Feeding cereal grains high in fermentable starch is an effective way to deliver energy in lactating dairy rations. But unlike monogastric pigs, ruminants walk a fine line in their ability to utilize those feedstuffs while maintaining digestive integrity.
Michigan State University researchers Kirby Krogstad and Barry Bradford recently took a deep dive into data sets evaluating starch in dairy diets, and its link to systemic inflammation. They conducted a literature review of studies that examined the relationship between dietary starch concentrations and inflammation.
Their findings, summarized recently in the Journal of Dairy Science, revealed:
- “Grain challenges” -- defined as an abrupt increase of grain to 20% or more of diet dry matter (DM) to experimentally induce a drop in rumen pH and ruminal acidosis -- have been used to measure markers of inflammation like luminal lipopolysaccharide (LPS) concentration and acute-phase proteins (APP). In the studies evaluated, forage also was removed and substituted with a 20% protein barley-wheat pellet, which added an additional load of starch. The grain challenges in these studies proved to significantly increase LPS and APP.
- When rumen fluid from grain-challenged donor cows was infused abomasally into non-challenged recipients, no increase in APP was observed. And in studies when starch was directly infused into the abomasum, no change in inflammation or gut-barrier integrity was observed, even though it did lower fecal pH. Furthermore, infusing starch abomasally has proven to dramatically increase fecal levels of butyrate, a short-chain fatty acid that has been linked to positive effects on gut health and integrity.
- Abruptly switching from alfalfa hay to pelleted alfalfa caused a drop in rumen pH similar to that incited by grain challenges. However, when rumen microbial population shifts were evaluated, the two challenge types created significantly different rumen microbiome changes. The presence of E. coli in the rumen was significantly higher in grain-challenge studies, and E. coli was found to be the greatest predictor of severity of acidosis. Alfalfa pellets also did not cause increases in the markers for inflammation.
- There is little evidence that feeding higher-starch diets to fresh cows increases their level of systemic inflammation.
- Barley and wheat were shown to incite greater systemic inflammation than corn-based diets. This inflammation was more pronounced in grain-challenge studies compared to feeding barley or wheat at high levels consistently in the daily ration.
Collectively, the researchers concluded that – based on currently available data -- feeding diets with less than 30% starch to lactating dairy cows in “chronic,” non-abrupt fashion does not contribute to systemic inflammation.
Krogstad and Bradford said there is an industry need for more research exploring the role of various carbohydrate sources and concentrations in influencing ruminant hindgut health, integrity, function, structure, and microbiome.
