Macrominerals

Question 1

Characteristics of phosphorus…?

Answer 1

most known functions
concentrated in bone
ESSENTIAL for:
- bone dev.
- nucleic acids, phospholipids, phosphoproteins
- energy metabolism (ATP)
- buffers

Question 2

Sources of phosphorus?

Answer 2

milk
cereal grains (phytates)
animal products containing bone
low in hays & straws

Question 3

Phosphorus deficiencies lead to…?

Answer 3

similar bone disorders to Ca
lameness, bone/wood chewing
low fertility
poor growth

Question 4

Characteristics of magnesium…?

Answer 4

enzyme activator
controls nerve impulses
Mg in bone & soft tissue unavailable - only 2% in body available - requires regular diet input
no hormonal control
mostly absorbed from reticulo-rumenvia ACTIVE transport

Question 5

How much availability of Mg (%)?

Answer 5

15-35% cattle

up to 66% sheep

Question 6

Where does Mg go in a cow?

Answer 6

Blood -> milk (0.13g/L); foetus (1.0g); kidney (urine); faeces

Question 7

Symptoms of Mg deficiency?

Answer 7

hypomagnesemia (grass tetany) - ruminants -> nervousness, tremors, excessive sweating

Question 8

Sources of magnesium?

Answer 8

legumes
wheat bran
Mg blocks
Causmag (MgO)
magnesium sulfate or chloride in troughs

Question 9

More about grass tetany…?

Answer 9

Rapid onset (late winter - early spring)
Causes -> hyperexcitability, twitching, staggers
reduced appetite
incoordination & recumbency (‘pedalling’)
convulsions & death
more variable in sheep (confused with preg. toxaemia or hypocalcaemia), usually in lactation
slow dev. (autumn) - low Mg -> staggers
subclinical - reduced milk yield & fat; irritability

Question 10

Diagnosis of grass tetany?

Answer 10

Low blood Mg (<0.75 vitreous humor)

Question 11

Treatment of grass tetany?

Answer 11

i.v. or s.c. Mg
usually as MgSO4 (200-300ml of 20% w/w) in cattle + Ca
50ml Ca borogluconate containing 25g Mg hypophosphite
diet rectification

Question 12

In what ways is Mg availability affected?

Answer 12

• low Mg in feed (spring pastures, fast growth post urea application, grasses - ryegrass lower than legumes)
• availability lower in pastures than conserved feeds
• K content -> reduces plant uptake & absorption of Mg + reduced uptake of Na in plants
• high RDN (high rumen NH4+ -> precipitates Mg out -> less absorption)
  genetics

Question 13

Prevention of low Mg/grass tetany?

Answer 13

• include Mg supplements (calcined MgO; avoid excess)
• Mg bullets (only release 1g/day)
• daily oral dose in milkers
• Mg in licks
• MgCl in water
• pasture topdressing (20kg/ha MgO)
• Mg rich plants (chicory, plantain)
• Reduce K fertiliser
• Na licks

Question 14

Mg content in milk?

Answer 14

low but constant (0.3mmol/L) - not affected by diet; higher in colostrum
absorbed better by young ruminants - declines with age until 8 weeks

Question 15

A bit about sodium (NaCl)…?

Answer 15

body fluid regulation
acid-base balance
muscle & nerve activity
exercising/lactating/diarrhoea animals need more
most feeds are low in NaCl except animal & marine feeds

Question 16

A bit about chlorine…?

Answer 16

acid-base relationship
osmotic reg.
gastric secretion
deficiency -> alkalosis

Question 17

A bit about potassium (K)…?

Answer 17

osmotic reg. & acid-base balance (cation - K+)
muscle & nerve function
CHO metabolism
deficiency & excess RARE, but deficiency -> reduced appetite, growth, lethargy

Question 18

Sources of K?

Answer 18

forages - high

grains - low

Question 19

A bit about sulfur

Answer 19

most confusing slide ever! #26

- unlikely to be deficient except if high urea