A cow eats hay or fresh grass but walks away from her grain. On a larger dairy, several cows leave fine concentrate-rich material in the feed bunk while continuing to pull out the longer forage. Both situations call for a closer look at the feed and the animal, although they may have different causes.
Start by checking whether one cow or the whole group is affected, whether the concentrate has changed, and whether rumination, manure, water intake or milk production has also changed. On a small pasture-based farm, the problem may involve supplement timing or palatability. In a commercial TMR-fed herd, feed separation, ingredient handling and uneven access can produce a similar pattern. A recently calved cow with a sudden drop in grain intake may need a veterinary examination.
The following checks are designed for both individual-cow owners and commercial dairy managers. They provide a practical order of investigation, with extra equipment checks for farms that prepare and distribute total mixed rations (TMR).
1. Is It One Cow, or Did an Entire Group Start Refusing Concentrates?
Ask the person who feeds the cattle five questions before changing the diet:
- Which animals are affected? Record cow IDs, pen or paddock, and when the change was first noticed.
- What changed in the feed? Check the latest concentrate delivery, supplier, ingredient formulation, amount offered and feeding time.
- How is the cow behaving? Observe rumination, drinking, manure, alertness, movement and, for dairy cows, milk yield.
- What does the rejected feed look like? Check for fines, unusual odor, dampness, caking, heat, or material that separates during handling.
- How is the ration offered? Determine whether grain is fed separately, alongside pasture, or as part of a TMR.
One cow refusing a familiar concentrate needs an individual health and feeding assessment. Several cows rejecting the same delivery points the investigation toward a shared feed, water, mixing or management event, while illness affecting multiple cows must also be considered.
When to contact the veterinarian promptly
Arrange a veterinary assessment without waiting for a routine ration trial if the cow has a marked drop in rumination or milk yield, depression, abdominal pain or swelling, severe diarrhea, dehydration, weakness or difficulty standing. Recent calving makes a sudden appetite change especially important. Ketosis and displaced abomasum can affect concentrate intake in fresh cows; a feed-choice observation by itself cannot identify the condition. For clinical background, see the Merck Veterinary Manual's reviews of hyperketonemia and abomasal displacement.
If several animals develop fever, excessive salivation, mouth lesions, unusual lameness or other similar illness signs, seek urgent veterinary and local animal-health guidance. Keep the affected feed lot and animal records available for the investigation.
2. Examine the Concentrate: Batch, Storage and Physical Quality
When the timing matches a new delivery, check that lot first. Keep the delivery label or lot number and compare a representative sample with the previous feed, where one is available.
Look for damp pockets, internal heating, sour or rancid odor, visible mold, insect damage, excess dust, changes in particle size and hard lumps. Check grain processing as well: cracked, ground or steam-flaked ingredients may differ between deliveries even when the ration sheet shows the same ingredient name.
For stored dry grain, moisture is one useful specification. North Dakota State University Extension gives a long-term storage target of approximately 13–14% moisture for corn, while wheat and other grains have their own limits. A shorter holding period under cool conditions may allow a different moisture level. The safe moisture target depends on the grain type, storage temperature and planned storage duration. See the NDSU grain-storage guidance.
| What staff find | What to check next |
|---|---|
| Caking, warming or moisture | Bin condition, roof leaks, condensation, turnover and the affected lot |
| Unusual odor or visible spoilage | Isolate the suspect lot and obtain qualified advice on sampling, testing and disposition |
| More dust or fine particles | Grinding settings, transport segregation, pelleting quality and cow acceptance |
| Different processed grain | Batch specifications, processing method and the ration's effective starch supply |
| Only one pen affected | Which delivery, bin, mixer batch or feed route served that pen |
If spoilage or contamination is suspected, segregate the lot, keep representative samples and stop distributing it pending assessment. Mycotoxin risks may require laboratory testing selected with the veterinarian or nutritionist. A feed's appearance and smell help identify problems but cannot quantify mycotoxins.
If the feed is sound but unfamiliar, review palatability and the transition plan before changing multiple ingredients at once. Record what was offered and actually eaten so the outcome can be assessed.
3. Does the Cow Have a Reason to Eat More Forage Than Concentrate?
A grazing cow with access to abundant pasture may take less supplementary feed at a particular time of day. The pasture's dry-matter yield, nutritional quality and the cow's milk-production or growth requirements determine whether that lower supplement intake is acceptable. Check body condition and production trends rather than relying on how green the field looks.
For cows eating forage and concentrate separately, inspect the concentrate trough for rejected pellets or fines. Also observe whether the cow has an opportunity to eat her allowance without being displaced by dominant animals.
For cows receiving TMR, identify what is being selected. The material left after a feeding provides important information:
| What is left in the bunk? | What the pattern may mean | First checks |
|---|---|---|
| Disproportionately long forage | Cows may have selected the shorter, often more concentrate-rich fractions first | Fresh TMR particle size, forage length and changes in starch/fiber distribution |
| Disproportionately fine or concentrate-rich material | A feed-quality, physical separation or palatability issue may be involved; individual illness also needs consideration | Fine-feed odor and condition, clumps, dry pockets, mixing uniformity and animal-health observations |
| Similar composition to the original ration, but more feed remains | Overall intake or access may be reduced | Cow health, feed delivery, heat stress, water, stocking and feed availability |
Feed sorting is not always in the same direction. Dairy-cow studies commonly find selection for shorter particles and against long forage, while research in heifers has also documented selection for longer particles under particular diet conditions. The comparison between fresh feed and refusals is more informative than labeling every uneven feed bunk as grain refusal. See the dairy-cow sorting study and heifer particle-size study.
4. When Could Rumen Fermentation Be Involved?
A rapid increase in starch-rich concentrates, a weighing error, insufficient effective fiber or an extended gap followed by a large grain meal can disrupt rumen fermentation. Reduced or uneven intake, changes in manure and a fall in rumination may justify a herd nutrition and health review.
Subacute ruminal acidosis (SARA) is associated with prolonged periods of reduced rumen pH. Ontario's dairy guidance describes extended periods below approximately pH 5.5–5.6 as concerning in its diagnostic framework; values around 5.6–5.8 may be marginal depending on the method and sampling time. Rumen sampling and interpretation belong with trained professionals. See Ontario's SARA guidance.
Rumination data can support the investigation. A major review of dairy-cow studies reported average daily rumination around 430–440 minutes, with substantial variation among cows and diets. For a cow with reliable monitoring history, a sharp change from her own usual pattern is generally more useful as an initial observation than a universal minute-per-day cutoff. See the review of eating and rumination activity in dairy cows.
Check ingredient weights, forage dry matter, ration starch and physically effective fiber with the farm nutritionist before making substantial adjustments. Large increases in concentrate allowance should be introduced through an appropriate adaptation schedule. For a fresh cow that is losing appetite or milk production, arrange the clinical examination in parallel.
Can monitoring technology help?
For fresh cows and groups with feeding concerns, a compatible behavior-monitoring collar and analytics platform can help staff follow rumination and activity trends. Depending on the selected hardware, NexAgri-Sense smart ear tags can add animal identification and temperature observations. These records give staff more context when deciding which cows need closer inspection, alongside direct observation and veterinary assessment. Explore NexAgri livestock monitoring systems.
5. How to Check a TMR Mixer When Cows Leave the Fine Feed
When cows pull longer forage out of a mixed ration while fine material accumulates at the bottom of the bunk, investigate two areas: what the mixer delivered and what happened to the ration after delivery.
To check discharge consistency, keep fresh TMR samples from the beginning, middle and end of unloading separate and label their positions. For sorting, compare representative fresh TMR with a separately collected refusal sample, recording collection times. Compare particle distributions and note wet clumps, concentrate pockets and unprocessed forage.
An uneven mix can arise from incorrect loading order, over- or underfilling, insufficient mixing after the last ingredient, overly long forage, worn knives, inaccurate load cells or ingredients added in concentrated wet spots. Material can also segregate during discharge and transport. The Penn State TMR management guide discusses how batch weights, dry matter, loading and mixing practices affect ration consistency.
Practical Penn State Particle Size Separator reference
For the 2013 four-compartment Penn State Particle Separator, guidance for a typical lactating-cow TMR uses the following fresh feed distribution as a starting reference:
| Fraction | Particle size | Reference share of fresh TMR |
|---|---|---|
| Top sieve | Over 19 mm | 2–8% |
| Middle sieve | 8–19 mm | 30–50% |
| Lower sieve | 4–8 mm | 10–20% |
| Bottom pan | Below 4 mm | 30–40% |
These ranges describe the as-fed fresh TMR sample. Actual targets depend on ration ingredients, forage sources and the separator version. Follow the Penn State Particle Separator instructions, then compare fresh TMR with refusals. The fine fraction may contain both concentrate ingredients and small forage particles; starch, NDF or other laboratory analyses can help clarify the composition.
If long forage accumulates in refusals, investigate preferential consumption of smaller fractions and whether other cows are later offered a ration with more fiber than intended. If fine material accumulates, examine its odor, moisture, physical form and distribution in the original mix while checking the affected cows' health and feeding access. The direction of the difference guides the next test.
6. Check Bunk Access, Feed Availability and Water
Feed intake changes when cows cannot comfortably reach fresh feed. Walk the feeding line shortly after delivery and again before the next feeding. Note crowding, broken or blocked headlock positions, unreachable feed, empty stretches of bunk and waiting cows.
Check water-trough refill rates and cleanliness, particularly where high-producing cows return from milking. Record usable feed positions and the amount of feed actually accessible along the bunk. Regular feed push-up routines, whether manual or mechanical, help keep the ration within reach between deliveries.
How much feed should remain?
Track refusals by cow group, not by a single whole-farm percentage. University of Wisconsin–Madison Extension describes illustrative ranges of 3–5% for fresh cows, 1–5% for high-producing cows and 0.5–3% for later-lactation cows. These ranges help plan delivery and monitor intake; the farm should set its own targets with the nutritionist, considering cow access and production goals. See the Wisconsin feed-bunk management guide.
Refusal rate (%) = (feed offered − feed consumed) ÷ feed offered × 100, using consistent weights and measurement periods. A low number has little value if the bunk is empty for hours or timid cows cannot eat.
7. A First-Shift Troubleshooting Checklist
Use the checklist when a cow or pen changes feeding behavior. Record urgent health findings and seek veterinary assistance immediately where necessary; the remaining management checks can continue alongside that response.
| Check | What staff record | Next action |
|---|---|---|
| Animals affected | Cow IDs, group, onset, recent calving | Decide whether clinical or shared-feed investigation takes priority |
| Cow condition | Rumination trend, alertness, water, manure, milk yield | Escalate significant changes to the veterinarian |
| Feed lot | Supplier, delivery date, storage bin and physical findings | Isolate suspect material and arrange appropriate testing |
| Ration changes | Ingredient weights, grain processing and feeding schedule | Review the nutritionist's specification and recent adjustments |
| Mixing and delivery | Batch size, order, mixing time, discharge appearance | Check scales, knives, augers, ingredient distribution and procedures |
| Fresh TMR versus refusals | Relative long, medium and fine particle fractions | Identify the direction of sorting or whether total intake fell |
| Access and water | Usable feed positions, push-up timing, trough operation | Correct supply or access issues and record follow-up |
For an individual pasture cow, the list may take only a few minutes. For a commercial TMR operation, photographs, batch sheets and representative feed samples make it easier to distinguish a feed-lot problem from a mixer or bunk-management problem.
8. How NexAgri Can Help With Feeding Equipment Selection
A dairy feeding system works best when ration characteristics, mixer batch size, feeding-line layout and water access are planned together. NexAgri offers trailed and stationary TMR mixer configurations, self-locking cattle headlocks and stainless-steel drinking troughs for commercial barns.
For a TMR mixer enquiry, useful details include herd size by group, daily as-fed ration volume, major forage types, typical batch weights, feeding frequency, tractor or electrical power, and the width of delivery alleys. For a feeding-line upgrade, include usable bunk length, current headlock spacing and water-trough locations. These details allow an equipment proposal to address both feed preparation and access at the bunk.
To plan a practical feeding-line or monitoring upgrade, contact NexAgri with your herd size, feeding method and barn layout.
Frequently Asked Questions
Why does my cow eat hay but refuse grain?
Check whether she is otherwise eating and behaving normally, whether the grain is new or spoiled, and whether the change affects other cows. Recent calving, falling milk production or reduced rumination warrants veterinary attention.
Does leaving fine particles in the TMR bunk mean the cow has acidosis?
The pattern identifies a feeding question, not a diagnosis. Compare fresh and refused feed, examine the fines for quality and segregation, and review the cow's health. A veterinarian and nutritionist can assess whether rumen fermentation is involved.
What does it mean when long forage is left behind instead?
Cows may have selectively consumed shorter, often more concentrate-rich particles. Compare the fresh ration and refusals using particle-size measurements to confirm the direction of sorting.
What particle-size target should I use for a dairy TMR?
Penn State's 2013 four-compartment separator gives a 2–8% top-sieve reference for typical lactating-cow TMR, alongside ranges for the other fractions. The nutritionist should interpret results according to the forage and ration design.
Can better TMR mixing and feed push-up help with concentrate refusal?
A mixer matched to the ration and batch size helps deliver a more consistent TMR. Regular feed push-up helps cows reach fresh feed between deliveries. Compare fresh feed, refusals and cow health to identify which improvement will make the most difference.
Conclusion
When a cow eats grass but leaves concentrate, the fastest useful clues are which animals are affected, what changed in the feed, what remains in the bunk, and whether the cow's health or production has changed. For TMR-fed herds, look at the direction of sorting before changing mixer settings. A consistent record of feed lots, actual mixing, animal behavior and refusals makes the next action clearer.
NexAgri can help commercial farms select suitable mixing, feeding-line and watering equipment around the farm's herd groups, ration and barn layout. A well-matched system makes it easier for staff to deliver the intended feed consistently and recognize departures from the routine.
