Understanding Fibre in the Beef Cow Diet
By Colby Elford BSc. PAg., Livestock and Feed Extension Specialist, Moose Jaw
When we talk about feed quality, we often focus on protein and energy. While these are very important feed ingredients, they are not the only things that need to be considered when planning for winter feeding. The feed’s fibre value, expressed as Acid Detergent Fibre (ADF) and Neutral Detergent Fibre (NDF) are also important as they have a great impact on feed digestibility and dry matter intake.
ADF refers to the least digestible fibre portion of the forage. The ADF value represents the amount of lignin, cellulose, silica and insoluble forms of nitrogen in the feed. As the amount of ADF in the forage increases, digestibility decreases. The digestibility of a feed relates to its energy value; if the feed has a higher percentage of ADF it will have a lower energy (total digestible nutrient) value and vice versa.
NDF measures cellulose, hemi-cellulose, lignin, silica, tannins and cutins. While ruminants have some ability to digest this part of the feed, some remains indigestible. This fibrous bulk is used to predict intake. As the NDF in forages increases, animal intake decreases. This effect is further compounded as low quality forages also contain low levels of essential nutrients (i.e. protein and energy), resulting in lowered feed intake as well as lower nutrient supply.
Throughout pregnancy and into lactation, a cow’s nutrient requirements increase. As the fetus grows, it puts pressure on the internal organs and reduces the amount of space available to the rumen. Ultimately, this means that there is less space available to digest feed. Furthermore, in Saskatchewan, beef cow pregnancy usually occurs during the coldest months of the year, pushing requirements even higher. For these reasons, feeding more of a highly fibrous or poor quality feed will not meet a cow’s nutritional requirements and increases their risk of impaction. A nutrient dense feed source (i.e. pellets, grain or high quality hay) must be used to supplement high ADF and NDF forage to meet their requirements.
Generally, more mature feeds will have higher fibre values, but a feed test will tell the complete story. Feed tests are very inexpensive when compared to the alternatives of loss of body condition in late pregnancy or difficulty rebreeding as a result of poor nutrition. A forage probe for collecting feed samples may be borrowed from your local Ministry of Agriculture regional office and Saskatchewan Crop Insurance Corporation office. Our livestock and feed extension specialists can assist with selecting feed test packages and interpreting results as well as developing rations.
For more information on this topic, accessing a forage probe or assistance in interpreting feed test results, call the Agriculture Knowledge Centre at 1-866-457-2377 to be connected with your local livestock and feed extension specialist.
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