Corn grazing is about finding right balance

Trials compare different corn allocations to make sure grazing cattle obtain the correct amount of nutrition and fibre

LANIGAN, Sask. — How do you manage the behaviour of cattle if they’re always going to eat their dessert first?

It’s a question of balance, said Breanna Anderson, a University of Saskatchewan graduate student who is looking for answers at the Western Beef Development Centre near Lanigan.

“We’re trying to create a balanced diet because they’re not going to nutritionally balance themselves,” she said during the WBDC’s 2016 winter field day.

“Just like kids in a candy shop.”

The WBDC typically recommends that producers use a three-day allocation of standing corn, but the two-year study is comparing three and nine-day allocations of fresh grazing corn with and without the provision of a fibre source.

The four treatments include:

  • three days of corn with fibre
  • three days without fibre
  • nine days of corn with fibre
  • nine days without fibre

“With all the corn grazing trials we’ve done out here for 15 years, we’ve learned that cows are very selective,” said Bart Lardner, senior research scientist at the centre.

He said cattle prioritize certain plant structures based on taste, sight and preference, which involve the cob, leaf, tassel and stalk.

“We find that they will go for the cob first, the ice cream part of the plant,” he said.

“That’s not bad, but you need to control that. We want them to have the other essential nutrient parts of the plant as well.”

The corncob is full of starch, while the rest of the plant is mostly fibre.

Lardner said it’s about balancing the starch and fibre that goes into the rumen every day.

“It’s the same as a cow that’s going to get nothing but straight barley. She’s potentially going to bloat on that barley. That’s why we have some fibre in with that barley,” he said.

“In that total mix ration, we’re going to have some barley grain, but we’re also going to have some forage, hay and green feed and some straw.”

The rumen should have a pH of six to 6.2, but eating too much starch without adequate fibre content will lower it and create an acidosis type environment. As the pH drops, so does fibre digestibility, while the risk of sub-acute rumen acidosis goes up.

“This can be quite harmful to the animal,” said Anderson.

Added Lardner: “It’s basically a cow with a bellyache.”

Part of Anderson’s research is conducting a preference trial, which looks at the disappearance of the cob, leaf, husk, tassel and stem over time.

“It’s to give us data to show what the cows are picking,” she said.

She takes a daily representative sample from each field of 10 to 15 plants. The proportions of each plant are then weighed.

“As the days progress that the cows are in that amount of feed, what disappears first is the cob, leaf and husk, and at the end you’re left with almost 100 percent stem, whereas at the start you’re closer to 40 to 50 percent cob,” she said.

A total of 112 cows are being used for the study with 14 per paddock spread out over eight fields.

Two cows per paddock have a rumen cannula installed to provide a basic research application.

Researchers use probes in the cannulated rumen to monitor pH fluctuations .

“We can track through the three or nine day allocation, with or without fibre, and compare how their pH is changing each day to see how their diet is changing each day,” said Anderson.

Separate samples can also monitor production of volatile fatty acid and rumen ammonia, which indicates how well the feed is being digested.

One animal per paddock wears a GPS collar to monitor grazing behaviour every 24 hours.

Researchers can then accurately determine what times of day cattle are grazing, how much time they are spending in the corn, eating hay or at the windbreak or water trough.

“It’s to get a better understanding of how our management affects their grazing behaviour because grazing behaviour will directly affect their diet — what parts of the plant they’re selecting, how much they’re eating, how many meals a day they’re having,” she said.

Soil samples in spring and fall are also taken to better understand how manure affects the nitrogen, potassium, phosphorous and sulfur profile in the soil.

The grazing perimeter of the nine day cycle is three times that of the three day cycle and three times the amount of food.

“So if on a three day group I’m giving them 1,000 pounds of feed on the nine day feed, I’m giving them 3,000 pounds of feed,” she said.

“Is this going to affect rumen acidosis? Is this going to affect how much they waste, how much they’re gaining?

“We’re trying to push the limits and see if this changes their behaviour. Are they still going after the cobs?”


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