23 October 2023
Assessing silage quantity and quality
Last week’s rainfall has forced many if not most dairy farmers to house cows on silage. In many cases, grazing will and should continue at least by day for a few weeks more, however conserved forage is now part of the cows’ diet until next spring.
Joe Patton, Head of Dairy Knowledge Transfer, outlines the importance of assessing both silage quality and quantity on your farm.
We recently surveyed hundreds of dairy and beef farmers to assess fodder stocks on farm. Fewer than 10% of those farms had tested quality for the coming winter. This means that the majority of farms have many tonnes of feed sitting in the yard with no information as to its quality. Would we be satisfied to receive a delivery of concentrate without getting a docket on its ingredients and feed value? Most likely not! However, silage quality is by far the more important issue for the cost and performance of the winter diet.
A simple, cheap test will give much valuable information on this year’s feed and give good guidance on what to improve for next year. Table 1 shows the main factors used to measure quality of grass silage. These are divided into two main categories – feed value (determined by type of grass sward harvested) and preservation (determined by how well the harvesting and ensiling process was carried out).
Table 1: Main parameters for assessing grass silage quantity and quality
| Measure | Dry cows | Milking cows and youngstock | Comment |
|---|---|---|---|
| Feed value metrics | |||
| DMD % | 68-70 | 74+ | Key determinant of overall feed value |
| UFL (energy) per kg | 0.72-0.75 | 0.83-0.88 | Higher UFL means more feed energy for milk solids and weight gain |
| Crude protein % (CP) | 12 | 14+ | Lower DMD and/or N application reduce CP |
| PDIE g/kg (protein) | 75+ | 80+ | Determined by UFL and CP levels in silage |
| Intake value g/kg LW0.75 | 90-95 | >105 | Higher values indicate better intake potential |
| Potassium (K) content | <2.2% for dry cows | >2.4% no issue for milking cows | High K silage fed from two weeks pre-calving creates milk fever risk |
| Preservation metrics | |||
| Dry matter % | 24-28% | Silage should be costed on a DM basis | |
| pH | 4.0-4.2 (4.4 for drier crops) | Too high pH indicates poor preservation, too low may affect intake | |
| Ammonia | Less than 8% of N | High ammonia indicates poor preservation and reduces intake | |
| Lactic acid | 8-10% of DM | Higher values indicate a stable, palatable silage | |
| Ash | <8% of DM | High ash indicates soil contamination | |
In terms of quality, for dairy cows in milk and growing heifers, DMD (dry matter digestibility) should be at least 72%, and 75% for freshly-calved winter milk cows. Dry cows needing moderate body condition score gain will need silage at 68-70%. National average DMD (based on the farms submitting samples) is around 66% DMD, so overall it is likely that most farms have silage stocks that are below target quality.
How does your winter feed stock compare to target? The advice is to test silage pits and bales to find out. Discuss with your Teagasc advisor who will also help with interpreting results.
National Fodder Survey
The national fodder survey also showed that 75% of farms surveyed have a surplus of winter feed in stock. The proportion of farms short of silage ranged from 9% to 15% depending on region, with the North West tighter for feed supply than average. The survey also identified a cohort of 10% to 20% of farms (depending on region) that are at risk of being tight for winter feed, depending on duration of winter. These data are consistent across enterprise type within region and tally.
Table 2: Winter feed balance by region and enterprise October 2023
| Region | Adequate or surplus silage1 | Some risk / tight supply2 | Short |
|---|---|---|---|
| Midlands / North East | 81% | 10% | 9% |
| North West | 67% | 18% | 15% |
| South East | 68% | 20% | 12% |
| South West | 82% | 10% | 8% |
| 1Based on planned winter feed demand and current feed stocks. 2At risk = supplies may be inadequate for an extended duration of winter. | |||
Other results from the survey showed that 16% of farms (predominantly drystock) had fewer animals this year, and approximately 17% had less silage on hand compared to last year. Of the farms identified as being short or at risk of being short of feed, 53% intended to purchase silage, 25% intended to reduce stock and 23% were planning a combination of both.
In summary, the national picture for winter feed availability is relatively secure, with a requirement for close monitoring on 10% to 20% of farms, and corrective action needed on 10% to 15% of farms. Such farms are advised to act early to balance feed budgets.