Taking stock of winter feed for dairy herds
January 9, 2025
January is an important time to assess remaining winter fodder stocks. The year 2024 presented significant challenges for grass growth, leading to insufficient silage on many farms by the turn-out date. Elizabeth Calvin is a Dairying Adviser at the College of Agriculture, Food and Rural Enterprise (CAFRE). She offers timely advice: “It is important to re-assess your fodder budget. If necessary, take steps sooner rather than later. This will help stretch silage stocks or reduce demand.”
Fodder Budget
The first step is to calculate the volume of fodder in stock. Firstly, measure the silage in the pits and count the number of bales in stock. Then, use the dry matter percentage (DM%) to identify the density of the forage conversion factor from Table 1. For a pit silage calculation – multiply the length by width by average height (in metres) of silage in the pit to give a volume (m3). Use the appropriate conversion figure based on the dry matter of the silage from Table 1. Multiply the volume by the conversion figure. This will give you the weight of silage in tonnes.
For baled silage calculation – multiply the number of bales by an average weight of a silage bale to give a total weight in kgs. Then multiply the total weight by the appropriate conversion figure (from Table 1) to give a total weight of silage in tonnes.
Take an example of a silo clamp –
Length 18m x width 10m x average height 4m = 720m3 @ 25%DM (720m3 x 0.68) = 489.6 tonnes fresh weight of si\lage.
And a bale stack of 120 bales @ 0.8T/bale) = 96 tonnes fresh weight.
Therefore, the current total silage stock on farm in the clamp and including the bales= 586 tonnes.
Table 1: Forage Volume to Weight Conversion Factors
| Forage Type | Silage Dry Matter Content (%) | Conversion (volume in m3 to tonnes of fresh silage) |
|---|---|---|
| Grass Silage | 20 | Multiply by 0.77 |
| 25 | Multiply by 0.68 | |
| 30 | Multiply by 0.60 | |
| 35 | Multiply by 0.54 | |
| 40 | Multiply by 0.48 | |
| Whole Crop | 40 | Multiply by 0.60 |
| Forage Maize | 30 | Multiply by 0.60 |
The next step involves calculating the herd’s total demand and comparing it to the silage stock to identify potential shortfalls. Table 2 shows the generic intake figures for dairy cows, dry cows and youngstock, assuming the silage DM is 25%. Elizabeth stresses “it is important to account for every animal on farm that is eating silage, and also to use actual intake figures plus an allowance for waste/safety margin.”
Table 2: Conserved Forage Demand Example Calculation
| Animal type | No. of stock | No. of months (Mid-April Turn out) | Silage required (t/animal/month) | FW tonnes silage per month (t/animal/month x no.of stock x no. of months) |
|---|---|---|---|---|
| Dairy cows – milking (average) | 100 | 3.5 | 1.4 | 490 |
| Dairy cows – dried off (average) | 20 | 3.5 | 1.2 | 84 |
| In Calf Heifers | 25 | 3.5 | 0.8 | 70 |
| Youngstock | 25 | 3.5 | 0.6 | 52.5 |
| Total: | 696.5 | |||
| Total incl. 10% safety margin | 766.15 |
In this example the silage in stock of 586 tonnes is not sufficient to meet herd demand of 696.5 tonnes (excluding safety margin). Therefore there is a minimum deficit of 110 tonnes.
The conserved forage demand calculation can be done with your CAFRE dairy adviser or nutritionist. This ensures that it is tailored to the silage you have on-farm. It also aligns with the diet formulation you are using. At this stage of the winter, we have the benefit of hindsight. We can cross-check this calculation with what has been used in previous months to ensure it is accurate. This is especially important if you are working on tight margins.
Dealing with a Deficit
So, where a deficit is identified Elizabeth has suggested that there are several options to stretch forage and ensure there is enough available feed to get through the winter season.
She continues that “Firstly it is important to consider culling unproductive stock, for example, infertile, lame, high somatic cell count, and older poorer performing cows. This will reduce demand on silage and provide an additional source of income and help cashflow. Make these decisions as soon as possible to make a bigger impact on lowering demand for silage”.
Secondly, reduce silage dry matter in the diet and increase concentrates. Current milk to concentrate ratio price is favourable to feed extra concentrates and reduce forage levels accordingly. Increasing the level of concentrates in the diet can increase the cow’s energy intake, potentially improving milk performance, quality, condition, and fertility. Elizabeth emphasises that dairy farmers must remember that cows are ruminants and require at least 40% forage in their diet. A typical cow diet is 40% forage: 60% concentrate on a dry matter basis. If forage content is reduced to below 40% of the diet, there is a risk of digestive upsets. In addition, if silage is wet and acidic then consider feeding a fibre-based concentrate rather than starch based to reduce risk of rumen upset.
Thirdly, stretch silage by considering using soya hulls or sugar beet pulp. For example, 1 kg soya hulls will replace 4 kg silage on a fresh weight basis (assuming silage is 25% dry matter).
Fourthly, consider feeding dry cows a 50:50 straw/silage diet on a dry matter basis. This is good for rumen function and health; however, cows will require a higher level of concentrate feeding. Straw offers limited nutrition, requiring the addition of concentrates to achieve adequate energy intake for the cow and unborn calf.
Fifthly, consider feeding all youngstock on a straw and concentrate diet. For example, a maiden heifer, assuming in good condition, could be fed 4 kg straw and 4 kg concentrate (on a DM basis). Because straw has a lower energy content than silage (4 versus 10 MJ/kg DM), more concentrate feeding is necessary.
If possible, purchase additional silage and prioritize the best silage on the farm for fresh calved and high-yielding cows. Use any lower quality forage for youngstock.
Elizabeth advises that animal needs must be met, and any diet changes should be made gradually. For any option considered, it is important that the diet is re-formulated. This should reflect the different level of nutrition available to the cow or heifer. It may also be necessary to look at cash flow to support the purchase of extra inputs.
Consult your CAFRE dairy adviser or nutritionist as soon as possible so action can be taken to deal with a deficit. The options available are best put in place sooner rather than later.