Rain does not automatically change the nutritional value of every load of silage. But when rainwater reaches exposed forage, wet by-products, a mixer wagon, or an uncovered feed bunk, the amount of dry matter delivered to cows can change without anyone updating the ration sheet.
To keep a total mixed ration (TMR) stable on rainy days, protect feed from direct rainfall, check the condition and dry matter (DM) of affected ingredients, adjust their as-fed loading weights when needed, and verify that the updated ration is actually delivered. Keep visibly spoiled or contaminated material out of the mixer. A DM calculation can correct moisture-related weighing differences; it cannot make spoiled feed safe.
Keep the nutrients, physical structure and amount of feed available to cows consistent as conditions around the feed center change. Use measured ingredient changes to decide whether the loading sheet needs updating.
Where Does Rainwater Enter the TMR Feeding Process?
The silage bunker is only one possible source of unexpected moisture. The most vulnerable points depend on how a dairy farm stores, loads, mixes, and delivers its ingredients.
| Location | What can happen | First practical check |
|---|---|---|
| Silage feedout area | Exposed material or loader buckets can collect rainwater and contaminated runoff. | Check covers, exposed feed, drainage, and the condition of the material being removed. |
| Hay and by-product storage | Wet brewers’ grains or uncovered forage may take up additional water; hay may deteriorate if wetted. | Inspect each affected lot separately rather than assuming every ingredient changed by the same amount. |
| Loading and mixing | Rain may fall directly into an uncovered wagon or onto ingredients waiting to be loaded. | Check loading conditions, standing water, and the actual ingredients entering the mixer. |
| Delivery and feed bunk | Uncovered TMR may be soaked after mixing or left in standing water at the bunk. | Compare fresh delivery with the feed cows can actually reach and eat. |
A covered bunker with sound drainage may show little change after a storm. Conversely, an uncovered by-product pile or feed wagon can become wetter even when the bunker itself remains protected. Rainfall is a reason to inspect and, where necessary, retest—not a substitute for measuring DM.
What Should a Dairy Farm Check Before Heavy Rain?
Preventing water from reaching feed is generally simpler than correcting a variable ration afterward. Before a forecast storm, focus on the areas where water can enter or become trapped.
- Protect the ingredients. Inspect silage covers and edges, hay storage, and temporary stockpiles of wet by-products. Repair damaged covers and prevent roof runoff from draining onto feed.
- Keep loading and mixing areas usable. Clear existing drains, control puddles in loader routes, and keep mud and runoff away from feed handling areas. Do not create new channels that direct contaminated runoff into waterways or other clean areas.
- Plan a practical loading route. Reduce the time loose feed is exposed to rain, use suitable covers where they can be handled safely, and keep dry ingredients protected until they are loaded.
- Have a backup for suspect feed. Know which approved lot can be used if exposed material must be held for inspection. Avoid automatically mixing questionable feed with good material to reduce losses.
For farms considering permanent improvements, sheltered ingredient handling and a properly drained mixing pad may be more valuable than adding another mixer feature. The layout should be checked against vehicle access, safe working clearances, and local runoff requirements.
When Should You Test Silage Dry Matter After Rain?
Test when there is a credible reason to believe the ingredient changed: a cover was displaced, loose feed was rained on, a feedout area flooded, wet by-products were exposed, or the material being loaded looks substantially different from the established baseline.
Even without a storm, silage and other wet ingredients need a regular DM-monitoring routine. The University of Minnesota Extension’s TMR feeding guidance recommends testing ensiled forages and wet feeds regularly because ration formulation is based on dry matter, while mixer operators load feed by its wet weight.
Sample the material that will actually be fed
For a bunker silo, collect representative portions from fresh material removed during normal mechanical feedout, at a safe location away from the face. If a loader removes only one narrow part of the face, that sample may not represent other areas. Record which bunker, section, and feedout period the sample represents.
Do not stand beneath or climb a high silage face to collect samples. A face can collapse without warning. Penn State Extension recommends removing material with a loader and sampling it away from the face in its horizontal silo safety guidance.
Keep visibly moldy, hot, muddy, or otherwise suspicious material separate from a routine nutritional sample. Such material calls for its own risk assessment; averaging it into a normal sample could obscure the problem. For additional sampling and storage safety guidance, follow Penn State Extension’s horizontal silo safety recommendations.
How Do You Adjust Silage Weight When Dry Matter Changes?
Dry matter is the portion of feed that remains after water is removed. If a ration calls for a certain amount of silage DM, the wet loading weight must change when the measured DM percentage changes.
Adjusted silage weight = Original silage weight × Original DM (%) ÷ New DM (%)
For example, consider a batch that normally uses 25 kg of corn silage at 32% DM. It provides 8 kg of silage dry matter. If a representative test of the same ingredient now gives 30% DM, the batch needs approximately 26.7 kg of that silage to provide the same 8 kg DM.
This calculation assumes that the nutritional composition of the silage dry matter has not materially changed. It is not valid as a way to compensate for spoilage, soil contamination, or major nutrient-quality changes. The Penn State batch-mix guidance explains the same distinction between dry-matter ration targets and as-fed ingredient weights.
TMR Silage Dry Matter Adjustment Calculator
Enter the weights for one consistent unit: per cow, per group, or per mixer batch. Use that same unit for both silage and added water.
Use only for an ingredient that has been checked and accepted for feeding. This tool corrects dry matter quantities, not spoiled feed quality or the full nutrient formulation.
Calculated Ingredient Adjustment
- Original silage dry matter
- —
- Adjusted silage weight
- —
- Change in silage weight
- —
- Change in water carried by silage
- —
The result is a single-ingredient arithmetic adjustment, not an automatically approved TMR recipe. Review the updated batch sheet and whole-ration moisture with the farm nutritionist or feeding manager before use.
Should you automatically reduce water added to the mixer?
No. When wetter silage supplies the same dry matter, it also brings more water into the batch. Whether the mixer-added water should be reduced depends on whether water is already part of the recipe, the desired total-ration moisture, and the other ingredients.
If a batch has no separately added water, there is nothing to subtract. If there is added water, any mathematical adjustment still needs review against the full ration. The calculator makes the distinction visible rather than telling every farm to remove a fixed amount of water.
Do not automatically return to the old loading weight just because the rain has stopped. Return only when fresh measurements and the ingredient’s condition support the original recipe.
What if the Silage Is Wet and Also Spoiled?
A moisture adjustment only works for feed that remains suitable for feeding. Rain intrusion may also expose silage to oxygen, cause runoff or leaching, and worsen existing feedout problems. Check for visible mold, unusual heating, foul odors, soil contamination, or obviously deteriorated areas.
Hold and identify suspicious material rather than loading it into the TMR. Have the responsible farm manager and, where appropriate, a nutritionist or veterinarian determine the extent of the problem and whether testing or disposal is needed. Do not use a small group of cows to test whether suspect material is safe.
Control clean rainwater before it reaches feed storage. Keep potentially contaminated silage runoff separate from clean stormwater and manage it according to the site’s drainage plan and local rules. Do not send workers to excavate temporary channels beneath unstable silage faces or direct effluent toward streams. For practical covering and drainage considerations, see University of Wisconsin–Madison Extension’s drive-over silage pile construction guide.
How Can You Check Whether the TMR Is Still Consistent?
If cows leave more feed after a storm, avoid treating the situation as a silage moisture problem without checking what they actually received.
- Look at the bunk and the cows. Note whether feed is inaccessible, waterlogged, heated, visibly sorted, or refused. Check group appetite, behavior, and any urgent health signs.
- Compare the ingredients. Check measured DM, lot identity, condition, and any ingredient recently exposed to rain. An isolated suspect lot should be held separately.
- Review the loading sheet. Confirm the current ration version, ingredient weights, actual scale readings, and whether the operator applied the updated DM figure.
- Inspect the mixing and delivery process. Check mixer loading order, working fill level, knife and auger condition, discharge consistency, and whether additional water was added by habit.
- Review the wider farm conditions. Heat stress, poor ventilation, water access, health problems, and changes in group size can also affect intake.
Collect separate TMR samples from different delivery positions if the concern is uneven discharge. A single composite laboratory sample may describe the average ration but can hide front-to-back differences. Particle-size assessment and visual sorting checks can complement laboratory analysis.
What Can a TMR Mixer Actually Improve in Wet Weather?
A suitable TMR mixer provides a controlled place to weigh, combine, and deliver feed ingredients. Its weighing equipment can help staff follow updated as-fed batch quantities after the measured DM of an ingredient changes.
However, a mixer does not measure an ingredient’s DM automatically merely because it has a scale. Nor can it restore spoiled feed, correct the wrong recipe, or guarantee that cows never sort the ration.
Useful operating checks include scale calibration, correct ingredient loading order, appropriate batch size, and mixing time validated for the actual forage and equipment. The University of Minnesota’s TMR guidance notes that mixing time depends on mixer type, load, and condition. A fixed number of minutes is not a universal setting for every dairy.
The most reliable rainy-season routine links four actions: measure ingredient DM, approve the revised batch sheet, load by the corrected as-fed weights, and verify the delivered TMR.
A Practical Rainy-Weather TMR Check
| Check | Routine action | Additional action after rain or a change |
|---|---|---|
| Ingredient condition | Observe appearance, odor, temperature, and storage conditions during loading. | Inspect exposed lots and isolate suspicious material. |
| Forage dry matter | Test ensiled and wet feeds on a regular schedule. | Resample when exposure or feed condition suggests a meaningful change. |
| Batch sheet and loading | Verify the active recipe and actual mixer weights. | Issue and acknowledge revised weights before the affected batch is fed. |
| Mixer-added water | Follow the approved recipe, not a visual guess. | Review water only if ingredient moisture or the intended TMR consistency changes. |
| Delivered TMR and refusals | Check accessibility, sorting, freshness, and group intake. | Compare affected and unaffected groups and investigate significant changes. |
| Drainage and feed hygiene | Maintain clean loading routes and protected feed storage. | Clear safe drainage routes and prevent contaminated runoff entering feed. |
Record the date, ingredient and lot, measured DM, approved batch-sheet version, operator, and any feed or herd abnormalities. A simple record that the team actually uses is more useful than a detailed form that is never checked.
Frequently Asked Questions
Does every rainfall mean I need to increase corn silage weight?
No. Only change the as-fed weight when representative DM measurements and the approved feeding plan show that a correction is needed. Well-protected silage may not have changed substantially.
Can I use the calculator if the silage smells spoiled?
No. The calculator assumes a suitable ingredient with a changed moisture percentage. Stop and assess suspicious feed instead of trying to compensate by adding more of it.
Does wetter silage always mean more water should be removed from the mixer?
No. Not every TMR recipe contains separately added water. Where added water is used, any change should be considered in the context of the whole ration, not applied automatically.
Can a TMR mixer correct uneven silage moisture on its own?
No. Mixing equipment follows the quantities loaded into it. Consistent feeding depends on representative testing, a current recipe, accurate weighing, sound mixer operation, and checking the feed delivered to cows.
Conclusion
Rainy-day TMR stability starts with keeping water out of stored and handled feed. When an ingredient is actually wetter, use a representative DM measurement to calculate the corrected as-fed weight and make sure the new loading instruction reaches the operator.
Separate moisture changes from spoilage, manage bunker and feed-center drainage safely, and monitor the delivered ration and herd response. Record who approved the revised batch sheet and confirm that the mixer operator used it.
