Achieving an appropriate calcium balance in dairy cows is critical near calving, but not only to ensure a healthy transition to lactation. Calcium added to acidified prepartum diets can improve many postpartum outcomes -- such as reduced rates of uterine infection and quicker return to ovulation.

Research has shown that 50 percent of multiparous cows -- those on a second or third pregnancy -- suffer some calcium deficiency. Feeding an acidified diet prior to calving forces the cow to make and redistribute calcium from her bones. Activation of internal calcium production carries the cow through to lactation, when she resumes consuming calcium in her diet.

Producers commonly feed negative dietary cation-anion-difference diets in weeks before calving. The diets are usually supplemented with a small amount of calcium – 1 percent of dry matter. The practice is typically enough to avoid milk fever or clinical symptoms of calcium deficiency.

But there has been little guidance on how much to acidify the diet to remobilize the optimal amount of calcium and avoid excretion in the urine. No one has tested the effects of adding different concentrations of dietary calcium to the fully-acidified dietary cation-anion-difference diet.

Calcium is important for many cellular processes. Without adequate calcium concentrations, tissues don’t work optimally. They’re subject to inflammation and susceptible to disease. We wanted to test whether an increased amount of calcium – 2 percent of dry matter – added to an acidified diet during the last month of pregnancy could prevent those issues and lead to more-favorable reproductive outcomes.

We fed 76 multiparous Holstein cows one of three diets in the month before calving.

  • control diet – a non-acidified dietary cation-anion-difference diet with no added calcium
  • acidified dietary cation-anion-difference diet at -24 milliequivalents per 100 grams of dry matter with no added calcium
  • acidified dietary cation-anion-difference diet at -24 milliequivalents with added calcium at 2 percent of dietary dry matter

The dietary cation-anion-difference formulation was mixed with typical forages and corn silage in prepartum diets. After calving all cows were switched to a typical postpartum diet with 1 percent of dietary dry-matter calcium. We then monitored changes in the blood, uterus, ovaries and pregnancy status at two and four weeks post-calving.

There was a tendency for cows fed the negative dietary cation-anion-difference plus-calcium diet to become pregnant at a greater rate than cows fed the control diet. But we need to test that in a larger population to be sure of the results.

Cows fed the diet with added calcium required less time to ovulate. And they had reduced levels of uterine infection compared to cows on the other diets. That was likely due to the fact that cows on the calcium-added diet had more-tight junction proteins in their uterine lining. Those proteins bind adjacent cells, preventing “leaky” tissue that could allow pathogens to enter the bloodstream during calving.

The study showed tight-junction proteins exist even in the uterus of the dairy cow. Results also indicate that added calcium improves their number and function.

Cows fed the calcium-added diet had more favorable disease-fighting antioxidants in their blood and more glands in their uterine lining. That keeps the organ clean and produces hormones that can prompt ovulation. That could be why we saw better pregnancy rates.

Many producers have been using a negative dietary cation-anion-difference strategy for decades. But they aren’t acidifying the diet enough, taking it to only -5 milliequivalents and not adding calcium, or adding it at just 1 percent of dietary dry matter. The study shows the need to feed -20 milliequivalents and as much as 2 percent of dietary dry matter for calcium.

A negative dietary cation-anion-difference diet with added calcium helps the cow through the transition to lactation. It can help improve future pregnancy outcomes in the herd.

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Felipe Cardoso is an associate professor in the animal-science department at the University of Illinois-Urbana.