printStock Journal Technical Column - October 2023
Author: Deb Scammell, Talking Livestock
Stubbles are a useful grazing option over the summer period in a mixed farming enterprise. However, it’s important to assess stubbles to determine the nutritional value and suitability for each class of stock on the property.
As harvesting efficiency increases and with better weed control, without a substantial weather event pre-harvest, stubble paddocks contain a lot less grain and fewer weeds than in the past. This often reduces their overall nutritional value and decreases the time stock can graze stubble paddocks.
When we look at the overall nutritional value in stubbles, the first thing to determine is how much grain is likely to be in the stubble per hectare. You can do this by counting the number of grains in a 0.1m2 (25 x 40 cm) quadrat and work out the equivalent kg/ha of grain quantity. To provide 100kg/ha of grain in stubbles you would need 28 grains of wheat or oats, 25 grains of barley, 8 grains of lupins, 5 of peas and 2 of beans in the quadrat. Once you have determined the quantity of grain across the paddock you can determine the sheep grazing days available until the grain is likely to run out.
Green shoots in stubble can provide some nutrition to stock, however often the fresh shoots are around 90% water so there would need to be quite a large quantity of more mature shoots to provide enough dry matter to assist with the overall energy required for maintenance or growth of stock.
Once the valuable components have been grazed, the remaining feed is lower quality leaf, chaff and stem. When we look at pasture quality, we measure the digestibility of the feed. Stubble leaf and chaff can be as low as 45 – 55% digestible giving us low energy values of around 6 – 7MJ/Kg. The stalk will be even lower digestibility again giving us only 3 – 4MJ/Kg of energy. Digestibility also declines in stubbles by about 2% a week post – harvest so the energy available decreases over the season, if there is a rainfall event on the stubble straw and leaf, energy will drop substantially with each event.
Due to the low digestibility and high fibre content of the leaf and straw feed intakes go down as stock can’t physically process and break down enough of this low-quality feed in a day. Stubble leaf, chaff and straw is also very low in protein and well under requirements of growing stock. Often we’ll see weight loss for all classes of stock on stubbles if grazed too long.
When working out a stubble grazing plan often wether lambs or ewe lamb replacements are the most beneficial class of stock to graze stubbles initially, or given priority paddocks with legume grain or high grain counts. Older mature ewes can then graze afterwards or go onto the lower value stubble paddocks. Ideally stock should be moved off stubble paddocks once ground cover gets to 50 to 70% to reduce erosion risk and reduction of organic matter on the paddock.