L11: Mineral Nutrition I (principles and Ca) Flashcards
What is a macromineral?
required in greater amounts
What is a micromineral?
Required in smaller amounts
What are the general functions of minerals?
- structural (bone, muscle)
- enzymes/cofactors
- catalytic function Ca + P = bone
- regulatory (Zn)
- regulating osmotic pressure
- pH
- nerve and muscle function (physiological)
- Na, Cl, K
- facilitated transport
- vitamin, blood and hormone synthesis
*Describe generally how mineral deficiencies occur and how form in digesta effects availability
Describe generally how mineral deficiencies occur
- Insufficient in diet (liebigs law of minimum
- low absorption -need continual exposure or supplementation
- Mineral interactions
- formation of unabsorbable compounds
- competition for metabolic pathways
- induction of metal binding proteins
- Toxic accumulation
_*Describe generally how mineral deficiencies occur and how form in digesta effects availability_
Availability -in digesta, minerals occur as?
- Easily absorbed -metallic ions in solution eg Na, K
- Partially absorbed -chelated
- Not absorbed -parts of insoluble substances
The conversion of minerals between different forms (active or inactive) is …. dependent
pH
Give examples of mineral availabilty
- P often present as phytic acid -need phytases (enzymes) to access, is then easily absorbable
- Chelated minerals
- exist as cyclic compound w/ organic molecule
- protects from reacting with other elements eg when passing through GIT
- enzymes can change this coating
_*Describe the functions of Ca in the body_
- Most abundant mineral in body, [] in bone
- essential for:
- bone and teeth
- enzyme sys. for normal muscle and nerve function
- blood clotting
- Blood calcium homestatic at ~80-120mg/L
- hormonal regulation by calcitonin
_*List good dietary sources of Ca_
- milk
- green, leafy crops (legumes)
- animal products containing bone
- limestone
- Grains LOW source
*Describe how Ca deficiency can occur and the potential consequences
What is the recommended Ca:P ratio?
What happens if there is excess P?
- 1:1 or 2:1
- excess P binds Ca reducing absorption
*Describe the role of Vitamin D
What are the two bioactive forms of VD?
How is VD produced?
Where is it found (source)?
Where is it stored and what does it work with and why?
- bioactive forms are VD2 and VD3
- Produced in skin by exposure to UV light
- Found in cut forages, sunlight, sun-cured forage
- Stored in liver
- works w/ PTH to maintain plasma Ca []
_*Describe role of VD in calcium homeostasis and how Ca hom. is maintained_
- See lecture for diagram
- VD from sun or diet enters body, goes to liver, passes to kidney where it is paired with PTH
- stimulates intestines to increase Ca absorption
- Stimulates Ca uptake into bones by calcitonin if Ca in excess
- Or stimulates Ca release into blood
_*Describe how Ca deficiency can occur and the potential consequences_
- Lack of sunlight or dietary supplementation, grazing on high P pastures
- Consequences:
- big head
- osteoporosis (brittle bone)
- Osteomalacia
- rickets
- DOD
- Milk fever (hypocalcemia)
What is the most common mineral-related problem of the transition cow?
MILK FEVER (HYPOCALCAEMIA)
*Describe how milk fever occurs and how dietary management can prevent it
What are the symptoms of clinical milk fever?
Plasma []?
- symtpoms include inappetence, lateral recumbency, coma, death
- Plasma [Ca} <1.4mmol/L or <56mg/L
_*Describe how milk fever occurs and how dietary management can prevent it_
What are the symptoms of subclinical milk fever?
Plasma [] ?
- can reduce subsequent production
- Plasma [Ca} 1.4-2mmol/L
_*Describe how milk fever occurs and how dietary management can prevent it_
What causes milk fever?
- Inability to absorb from gut and mobilise from bone enough Ca to meet sudden demand imposed on plasma Ca pool by lactogenesis
- Low diet levels and reserves
- Binding by high P
- Ca req. doubles in lactation
- Takes at least 3-4 days to increase Ca mobilisation from bone and increase absorption
_*Describe how milk fever occurs and how dietary management can prevent it_
Describe dietary management of milk fever
- Dietary supplementation of Ca and VD
- VD injections
- feeding anionic salts (DCAD manipulating)
- efficiency of absorption declines as diet [Ca] increases
- Low Ca intake (low Ca diet) pre-calving stimulates calcitriol synthesis
- means better able to respond to Ca plasma drain at lactogenesis
What is the role of Potassium (K)?
What does an excess of K cause?
- Helps retain Ca in blood -decreases loss through urine
- excess causes metabolic alkalosis
- PTH increases, no Ca release
- Reduces bone sensitivity and renal tissue to PTH
What is the role of Magnesium?
- Poorly absorbed from diet, 0.2-0.4% needed for maintenance level
- needs to be supplemented
- High dietary K can reduce plasma [Mg]
- Hypomagnesaemia means less able to mobilise Ca from bone
What can excess P cause?
- Increased mobilisation of Ca from bone regardless of [Ca] in diet
- induce hypocalcaemia
- inhibits PTH action on renal tissue
- Keep diet P to <35g/d pre calving
What is DCAD?
- Dietary Cation-Anion Difference
- lowering reduces blood and urine pH
- improves Ca homeostasis
