Like a shy teenager at a school dance, chloride levels in forages haven't gotten enough attention, says Dave Casper.

“Forages have the greatest impact on the dietary supply of chloride,” says Casper, a dairy nutritionist with Agri-King, Fulton, IL. “Unfortunately, measuring the level of chloride in forages using laboratory analysis has been difficult, time-consuming and expensive, so it has seldom been done. But it's very important for dairy producers to know the chloride content of what they're feeding.”

An anionic mineral, chloride works with sodium and potassium to maintain osmotic pressure and the acid-base and fluid balances in a cow's body tissues. The primary independent function of chloride is in gastric acid secretion in the abomasum. It's readily absorbed from the rumen and intestinal tract.

Transition cows must have enough chloride in their diets, warns Casper. “If a cow has milk fever, she's lacking the appropriate balance of chloride and potassium.”

To determine the chloride concentrations of forages, Casper summarized thousands of samples of corn silage, alfalfa haylage, alfalfa hay, oatlage and all types of pasture that were submitted to Agri-King. The results are shown in the table on page 26.

“Chloride concentrations can vary greatly within and between forage types,” says Casper. “Some of the samples had almost no chloride, while others contained over 3%.”

Some highlights of his findings:

  • The average chloride content of corn silage was about 0.27% of dry matter, but a wide range was observed.

  • On average, the chloride concentration of haylage and hay was about twice that of corn silage.

  • Pasture chloride levels, on average, were greater than those of haylage, hay and corn silage.

Generally, grains, protein sources and by-product feeds are low in chloride.

For most transition cows, the percentage of chloride to shoot for in the TMR is 0.65%-0.80%. That will prevent milk fever unless potassium intake is excessive, says Casper. For lactating dairy cows, a chloride level of 0.50% is adequate.

Using X-ray spectrometer technology borrowed from the metallurgy industry, Agri-King offers a fast lab test to determine chloride levels. A feed analysis, which includes the chloride test, costs about $20.

“The advantage of X-ray technology is that it is rapid, accurate and precise in measuring the chloride concentrations in a large number of samples,” says Casper. He recommends a monthly chloride analysis of all forages. “To the best of my knowledge, no other commercial testing labs offer this technology.”

If your forages are short on chloride, he recommends adjusting your fertilization program.

“When potash is applied to alfalfa, it's generally potassium chloride. So, at the same time you're putting potassium on, you're also applying chloride. But not all sources of potash are potassium chloride. For example, potassium sulfate is also a potash source, but it doesn't contain chloride. Calcium chloride is another good option to increase chloride in the soil without adding potassium.”

Over time, chloride is depleted more quickly from the soil than is potassium.

If a TMR is short on chloride, adding salt and/or potassium chloride can bring the level up. For transition cows and milk fever prevention, Soychlor, Biochlor, calcium chloride or ammonium chloride can be added.