Calcium’s role in dairy cows may be underrated: study

New research finds that adding calcium to prepartum diets can lower the possibility of uterine infection and return a cow to ovulation quicker

Achieving the right calcium balance in dairy cows is critical when they approach calving to ensure a health transition to lactation.

Now a new study from the University of Illinois has shown that calcium added to prepartum diets can improve not only postpartum outcomes but also lower the possibility of uterine infection and help a cow return to ovulation quicker.

Producers often feed negative dietary cation-anion difference (DCAD) diets in the weeks leading to birth, often supplemented with just a small amount of calcium (one percent dry matter). The procedure is usually enough to avoid milk fever or clinical symptoms of calcium deficiency.

“Others have looked into the relationship of low-DCAD and calcium concentrations in prepartum diets,” said Phil Cardoso, associate professor at the university’s Department of Animal Sciences. “However, we are the first ones looking into dietary calcium concentration and urinary acidification (an indication of the efficacy of the low-DCAD in the diet). The same degree of negative DCAD can lead to different degrees of acidification (i.e., urine pH).”

He said calcium metabolism in dairy cows is important and past research has shown that 50 percent of cows in their second or third pregnancies suffer some level of calcium deficiency. The common practice of feeding an acidified diet before calving forces the cow to produce calcium for her bones. It carries her through lactation.

He said that feeding an acidogenic diet using supplemental chlorides and sulfates lowers blood and urine pH.

“When a negative-DCAD diet is fed, there is a greater balance of negatively charged chloride and sulfur ions compared to positively charged potassium and sodium ions, and more of these negatively charged ions are absorbed from the digestive tract into the blood. Feeding a negative-DCAD diet results in compensated metabolic acidosis, in which urine pH is significantly reduced, while blood pH is maintained in a safe range.”

He added that metabolic acidosis brought about by feeding a negative-DCAD diet does not cause ruminal acidosis.

“Low-serum calcium concentrations at calving stimulate the secretion of the parathyroid hormone (PTH), which increases calcium release from the bone and vitamin D activation in the kidney (which, in turn, improves calcium absorption in the digestive tract). Feeding a negative-DCAD diet reduces blood pH slightly, which improves the responsiveness of the target tissues to PTH, increasing calcium release from bone and vitamin D activation in the kidney.”

He said that when urine pH is reduced, calcium excretion through the urine increases. Greater urinary calcium excretion can improve calcium status after calving by increasing calcium flux.

“Calcium flux is the movement of calcium into and out of the blood of the cow. When urine pH is reduced, and urinary calcium excretion is increased, more calcium exits and enters the cow’s blood and calcium flux is increased.”

Calcium excreted in the urine when an acidogenic diet is fed becomes available to meet the sudden increase in calcium demand when colostrum production begins right at calving. This helps to overcome a calcium deficit.

Dairy farmers are well informed of the need for calcium supplements, but a focus of the research was to try to provide calcium through the diet and avoid the use of supplements. He said that Jersey cows benefit from a higher inclusion of calcium in their diets since, according to anecdotal evidence, the breed seems to be more prone to hypocalcemia.

Cardoso’s team fed 76 multiparous Holstein cows one of three diets in the month before calving. They had either a non-acidified DCAD diet with no added calcium, an acidified DCAD diet (-24 milliequivalents per 100 grams of dry matter) with no added calcium, or an acidified DCAD diet (-24 milliequivalents) with added calcium at two percent of dietary dry matter.

The DCAD formulation was mixed with typical forages and corn silage. After calving, cows were switched to a typical postpartum diet with one percent of dietary dry-matter calcium.

The team monitored changes in the blood, uterus, ovaries, and pregnancy status at two and four weeks, following calving. They found that there was a trend toward cows fed the negative DCAD plus calcium diet to get pregnant at a higher rate than cows fed the control diet.

That needs to be tested on a larger population of cows. However, Cardoso is confident 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 he believes was due to the fact that cows on the calcium-added diet had more tight junction proteins in the uterine lining.

“Tight junctions are the proteins that keep the cells attached,” he said. “The ones we tested are calcium dependent. They should exist in a different number of systems, like the digestive system. Without sufficient attachment between cells, there is an opportunity for bacteria to leak into the blood circulation and cause disease. Ours is the first study showing tight junction proteins even exist in the uterus of a dairy cow and the study clearly indicates that added calcium improves their number and function.”

In the news release, Cardoso said that cows fed the calcium-added diet had more favourable disease-fighting antioxidants in the blood and more glands in the uterine lining, which keep the organ clean and produce hormones that can kick-start ovulation. That, he suggests, is why they saw better pregnancy rates.

The study was published in the journal Theriogenology.

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