Lecture 3

Unit 3

 Evaluation of Food Energy and Protein Quality

1. Energy Partitioning in Livestock
2. Measurements of energy
3. Expression of Energy system
4. Protein Evaluation of feed
5. Calorie- Protein Ratio

1. Energy Partitioning in Livestock

Energy is the capacity to do work, expressed in calories, where one calorie is the energy required to raise the temperature of 1 gram of water by 1°C. 

Another unit: Joule (1 calorie= 4.184 joules; 1 joule= 0.239 calories)

Partitioning of Energy

• Gross Energy (GE)

• Digestible energy (DE)

• Metabolizable energy (ME)

• Net energy (NE)

Gross Energy (GE):

The total energy present in a feed. Obtained by the complete oxidation of feed in a bomb calorimeter. Not all the gross energy is useful to the animal. 

Digestible energy (DE): DE=GE−Faecal Energy 

Apparent vs. True Digestible Energy

• Apparent Digestible Energy (Apparent DE): In which does not account for endogenous losses (e.g., metabolic products derived from body tissues present in the faeces). 
• It is calculated as: Apparent DE=GE−(FE+Metabolic Endogenous Losses)
• True Digestible Energy (True DE): Considers endogenous faecal energy losses, those from intestinal cells, enzymes, and microbes. 
• It is calculated as: True DE=GE-(FE-Metabolic Endogenous Losses)

True DE is always greater than apparent DE

• Ruminants: Roughages-higher faecal energy losses (40-50%) 

                      concentrates lower losses (20-30%)

• Horses: Faecal energy loss is 40%
• Pigs: Faecal energy loss is 20%

Metabolizable Energy (ME)

Metabolizable Energy is the portion of feed energy that is available for metabolic processes and transformations in animals after accounting for energy losses through urine and gasses. 

ME=DE−Energy loss through urine and gasses

1. Urinary Losses:
   • In cattle: 4-5% of GE
   • In pigs: 2-3% of GE
2. Gaseous Losses:
   • Methane production :7-8 % of GE in ruminants
   • ME=DE×0.82

Poultry: Estimating ME is easy  because both urinary and faecal losses are voided together.

 Net Energy (NE)

Actual useful form of energy available to the animal for maintenance, growth, reproduction, and production. NE=ME−HI

Heat Increment (HI)

Heat Increment (HI)/specific dynamic effect/calorigenic effect/thermogenic action, is the amount of heat lost in physical and chemical processes associated with digestion and metabolism. HI includes:

1. Work of Nutrient Metabolism: Energy expended in the metabolic processes of nutrients.
2. Heat of Fermentation: In ruminants due to microbial fermentation in the rumen.
3. Work of Excretion by the Kidneys: Energy used in the excretion of waste products.
4. Work of Digestion: Energy used in the mastication of food and its propulsion.
5. Increased Muscular Activity: Energy used by various organs due to the metabolism of nutrients.

2. Measurements of energy

1. Calorimetry method

2. Carbon- Nitrogen balance

3. Comparative slaughter methods

2.1. Measurement of energy by Calorimetry

Types of Calorimetry:

A) Direct calorimetry

B) Indirect calorimetry

Direct calorimetry measures the heat produced by an animal to determine its energy expenditure directly . There are two types of heat loss: sensible and insensible heat loss.

Indirect calorimetry is a method used to estimate heat production and energy expenditure in animals by measuring gaseous exchange. Energy from the oxidation of nutrients, which involves the consumption of oxygen (O₂) and the production of carbon dioxide (CO₂).

Types of Indirect Calorimetry Systems

There are two main types of systems used in indirect calorimetry: open circuit and closed circuit systems.

Open Circuit System

• Mechanism: The animal breathes atmospheric air, and the exhaust air is collected or metered and sampled for O₂ and CO₂ content.
• Process: The composition of the incoming and outgoing air is analyzed using chemical, volumetric, or manometric techniques.
• Advantages: Allows for continuous measurement and is less restrictive for the animal.

Closed Circuit System

• Mechanism: The animal rebreathes the same air within a sealed system.
• Process:
  • CO₂ is absorbed using a suitable absorbent, and its rate of production is determined by weighing the absorbent before and after use.
  • The decrease in volume of the respiratory gas mixture, due to O₂ consumption, is measured.
  • O₂ consumed by the animal is replaced by a metered supply of pure oxygen.
  • Both O₂ consumption and CO₂ production are corrected for any differences in the amounts present in the circuit air at the beginning and end of the experiment.
  • Methane (CH₄) is allowed to accumulate and is measured at the end of the experiment.
• Advantages: Provides precise measurements of gas exchange but can be more restrictive for the animal.

Respiratory Quotient (RQ)

• Definition: RQ is the ratio of CO₂ produced to O₂ consumed.
• Values:
  • Carbohydrates: RQ = 1.0
  • Fats: RQ = 0.70
  • Proteins: RQ = 0.80
  • Fattening animals (conversion of carbohydrates to fat): RQ > 1.0

Advantages of Indirect Calorimetry

• Non-invasive: Does not require direct measurement of heat loss from the animal’s body.
• Versatile: Can be used to measure energy expenditure in various species and under different conditions.
• Detailed: Provides information on the type of nutrients being metabolised.

2.2. Measurement of Energy Retention by Carbon and Nitrogen Balance Technique

Carbon-Nitrogen Balance involves calculating the amounts of these elements entering and leaving the body to determine the nutrient retention. The retained carbon and nitrogen can then be used to estimate the energy retained in the body.

Steps in Carbon-Nitrogen Balance Technique

1. Measurement of Intake and Excretion:
   • Carbon (C): Enters the body through food and leaves as CO₂ and methane (CH₄).
   • Nitrogen (N): Enters the body through food and leaves through faeces and urine.
2. Calculation of Retained Nutrients:
   • Carbon Retained=Carbon Intake−Carbon Excreted 
   • Nitrogen Retained=Nitrogen Intake−Nitrogen Excreted Faeces Urine 
3. Nutrient Retention:
   • Protein: Calculated by multiplying the nitrogen balance by 6.25 (since body protein is assumed to contain 16% nitrogen).
   • Protein Retained=Nitrogen Retained×6.25
   • Fat: The remaining carbon is assumed to be stored as fat.
4. Calculation of Energy Retained:
   • Energy from Protein=Protein Retained×5.64kcal g
   • Energy from Fat=Fat Retained×9.39kcal g
5. The total energy retained is the sum of the energy from protein and fat.

2.3. Measurement of Energy Retention by Comparative Slaughter Method

• It is used to calculate the net protein (NP) required for growth.
• It is costly and time-consuming when used on larger animal species.

Methodology of Comparative Slaughter Method

1. Initial Group:
   • Animals are selected from the same population with the same sex, genotype, and body weight to ensure comparable body compositions.
   • After a two-week adaptation period on a standard meal of known energy, a group of animals is slaughtered to establish baseline data on their body composition and gross energy content.
   • The energy content of these animals is determined using bomb calorimetry.
2. Experimental Group:
   • The remaining animals are fed the same diet for a set period.
   • After the feeding period, these animals are slaughtered, and their body composition is assessed.
   • The difference in body energy content between the initial baseline animals and the experimental animals is used to calculate energy retention.

3. Expression of energy system

3.1. Total digestible nutrients (TDN)

• Expressed in terms of the weight (Kg or %) of digestible material in the feed.

• TDN (%) = % Dig. CP + Dig. CF + % Dig. NFE + (2.25 x % Dig. EE)

• Determined by digestibility trials

• 1 Kg TDN = 4400 Kcal DE (1 g TDN is 4.4 Kcal DE)

Factors affecting TDN value of feed

• % Dry matter- high DM= less Moisture= high TDN
• % Digestibility of dry matter- Higher indigestible substances (lignin, acid insoluble ash)= low TDN values.
• Presence of minerals: lower TDN (minerals as such contribute no energy).
• % Digestible fat in the feeds: Higher fat= high TDN

 Merits:

• Easiest to determine 

• The energy requirements of ruminants are expressed in TDN

Limitations:

• Errors in chemical analyses

• Errors in digestibility trials

• It over estimates the value of roughages 

• If feeds are high in fat content, the TDN value sometimes exceeds 100%.

• Micronutrients like minerals have not been included.

3.2 Starch equivalent By Kellner

• Fat producing power of feed

• Number of Kg of starch that produces the same amount of fat as 100 kg of the test feed.

• Concentrate – Golden number (0.95)

• Actual SE of concentrates =Calculated production value x 0.95

• Roughages (correction factor)

• Actual SE of roughages = Calculated production value x (CF% x 0.58)

3.3 Scandinavian food unit system

• Niels Hansson developed this system in Sweden for feeding milking cows.

• In this system the value of feeds is not expressed in energy terms, but relative to the value of

common feedstuff, barley.

3.4 Physiological fuel value: by Atwater

Correction factors: because of metabolic losses

Nutrients	GE value	Physiological fuel values (ME value factors)
Carbohydrate	4.15 Kcal/gram	4
Fat	9.4 Kcal/gram	9
Protein	5.65 Kcal/gram	4

4. Protein Evaluation of Feeds

2.1 Measures of Protein Quality in Ruminants and Non-Ruminants

1. Crude protein:  True + NPN

2. Digestible crude protein (DCP):

• For concentrates = CP x Dig. Coef. (dig. Almost similar and CP is high)
• For roughages = DCP ( g/kg DM) = CP(g/kg DM) X 0.9115 – 36.7
• (greater variability and relatively greater MFN with low CP content)

3. Degradable and undegradable protein = Rumen degradable (RDP) + Undegradable dietary Protein (UDP)

4. Metabolisable protein = UDP + Microbial protein

Evaluation of protein quality for poultry

1. Chemical evaluation:

a. Chemical score: the quality of a protein is decided by that essential amino acid which occurs in greatest deficit when compared with a standard (egg). 

Exapmle: wheat: greatest deficit in lysine. The lysine content of egg and wheat protein is 72 and 27g/kg DM respectively. So, the chemical score for wheat protein is 27/72=0.37.

Disadvantage: No account is taken of the deficiencies of AA other than that in greatest deficit.

b. Essential amino acid Index (EAAI): Is defined as the geometric mean of the egg ratios of essential

amino acids. It is calculated as

                       EAAI = n a/ae x b/be x c/ce x ……… x j/je

Where: a,b,c,…j = concentrations (g/kg) of essential amino acids in feed, ae,be,ce,…je = concentrations (g/kg) of essential amino acids in egg protein

Advantage: consider all AA and predict the effect of supplementation in combination of proteins.

Disadvantage: Proteins having different amino acid profiles may have the same or a very similar index.

2. Biological experiments:

a. Digestibility Coefficient: percentage of the ingested protein absorbed into the bloodstream after the process of digestion is complete.

b. Protein efficiency ratio (PER): the weight gain per unit weight of protein eaten 

                                                          (weight gain/ protein consumed)

c. Net protein retention (NPR): A modification of PER method, where the weight gain of the experimental group is compared with a group on a protein free diet.

NPR = (Weight gain by test protein group – weight loss of non protein group)/ Weight of protein  consumed

d. Gross protein value (GPV): = weight gain/g test diet divided by weight gain/g basal diet.

Basal diet: casein as basal protein; test diet = basal protein+ test protein

e. Biological value: Direct measure of the proportion of food protein which can be utilized by the animal for synthesizing body tissues and may be defined as the percentage of the nitrogen absorbed which is retained by the animal. (BV of egg = 100%)

f. Net protein utilization (NPU): The usefulness of a protein to animals will depend upon its digestibility as well as biological value.

The product of these two values is Net protein utilisation.

g. Protein Replacement Value (PRV): measures the extent to which a test protein will give the same N-balance as an equal amount of a standard protein = PRV = NA – NB / N-intake

Note: PRV measures the efficiency of utilisation of the protein given to the animal. Other methods measure the utilization of digested and absorbed protein.

13. Which of the following is true about the Protein Replacement Value (PRV)?
A) It measures the digestibility of protein
B) It is calculated using the geometric mean of amino acid ratios
C) It measures the efficiency of utilization of the protein given to the animal
D) It is the same as the Net Protein Utilization

5. Calorie-Protein Ratio 

Used to evaluate the balance between the caloric content and protein content of feeds, to ensure adequate protein relative to energy intake.

1. Importance in Poultry Nutrition: to ensure optimal growth and production. 

• Broiler chick feed – 140:1 
• Broiler finisher feed – 160:1

2. Nutrient Requirements and Feed Formulation:  Helps in formulating balanced rations that meet the specific energy and protein needs of different animals, ensuring efficient growth and production.

• Wider Calorie- Protein ratio:Higher fat deposition of carcass, hence using in broiler finisher Stage or for layers.
• Narrower Calorie- Protein ratio:lower fat and higher protein deposition on the caress hence used for lean meat broiler production.

Nutritive Ratio: Evaluate the balance between protein and non-protein nutrients in animal feed, indicating the proportion of digestible protein to digestible non-protein nutrients.

1. The nutritive ratio is calculated by dividing the sum of digestible carbohydrates and fats by digestible protein.
2. Application: A narrow nutritive ratio indicates a higher protein content relative to energy, suitable for growing and lactating animals, while a wider ratio is used for maintenance diets