Achieving an appropriate calcium balance in dairy cows is critical near calving -- but for more than simply ensuring a healthy transition to lactation.

A new study from the University of Illinois is showing that calcium added to acidified prepartum diets may improve a whole suite of postpartum outcomes, including lower rates of uterine infection and a quicker return to ovulation, according to an announcement from the university.

"We know that calcium metabolism in dairy cows is very important. There's research saying that 50% of multiparous cows [those on their second or third pregnancy] suffer some sort of deficiency of calcium," said Phil Cardoso, associate professor in the University of Illinois department of animal sciences.

Cardoso explained that the common practice of feeding an acidified diet prior to calving forces the cow to manufacture and redistribute calcium from her bones. This activation of internal calcium production carries the cow through to lactation, when she resumes consuming calcium in her diet.

In the weeks before calving, producers commonly feed negative dietary cation-anion difference (DCAD) diets, usually supplemented with a small amount of calcium (1% of dry matter), he noted. The practice is typically enough to avoid full-blown milk fever, or clinical symptoms of calcium deficiency. However, Cardoso said 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.

He also noted that no one has tested the effects of adding different concentrations of dietary calcium to the fully acidified DCAD diet.

"Calcium is important for many cellular processes. Without adequate calcium concentrations, tissues don't work optimally and are subject to inflammation and susceptible to disease. We wanted to test whether an increased amount of calcium — 2% 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," Cardoso said.

His team fed 76 multiparous Holstein cows one of three diets in the month before calving: (1) a control, non-acidified DCAD diet with no added calcium; (2) an acidified DCAD diet (-24 milliequivalents [mEq] per 100 g of dry matter) with no added calcium, and (3) an acidified DCAD diet (-24 mEq) with added calcium at 2% of dietary dry matter. The DCAD 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% of dietary dry matter calcium.

The researchers 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 DCAD plus calcium diet to get pregnant at a higher rate than cows fed the control diet, but we need to test that in a larger population to be sure of that result," Cardoso said.

What he is sure of is that cows fed the diet with added calcium took less time to ovulate and had lower levels of uterine infection than cows on the other diets. This was likely due to the fact that cows on the calcium-added diet had more tight junction proteins in the uterine lining; these proteins bind adjacent cells, preventing a "leaky" tissue that could allow pathogens to enter the bloodstream during calving.

"Ours is the first study showing tight junction proteins even exist in the uterus of the dairy cow and also clearly indicates that added calcium improves their number and function," Cardoso said.

Cows fed the calcium-added diet also had more favorable disease-fighting antioxidants in the blood and more glands in the uterine lining that keep the organ clean and produce hormones that can kick-start ovulation. "That could be why we saw better pregnancy rates," Cardoso said.

He pointed out that many producers have been using a negative DCAD strategy for decades but aren't acidifying the diet enough, are taking it to only -5 mEq and are not adding calcium or are adding calcium at only 1% of dietary dry matter.

"We are saying that you need to go to -20 mEq and up to 2% of dietary dry matter for calcium," he said.

The message to the dairy industry is clear: A negative DCAD diet with added calcium is helpful not only to get through the transition to lactation; it can help improve future pregnancy outcomes in the herd. Cardoso said he wants to get the message out to both nutritionists and veterinarians, who he'd like to see talk to each other more often to create strategies for improved reproduction.

The article, "Increased Dietary Calcium Inclusion in Fully Acidified Prepartum Diets Improved Postpartum Uterine Health & Fertility When Fed to Holstein Cows," was published in Theriogenology. Authors included K.T. Ryan, A.R. Guadagnin, K.M. Glosson, S.S. Bascom, A.A. Rowson, A.J. Steelman and Cardoso. The study was supported by Phibro Animal Health and the U.S. Department of Agriculture's National Institute for Food & Agriculture.

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