Does feeding starch contribute to the risk of systemic inflammation in dairy cattle?

Graphical Abstract Summary: Grain challenge experiments, where a portion of the diet is suddenly replaced by highly fermentable grains, result in systemic inflammation. Both high starch fermentability and sudden diet changes likely play a part in causing this inflammation. Abomasally infusing starch does not seem to result in inflammation but it does consistently reduce fecal pH and increase fecal butyrate concentrations. Direct effects of starch on the hindgut epithelial barrier and mucosal layers are unknown in dairy cattle. Increasing starch concentration in dairy cow rations does not consistently result in inflammation even though it reduces rumen and fecal pH. Research investigating the effects of different grain sources and processing methods on systemic inflammation is warranted.


Summary
Grain challenge experiments, where a portion of the diet is suddenly replaced by highly fermentable grains, result in systemic inflammation. Both high starch fermentability and sudden diet changes likely play a part in causing this inflammation. Abomasally infusing starch does not seem to result in inflammation but it does consistently reduce fecal pH and increase fecal butyrate concentrations. Direct effects of starch on the hindgut epithelial barrier and mucosal layers are unknown in dairy cattle. Increasing starch concentration in dairy cow rations does not consistently result in inflammation even though it reduces rumen and fecal pH. Research investigating the effects of different grain sources and processing methods on systemic inflammation is warranted.
S tarch and the cereal grains that typically supply it play an important role in dairy cattle nutrition. Starch is a highly digestible energy source that may increase milk yield (Sánchez-Duarte et al., 2019), milk protein yield (Dias et al., 2018;McCaughern et al., 2020;Morris et al., 2020), and body tissue accretion (Boerman et al., 2015) compared with feeding NDF or specific fatty acids. Furthermore, increasing the concentration of starch from ~20% to ≥28% of diet DM reduces ruminal (Salfer et al., 2018) and hindgut (Neubauer et al., 2020) pH. Reducing digesta pH may be one factor contributing to diminished gut health and integrity. Increased luminal LPS concentration (Li et al., 2012(Li et al., , 2016 and osmolality (Chibisa et al., 2016) when feeding starch may also be contributing factors.
This mini-review summarizes current research investigating systemic inflammation in lactating dairy cows provided different dietary starch concentrations during grain challenges, feeding experiments, or hindgut infusions. We use "grain challenge" when referring to experiments where grains are abruptly increased to ≥20% of diet DM for the purpose of causing ruminal acidosis. These grain challenges have resulted in an increase in circulating markers of inflammation such as LPS and acute phase proteins (APP; Khafipour et al., 2009b). A meta-analysis evaluating acidosis grain challenge data indicated that >44% concentrates or <39% NDF in diets fed to dairy cattle increases the risk of inflammation and increased circulating APP (Zebeli et al., 2012). Furthermore, ruminal acidosis grain challenges break down the rumen epithelial barrier (Steele et al., 2011), which may lead to an inflammatory response due to rumen bacteria or their components moving across the epithelium and interacting with circulating and tissue-resident immune cells. Inflammation may also result from free ruminal LPS binding its receptor, toll-like receptor 4 (TLR4), on the rumen epithelium, which has been shown to increase mRNA abundance in rumen tissue during acidosis (Pederzolli et al., 2018). Either may lead to the release of proinflammatory cytokines and eventual increases in circulating APP, but consensus on the mode of action is lacking.
Experiments that involve feeding elevated starch concentrations, usually ≥28% of diet DM as starch, and measuring its effects on inflammation have increased in the last 2 decades. Investigators have observed increases in plasma LPS, serum amyloid A (SAA), haptoglobin (Hp), and LPS binding protein during these rumen acidosis grain challenge experiments (Gozho et al., 2007;Khafipour et al., 2009b;Li et al., 2016). One experiment reported increases in serum Hp from nondetectable concentrations to 600 µg/mL in grain-challenged cows (Khafipour et al., 2009c). Interestingly, feeding pelleted alfalfa hay induced similar reductions in rumen pH and increases in ruminal LPS and VFA, but did not increase plasma LPS or APP (Khafipour et al., 2009a,c), which indicates that inflammation likely does not stem from reduced rumen pH and increased rumen LPS concentration alone. Other factors such as diet adaptation or gut microbiome may play a role in this diet-induced inflammation (Plaizier et al., 2017). We do not know whether the APP responses observed during acidosis challenge studies originate from the rumen or intestine, although the rumen epithelium clearly degrades during severe ruminal acidosis (41% dietary starch; Steele et al., 2011). Abeyta et al. (2022) also observed increased APP in plasma during a severe acidosis challenge (2.75% of BW as corn; ~21 kg). When rumen fluid from

Does feeding starch contribute to the risk of systemic inflammation in dairy cattle?
K. C. Krogstad* and B. J. Bradford these grain-challenged donor cows was abomasally infused into nonchallenged recipients, they did not observe an increase in APP.
Data suggest that rumen adaptation plays a role in the APP response. In the non-grain-challenge model (Khafipour et al., 2009a,c), where alfalfa hay was gradually replaced by pelleted alfalfa hay over 6 wk (22% dietary starch), there was no systemic inflammatory response, whereas abrupt diet change in the grain challenge experiments led to an APP response (Khafipour et al., 2009b). Gott et al. (2015) found that a high-starch diet with corn grain (~29% starch) did not increase SAA, whereas an acidosis induction diet that provided corn and wheat grain (~32% starch) suddenly fed for 2 d after cows had been on a control diet (~24% starch) resulted in increased SAA. Sudden dietary changes may be more to blame for the APP response than chronically elevated dietary starch. Others have also observed no significant difference or reductions in circulating Hp when increasing dietary starch (Table  1; Ertl et al., 2015;Dias et al., 2018;McCaughern et al., 2020;Haisan et al., 2021).
Increasing dietary starch reduces measurements of bacterial diversity (Deusch et al., 2017;Plaizier et al., 2017;Neubauer et al., 2020). Also, grain versus pelleted alfalfa acidosis induction results in different microbial population shifts. Khafipour et al. (2009c) investigated the microbial population in the rumen of dairy cows who were subject to either grain or alfalfa acidosis challenges. They observed a 64-fold increase in ruminal Escherichia coli during the grain challenge experiment. They also discovered that ruminal E. coli concentrations were the greatest predictor of severity of acidosis, which was determined by serum Hp, rumen pH, and free rumen LPS. Grain-based acidosis shifted the E. coli populations to strains with greater virulence compared with that induced by alfalfa-based challenges (Khafipour et al., 2011). The genes associated with virulence were related to adhesion of E. coli to epithelial cells. Increases in strains of E. coli with greater adhesion capabilities during grain-based acidosis challenges may be related to the increased inflammation observed in grain versus non-grain challenges. Increased adhesion capability is problematic during acidosis because nonkeratinized cells that are exposed to rumen contents are more susceptible to adhesion by microbes like E. coli (Gálfi et al., 1998). By increasing both E. coli and the sloughing of the stratum corneum during acidosis (Steele et al., 2011), grainbased acidosis challenges may present more risk of inflammation compared with chronic feeding models.
A more thorough investigation of the digestive tract microbiome was conducted by Plaizier et al. (2017). They observed increased E. coli in cecal and fecal contents of cows subjected to grain acidosis challenges. It seems that increasing starch in the rumen or its flow to the hindgut may increase problematic microbial populations, such as E. coli. This alteration in gut bacteria may increase the risk of inflammation when feeding high-starch diets, but investigations in a greater diversity of diets are warranted.
Increases in APP may occur when starch concentrations are ≥30% of diet DM and when barley is the primary grain being fed. Late-lactation cows fed 32% starch diets (barley grain and barley silage as starch sources) had elevated serum Hp (1,500 µg/mL). Peak-lactation cows fed 45% of diet DM as barley grain (45% NFC, 25% NDF, 30% forage) had reduced rumen pH, increased ruminal LPS, and increased SAA, but milk yield increased by 4 kg/d nonetheless, whereas milk fat yield was reduced (Emmanuel et al., 2008;Zebeli and Ametaj, 2009). Pan et al. (2017) increased dietary starch from 20 to 33% of diet DM by increasing corn grain and observed reduced rumen pH and a 10-fold increase in ruminal LPS. Plasma IL-1β and IL-6 increased by 50 and 20%, respectively. Rumen epithelial protein abundance of TLR4 and proinflammatory cytokines was increased, pointing to the possibility that the rumen was the source of increased cytokines in plasma. Pan et al. (2017), similar to Emmanuel et al. (2008), observed increased milk yield although component yields were similar, because component concentrations were reduced in response to increasing dietary starch. diets, and greater starch increased plasma Hp from 700 to 1,000 µg/mL. Increasing starch also increased plasma glucose and insulin and reduced plasma nonesterified fatty acid and BHB concentrations. Increases in monocyte function (Yasui et al., 2016) and improved energy balance (McCarthy et al., 2015a) may indicate improved health and resilience of the transition dairy cow fed additional starch. Albornoz et al. (2020) investigated both starch concentration (22 vs. 28%) and starch processing method (dry ground vs. high moisture) and observed greater reactive oxygen and nitrogen species when feeding high-moisture corn. They also observed increased Hp when increasing dietary starch in the high-moisture corn diets, which may indicate that enhancing rumen fermentability when feeding greater concentrations of starch is problematic. In contrast, Haisan et al. (2021) found that high-starch diets (32%) postpartum resulted in lower Hp and SAA. Feeding greater dietary starch to transition dairy cows does not consistently alter APP (Figure 1).
Abomasally infusing starch has not resulted in inflammation or gut barrier integrity loss even though it reduces fecal pH. Abeyta et al. (2019a) and Abeyta et al. (2019b) infused 4 kg/d of starch into the abomasum and fecal pH decreased from 6.8 to 5.9 and from 7.2 to 5.8, respectively. van Gastelen et al. (2021a) and van Gastelen et al. (2021b) infused up 3 kg of corn starch and 3 kg of ground corn, respectively, directly into the abomasum and fecal pH declined from 6.5 to 5.15 and from 6.8 to 6.0. Even though fecal pH was reduced, SAA and Hp were unchanged as a result of starch infusion. van Gastelen et al. (2021a) infused cows with Co-EDTA (an indigestible marker to estimate gut permeability) and did not observe any changes in gut permeability. These data indicate that increasing intestinal starch supply, independent of other factors, does not result in systemic inflammation.
Infusing starch abomasally dramatically increased fecal butyrate (van Gastelen et al., 2021a,b). Ruminal butyrate concentrations increase during ruminal acidosis as well (Khafipour et al., 2009b). Butyrate is an endogenous ligand for the hydroxycarboxylic acid receptor 2 (HCA2), which is involved in inflammatory signaling and tight junction formation (Plöger et al., 2012;Li et al., 2021). Butyrate produced during hindgut starch fermentation may provide benefits to the gut (Figure 2). Butyrate increased mRNA abundance of IL10 (encoding an anti-inflammatory cytokine) in intestinal dendritic cells and macrophages, which, when incubated with naive CD4 + CD25 − T cells, promoted development of regulatory T cells, which suppress inflammatory signaling (Singh et al., 2014). Butyrate also increased IL-18 secretion in colon epithelial cells (Singh et al., 2014), which supports a cell-mediated T-cell response that may promote inflammation. Butyrate modulates intestinal barrier function and integrity by increasing tight junction protein expression (Peng et al., 2009;Yan and Ajuwon, 2017). Supplementing butyrate to calves promotes rumen and hindgut development (Górka et al., 2018), but the authors acknowledge that little is known about the role of butyrate in the ruminant hindgut.
These data are compelling but there are gaps in our understanding of the effects of starch on gut health. For example, increased fecal butyrate indicates that butyrate concentration in the distal colon is increased, but we have yet to determine whether butyrate is increased in other areas of the hindgut. Furthermore, feeding additional starch may affect mucosal barriers that provide further protection for the hindgut tissue (Kim and Ho, 2010;Steele et al., 2016), but this has not been investigated in dairy cattle.
The potential effects of increasing dietary starch on systemic inflammation has been widely discussed in the dairy industry. During grain challenges in which diets are suddenly changed and forages are replaced by highly fermentable grains, acidosis and systemic inflammation occur. Extremely high concentrations of starch (≥30% of diet DM) in barley-or wheat-based diets may also lead to increased APP, but data indicate that sudden diet changes contribute to inflammation more than chronically elevated dietary starch. Altering dietary starch (20-32% of diet DM) for transition cows does not consistently affect APP. Starch infusion experiments demonstrate that increasing the supply of starch in the small intestine does not cause inflammation, even though fecal pH is reduced. Increasing intestinal starch supply increases fecal butyrate concentrations, which may provide benefits in the gut, but further investigation is needed. Evaluation of the gut microbiome and hindgut mucosal layers may yield important insights into the effects of starch on gut health and inflammation. Krogstad and Bradford | Starch and inflammation Figure 2. Possible effects of butyrate in the hindgut of dairy cows resulting from increased starch supply to the large intestine. Butyrate can increase tight junction mRNA and protein abundance in model species and cells. It also promotes IL-10 expression (anti-inflammatory) in dendritic cells and macrophages, which helps to promote T-regulatory cell development (inflammation-suppressing cell type). These effects may help to mitigate the risk of intestinal inflammation.