Corn Test Weight – Does It Affect Performance of Cattle?

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Source: Ontario Ministry of Agriculture, Food and Rural Affairs

The 2019 growing season presented challenges in many parts of the province. Delayed planting and variation in maturity at harvest resulted in variability in the grade of the corn crop in Ontario. When corn fails to reach physiological maturity (black layer) before a frost, there are potential consequences to test weight. This has left many livestock producers asking “what is the impact of low test weight corn on the performance of my livestock?”. We can look to research that has been done on finishing cattle to help answer this question.

Corn quality is assessed using standard measurements. If you take corn to the local elevator, your corn will be graded, and you will be paid accordingly. Test weight is one factor that is considered as part of the grading scheme and thus light test weight corn is often discounted according to elevator discount schedules. Minimum test weights are specified for each grade in the Official Grain Grading Guide by the Canadian Grade Commission. Test weight is a measure of grain density; it is measured by weighing a known volume of grain and in Canada it is assessed before removing cracked corn and foreign material. Samples are graded sample weight if the test weight is lower than the minimum test weight established for corn. In Canada test weight is expressed as kilograms per hectolitre (kg/hL) or grams per 0.5 litre (g/0.5 L), but test weight is also commonly referred to as bushel weight, expressed as pounds per bushel (lb/bu).

Is corn test weight a good predictor of feeding value of corn for cattle? Several studies have looked at the impact of light test weight corn on cattle performance, most of which found little to no performance differences in cattle fed moderately low-test weight corn (59.3 kg/hL or 46.18 lb/bu) versus normal test weight corn. In a published study by Weichenthal et al. (1999), light-test weight corn (59.2-61.5 kg/hL or 46 to 48 lb/bu) and normal corn (72 kg/hl or 56 lb/bu) were fed to cattle consuming growing and finishing diets in a beef feedlot. The growing diet consisted of 32.9% corn silage, 22.3% alfalfa haylage, 37% dry rolled corn, and 7.8% protein supplement on a dry matter basis, and the finishing diet included 9.2% corn silage, 86.2% dry rolled corn, and 4.6% protein supplement on a dry matter basis. Average daily gain, feed efficiency, and carcass measurements were similar between treatment groups in both growing and finishing cattle. Birkelo et al. (1994) used metabolism facilities to study energy partitioning and net energy estimates of finishing diets that consisted of 77.7% light test weight (52.6 kg/hL or 40.8 lb/bu) or normal test weight (69.3 kg/hL or 53.8 lb/bu) whole corn. They found that low test weight corn was slightly greater in net energy for maintenance and gain due to reduced fecal losses associated with low test weight corn and concluded that low test weight corn is not inherently lower in net energy content than normal test weight corn. A study out of North Dakota State University found slightly different results. The study looked at the impact of feeding high (68.5 kg/hL or 53.7 lb/bu), medium (60.1 kg/hL or 46.9 lb/bu), and low test weight corn (50.4 kg/hL or 39.1 kb/bu) to finishing steers, and while they found that test weight did not impact performance in terms of ADG, they did observe a response of increasing dry matter intake and feed:gain (F:G) with decreasing test weight, suggesting that it may take more light test weight corn to achieve the same gains. The authors concluded that cattle feeders buying low test-weight corn must assess the benefits of taking advantage of discounts on low test corn versus the potential for reduced F:G.

Collectively this research tells us that it is important to analyze and consider all nutrients and use current net energy equations when formulating rations and determining feeding rates. Although starch content tends to be lower in low test weight corn, low test weight corn often has higher protein, fibre, and mineral concentrations and rate of starch digestion may differ between low-test weight corn and normal test-weight corn. These research outcomes also serve as a good reminder that it is important to add ingredients to the ration by weight rather than by volume.

In short, corn with moderately low-test weight does not appear to impact performance of cattle. However, with every new crop commodity or ingredient introduced to your ration, it is important to understand the quality and nutritional attributes of your feed inputs and monitor the condition and performance of your cattle. Work with your feed advisor to balance your rations and identify and mitigate risks associated with quality issues.

References:

  • Birkelo, C.P., Pritchard, R.H., Buhman, M., Grosch, S., and C. Willms. 1994. Net energy of finishing diets containing light or normal test weight corn. South Dakota State University Beef Report. 94:2.
  • Canadian Grain Commission. 2019. Test Weight for Canadian Grains.
  • Lardy, G.P., and D.M. Larson. 2006. Effect of Corn Density on Finishing-Steer Intake, Performance, and Carcass Characteristics. NDSU Carrington Research Extension Center Feedlot Research Report, Volume 29.
  • Luebbe, M. 2012. Feeding Light Test Grain to Cattle. University of Nebraska-Lincoln.
  • Manhanna, Bill. 2012. Should test weight be a concern with corn? Feedstuffs. 84:24.
  • Noon, C.D., Seoane, J.R., S.L Scott. Use of corn and barley in diets for veal calves: effects on performance, diet digestibility and carcass quality. Canadian journal of animal science. 78 (3): 351-358.
  • Wand, C. Corn and Barley in Veal Diets. Ontario Ministry of Agriculture, Food and Rural Affairs.
  • Weichenthal, B.A., Rush, I.G., and B.G. Van Pelt. 1998. Light-test weight corn from growing and finishing steers. The Professional Animal Scientist. 14: 114-117.

Author: Megan Van Schaik – Beef Cattle Specialist, OMAFRA

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