Week 7 Grazing Management 2

Question 1

Assessment of herbage mass (4)

Answer 1

1. Visual estimation
2. Rising plate meter
3. Cuts
4. Sward stick/ wellington boot

Question 2

Slide 10 + 11 Advantages and Disadvantages of all different Grass measurement technology

Question 3

What do you take grass cuts with?

Answer 3

Quadrat and Shears
method

Question 4

Estimate of grass available on each
paddock using shears/ quadrant - steps:(5)

Answer 4

1* Based on visual assessment during a farm walk.
2* Measured yield compared to pre-estimated yield
3* 0.25 m2 quadrat is cut to 4 cm
4* The herbage is weighed and the yield is then
calculated, knowing the DM content.
5* DM content (DM guide or microwave)

Question 5

What is the Equipment required for pasture estimation? (5)

Answer 5

1* Grass shears
2* Hand scales: Salter Spring Balance S/S (1 kg x 5g)
may be sourced from AGB Scientific/ Grasstec
3* Quadrat: (0.25m2) quadrat can be made by
welding 0.5m iron 2 segments together
4* DM content: Estimate or actual
5* Microwave
= 50g of grass dried
to a constant
weight

Question 6

How is the yield/ha calculated?

Answer 6

• Yield (kg DM/ha) =
  Fresh wgt (g) x DM % x 0.4
• Example
  Size of quadrat = 0.25 m2
  Weight of grass in quadrat = 200g
  DM content of grass =15%
  Yield (kg DM/ha) =
  200 * 15 * 0.4 = 1,200 kg DM/ha

Question 7

Estimating grass DM %
1- Continous rain:
2- Mixed sunshine and rain showers/second rotation
3- First rotation in spring/drier weather
4- Over a week of continuous sunshine and high temperatures
5-Drought conditions

Answer 7

1- 12-15
2- 14-17
3- 18-19
4- 20-21
5- 22-23

Question 8

What is farm cover?

Answer 8

Farm grass cover is the total supply of
available grass (>3.5-4 cm) on all paddocks for
grazing.

Farm cover = sum total cover* (kg DM)/
Area available for grazing (ha)

*Total cover = Paddock DM yield (kg DM/ha) X
Paddock area (ha)

Question 9

Target pre-grazing yield kg DM formula=

Answer 9

stocking rate (cows/ha) *
allowance (kg DM/cow/day) * rotation length (days) + residual

Example Pre-grazing yield =
3.27 (SR) * 18 (allowance) * 21 (days) + 100 (residual)
= 1336 kg DM/ha

Question 10

What is Post-grazing sward height (PGSH)?

Answer 10

PGSH is the average height (cm) to which a
paddock is grazed when the cows have
finished grazing.

• Include both dung pads and non-dung pad
  areas.

Question 11

What is Post-grazing sward height (PGSH) used as an indication of?

Answer 11

– residual grass yield
– pasture quality**
– Allocation/ day
– Utilisation

Question 12

Range of PGSH severity scores for PRG
swards:

Overgrazed

Good grazing

Slightly undergrazed

Undergrazed

Grossly undergrazed

Whats the grazing scores and grazing height of these?

Answer 12

Overgrazed - 1 , <3.5cm

Good grazing- 2, 3.5-4.5cm

Slightly undergrazed- 3, 5-6cm

Undergrazed- 4, 6.5-7.5cm

Grossly undergrazed- 5, >7.5cm

Question 13

Relationship between PGSH and
Residuals
Slide 28

Question 14

100kg of fresh grass:
1- how much dry material?
2- How much water?

Answer 14

1- 17kg of dry material
2- 83kg of water

Question 15

Nutritive Value of Grazed Grass:
1- Energy UFL/kg DM
2- Protein %
3- NDF %

Answer 15

1- 0.85-1.05

2- 16-28

3- 35-50

Question 16

What should you graze grass?

Answer 16

Graze at 2.5-3 new leaves when reserves are restored

3rd new leaf

Question 17

The younger leaf has…

Answer 17

High
Energy,
High OMD
= High
quality
More
digestible

Question 18

The older leaf has…

Answer 18

Low
Energy,
Lower
OMD =
Poorer
quality
Less
digestible

Question 19

How is pasture quality determined?

Answer 19

Organic matter digestibility (OMD)

• Grass OMD is used to calculate the grass energy
  content – UFL/ UFV value

Question 20

High OMD=

Answer 20

➢ high UFL/UFV value
➢ Lower fibre, less filling – increased DMI

Question 21

Low OMD=

Answer 21

➢ low UFL/UFV value
➢ higher fibre, more filling – decreased DMI

Question 22

Whats the influencing factors of pasture quality - multifactorial: (7)

Answer 22

➢ Soil fertility
➢ PGSHs
➢ Rotation length
➢ Herbage mass (pre grazing)
➢ Pasture species (% PRG, clover)
➢ Topping
➢ Season

Question 23

Pasture Quality
Slide 37 - Table

Question 24

Steps to Calculating % live leaf in a sward

Answer 24

1* Take a range of grass samples from the
sward (cut to 4cm).
2* 50 g sub sample.
3* Divide sub sample
– live leaf
– vegetative material (stem/dead)
4* Dry both samples in a microwave oven.
4* Weigh the dried samples.

Example:
Dried sample of live leaf = 6.5g
Dried sample of all other material = 2.5 g
Total weight = 9.0 g
Live leaf as a percentage of total weight
is 72%

Question 25

Whats the Chemical composition of grazed
grass (g/kg DM)
1-Crude Protein (CP)
2-Neutral Detergent Fibre (NDF)
3-Acid Detergent Fibre (ADF)
4-WSC

Answer 25

1-Crude Protein (CP) 180-250

2-Neutral Detergent Fibre (NDF) 350-400

3-Acid Detergent Fibre (ADF) 180-250

4-WSC 150-200