Research Note
Optimal Starch vs. Acidosis & Inflammation
Optimizing starch in lactating cow diets can significantly improve income-over-feed-costs (IOFC), especially in a time of high cost for other dietary energy sources.
Recent research suggests that starch up to 30% of diet dry matter (DM) can sustain high milk yield and components, and do so without rumen acidosis or unwanted health effects such as chronic inflammation, if managed carefully.
The upper limit of inclusion depends on the grain source, processing, stage of lactation, level of management, and other factors. Fortunately, says Michigan State’s Dr. Barry Bradford, we now know more about total tract starch digestion, particularly rumen versus post-ruminal digestion.
“To optimize starch inclusion,” Bradford says, “means finding the optimal balance between ruminal and post-ruminal starch supply.”
He notes there are many studies to show that a sudden increase in starch concentration or digestibility leads to rumen acidosis and the breakdown of the rumen epithelial barrier, thereby increasing circulating lipopolysaccharide (LPS) and acute phase proteins (APP). Such “challenge models” typically do not apply to adequately adapted cattle.
“However, in chronic feeding studies,” Bradford says, “increasing starch does not consistently increase inflammation in early-lactation cows that already experience inflammation. Moreover, in mid- and late-lactation cows, although increasing starch above 30% may increase APP, the response is inconsistent.”
Bradford also points to abomasal starch infusion experiments in which increasing the intestinal starch supply consistently increases fecal acidity but does not lead to an APP response or changes in gut integrity.
“It’s interesting,” Bradford adds, “that increasing intestinal starch supply also increases fecal butyrate. In other species and experimental models, butyrate can have positive effects on gut health and integrity.”
In any case, he says, optimizing starch requires a nuanced approach:
- Try to balance ruminal and post-ruminal starch supply. For example, there may instances when feeding ensiled high-moisture corn may be preferrable to finely-ground dry corn on an energy basis, but using dry corn improves IOFC thanks to greater DMI and milk yield. However, if low RFOM (rumen-fermentable organic matter) supply limits productivity, then providing at least some high-moisture or steam-flaked corn can support greater milk yield.
- Even with a balanced ruminal and post-ruminal starch supply, be careful that the total supply of starch is not so much as to interact with other gastrointestinal stressors and contribute to leaky gut and systemic inflammation.
- Insist on superior management, including consistency in grain processing, dependable feed availability, adequate bunk access, and difficult-to-sort TMR (total mixed rations).
Sourced from a variety of grains or silage, starch excels as a key nutrient supporting microbial growth in the rumen and supplying energy to high-producing dairy cows. It’s a a total tract dietary energy source that, when used with care, Bradford says, can increase milk yield, milk protein yield, and body tissue accretion compared with feeding neutral detergent fiber sources.
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