Dairy nutrition
May 2013
Dairy production model
The five systems of NZ dairy
farming
• 1) all grass, self contained
– No supplement fed to the herd, except
supplement made on the milking area
– No grazing off of milking area
• 2) feed imported either as supplement or
grazing off and fed to dry cows (4% to
14% of feed imported)
• 3) feed imported to extend lactation and
for dry cows (10% to 20% of feed
imported)
– Includes farms feeding 1-2 kg of meal or grain
for most of the season
• 4) feed imported and used at both ends of
lactation and for dry cows (20% to 30% of
feed imported)
• 5) imported feed used all year (30% to
40%, but can be up to 55%) of feed
How do pastures grow
• Made up of grass and clover plants
(usually ryegrass and white clover)
• In a pasture there are two processes
taking place (growth and decay)
• Grazing management is the use of stock
to harvest grass, thereby controlling
growth and quality
Points to remember
• Net growth is the rate at which new leaves
appear, less the rate of decay
• Grass leaves appear more quickly in spring (7
days) and more slowly in winter (30 days)
• Grass leaves die after 21 days in spring and 90
days in winter
• Dead leaves accumulate in the bottom of the
pasture and reduce intake and quality (8 MJ ME)
Quantity
• Quantity of pasture is measured by:
– Kilograms of dry matter per ha (kg dm/ha)
• Can be done in several ways:
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Eye appraisal
Cut and dried
Plate meters
Electronically
By satellite
Based on production (12 kg dm/kg ms)
What is Quality
• Very digestible
• High in energy
• High in protein
• Easily harvested by cows (bite size)
– Allows high feed intake
– Allows high milk production
How do we assess quality
• Visually
– Less than 20% dead material in base
– Less than 10% seed head
– More than 60% to 70% green leafy material
• Laboratory
– Energy (MJ of ME over 12)
– Crude Protein (22% early lactation, 16% mid
lactation, 14% late lactation)
– Neutral detergent Fibre (30% to 40%)
Management for quality
•
– Keep the pasture in a wedge over the entire season
(see overhead)
– Graze the pasture consistently down to a low post
grazing residual
– During periods of growth exceeding demand,
“increase” the stocking rate by dropping paddocks
from the grazing round and conserving
– Grazing round should be set at three times the
number of days it takes for each new leaf to appear
Effects on milk production of quality for
a 500 kg cow
• High quality pasture (12.5 MJ ME)
– Intake will be 17 kg dm per day
– 17 kg X 12.5 MJ ME = 212 MJ ME
– If 64 MJ ME required for maintenance, then
148 MJ ME available for milk (non pregnant,
no weight gain)
– If it takes 70 MJ ME per kg of MS, then
production will be 2.1 kg MS (148/70=2.1)
Quality continued…
• Lower quality pasture (10.5 MJ ME)
– Intake will be reduced to 14 kg dm (due to
increased fibre, being slower to digest and
filling the rumen—thus reducing appetite)
– 14 kg x 10.5 = 147 MJ ME
– Maintenance is 64, so MJ ME available for
milk production is 83 MJ ME
– At 70 MJ ME per kg MS, then potential
production is 1.2 kg (83/70=1.2)
Why feed supplements
• In early lactation to boost intake, so as to
better meet cow requirements
• To improve body condition
• To overcome pasture deficits
Why continued..
• As a carrier for other items, e.g. minerals
• To boost production above what is
possible with grass alone
• To extend lactation
Best responses
• When the level of feeding is low (quantity)
• When the quality of pasture is low
• When high quality supplements are
available at a reasonable price
• If supplement is easily eaten
In NZ energy is most common problem
• Dairy cows energy requirements are:
– Maintenance
– Pregnancy
– Bodyweight gain
– Lactation
What’s the true cost of
supplements?
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Need to consider:
1) cost per kg of dry matter
2) utilisation
3) cost of machinery to feed out
4) cost of labour to feed out
5) production response