Maintenance Requirements Flashcards
Who publishes the gold standard and the legal standard for animal nutrient requirements?
NASEM (National Academies of Sciences, Engineering, and Medicine)
formerly NRC (national research council)
What is always considered first when balancing a diet?
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.
Why is energy the “pacesetter” for the requirements of other nutrients?
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
What type of model can be used to demonstrate how nutrients are influenced by energy?
Broken Stick Model
Shows how energy is a major limitation of nutrients depending on its level. When a requirement is met, the stick breaks.
What is nutrient partitioning?
The direction of nutrients to areas of need.
ex. brain and CNS are high priority, fat is low priority
What are the functions of hormones?
- Hormones send signals between tissues
- secreted and carried to another through the blood - Hormones conduct cell to cell communication
- must be secreted from a cell
- the target tissue must have a receptor - Hormones regulate …
- nutrient metabolism
- growth
- tissue mobilization - Signal transduction systems in the cell are operated by hormones
- relays and amplifies signals - Synthesis and release of some hormones depends on…
- nutrients available
- nutritional status
- environment
- physiological state
How do hormones regulate and direct nutrient use?
Homeostasis and hemoeorhesis
Define homeostasis
Homeostasis is maintenance of the normal body state; it must be maintained for life to persist
- blood glucose and calcium
Define homeorhesis
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
What nutrient partitioning occurs in early growth?
bone and muscle
What nutrient partitioning occurs in late growth?
muscle and adipose tissue
What nutrient partitioning occurs in late pregnancy?
gravid uterus and mammary gland
What nutrient partitioning occurs in early lactation?
mammary gland for milk synthesis
What is nutrient repartitioning?
movement of nutrients from one tissue to another that occurs when nutrient supply is low
What is maintenance requirement?
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
What are some examples of animals with requirements that are close to maintenance?
Adult males outside of breeding season
Females when not pregnant or lactating
Castrated male sheep used for wool production only
How is NE broken up?
NE is broken up into NE for maintenance and NE for other specific functions
NE is energy retained, everything else is heat increment
Describe “dilution of maintenance”
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
What is basal metabolism?
minimal metabolic rate (measured as heat production)
Measurement requires:
- post-absorptive state
- minimal physical activity
- minimal psychic stress
What is basal metabolism affected by?
A. body size
B. species
C. age and neuroendocrine factors
D. previous level of nutrition
E. climate
F. breed
How is basal metabolism affected by body size?
bigger animals have more tissue, which requires greater energy to maintain and produce more heat
Smaller animals have a higher heat production per pound
Describe heat production per metabolic body size
Heat production per metabolic size is pretty similar between animals
What is the best way to compare metabolism across species?
The most appropriate way to compare metabolism across species is to use metabolic body weight
It make it easier to compare species
How is basal metabolism affected by species?
BW^0.75 is not appropriate within species
How is basal metabolism affected by age or neuroendocrine factors?
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
How do gonadal steroids impact metabolic rate?
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
How do glucocorticoids (stress hormones) impact basal metabolic rate?
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.
Describe catecholamines.
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
What are beta-agonists and what are they used for?
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.
How is basal metabolism affected by previous levels of nutrition?
Animals fed more have a higher maintenance cost.
Some animals may undergo compensatory growth if underfed.
How is basal metabolism affected by climate?
prolonged cold = increased basal heat production
prolonged heat = decreased basal heat production
