Grazing crops and stubbles

Cereal crops and stubbles are a valuable source of feed during winter in southern Australia.  The information provided in this section of the FOO Library was mainly obtained from the Grain and Graze project www.grainandgraze2.com.au , the Department of Agriculture and Food WA website www.agric.wa.gov.au and the Grains Research and Development website www.grdc.com.au

The Grain and Graze project has recently released a comprehensive book setting out the best ways to manage and use crops for grazing and grain. It covers all aspects of forage and grain yield, potential animal health impacts, weeds, soil issues, crop disease and stubbles.  The booklet can be downloaded at

http://www.grainandgraze3.com.au/resources/Grazing_Cropped_Land_June_2016_.pdf

Estimating FOO of cereal crops

In can be more difficult to evaluate the likely performance and potential for animal health problems with sheep grazing crops and stubbles compared to annual and perennial pastures.  The following information can be used to estimate the quantity and quality of feed on offer from crops and stubbles but detailed information should be sought before  deciding on the most appropriate stock to use these feed sources and the best way to graze the paddocks.

When estimating the quantity and quality of Feed On Offer (FOO) in a cereal crop, consider the following points:

  • For all green cereal crops, the energy content is usually 10-11 MJ/Kg or 72-78% digestibility.
  • If the crop is less than 25 cm high and sown on 17.5 cm (7  inch) row spacing, use the following FOO values:
    • o   Wheat: 1 cm = 60 kg/ha DM
    • Triticale: 1 cm = 65 kg/ha DM
    • o   Barley: 1 cm = 75 kg/ha DM
  • For 15 cm (6 inch) row spacing, add 10% to all FOO values.
  • For 20 cm (8 inch) row spacing, reduce the FOO values by 10%.

Estimated FOO for Wheat crops grown on 17.5 cm (7 inch) row spacing

Crop height (cm) Estimated Feed On Offer (kg/ha)
3 180 kg/ha
4 240 kg/ha
5 300 kg/ha
6 360 kg/ha
7 420 kg/ha
8 480 kg/ha
10 600 kg/ha
12 720 kg/ha
14 960 kg/ha
16 1040 kg/ha
20 1200 kg/ha
24 1440 kg/ha

Decisions on when to start and stop grazing to avoid damaging crops is important but beyond the scope of this article.  It is strongly recommended not to graze cereal crops beyond Growth Stage 30.  For detailed information is of the impact of grazing on subsequent grain yield, go to the Grain and Graze website or consult your agronomist.

Estimating FOO of canola crops

There is now some interest in grazing canola sown in early autumn, during winter or sowing canola in spring and grazing over summer then harvesting the following summer.

Yield of brassica’s is difficult to estimate from height and row spacing as the density and “cabbaging” of these crops is greatly influenced by soil moisture and nutrient levels.  Yield is best calculated by cutting and drying a 1 m row length and extrapolating yield based on row spacing.  Canola yields are typically 2 – 4 t/ha in August for mid-April sown crops.

Forage quality will be influenced by the ratio of leaf to stem on the plants but should be in the range of 10-11 ME/Kg or 72-78% Digestibility. Sheep can grow at over 200 g/d when grazing canola crops.

Animal Health issues grazing vegetative crops

Green cereal and brassica crops are generally monocultures and while providing high quality forage, can lead to some metabolic issues.

  • For cereals, low mineral content particularly Calcium and Sodium which may be caused by imbalances in other minerals, can be an issue. This is especially important in late pregnancy, at lambing and in early lactation.
  • Canola is lower in glucosinolates then other forage brassica crops which means it is quite palatable to stock.  However, stock should be introduced to the crops slowly to allow time for adaptation.  Brassicas can be high in Calcium so care should be taken if grazing leading up to lambing and then suddenly moving stock to a pasture paddock with lower Ca levels.
  • Other animal health issues with canola can be problems with Iodine metabolism, high Sulphur levels and potential Nitrate poisoning risks.

If grazing crops for the first time especially with late pregnant or lactating ewes, seek local information about the need to include roughages sources or mineral supplements.

Cereal stubbles

Cereal stubbles contain 4 sources of FOO with very different forage quantity and quality;

  • 1) Dry standing stems and leaves, commonly 1000 -3000 kg/ha with ME 4.0 – 5.5 MJ/kg, Digestibility 35 – 42%.
  • 2) Loose material on the ground, “cocky chaff” and other material, commonly 1000 – 2000 kg/ha, ME 4.0 – 6.0 MJ/kg, Digestibility 35 – 45%
  • 3) Grain on the ground, can be anywhere between 0 – 200 kg/ha, with ME 12 – 13 MJ/kg, Digestibility 75 – 85%.  Amount available depends on wind damage and efficiency of the heading operation.  Note that in a tight short spring, high quantities of pinched grain (300-500 kg/ha) can be available behind the header as the settings cannot deal with the low test weight grain.
  • 4) Green material, weeds or germinating grain, again anywhere between 0 – 1000 kg/ha depending on rainfall and the efficiency of the heading operation. The quality of the green feed depends on species but is commonly in the range of ME 10 – 12 MJ/kg, Digestibility 64 – 75%.

Animal health issues with stubbles

  • Some summer active weeds such as heliotrope and wireweed can be toxic to some stock at some times.  If unusual species are present in the stubble, seek advice before grazing livestock.
  • If large amounts of grain are present on the ground, acidosis may also be an issue to consider.  Consider trail feeding the sheep on pasture before introduction to stubbles.  Alternatively, move stock on and off the stubble to allow the rumen time to adjust.
  • Stubbles are typically low in both sodium and calcium

Sheep performance on cereal stubbles

Predicting sheep performance on stubbles is less reliable than for pastures.  Sheep may take some time to adapt to the different feed source and find the grain at the base of the crop or eat the unusual green species.  The green feed, sprouted grains and shot grains are very high energy and protein sources for sheep and can provide high animal intake and growth rates.

The order of selection of these fractions is:

  1. Spilt grain
  2. Green weeds or shot grain
  3. Flag leaf and header trash
  4. Standing straw

A number of trials have found that sheep will usually gain weight if there is:

  • Greater than 40 kg/ha grain available
  • Greater than 40 kg/ha green herbage.

The values for green herbage in stubbles assumes this is mainly grain sprouts and so are quite sparse but tall, 3-5 cm high.  This sparse material can be quickly grazed out and then sheep will lose weight.

Estimating Grain yield

To estimate grain yield, count the number of grains on the ground in a 0.1 sq m quadrant, (square wire quadrant with 30 cm sides) doing at least 20 counts per paddock.   Approximately 40 kg/ha is equivalent to:

  • Wheat and oats = 13 grains
  • Barley = 12 grains
  • Lupins = 4 grains
  • Field peas = 2 grains
  • Chick peas = 2 grains
  • Faba beans  = 1 grain

Assessing sheep performance from cereal stubble is more difficult than for pastures so it is important to regularly weigh and/or condition score sheep grazing stubbles to assess if they are maintaining, gaining or losing weight/condition.

Estimated green shoot yield

It can be hard to estimate FOO values for shoots in stubble. The table below provides estimates of the yield of green material based on the number of shoots in a 0.1 sq m quadrant.

Green shoots/ 0.1 m2 Feed On Offer (kg/ha)

7

20

14

40

18

50

21

60

28

80

Once there is over 100 kg/ha present, the FOO Library photos can be used to estimate pasture yield.  The Lifetime Ewe Management ECM tables can then be used to estimate sheep performance, based on FOO, pasture height and pasture ME values.