Effects of a hot dry summer on forage quality

  From the August 27, 2018 issue of Agri-News
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 In many parts of the province, a hot dry summer has hastened the maturity and dormancy of native and improved pastures. Barry Yaremcio, beef and forage specialist at the Alberta Ag-Info Centre, looks at how these factors reduce the quality and digestibility of the plant material as compared to a year with cooler temperatures and higher amounts of rainfall.

“Plants do not grow as tall as normal in dry conditions,” says Yaremcio. “Fibre levels increase faster and overall energy content of the forage is reduced. Fibre is the most difficult part of the plant for rumen microbes to break down. Feed remains in the rumen for longer periods of time. The longer the feed is resident in the rumen, the less an animal is able to eat, resulting in lower total daily nutrient intake.”

Hot dry conditions also limit the amount of water and nutrients available to the plant. Explains Yaremcio, “The amount of nitrogen absorbed by the roots and transferred into the plant is lower, resulting in lower protein production and less protein available in the leaf material. Protein is required to keep rumen microbial levels high to maintain proper digestion. A lack of protein in the plant material limits microbial growth in the rumen. A reduction in feed intake occurs and animals may drop body condition.”

Protein content in the forage drops more rapidly than normal in stressed plants. “Instead of pasture forage meeting protein requirements until mid-to-late September, it is possible that protein requirements of the lactating cow will not be met by mid-August. As result, you can expect reduced milk production and lower calf growth rates,” adds Yaremcio.

More mature forages can become very hard and brittle, especially the wheatgrasses and fescues. “It may seem from a quick drive-by inspection that there is sufficient forage for the animals to eat,” says Yaremcio. “If cattle ignore these plants and don’t want to eat them, you should consider this material as having no feeding value. It should not be considered as a potential feed supply. Take time, walk the pastures, and determine what is left behind. It is possible to have cows in over-mature unpalatable grass that is up to their knees or bellies, and they are unwilling or unable to eat enough to meet nutrient requirements.”

Yaremcio adds that overgrazing a pasture this fall can reduce winter survival of certain species. “Alfalfa and orchard grass are two prime examples. Plant counts next spring could be substantially lower when pastures are grazed at the wrong time of year or too extensively. Overgrazing this fall may also delay plant development next spring which delays turnout, and could also reduce next year’s yield potential.”

For more information, call the Alberta Ag-Info Centre at 310-FARM (3276).

Alberta Ag-Info Centre
310-FARM (3276)

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For more information about the content of this document, contact Barry Yaremcio.
This document is maintained by Christine Chomiak.
This information published to the web on August 20, 2018.