Maintenance and Growth

Question 1

An animal is in a state of maintenance when:

Answer 1

1. the body composition remains constant (animal neither gains or lose weight)
2. no products produced (e.g milk, eggs , wool)

3.no work is performed on the environment (e.g running)

Question 2

What is NEGATIVE energy balance?

Answer 2

When animals are deprived of food and use their body reserves to provide energy for essential bodily functions like respiration and circulation

Question 3

define maintenance requirement

Answer 3

• it is the amount of a particular nutrient an animal needs to make sure it neither gains nor loses that nutrient
• minimum quantity of nutrients required to maintain zero balance

Question 4

Define basal metabolism

Answer 4

• it is the amount of heat produced by the body during maintenance, providing an estimate of energy needed for basic bodily functions.
• Direct estimate of energy from feed to meet maintenance energy requirement

Question 5

Measurement of basal metabolism can be complicated , how?

Answer 5

heat is also produced by:
* Digestion and metabolism of feed - heat increment
* Voluntary muscles movement
* Maintaining body temperatures in colder environment

Question 6

How is basal metabolism measured in aniamls?

Answer 6

• typically measured by fasting animals to eliminate the heat increment of feeding
• Ruminants fasted for 4 days

Question 7

When is post-absorptive state reached when

Answer 7

• post-absorptive stat = indicates completion of digestion and metabolism of previous meals
• reached when
  1. Heat production is constant
  2. Respiratory quotient constant
  3. Decline in methane production

Question 8

Term “fasting metabolism” more accurate than “basal metabolism” , explain

Answer 8

it is difficult to achieve complete relaxation necessary for “basal metabolism” measurement as animals exhibit some form of activity e.g standing which produces heat during fasting.

Question 9

How is metabolic rate affected by SA : BW ratio

Answer 9

• metabolic rate is a factor of SA:BW ratio
• As animals grow larger and their body weight (BW) increases, the SA:BW ratio decreases.
• smaller SA means there is less surface area available for heat exchange , resulting in a lower metabolic rate

Question 10

Why do we use the metabolic weight of animals when estimating maintenance requirements?

Answer 10

• it is diifficult to determine surface area of animals due to variations in shape , sizes , furthers , fur etc
• a relationship between body weight and surface area is determined to estimate surface area

Question 11

Why is it a challenge to determine maintenance needs/requirements on farm from fasting metabolism ?

Answer 11

1. Animals on farms use energy for voluntary muscular activity, which is not accounted for during fasting metabolism measurements.
2. Productive livestock have higher metabolic rates than fasted animals, leading to increased maintenance costs.
3. Animals on farms experience climate extremes and may need additional energy to maintain normal body temperature.

Question 12

Explain how the fact that animals on the farm commonly use more energy for voluntary muscular activity make it a challenge to determine maintenance requirements from fasting metabolism ?

Answer 12

• Animals on the farm engage in more voluntary muscular activity, which adds to their maintenance energy requirements.
• the energy cost of eating and ruminantion is included in the k value
• Grazing animals expend more energy on movement, resulting in a higher maintenance requirement compared to non-grazing animals.
• an Average of 20 – 25% higher maintenance requirement for grazing animals

Question 13

Explain how that fact that high productive livestock have higher metabolic rates than fasted animals make it a challenge to determine maintenance requirements from fasting metabolism ?

Answer 13

• The value obtained for fasting metabolism depends on the previous energy status of the animal.
• Animals on a high plane of nutrition will have a higher metabolic rate during fasting due to their increased energy intake
• Animals can adapt to low-level rations by
  1. improving energy utilization efficiency
  2. reducing non-essential muscular activity.
• There’s a risk of underestimating the maintenance requirement of high-producing animals due to their higher metabolic rates.
• However, this error is compensated for by increasing maintenance requirements as energy intake increases.

Question 14

Discuss the difference in fasting metabolism between cattle and
sheep.

Answer 14

• Sheep have a lower fasting metabolism
• cattle have a higher fasting metabolism
• the differences arise because sheep have a higher fat % and lower protein % compared to cattle

Question 15

Discuss the difference in fasting metabolism between younger and older animals ?

Answer 15

• older animals have a lower fasting metabolism
• younger have a higher fasting metabolism
• the differences arise because older have a higher fat % and lower protein % compared to younger animals

Question 16

Influence of climate on energy metabolism and requirements for maintenance

Answer 16

• Farm animals, both mammals and birds, are homeotherms, striving to maintain constant body temperature.
• heat loss mechanisms include
  1.sensible loss
  2. evaporative loss
• Heat loss depends on:
  1. Animal characteristics (e.g insulation from fur)
  2. Environmental characteristics(e.g temp)
• Fed animals have a wider thermoneutral zone compared to fasted animals, with increased reliance on evaporative heat loss at higher temperatures.
• Ruminants generally have wider thermoneutral zones and lower critical temperatures

Question 17

list the heat loss mechanisms

Answer 17

1. Sensible
   - (radiation, conduction, convection)
2. Evaporative
   - (water loss from body surface and lungs).

Question 18

Why do ruminant animals have a larger thermoneutral zone and lower critical temperature than
monogastric animals? (3)

Answer 18

1. Greater capacity to regulate evaporative heat losses
2. Higher heat increment of feeding (lower k values than monogastrics)
3. Produce heat more constantly throughout the day

Question 19

Why do fed animals have a wider thermoneutral zone compared to fasted animals?

Answer 19

1. fed animals have a heat increment of feeding
2. fed animals have energy from nutrients to maintain physiological functions and heat production.
3. fasting animals conserve energy by reducing heat production

Question 20

How do ruminants animals survive in colder areas?

Answer 20

• feed them diets with higher roughage content
  and lower energy efficiency utilization
• roughage require more energy to digest , generating heat .
• low energy efficiency ensures that energy is used to generate heat instead of growth or lactation

Question 21

How is heat stress in hot climates can be managed ?

Answer 21

• through
  1. diet manipulation
  2. panting
  3. sweating
  4. environmental modifications.

Question 22

Ruminants, like cattle and sheep, struggle in hot climates , why

Answer 22

• their diets mainly consist of low-quality roughage with lower efficiency of energy utilization
• so they produce more heat during digestion compared to concentrated feeds.

Question 23

How is nitrogen loss on Nitrogen-Free diet posible?

Answer 23

• Animal consuming N free diet will still excretes N in faeces and urine
• FECAL N loss consists of
  1. enzymes,
  1. sloughed cells
  1. microbial residues.
• nitrogen in faeces is called metabolic faecal nitrogen

-URINARY N loss includes nitrogen from part of materials that the body uses up and cannot recycle for further use
-comprises of urea , a by-product of amino acid catabolism.

Question 24

What happens when an animal is fed a N free diet and later then fed a diet with N ?

Answer 24

*N free diet
- the amount of nitrogen in the urine decreases gradually over a few days.
- eventually , it stabilizes at a lower level.
- The body starts depleting its nitrogen reserves.
- Most metabolically active tissues, like the liver, are the first to deplete their nitrogen reserves.
- Once the nitrogen reserves are depleted, urinary nitrogen excretion reaches a minimal and constant level.
- if energy intake is adequate, the minimal level of urinary nitrogen excretion is maintained.
- If protein is catabolized for energy, urinary nitrogen excretion increases again.

*N reintroduced
- There’s a lag in re-establishing equilibrium in nitrogen levels
- This delay suggests the presence of a protein reserve that can be utilized during scarcity.
- Nitrogen sources, like the liver, are replenished when nitrogen is available again.

Question 25

What is used for
the indication of protein requirements for maintenance ?

Answer 25

Endogenous urinary N
- smallest loss of nitrogen from the body when there’s enough energy available.

Question 26

If a ruminant animal is maintained on a N free diet for an extended period of time, what would cause
urinary N excretion to increase?

Answer 26

Inadequate supply of energy results in catabolism of body reserves and an increase in urinary N excretion in response.

Question 27

Why do ruminant animals have lower urinary N loss than monogastric ?

Answer 27

• Urea recycles back to rumen .
• Nitrogen that would have been excreted in the urine of monogastric animals is instead used for microbial protein synthesis in ruminants and subsequently excreted as microbial residues in the feces.

Question 28

Basal endogenous N equation

Answer 28

= Endogenous urinary N + Metabolic faecal N

Ruminants basal N requirements = 350 mg N/kg x W^0.75

Question 29

source of exogenous urinary N

Answer 29

nitrogen from feed , not body reserves

Question 30

Microbial protein alone sufficient to supply maintenance requirements of ruminants .TRUE or FLASE

Answer 30

True - No contribution needed from DUP

Question 31

why is the predicted energy value of growth decreased by 15% for males and later maturing animals

Answer 31

• they have less fat deposit and fat is very enrgy dense
• so they will have a lower energy content

Question 32

Explain energy requirements for growth for sheep

Answer 32

• Energy Value of growth is significantly influenced by sex, requiring different equations for males, females, and castrate
• Breed has a minor effect on energy value

Question 33

Define standard reference weight

Answer 33

• Liveweight achieved by animal when skeletal development is complete
• And BCS in middle range
• SRW varies between breeds and sexes