Fecal starch analysis – What can it tell you about your feedlot ration? An Important Feedback Mechanism for your Feeding Program

Source: Ontario Ministry of Agriculture, Food and Rural Affairs

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. While feed efficiency is often measured through a feed conversion ratio, taking other measurements such as fecal starch into consideration helps to improve feed use efficiency. A fecal starch analysis is an effective tool for monitoring starch digestion as fecal starch represents starch in the ration that has gone undigested. It provides a measure of the concentration of undigested starch and this unutilized starch represents a direct cost to the feedlot operator. Researchers have found that an increase in 1% fecal starch results in a 0.162 Mcal reduction in net energy for maintenance (NE_m) in cereal grains. Thus, a fecal starch analysis provides important insight into feed utilization efficiency and high values should prompt a review of areas where feed utilization efficiency could be improved.

Most commercial labs offer fecal starch analysis, either by NIRS or wet chemistry, within a $20-$25 price range. NIRS tends to be more cost effective than wet chemistry with quicker results. For the sake of accuracy, integrity in sample collection and submission is important. A few considerations for sample collection protocol include:

• Contact an accredited laboratory for detailed sample collection instructions and sample jars (do not use plastic sample bags!)
• Take multiple samples rather than a spot sample for a representative sample. Take at least 5 samples from different animals at random per pen to mix together, making a composite sample.
• Samples obtained should be taken as freshly expelled manure. Look for cattle defecating and immediately take samples from fresh manure. Make sure the samples aren’t contaminated by bedding or other substances as this can lead to inaccuracies in results.
• Composite (mix) individual samples proportionally and freeze samples prior to sending to the lab.

How do your feedlot fecal starch results stack up?

The objective of a feeding program is to optimize feed efficiency to reduce feed costs whilst maximizing gains in cattle. A high fecal starch result indicates lost opportunity and inefficiencies in feed utilization. Ideally, fecal starch levels should be as low as possible but a fecal starch value of greater than 13% suggest that changes need to be made to increase feed utilization efficiency. Data was collected in 2019 on Ontario feedlots (Figure 1; n=16), and Table 1 provides the results from the Ontario benchmarking study as well as data collected in a study by Schwandt et al. (2017) in the American Midwest.

Table 1. Fecal Starch (% of fecal DM) results from Ontario and Midwest US benchmarking studies

*n represents the number of farms from which composited fecal samples were taken

Figure 1. Distribution of fecal starch concentration based on pooled fecal samples from 16 commercial feedlots in Ontario (2019)

What factors need to be considered when fecal starch is high for cattle fed corn-based diets

• Particle Size Distribution – 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. Increased degree of processing is related to improved dry matter and starch digestibility. However, the extent of fines produced must be monitored to manage risk of reduced rumen pH and digestive upsets (e.g. bloat). Particle size distribution is influenced by processing method and settings/maintenance on processing equipment. Processing grains through steam-flaking, rolling, or grinding with a hammermill enhances total tract starch digestibility.
• Corn Vitreousness – Vitreousness describes the nature of the endosperm of the corn kernel. Increased vitreousness reduces starch digestibility and vitreousness varies depending on the corn hybrid and maturity. Ensiling and steam flaking reduce the impact of vitreousness on starch digestion.
• Kernel Processing: Corn Silage – Particularly important in rations with high corn silage inclusion (e.g. grower rations), the degree of kernel processing in corn silage impacts starch utilization

References

Mahanna, B. 2009. Digestibility of corn starch revisited: Part 1. Feedstuffs, volume 81 issue 6.

Mahanna, B. 2009. Digestibility of corn starch revisited: Part 2. Feedstuffs, volume 81 issue 10.

Stanford, K., Swift, M., McAllister, T., Gibb, D. 2015. Fine tuning fecal starch can cut your feed bill. Beef Cattle Research Council. Retrieved April 27, 2020.

Schwandt, E.F., Thomson, D.U., Bartle, S.J., Reinhardt, C.D. 2017. A Survey of Dry Processed Corn Particle Size and Fecal Starch in Midwestern US Feedlots. Kansas Agricultural Experiment Station Research Reports. Volume 3: Issue 1.

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