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Defining mineral needs of pregnant cows.

Everyone knows the recipes by heart: "snips and snails and puppy-dogs' tails" for boys, "sugar and spice and everything nice" for girls. Now William A. House and Alan W. Bell have a recipe for healthy dairy calves, too.

House is a research animal physiologist at ARS' U.S. Plant, Soil, and Nutrition Laboratory at Ithaca, New York. He and animal science professor Bell of Cornell University teamed up in 1992 to produce a complete profile of fetal mineral content for dairy cattle, including a look at how the proportion of various minerals changes as the fetus progresses through gestation.

This information is important to cattle producers who want to ensure that they're feeding the right amounts of minerals to pregnant dairy cows to ensure the birth of healthy calves.

"For example, pregnant cows absorb about 45 percent of the calcium in their diet," House explains. "The absorbed calcium is used by the cow to maintain her own body and to support the growth of the fetus.

"We estimate that a 1,600-pound cow needs 12 grams of calcium per day for maintenance. Also, we know that the fetus needs 10 grams of calcium each day in late gestation. Since the dry pregnant cow absorbs less than half the calcium in her feed, she needs to be eating about 50 grams of calcium per day to meet her 22-gram requirement."

House and Bell analyzed the mineral content of fetuses taken from 19 pregnant 1,600-pound Holstein cows slaughtered at 190 to 270 days after conception. The gestation period for Holsteins is about 280 days.

Before House and Bell began their cooperative study, only calcium and phosphorus content of the dairy fetus had been measured, back in 1950. More complete analyses of mineral content had been completed for beef cattle, pigs, and sheep, according to House.

He and Bell measured not only calcium and phosphorus content in the dairy fetus, but also levels of potassium, sodium, magnesium, iron, zinc, copper, and manganese.

Measurements took into account the entire "conceptus" - the fetus itself, plus fetal membranes, fetal fluids, and placental tissue.

"At day 200 of gestation, die fetus is depositing about 2 grams of calcium and 1.3 grams of phosphorus per day," says House. "At day 270, the calcium has increased to about 10 grams and the phosphorus to nearly 5 grams."

House attributes the increase in deposition of fetal calcium and phosphorus during late pregnancy to the accelerated rate of accumulation of these minerals in bone.

Concentrations of magnesium also increased with fetus age, House notes, while concentrations of potassium and sodium decreased.

During the latter stages of gestation, the bovine conceptus each day accrues an average 0.2 grams of magnesium, 1.0 grams of potassium, 1.4 grams of sodium, 18 milligrams of iron, 11.7 milligrams of zinc, 1.6 milligrams of copper, and 0.3 milligrams of manganese, House reports.

"The general practice among producers is to manage dairy cows to |dry off' - so they're putting their energy into producing a fetus rather than producing milk," House says. dry cow haven't gotten a lot of "The nutritional requirements of the dry cow haven't gotten a lot of attention in the past.

"Now we have a data set that gives us a better understanding of mineral nutritional requirements of dairy cows during this phase."
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Author:Hays, Sandy Miller
Publication:Agricultural Research
Date:Aug 1, 1993
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