Silage Testing and How We Use the Results
Dr. David Lawrence
Head of Nutrition, Agritech
It is that time of year again when silage pits are sampled across the country and analysed to see the potential feed value. The most important step in testing silage is knowing what actions to take based on your analysis.
What do the results mean?
The FAA accredited labs in Ireland testing silage typically measure dry matter (DM), which is the weight left in a sample after all the moisture has been removed (typically 24-32%), crude protein and PDI, which are measures of the protein in the sample. Digestibility of the DM (DMD%) is the proportion of the silage DM that is available for the cow to digest. Energy is recorded as ME (metabolizable energy) or UFL/UFV (net energy). Some samples may indicate the intake potential of the silage. There are also NDF, which is fibre and Ash, which is the inorganic material (mineral component and sometimes soil contamination).
Understanding all this information can be simplified by putting silage into three categories. Suitable for dry cows (66-71% DMD), Suitable for productive cows (72% DMD and beyond) and silage that will need considerable supplementation regardless of stock type (<65% DMD).
Dry cows need to be monitored for body condition gain beyond 68% DMD. Straw is increasingly helpful here the higher the DMD of the silage. Milking cows need to be on the best quality available (>74% DMD). A 74% DMD silage will require 4-4.5 kg of concentrate to produce a mere 18 litres of milk. This increases approximately 1 kg of concentrate for each additional 2 litres, or 1 kg of concentrate for every 4 DMD points. A milking cow will require 6kg of concentrate plus silage to achieve 18 litres on 66% DMD silage. This will have a similar response on growing stock who will require 2 kg of concentrate on poor silage vs. 0.5kg on very good silage. Dry cows on <66% DMD silage will require additional concentrate energy to maintain or gain body condition.
Silage made in late September/early October will have a higher protein and nitrogen content than normal, and lower dry matter content. This highly digestible forage is a welcome addition to tight fodder budgets; however, the utilisation of this silage needs careful consideration. It is likely to cause loose dung in growing cattle and is also too rich in protein and energy for dry cows. It is suitable for milking cows; however, it needs to be diluted with drier, lower protein forage to balance. The best approach for utilising these sodden bales is to feed them at a low rate for the winter, trickling through your stock until they are used up. They are not suitable for carrying forward but will make a welcome addition to forage stock. For further advice, contact your local Agritech Sales Advisor or visit www.agritech.ie