Maintenance Requirements

Question 1

Who publishes the gold standard and the legal standard for animal nutrient requirements?

Answer 1

NASEM (National Academies of Sciences, Engineering, and Medicine)

formerly NRC (national research council)

Question 2

What is always considered first when balancing a diet?

Answer 2

Energy

All dietary constituents except minerals and water contain energy.
Feed ingredients mostly fed for energy account for most of the ration in terms of weight and cost.

Question 3

Why is energy the “pacesetter” for the requirements of other nutrients?

Answer 3

The rate of energy supply and utilization dictates the use of other nutrients.

ex. low energy diet has a lower protein requirement b/c you have lower maximal growth

Question 4

What type of model can be used to demonstrate how nutrients are influenced by energy?

Answer 4

Broken Stick Model

Shows how energy is a major limitation of nutrients depending on its level. When a requirement is met, the stick breaks.

Question 5

What is nutrient partitioning?

Answer 5

The direction of nutrients to areas of need.

ex. brain and CNS are high priority, fat is low priority

Question 6

What are the functions of hormones?

Answer 6

1. Hormones send signals between tissues
   - secreted and carried to another through the blood
2. Hormones conduct cell to cell communication
   - must be secreted from a cell
   - the target tissue must have a receptor
3. Hormones regulate …
   - nutrient metabolism
   - growth
   - tissue mobilization
4. Signal transduction systems in the cell are operated by hormones
   - relays and amplifies signals
5. Synthesis and release of some hormones depends on…
   - nutrients available
   - nutritional status
   - environment
   - physiological state

Question 7

How do hormones regulate and direct nutrient use?

Answer 7

Homeostasis and hemoeorhesis

Question 8

Define homeostasis

Answer 8

Homeostasis is maintenance of the normal body state; it must be maintained for life to persist
- blood glucose and calcium

Question 9

Define homeorhesis

Answer 9

Homeorhesis is the coordination of metabolism in support of a dominant physiological process
- priorities partitioning of nutrients
- directs nutrients in a certain “direction”
- acts as a conductor that coordinates nutrient movement

Question 10

What nutrient partitioning occurs in early growth?

Answer 10

bone and muscle

Question 11

What nutrient partitioning occurs in late growth?

Answer 11

muscle and adipose tissue

Question 12

What nutrient partitioning occurs in late pregnancy?

Answer 12

gravid uterus and mammary gland

Question 13

What nutrient partitioning occurs in early lactation?

Answer 13

mammary gland for milk synthesis

Question 14

What is nutrient repartitioning?

Answer 14

movement of nutrients from one tissue to another that occurs when nutrient supply is low

Question 15

What is maintenance requirement?

Answer 15

The amount of energy needed to maintain an animal in zero balance of that nutrient (not gaining or losing)

Strict definition applies to mature non-productive animals (not pregnant or lactating)

Other non-productive requirements are also needed to survive in the animal’s environment

Maintenance and non-productive are usually combined into the same requirement

Question 16

What are some examples of animals with requirements that are close to maintenance?

Answer 16

Adult males outside of breeding season

Females when not pregnant or lactating

Castrated male sheep used for wool production only

Question 17

How is NE broken up?

Answer 17

NE is broken up into NE for maintenance and NE for other specific functions

NE is energy retained, everything else is heat increment

Question 18

Describe “dilution of maintenance”

Answer 18

It increases the proportion of energy used for production and thus increases conversion of feed to product; increased efficiency

accounts for improvements in efficiency, dilutes out maintenance costs

Question 19

What is basal metabolism?

Answer 19

minimal metabolic rate (measured as heat production)

Measurement requires:
- post-absorptive state
- minimal physical activity
- minimal psychic stress

Question 20

What is basal metabolism affected by?

Answer 20

A. body size
B. species
C. age and neuroendocrine factors
D. previous level of nutrition
E. climate
F. breed

Question 21

How is basal metabolism affected by body size?

Answer 21

bigger animals have more tissue, which requires greater energy to maintain and produce more heat

Smaller animals have a higher heat production per pound

Question 22

Describe heat production per metabolic body size

Answer 22

Heat production per metabolic size is pretty similar between animals

Question 23

What is the best way to compare metabolism across species?

Answer 23

The most appropriate way to compare metabolism across species is to use metabolic body weight

It make it easier to compare species

Question 24

How is basal metabolism affected by species?

Answer 24

BW^0.75 is not appropriate within species

Question 25

How is basal metabolism affected by age or neuroendocrine factors?

Answer 25

Gender, thyroid status, and physiological state can alter basal metabolism.

ex. castration decreases basic metabolic rate

gonadal steroids (sex hormones) impact basal metabolic rate

glucocorticoids (stress hormones) impact basal metabolic rate

catecholamines regulate short-term stress; epinephrine and norepinephrine

beta-agonists

Question 26

How do gonadal steroids impact metabolic rate?

Answer 26

Steroid hormones include estrogen and progesterone from ovary or testosterone from the testes

• secretion is increased at puberty
• regulated by FSH and LH (anterior pituitary)

Actions: normally anabolic
- increase bone development
- increase protein synthesis
- IGF response to GH

Question 27

How do glucocorticoids (stress hormones) impact basal metabolic rate?

Answer 27

The most common of these hormones is cortisol, a steroid formed in the adrenal cortex and whose stimulation is stimulated by stress.

Immediate term effects (hours or days)

Actions = make nutrients available
- decrease glucose uptake by muscle and adipose tissue
- increase glucose synthesis in the liver
- increase muscle protein breakdown

Long term, these hormones can create insulin resistance and obesity.

Question 28

Describe catecholamines.

Answer 28

Catecholamines regulate short term stress, and they include epinephrine and norepinephrine.

They are secreted from the adrenal medulla.

Secretion is induced by many forms of stress, such as fight or flight, cold, trauma, etc.

Short term effects (minutes)

Actions:
- increased lipid mobilization
- increased glucose synthesis
- increased metabolic rate
- increased protein synthesis

Question 29

What are beta-agonists and what are they used for?

Answer 29

Beta-agonists are compounds used to increase lean gain by activating receptors for catecholamines.

They have a hormone-like mode of action, but are not hormones themselves.

They redirect nutrients from fat to protein deposition.

Nutrition: need to consider that there is a change in tissue deposition = change requirements.

These compounds are often used at the end of feeding periods to stimulate muscle growth over fat growth.

Question 30

How is basal metabolism affected by previous levels of nutrition?

Answer 30

Animals fed more have a higher maintenance cost.

Some animals may undergo compensatory growth if underfed.

Question 31

How is basal metabolism affected by climate?

Answer 31

prolonged cold = increased basal heat production

prolonged heat = decreased basal heat production