The paper “The effect of abomasal infusion of corn starch and β-hydroxybutyrate on hindgut microbial fermentation kinetics in early lactating dairy cows measured by the in vitro gas production technique“, published in The Journal of Agricultural Science, has been chosen as the latest Editorial Highlight and is freely available.

Two underrecognized conditions, metabolic and hindgut acidosis, are compromising dairy cow performance, impairing nutrient use, and increasing laminitis and immune suppression risks. Yet mechanisms behind these conditions — and their potential interactions — remain underexplored compared to rumen acidosis, their better-studied counterpart. Early in lactation, dairy cows commonly experience negative energy balance and mobilize fat reserves. This raises blood levels of ketone bodies such as β-hydroxybutyrate (BHB), which can influence systemic acid–base balance and lead to mild metabolic acidosis. To offset energy deficits, diets often include elevated levels of rapidly fermentable carbohydrates, mainly starch and fructans. While these provide quick energy, some carbohydrates reach the hindgut and contribute to hindgut acidosis. Hindgut acidosis can disrupt microbial balance and damage epithelial integrity.

Our aim was to explore how these two factors — excess carbohydrates reaching the hindgut (potentially causing hindgut acidosis) and circulating ketone bodies (contributing to metabolic acidosis) — influence hindgut microbial fermentation. We sought to elucidate their roles in these less studied acidosis forms and implications for nutritional strategies supporting dairy cattle health and production. While carbohydrates arriving in the hindgut alter fermentation patterns directly, blood ketone bodies may affect microbial activity indirectly, for example by impacting gut wall integrity. Therefore, we investigated in vitro the effects of abomasal infusion of maize starch (which can induce hindgut acidosis) and BHB (linked to compensated metabolic acidosis) on hindgut microbial fermentation capacity in early lactation cows.

Faecal inocula from individual cows receiving six abomasal infusion treatments were collected and incubated for 72 hours with different substrates. Treatments included a control (water only), two starch doses (1.5 or 3.0 kg maize starch per day) without BHB, BHB infusion alone (8.0 mol per day), and combinations of starch and BHB. Four substrates varying in starch or fibre content and expected fermentation rates were tested to simulate diverse hindgut conditions.

Inocula from BHB-infused cows had limited impact on in vitro fermentation characteristics. In contrast, increased starch levels markedly reduced microbial fermentation capacity across substrates. Inocula from the 3.0 kg maize starch per day treatment stimulated early gas production, indicating rapid microbial activity. However, by 72 hours this level lowered total gas and methane production, decreased pH and ammonia concentration, and reduced in vitro organic matter digestibility, especially cellulose. Inocula from starch-infused cows also shifted fermentation patterns toward higher proportions of propionate and butyrate.

Our study revealed that abomasal infusion of maize starch (3.0 kg per day, and to a lesser extent 1.5 kg per day; both linked to hindgut acidosis) altered in vitro fermentation of faecal inocula, whereas 8.0 mol BHB per day (linked to compensated metabolic acidosis) had negligible effects. These findings highlight impaired microbial fermentation capacity, and the need to carefully manage dietary starch levels to maintain optimal hindgut fermentation and reduce methane emissions, supporting cow health and production during the critical early lactation period.

The Journal of Agricultural Science Editorial Highlights are selected by the Editor-in-Chief and are freely available. View the recent selections here.