Forage minerals vary with season

Producers shouldn’t expect that tossing a salt or mineral block into the pasture every month is going to provide their cattle with the proper amounts of trace minerals in their diets.

A new study has found a difference in mineral content of Saskatchewan forages between the types of forage, soil zones and the grazing season.

The two-year study showed a clear difference between the trace minerals provided by forages in the spring and fall, said Leanne Thompson, executive director for the Saskatchewan Forage Council.

“Be aware of your mineral program from spring to fall to reflect forage quality,” said Thompson.

With more producers grazing cattle on pasture, it’s not as easy to provide a complete mineral package, including trace minerals in the animal’s diet.

“It used to be easy to do when cattle were in a dry lot and when they were fed a ration,” said Thompson.

The study is a reminder for farmers of the need to adjust their mineral program throughout the year, especially when the cattle are on pasture, she said.

Researchers wondered if there was a link between poor reproductive performance and increased pasture grazing. They also wanted to get updated data on trace minerals in forage crops across the province.

The study looked at pastures in the brown, dark brown, black and gray soil zones.

Water samples were also collected to assess the nutrients available to cattle on pasture.

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The study found iron concentrations were highest in forage sampled in the grey soil zone during the fall, but levels appeared adequate for grazing animals across all soil zones, forage types and season.

There wasn’t a significant difference between soil zones for manganese or zinc.

Copper tended to be lowest in the brown and dark brown soil zones during the fall.

In all soil zones, both zinc and copper were inadequate in all samples and in all soil zones to meet the de-mands of beef cows or growing beef calves.

Molybdenum was highest in the grey soil zone during the fall and lowest in the dark brown soil zone during spring.

The copper and molybdenum ratio was lowest in the grey soil zone in both spring and fall.

Selenium levels were highest in the brown soil zone and similar across the dark brown, black and grey soil zones.

Iron and selenium levels were near or adequate across all forage species sampled in both seasons.

“This is interesting,” said Thompson, adding that the message has long been to supplement selenium when grazing forages.

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“Maybe there is some other interaction going on.”

Manganese was adequate in more than 80 percent of meadow brome, smooth brome and western wheatgrass in spring and fall.

Crested wheatgrass was extremely low in manganese during the spring.

Zinc was below adequate in spring and well below adequate in fall across all species sampled.

Alfalfa showed slightly higher levels of copper in fall compared to spring. The opposite trend was noted for the grasses.

What was clear from the study was producers need to design a mineral program based on what is growing in the pasture, said Thompson.

“Use mineral programs that vary from spring to fall.”

All the information has been sent to forage and livestock specialists to help producers in all areas of the province develop mineral programs based on their region and forage type.

“If producers work with nutritionists of livestock and forage specialists, they should be able to help formulate a mineral requirement for your herd or area.”

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