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Australia

Monitor the digestibility of summer pasture

Key points

  • Pasture digestibility is a function of pasture species, rainfall, soil type, and landscape location. 
  • Recent results indicate that large variations in digestibility occur not only between regions but also within regions and even across paddocks on your farm.
  • Based on estimated pasture digestibilities, calculating your stock requirements across your farm, combined with good budgeting, could potentially save you money.
  • Consider monthly testing your key paddocks for weaners and maiden ewes as the pasture ‘hays’ off at the end of your growing season.
Pasture digestibility is a function of many variables – and can even vary from paddock to paddock within the same farm.

Producers often ask: ‘What is the pasture digestibility around my area doing at the moment?’ 

The simple answer is that it is highly variable and depends on many factors, such that using an average or assumed value to calculate feed budgets could potentially cost money.

This variation is caused by:

  1. The type of pasture; for example a ryegrass-dominant pasture compared with a silver grass dominant pasture.
  2. Stage of maturity and composition of the pasture sample submitted.
  3. The amount of rain that has fallen on the pasture prior to sampling as rain decreases digestibility.
  4. The districts the samples have come from, as variations in the stage and conditions of the growing season will influence the quality.
  5. The amount of clover or clover burr present in the sample.
  6. The amount of green material (if any) in the sample.

Although you might be able to estimate the digestibility of pasture across your farm, there can be significant variations between paddocks.  It is important to consider testing key paddocks each month so that you can re-calculate supplementary feeding rates as we feed through to after the autumn break.

The following table shows the average digestibilities based on four samples taken from four different paddocks from the same farm on the same day.

  Paddock 1 Paddock 2 Paddock 3 Paddock 4
DDM (per cent) 52.1 46.8 43.4 48.5

 

To set some benchmarks, a dry pasture that has an available mass of 1500 kg/ha dry matter, a digestibility of 45 per cent and digestible energy content of 6 MJ/kg, the intake of a 60 kg ewe grazing this pasture will be approximately 6 MJ of metabolisable energy (ME) per day.

If this ewe was found to be carrying a single lamb when scanned at 70 days, her energy requirement will be approximately 10.5 MJ ME/day, which leaves her 4.5 MJ ME short each day if she is only grazing the above pasture.  The inclusion of barley in her diet, which has an average ME content of 12.3 MJ/kg, will make up the deficit if she eats approximately 2.6 kg of barley each week. 

If for example, you tested your pasture and its digestibility was found to be 5%, then ME deficit of a single-bearing, 60 kg ewe reduces to approx. 2.7 MJ ME/day, which equates to approximately 1.5 kg of barley per head per week, saving you around 1.1 kg per head per week.

If you are running 2,000 breeding ewes, this represents a saving in supplementary feed of around 2,220 kg or 2.2 tonne per week.  Based on an average barley price of $250/t, this equates to a weekly saving of $550.00, minus the cost of your test ($66.00), which equals to a saving of $480.00 for the first week of feeding and $550 for each week thereafter per week.  Not a bad investment!

There is a strong argument in favour of testing your pasture digestibility over summer.  Consider starting in November or December and perhaps test two or three of your paddocks running weaners or joined ewes. 

In a ‘normal’ summer with little or no rain, it is a fair assumption to work on a decline in digestibility of 5%per month.  So if your pasture tested 60% digestibility in December, you would expect it to be, without any rain, 55% in January.

You need to have a starting point to work from, and if you receive summer rain, you may need to test your pasture quality more frequently.

Remember, once pasture digestibility drops below 55 per cent, it is difficult (in most cases) to maintain the weight and condition of sheep without supplementary feeding.

 

Dr Steve Cotton is an agricultural consultant working with Livestock Logic, and specialising in drench and vaccination programs for sheep and cattle, nutritional programs for livestock and manager of the Feed and Worm Logic laboratory.

Livestock Logic offers clients evidence based research, knowledge and experience in all aspects of animal and pasture management, specialising in feed testing, nutrition, veterinary advice and diagnostics.  With Australia's largest worm egg counting laboratory and drench resistance testing facility, livestock health and productivity is our focus."

Read more about Steve and Livestock Logic at http://www.livestocklogic.com.au/steve-cotton/
Dr Steve Cotton B.Ag Sci (Hons), PhD. Livestock Logic, Livestock Logic, Hamilton, Vic. E: s.cotton@livestocklogic.com.au