Source: Ontario Ministry of Agriculture, Food and Rural Affairs
Least cost-formulation of rations is dependent on commodity pricing and availability, which means that ingredients will move in and out of rations or inclusion rates will change depending on the price, availability, nutritional value, and antinutritional properties associated with an ingredient. In recent years, DDGS (dried distillers grains with solubles) and DGS (distillers grains with solubles) have become a mainstay in feedlot rations as it has been a cost-effective and widely available ingredient for feeding energy and protein to cattle. In addition, the low starch content and highly digestible fibre components make distillers a relatively “cool” source of energy for the animal, when compared to high starch feeds. Therefore, including distillers in a finishing rations to displace those rapidly fermentable grains can help reduce the risk of digestive upsets in the feedlot.
Recent reductions in ethanol production has created a shortage of DDGS and DGS, coproducts of the ethanol production process. As a result, the cost of these by-products has increased significantly and so there has been pressure to shift to more economical feed ingredients. To replace protein in the rations, other protein commodities, higher rates of non-protein nitrogen sources, such as urea, and in some cases, more wheat is going into rations to achieve higher protein levels and maintain energy levels at reasonable cost. To maintain the energy density of these finishing rations, cereal grains have been increased as a percentage of the ration. These higher inclusions of grains in rations increases rumen fermentation and risk of digestive upsets such as acidosis and bloat, and therefore careful management of these rations is very important. This article intends to outline some management considerations for rations with high grain inclusion rates.
Managing the Feed Bunk
Rations that include high levels of readily digestible carbohydrates (grains) require sound bunk management to mitigate risk of digestive upsets such as bloat and acidosis. Maintaining consistency in intake, diet, and management is key to minimizing these risks. Some of these strategies include:
- Ensuring adequate bunk space. Inadequate bunk space and aggression at the bunk can result in inconsistencies in dry matter intake and gorging by aggressive cattle at the bunk. Recommended bunk space (minimum) for finishing cattle is 6″ where fed ad libitum, 8-10″ when feed is present most of the time, and 18″ when limit fed. These recommendations are based on twice a day feeding.
- Adequately mixing the ration (TMR) to reduce feed sorting and inconsistency in intake. The objective with a TMR is to have consistency in feed with every mouthful. A mixer test can help determine if that consistency is being delivered in the TMR and a uniform mix is being achieved. Mixer tests should be done with any significant changes to the ration or after adjustments in equipment and mixing time are made. A mixer test should reflect your typical mixing routine (mixing time, order ingredients are added to the TMR, etc.) with adjustments being made as necessary according to your test results.
- Increase feeding frequency. Increasing feeding frequency helps to prevent gorging at the feed bunk, another risk factor for feedlot acidosis.
- Consistent timing of feeding. Similarly, consistent timing of feeding helps to prevent gorging at the feed bunk and inconsistent eating patterns. It is recommended that feeding occurs within 15 minutes of scheduled feeding time daily.
- Dietary transition and adaption. As with any ration change, slowly increasing the amounts of rapidly digestible carbohydrates in the ration provides opportunity for adaptation by the rumen microbes and helps to reduce risk of digestive upsets. A step-up approach to increasing energy in the ration is an effective means of reducing risk of acidosis.
- Include adequate levels of forage in the ration. The objective of including roughage in a feedlot ration is to provide adequate physically effective NDF to stimulate chewing and rumen motility to maintain rumen health and cattle performance.
Grain Type and Processing Method
Grain type and degree of processing influences the rate and extent at which they ferment in the rumen, which can impact cattle health and performance. As a rule, wheat and barley ferment the fastest whereas corn ferments the slowest, however this hierarchy is influenced by the type and extent of processing (Figure 1).
Figure 1. Rate of digestion as influenced by grain type and processing method. Adapted from Stock and Erickson (2006)
Grain is processed to achieve increased starch availability and digestibility in feedlot rations. Generally, the greater degree of processing is related to improved dry matter and starch digestibility, which can translate into improved feed conversion efficiencies. Table 1 provides a summary of the impact of various processing methods on corn as a feed ingredient for cattle. Processing grains through steam-flaking, rolling, or grinding with a hammermill enhances total tract starch digestibility. However, in any processing scenario, particle size distribution and specifically the extent of fines produced must be monitored to manage risk of reduced rumen pH and digestive upsets.
Table 1. Relative impact of processing methods on corn (no impact to major impact)
|Processing Method||Expose endosperm||Decrease particle size||Disrupt endosperm matrix||Disrupt starch granules||Increase rate of fermentation||Improve intestinal digestion|
|Dry rolling||Major||Minor||No impact||No impact||Medium||Minor|
|Grinding||Major||Major||No impact||No impact||Medium||Minor|
|Ensiling||Minor||No impact||Medium||No impact||Medium||Minor|
Adapted from Zinn et al. (2011)
In a summary conducted by Owens et al. (1997), the authors obtained data from various studies looking at the effects of grain type and processing on feedlot performance. Data was included only if roughage inclusion rates were under 15% dry matter (30% if corn silage was primary roughage source), if the grain portion of the ration was a single grain type and single processing method used, if the grain portion represented over 55% of the ration on a dry matter basis, and if feedlot cattle had been fed for more than 99 days.
Table 2. Feed efficiency of cattle fed grains processed by various methods (least square means)
|Processing Method||Feed efficiency (feed:gain)
|Feed efficiency (feed:gain)
|Feed efficiency (feed:gain)
|Feed efficiency (feed:gain)
Adapted from Owens et al. (1997)
a,b,c superscripts represent significant differences, where means within a column with different superscripts are significantly different (P<0.05)
The study found that more extensive processing (high moisture, steam rolling) generally improved feed to gain compared to dry rolling grain, suggesting that energetic efficiency was improved through extensive processing such as steam flaking (Table 2). Interestingly, the feed efficiency of whole corn appeared to be higher than that of dry rolled corn, which the author attributed to the low inclusion of roughage in the rations studied (on average 6 % DM for whole corn rations). More recent studies have yielded similar results, where dry corn ground to a fine particle size did not necessarily improve performance in finishing cattle, and dry matter intake tended to decrease in the late finishing period. Similarly, these results were thought to be attributed to a subacute acidotic response.
Where is the sweet spot for grind size and extent of processing? Unfortunately the answer is not straight forward, as it is a function of a number of variables, including overall composition of the ration, type of grain processing, and moisture levels. The amount of roughage and certain coproducts in the ration also has an impact on feed efficiency as related to grind size. Some studies have shown that the impact of processing method for corn grain may be influenced by inclusion of wet distillers grains, suggesting that there is a positive effect of wet distillers in binding fines and improving uniformity in the diet. However, more research is needed to fully understand the interaction between various feed ingredients and grain grind size.
In addition to providing physically effective fibre, the inclusion of forage in the ration may also offset the increased rate of fermentation associated with fine particle size and risk of digestive upsets. Work out of North Dakota (Engel et al., 2014) looked at the effects of fine grinding or dry rolling corn compared to whole corn in rations with higher inclusion rates of roughage. The outcomes of this study were different than those found through summarized reports by Owens et al., and the authors attributed this to higher levels of roughage in the ration. The authors concluded that when forage levels are adequate (greater than 15.5% DM) in the ration, improved feed efficiencies can be achieved when fine-grinding corn.
Steam-flaking or steam-rolling is a nice processing option that tends to increase the overall total tract digestibility of starch. This occurs because the combination of moisture and heat during the steam-flaking process gelatinizes the starch and disrupts the protein matrix encapsulating starch granules in the kernel. Steam flaking, and other forms of further processing such as ensiling, can also influence the site of starch digestion in the digestive tract. Steam flaking and ensiling grains tend to shift digestion to the small intestine which not only contributes to increasing digestive efficiencies, but also reduces risk of ruminal acidosis. Studies have shown that energetic efficiency can be increased by 20% when corn is flaked rather than dry rolled, although this may vary depending on other dietary factors. Keep in mind, however, that fines can still be produced during the steam-flaking process. Flakes that are thinner and are subjected to a longer steaming time before flaking results in a flake that is less brittle and less likely to produce fines.
University of Nebraska research suggests that feeding a combination of different grains or like grains subjected to different processing methods, such as a combination of high-moisture grain and dry grain, can have positive benefits to performance and can reduce risk of acidosis. According to University of Nebraska data, this blended approach to feeding grains can increase gain and feed efficiency. In their study, cattle gained 2.9% faster and were 4.3% more efficient when offered a diet where the grain fraction consisted of 67-75% high moisture corn and 33-25% dry corn. The beneficial effects of the blended grain approach were reduced as the proportion of high moisture corn decreased. The complementary effect of having two grain sources or grain processing methods is the result of balanced starch digestion between the rumen and small intestine.
Monitoring Particle Size
In the absence of hard and fast recommendations for particle size distribution across all feedlot cattle ration scenarios, it is important to have a sense of grain particle size distribution for ration formulation purposes and when trouble shooting animal performance and health issues. The underlying principals are that an abundance of fines from processing in the ration puts cattle at higher risk of digestive upsets and rations that include grains that are under-processed may not lend to desired performance results. Other factors such as the complement of ingredients in the ration, corn vitreousness, and moisture levels will also impact starch digestion and rumen health. Keep in mind that intended particle size distribution may differ from actual particle size distribution, and settings/maintenance on processing equipment must be monitored. How can particle size be monitored in grains?
- RoTap Sieving – This is the standard laboratory method for determining particle size distribution. This method involves a sieve stack, including 13 sieves and a bottom pan, and automated sieving motion. The RoTap procedure allows for calculation of the mean particle size and standard deviation of the sample. This procedure generates quantitative measures but is time consuming and the RoTap is inconvenient for on-farm use. Most feed mills have RoTap equipment and where possible, could be used on a sample for fine turning.
- Manual Sieve Stack/Relative Corn Index – A sieve stack that can be taken on farm to assess particle size distribution. The sieve stack consists of sieve mesh sizes of #4 (4.75 mm), #8 (2.4 mm), #16 (1.01 mm), #30 (0.54 mm) and a bottom pan. The Relative Corn Index was developed by Dr. Mike Hutjens (University of Illinois) and can be used as a relative measure to monitor particle size distribution in grains. This is a quick assessment that can be done on-farm and is particularly helpful in monitoring changes in particle size distribution; however, the RoTap method provides more quantitative results.
- Processing Index – An index that measures the degree of grain processing using bulk densities. The Processing Index is the bulk density of the processed grain expressed as a percentage of the bulk density of the grain prior to processing. Figure 3 illustrates the relationship between processing index and fecal starch concentration.
- Flaking density – The flaking density is used exclusively for flaked cereal grains and relates to the bulk density of the grain after processing. Bulk density is usually expressed in g/L.
Impacts of corn vitreousness
The form and make-up of starch and the proteins that interact with starch in the endosperm of corn kernels also impact digestibility of grain. The endosperm of the grain contains a protein matrix that encapsulates starch granules. Vitreousness describes the nature of the endosperm of the corn kernel, where high vitreousness represents “hard” endosperm and low vitreousness represents « soft » endosperm. Increased vitreousness reduces total-tract starch digestibility. Vitreousness varies depending on the corn hybrid and maturity. Flint corn has high vitreousness, flour corn has low vitreousness, and dent corn hybrids typically fall in between, depending on the genetic make-up of the variety. Vitreousness can be monitored through physical and chemical testing.
There are a number of ways to manage vitreousness, but keep in mind that most commercially available hybrids have a moderate range of vitreousness. On the front end, vitreousness is a trait that can be selected for or against during corn hybrid selection. Short season corn hybrids typically have more flint-based genetics than long season hybrids. On the back end, vitreousness can be managed through processing techniques. Ensiling and steam flaking reduce the impact of vitreousness on starch digestion. Steam flaking has been found to reduce the negative effects of vitreousness on starch digestibility in corn and interestingly, steam flaking more vitreous corn seems to yield less fines than vitreous corn.
Monitoring Fecal Starch
Monitoring starch digestion in feedlot cattle is an important aspect of assessing feed utilization efficiency, managing input costs, and gaining a better understanding of cattle performance and health. A fecal starch analysis is an effective tool for monitoring starch digestion. It provides a measure of the concentration of undigested starch and this unutilized starch represents a direct cost to the feedlot operator.
A fecal starch evaluation can be used as an indicator of the impact of grain processing on total tract starch digestion when grain is the primary or only source of starch in the ration. Most commercial labs offer fecal starch analysis, either by NIRS or wet chemistry.
Keeping tabs on roughage in the ration
All ruminant rations require some level of roughage to maintain rumen motility and balance in rumen microflora. Where high-concentrate diets are fed, roughage included in rations ideally should have a large enough particle size to stimulate chewing and saliva flow (good «scratch») with a goal of achieving uniform mixing and reducing feed sorting. Remember that not all roughage types are created equal. For the sake of defining forage levels, the common approach is to sum the hay components plus 50 percent of the corn silage. This is because digestibility of corn silage is higher. Different roughage sources provide varying degrees of effective fibre that contributes to scratch factor and influences overall rumen health. A Penn State Particle Separator in conjunction with lab analysis for NDF can be used to help determine levels of physically effective fibre in the ration. For maintaining rumen health, it is recommended that this level be 7-10% DM for feedlot cattle.
Cattle performance is always an important feedback mechanism and thought should be given to grain type, inclusion rates, and particle size when reflecting on gains, feed efficiency, and dry matter intake. Monitor feed intakes daily and make adjustments where necessary. Watch for potential indicators of digestive issues, such as drastic fluctuations of dry matter intake, feed refusals, foundering cattle, and inconsistencies in manure.
Understanding liver abscess rates is an important feedback mechanism for monitoring rapidly digestible carbohydrate load in the ration. High rates of condemned livers due to abscesses may indicate that ration adjustments are necessary. Having cattle on feed, especially a high carbohydrate diet, longer than anticipated, also increases risk of liver abscesses. Liver abscesses in fed cattle are on the rise in Canada. According to the National Beef Quality Audits, A+ liver abscesses (Elanco scoring system) increased from 2% in 1999 to 9.9% in 2010/2011 to 19.3% in 2016/17. Feedback on rate of condemnations due to liver abscesses is valuable feedback for your feeding program.
Cattle performance and health are influenced by ration formulation, and attention must be paid to the type, amount, and processing methods of grains included in the ration. When DDGS are replaced in finishing rations with higher rates of urea and grain, attention to bunk management and monitoring feedback mechanisms is prudent. Monitoring and fine-turning grain processing through measuring particle size distribution and monitoring fecal starch is an important aspect of avoiding digestive upsets in feedlots and optimizing feed utilization efficiency.
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Megan Van Schaik, Beef Cattle Specialist, OMAFRA
Dr. Katie Wood, Assistant Professor, University of Guelph