printStock Journal Technical Column - November 2023
Author: Deb Scammell, Talking Livestock
Grazing dry pasture and stubble over the summer and autumn months often results in a nutrient deficiency, dependent on the class of stock. Once the valuable components of a stubble, like the grain and green material, are gone, it will only leave stubble, leaves, and chaff. When grazing these components of stubble and dry pastures, they often won't meet the nutritional needs of even dry animals.
Stubble, leaves, and chaff can have as low as 45-55% digestibility, resulting in low energy values of only 6-7 MJ/Kg. Dry perennial or annual pastures will often have only 50-55% digestibility (dependent on the legume content), also resulting in low energy values. Once we get into the summer months, digestibility declines by around 2% a week, and digestibility and energy drop even quicker after a rain event.
Mature dry ewes can sometimes maintain condition on dry pasture, depending on the energy value. Ewes during gestation and young growing stock will often need some supplementation to maintain condition score and growth rates.
Fibrous plant material is broken down in the rumen, and rumen microbes play a crucial role in breaking down cellulose and other fibrous components of plant material. The microbes in the rumen require nitrogen to 'feed them' and allow them to function properly. As many of our dry pastures and stubbles are deficient in protein, this can slow down the function of the microbes and restrict the quantity of dry pasture or stubble that can be broken down in the rumen over a day.
If you have a bulk of dry feed and mature ewes that are dry or in early gestation, urea or other slow-release urea sources can be an effective supplement. They are non-protein nitrogen (NPN) sources, which are converted by microbes in the rumen into ammonia. This can then be used by the rumen microbes as a source of nitrogen, assisting stock to meet maintenance demands by enabling the rumen to break down extra fibrous feed.
If you are grazing these dry pastures with young growing stock or ewes during gestation, they will have a much higher requirement for energy and protein. So, it is better to consider supplementing with cereal grain, legume grain, or a full feed pellet to meet their higher requirements. You can compare these on a cost per unit of energy and protein to determine the most economical way to supplement.
Breeding stock grazing stubbles or dry pastures, supplemented with cereal grain, should always be given access to a calcium supplement to ensure they don't draw on bone calcium reserves that they will require later in gestation and through lactation. Stubbles and cereal grains are both very deficient in calcium.
Once ground cover of these pastures starts to drop below your on-farm targets (around 70% is ideal on dry pastures and down to 50% on stubbles) stock will need to be moved to another paddock or consider supplementing in a containment pen.