1.63kg of hay DM.
Energy content is 18MJ/KG DM
faeces = 0.76 kg DM, energy content 18.7 MJ/kg
What is the digestible energy?

intake= 1.63 kg (18 MJ/kg) = 29.3 MJ
output= 0.76 kg (18.7 MJ/kg) = 14.2 MJ

  DE =  29.3 - 24.2   = 0.52
                29.3