Feed System Effects on Milk Fever, Ketosis, and Lameness: What the Research Actually Shows

Ask ten dairy people whether a feeding system changes disease risk and you will get ten confident answers. Pasture advocates point to healthier feet. Confinement operators point to tight ration control and fewer weather swings. Both camps have a piece of the truth, but the research is less tidy than either story, and it is thinnest on the two diseases people most want a clean answer about: milk fever and ketosis.

This article separates what the published work supports from what is assumed. It is a reading guide, not a verdict on any system. Herds differ, and so do the cows within them.

Start with what each system changes

A feeding system is more than a diet. Moving cows from a confinement total mixed ration to grazing changes the feed, but it also changes the floors cows walk on, how long they stand, how much space they have, how weather reaches them, and how closely staff see each animal. When a study reports a difference in disease between systems, it is rarely possible to credit the feed alone.

That matters because a producer reading a headline may conclude that changing the ration will change the disease rate. Often the bigger lever is the surface, the stall or the handling, not the nutrient profile. Our guide to cow comfort in freestall barns covers the housing side.

Lameness: the clearest signal

Lameness is where the evidence leans most consistently toward pasture. A review by Arnott, Ferris and O'Connell in the journal animal concluded that pasture-based cows had lower levels of lameness, hoof pathologies and hock lesions than continuously housed cows. The same abstract reported lower mastitis and mortality on pasture, and it also noted a possible welfare risk from exposure to unpredictable weather.

A Teagasc end-of-project report on cow welfare in Irish grass-based systems, available through CORE, gives numbers from a controlled comparison of 23 cows per group. Clinical lameness at least once was recorded in 4 of 23 pasture cows and 13 of 23 housed cows, and housed cows had higher odds of lameness from about day 180 onward. That is a small trial in one country, so treat the size of the gap as indicative rather than universal.

For the practical side of finding and treating the problem, see lameness and hoof care in Holsteins.

Diet still plays a part inside any system

Even in a confinement barn, diet can push lameness up or down. Rations that drop rumen pH repeatedly are a recognized concern, and a 2023 study in first-lactation Holsteins found a dose-like pattern between days of subacute ruminal acidosis and lameness; we cover that work in our article on SARA and claw health. The takeaway is that a pasture-versus-barn label does not protect a herd from a poorly managed ration.

Mastitis and retained placenta: mixed picture

The Teagasc report recorded 24 mastitis cases in pasture cows against 44 in housed cows, a statistically significant difference in cases, although the number of cows affected was the same (30 in each group). So the housed cows were getting repeat cases rather than more individual cows being affected. Retained fetal membranes in the first ten days after calving occurred in 2 of 23 pasture cows and 3 of 23 housed cows, which was not a significant difference. With groups this small, the absence of a statistical difference is not proof of no difference.

Milk fever and ketosis: where I could not find clean comparisons

This is the honest part. In the sources I could verify, the Teagasc report treated milk fever and ketosis only as background transition-period disorders and did not report system comparisons. The abstract of the Arnott review does not mention either disease; it does flag physiological indicators of more severe negative energy balance as a potential concern for pasture-based cows. That is a reason to watch fresh cow intake and body condition closely on grazing systems, not a measured ketosis rate.

What can be said is that both diseases are driven by what happens in the last weeks before calving and the first weeks after, in any system:

• Milk fever (hypocalcemia) develops when calcium demand rises suddenly at calving and the cow cannot mobilize enough. University of Minnesota Extension lists herd alarm levels of 3% for clinical cases and 30% for subclinical.
• Ketosis follows negative energy balance, with a herd alarm level of 15%.
• Dry cow potassium load, close-up mineral program, body condition at calving and intake in the first days all matter more than whether the cows spend the summer on grass or under a roof.

Those thresholds come from Minnesota Extension's transition cow page, which also gives the cost per case as roughly $150 for hypocalcemia and $289 for ketosis. For the blood thresholds, the University of Illinois Dairy Focus series defines subclinical ketosis as BHB above 1.2 mmol/L and keeps the share of fresh cows at or above that level in week one under 15%.

What to do with this on your own farm

1. Measure before you change. Record fresh cow disease rates for at least a year. Compare yourself to the alarm levels above, not to a neighbor.
2. Do not credit or blame the feed system alone. If lameness is high, audit floors, stall comfort, standing time and trimming first. Then look at rumen health.
3. If you graze, watch the fresh cows. Check intake, body condition loss and BHB in the first two weeks, since the review flags energy balance as a concern.
4. If you confine, protect hooves. Walking surfaces and lying time are your levers.
5. Use your vet and nutritionist for diagnosis. Disease cause is rarely obvious from the outside.

Bottom line

The evidence most strongly supports lower lameness, mastitis and mortality on pasture, with caveats about weather and energy balance. For milk fever and ketosis, I could not verify head-to-head comparisons, and the drivers sit in transition management that applies equally to both systems. Read any single trial as one herd's story. For more directories and tools, see the agriculture directory, and for the wider farm community, farm.fm's dairy section.