Drought and Heat Stressed Growing Conditions Will Impact Feed Quality Of Corn Grain and Silage

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By Bill Seglar and Bill Mahanna

Droughty Conditions Result in Stressed Corn

Late planting challenges, due to wet weather followed by a growing season of severe drought and heat, results in stressed corn. Corn that is stressed has suppressed plant health and creates the opportunity for pathogens such as mold and yeast microbes to invade the plant. Harvesting corn acres with increased loads of pathogenic micro-organisms can have a negative impact on livestock production and health. Many producers miss desirable harvest moisture windows for making corn silage because of the rapid dry-down from heat and drought stressed corn. High dry matter silages may not achieve a desirable low pH and result in an environment for further yeast and mold activity in the silo. Feed quality of drought-stressed corn silage should be closely monitored. Changes in nutritional value will be apparent on forage and grain reports and need to be accounted for when formulating rations.

Dry Corn Silage Feeding Watch-Outs

Excessive amounts of corn grain can appear in manure when feeding cattle corn silage that was harvested at late maturity and not processed by choppers equipped with on-board processors. Research findings show corn silage with hard kernels is dictated by harvest maturity and is not influenced by the genetics of the hybrid. Dairymen often observe larger amounts of corn grain in manure just after opening their silos compared to later in the feeding season, because the silage acids and moisture tend to soften the grain and alter the starch complex making it more digestible by ruminants.

Corn silage ensiled dry and with less than ideal pack may appear brownish/black and indicates elevated bound protein. This is due to excessive heating during early fermentation due to extended air entrapment. Nutritionists need to reduce the crude protein and energy contribution in corn silage when it shows signs of bound protein. Dry corn silage may be hot when removed from the silo or rapidly become hot when mixed into TMR rations and placed in feedbunks. The heat is generated from yeast activity due to air penetration into the silo.

Molds and Mycotoxins

Hot droughty growing conditions followed by delayed harvest due to cold and wet weather provides suitable growing environments for the establishment of mold growth on corn grain. One of the most troublesome ear molds is Fusarium and can be found as two species: 1) Fusarium graminearum (pinkish mold) that produces vomitoxin and zearalonone and T-2 mycotoxin and 2) Fusarium moniliforme (whitish mold between the kernel and starburst on the kernels) producing fumonisin, a known carcinogenic mycotoxin. Toxicity levels of these toxins are dependent on toxin type and livestock fed.

Minimizing mycotoxins buildup during dry grain harvest may be accomplished by following the suggestions below.

  • Harvest the most heavily infected fields first.
  • Remove small, light broken kernels and pieces of cob and fines.
  • Use a grain cleaner prior to ensiling or drying.
  • Dry infected grain rapidly. (Cannot reverse toxin concentration but can stop productions of buildup.)
  • Aerate grain bins.

Additional points to consider:

  • Toxin levels are highest in the fines, cob and small kernels. (Don't feed fines of questionable origin.)
  • Toxin levels are higher in cobs than kernels.
  • Fungus goes dormant below 15% moisture.
  • Fermentation stops fungus growth.
  • Presence or absence of visible mold is a poor indicator of mycotoxins.

Nutritional Assessment of Stressed Corn

Mold activity occurs with excessive yeast activity, and produces corn silage that is musty and unpalatable. Mycotoxins may be an issue, but the observation of mold does not imply mycotoxins are present. In fact, mold free corn silage may contain mycotoxins that were produced during the growing season in the field. For corn silage, a sample should be sent to a laboratory with thin layer or gas chromatography capabilities to determine if mycotoxins are present. The ELISA technique can be used on corn grain samples, however ELISA should not be used on corn silage because of potential false positive results.

The nutritional value of drought stressed corn grain and silage will be substantially different from corn growing under normal conditions. Low-test weight corn grain can have lower starch and weight has reduced feed quality. Corn with greater than 45 lb. test weights shows minimal reduction of animal performance.

In addition to the routine nutritional analysis, corn silage should be analyzed for starch, sugar and neutral detergent fiber digestion (NDFD) to determine feed value to dairy cattle. Drought stressed corn will have low starch levels compared to normal years when starch levels are in the 28-32% range. Usually, higher sugar levels will exist in drought stressed compared to normal corn silage that usually has 1-3% sugar. Samples may also show higher NDF digestibilities, that is typical of corn forage growing under drought stressed conditions. Nutritionists should be aware that adding additional corn grain into a dairy ration to compensate for starch deficiencies from corn silage might result in rumen acidosis. The higher sugars and NDFD will contribute to net energy for lactation (NEL) and will be reflected by prediction equations such as the Schwab Shaver equation, which uses NDFD to predict NEL.

In addition, Michigan State University research shows that high NDFD corn silage increases passage rates in the rumen of dairy cattle. Therefore, drought stressed corn silage low in starch and high in NDFD may result in needing more silage in order to increase NDF in the diet, which will slow down passage rates so that rumen microbes have more time to utilize nutrients from the entire ration while in the rumen.