Bovine Nutrition and Metabolism 4 Flashcards
What is the expected DMI in dry cows?
~2% of bodyweight
10-15 kg/day
List two physiological factors that reduce DMI in cows
Increase calf size
Increase BCS and reduce appetite
What is the aim for BCS at drying off and calving?
2.5-3
What are the energy requirements of cows in at drying off and near calving ?
At drying off ~(65+15) = 80MJ/day
Near calving ~(65+45) = 110MJ/day
List three things that digestible undegraded protein is used for in the dry period.
Foetal growth
Increased milk yield and quality
Increased fertility
What is an advantage of a single ration for dry cows?
Avoids sudden change in diet during early dry periods which may maintain better improved energy balance and reduced risk of LDAs.
How would you offset the cost of a having a single ration dry cow diet?
+/- shorter dry periods to offset the cost
What is the calcium requirements in lactation?
~2g per litre of milk
List three methods to prevent milk fever
Calcium restriction
Magnesium supplementation
DCAD/DCAB manipulation
What is the ideal amount of calcium in a dry cow diet to prevent milk fever?
<20g/day
List three feeding strategies for calcium restriction
Grass/grass silage high in [Ca]
Dilute [Ca[ by increasing straw in ration
Tightly stock transition if at grass
Which ion that you can supplement improves calcium mobilisation?
Magnesium
List three feeding strategies of magnesium supplementation.
MgCl2 in TMR or drinking water
Can affect ration palatability
Will influence DCAD
What is the equation to work out the dietary cation anion difference?
DCAD = ([Na+] + [K+]) - ([Cl-] + [S2-])
What happens to cows who have diets with a low DCAD?
Metabolic acidosis in induced and more rapid mobilisation of Ca from body reserves around calving
List 4 disadvantages for a full DCAD
Expensive
Unpalatable (reduces dry matter intake)
Very soluble so wash out in the rain
Relative pH instability in the face of variable DMI
How would you feed a partial DCAD?
Manipulate feeds to reduce ration DCAD
What are two forages you can feed with a low DCAD?
Maize/wholecrop wheat silage
Straw (lowest)
What are two straights you can feed with a low DCAD?
Brewers grains
Wheat
Briefly describe how peripheral insulin resistance works in cows
High BCS +/- excess ME in early dry period.
Reduce tissue response to insulin.
Reduce dry matter intake increases negative energy balance and increases fat mobilisation.
Why is there fat deposition in the liver with a negative energy balance?
Lack of acetyl CoA leads to free fatty acid unable to eneter the TCA cycle.
Depletion of lipoproteins means the liver is unable to export fat.
Briefly describe the difference between the two types of ketosis in cattle.
Type 1 - energy intake < output, seen in peak lactation
Type 2 - insulin resistance, fat infiltration of the liver, see around calving
List two ways to prevent ketosis in cattle.
Minimise peripheral insulin resistance
Maximise DMI
What is the rumen buffered by?
Saliva
