Effective fibre – Does it have a role in feedlot rations?

Source: Ministry of Agriculture, Food and Rural Affairs

Today’s feedlot rations often contain a high inclusion of grains and grain byproducts with some level of roughage inclusion. While the objective of feeding finishing cattle a ration with a high amount of grains is to increase the energy density of the diet and improve ADG, rations must also be balanced to limit issues associated with digestive disorders while maintaining production. Promoting gut health can help reduce incidence of conditions that are related to digestive upsets, including acidosis, rumenitis, liver abscesses, and founder. This article explores what makes effective fibre so “effective” in promoting gut health and why effective fibre has a place in feedlot rations.

What is physically effective fibre and how does it contribute to rumen health?

It is well established that fibre inclusion in a ruminant ration is important to rumen health. The “bulk” of it is necessary to stimulate rumination, increasing saliva production to help buffer low rumen pH. Volatile Fatty Acids (VFA’s) are produced through ruminal fermentation and represent a significant energy source for cattle. Rapidly digested carbohydrates, grains, tend to lead to an increase in VFA production, which reduces ruminal pH. When the rate of VFA production is out of balance with VFA absorption, the pH of the rumen can drop too low for an extended amount of time, resulting in acidotic conditions. Acidosis is associated with reduced rumen motility, impaired fibre digestion, decreased nutrient absorption, inflammation and damage to the rumen wall. Acidosis is also associated with liver abscesses and founder (laminitis) in cattle, which have direct costs for producers (vet bills, decreased feed efficiency) and indirect costs (lower carcass grades and increased carcass trim). The National Beef Quality Audit (2016/17) reported that 19.3% of livers assessed from fed cattle scored A+, noting an increase from 9.9% in 2010/11 and 2% in 1999.

Inadequate inclusion of fibre in the diet is a risk factor for acidosis and related conditions in feedlot cattle. Fibre stimulates rumination and saliva production, which buffers the pH of the rumen. Neutral detergent fibre (NDF) is often used as an indication of how much fibre is in a ruminant ration. And can be tested by laboratory analysis. But the chemical fibre fraction (%NDF) is only part of the picture. It is not simply the amount of fibre in the ration that matters; it is also the physical form of fibre that influences rumen health and function. Some byproduct feed ingredients (e.g. DDGS, corn gluten feed, etc.) are high in dietary NDF, but don’t have the same “scratch factor” to stimulate rumen motility and salivation as long-stemmed hay. Similarly, ground roughage sources with a smaller mean particle size do not have the same capacity to stimulate chewing behaviour as forages with a longer mean particle size.

How is physically effective fibre measured?

Physically effective NDF (peNDF) is measured to predict the potential of the feed to stimulate chewing and saliva production and relates to the particle size of feed. Physically effective NDF is a function of NDF and physical effectiveness factor (pef) of a feed, where peNDF = pef x % NDF (DM basis). A Penn State Particle Separator (PSPS) can be used to measure the physical effectiveness factor, or particle length, of total mixed rations and forages. Unlike other established laboratory methods for assessing physically effective fibre, the PSPS is a fast and practical tool that can be used to estimate physically effective fibre in the ration on-farm. The newest version of the PSPS has 3 sieves (19 mm, 8 mm, and 4 mm openings with a bottom pan). The physically effective component of a ration is calculated as the amount of material retained on the three sieves, expressed as a percentage of the whole sample. To estimate physically effective NDF (peNDF), the proportion of feed on the top three sieves is multiplied by the NDF content of the feedstuff or ration. Caution must be taken when accounting for the 4 mm (bottom) screen, since this screen is meant to capture particles that are high in fibre, but other feed ingredients and byproducts can also be trapped on this sieve. When a large amount of grain and supplement is trapped on this bottom sieve, which is often the case with finishing rations, the bottom screen should be discounted when calculating peNDF.

Figure 1. Penn State Shaker Box used to measure particle size distribution in ruminant rations

Are there other factors that impact rumen health?

It must be noted that in addition to forage particle length, there are other factors that impact ruminal pH and the risk of acidosis in feedlot cattle (Table 1). Feeding management, animal behaviour and physiology, and ration characteristics all play a role in influencing rumen health and optimizing performance. While this article focuses on physically effective fibre and the role it plays in maintaining rumen health, it is important to pay attention to other management factors on-farm that also influence rumen health.

Table 1. Factors that impact ruminal pH and risk of acidosis in feeder cattle

Source: NRC Beef Cattle, 2016

Past, present, and future study on effective fibre in feedlot rations

The role of effective fibre in maintaining rumen health and influencing milk composition has been well-established in the dairy industry. The role of fibre inclusion in feedlot rations is not a novel concept for the feedlot sector, but often its importance is overlooked and inclusion under-evaluated in feedlot rations, especially when antimicrobial tools are used to mitigate the negative effects of poor rumen health. While optimal levels of effective fibre under various conditions and ruminal pH prediction models for feedlot cattle continue to be studied, researchers have used modelling to recommend peNDF ranges for feedlot cattle. These ranges are summarized in Table 2.

Table 2. Referenced peNDF (%) values for feedlot cattle rations

Although predictive modelling offers a general idea of target ranges for physically effective fibre in feedlot rations, the models do not account for all other factors that influence rumen pH (Table 1), fermentability of feed, or absorption of VFAs from the rumen. There is opportunity for more applied research on effective fibre in finishing rations to better understand optimal levels of physically effective fibre, the impact of various ingredient types on fibre requirements, the effect of grain processing on fibre requirements, and other aspects of effective fibre on rumen health. Ongoing research out of the University of Saskatchewan, University of Guelph, and Agriculture and Agri-Food Canada will shed more light on the role of effective fibre in feedlot rations and optimal inclusion rates for feedlot health and performance.

Key Messages

Maintaining rumen pH to reduce bouts of acidosis is important to overall cattle health. Evaluating and monitoring physically effective NDF in feedlot rations is one important aspect of reducing risk of acidosis. In a feedlot context, poor rumen health is not only a gut function and efficiency issue, but it is also associated with other health issues, such as ruminitis, liver abscesses and founder. The Penn State Particle Separator is an on-farm tool available to feed industry professionals, and with a modified approach, it can be used to monitor the inclusion of physically effective fibre in finishing cattle rations. Talk to your nutritionist or feed consultant about physically effective fibre in your ration, particularly around measuring effective fibre, forage types and inclusion rates, and other feeding management strategies to help reduce the risk of ruminal acidosis.

References

• Beef Cattle Research Council. Acidosis. Retrieved March 29, 2019.
• Beef Cattle Research Council. Beef Quality Audit. Retreived March 29, 2019.
• Gaylean, M.L. and M.E. Hubbert. 2014. Traditional and alternative sources of fiber – Roughage values, effectiveness, and levels in starting and finishing diets. The Professional Animal Scientist, 30:571-584.
• Fox, D.G. and O. Tedeschi. 2002. Application of Physically Effective Fiber in Diets for Feedlot Cattle. Proceedings of the Plains Nutrition Council Spring Conference, April 25-26: 67-81
• Jones, C. and J. Heinrichs. 2016. Penn State Particle Separator.
• Mertens, D.R. 1997. Creating a system for meeting the fiber requirements of dairy cows. Journal of Dairy Science, 80:1463-1481
• Mertens, D. R. 2002. Measuring fiber and its effectiveness in ruminant diets. Proceedings of the Plains Nutrition Council Spring Conference, April 25-26: 40-66
• National Research Council 2016. Nutrient requirements of beef cattle. 8th revised edition. The National Academics Press, Washington DC, USA.