Grazing After Frost and the Potential Ramifications of Opening the Gates to Canola


It’s been an interesting year for farmers and ranchers in much of western Canada, with short feed supplies in the summer, and excess, non-traditional feedstuffs available this fall.

For many, the conditions have meant assigning their four-legged residue management systems to canola re-growth. But, as you’ll learn in the following audio, grazing canola without care can come with consequences.

Continues below audio…

Barry Yaremcio talks about grazing annuals and perennials after frost. He also warns of the consequences of grazing canola without a feed analysis.

First, canola can accumulate high amounts of sulphur, which, if above 0.4% of the ration on a dry matter basis, can cause polioencephalomalacia (commonly referred to as polio) in ruminants. Second, canola forage can accumulate nitrates, and cause nitrate poisoning if managed incorrectly (check out Alberta Agriculture’s Nitrate Poisoning and Feeding Nitrate Feeds to Livestock).

But nitrate toxicity can also occur in other highly-fertilized annual crops, or those hit by frost.

Non-killing frosts halt photosynthesis aboveground, but do not impact root function. This means roots continue to send nitrates to the stems and leaves, though they have no means to handle the nutrients. Normally, nitrates are converted to nitrite and then to ammonia in a cow’s digestive system. But, when high-levels of nitrate are present in the feed, the second conversion can get behind, and nitrites will enter the bloodstream, bind to hemoglobin and limit the oxygen carrying-capacity of the blood.

Allowing ruminant microbes time to adjust, feeding more than once a day and ensuring a balanced ration are all ways to mitigate the risks of toxicity.

Legumes, fortunately, don’t see the same level of risk, thanks to their synergistic relationship with rhizobia. Nitrates are only released from root nodules as they are needed. That said, graziers should be cautious of bloat and over-grazing when turning animals into alfalfa in the fall and winter, respectively.

Related: Mitigating the Risk of Bloat in Fall-Grazed Alfalfa

And remember, it’s not just about potential toxicity. Ranchers should also consider changes to quality as seasons progress.

“I think we weigh too heavily on what nitrate accumulation can be,” Murray Feist, ruminant nutrition specialist with Saskatchewan Ministry of Agriculture told us in an interview last year. “We still have to capture the best quality forage that we can.”

Ultimately, knowing what’s in the forage and providing adequate supplements/adjustments to the feed boils down to getting into pastures and fields, sampling the growth and sending it out to get tested.

“It’s not a very expensive test,” said Feist, “it provides some numbers and gives you something to gauge against.”

WatchBeef Research School: Using a Feed Test to Maximize Profits & Avoid Pitfalls

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