Work

In Vitro Screening of Feed Additives for Maintaining Ruminal Fermentation Levels Under Heat Stress

Year: 2026

Type: article

Abstract: Heat stress (HS) alters rumen function and may compromise fermentation efficiency in dairy cows. This in vitro study evaluated the effects of six additives—betaine, sodium bicarbonate, bentonite clay, protected fat, Saccharomyces cerevisiae yeast, and Melissa officinalis (lemon balm)—on ruminal fermentation under increasing incubation temperatures (39.0 °C, 40.5 °C, 41.5 °C). This study was designed as an initial in vitro screening approach aimed at evaluating additive resilience under a conservative, worst-case thermal challenge. The highest incubation temperature (41.5 °C) was not used to reproduce the exact physiological rumen environment but rather served to identify additives capable of maintaining fermentation when exposed to extreme conditions that may occur during severe heat load. These results therefore constitute a preliminary step before in vivo validation under realistic HS scenarios. Fermentation was assessed after 24 h by measuring gas production, pH, redox potential, volatile fatty acids (VFAs), and ammonia (NH3) and performing protozoa counts. Temperature alone produced limited effects in the control, with numerical increases in gas, acetate, total VFAs, and NH3 at 41.5 °C. Betaine and yeast maintained overall stable fermentation across all temperatures, preserving gas production, pH, redox potential, and VFA profiles. Sodium bicarbonate increased the pH but reduced gas production. Lemon balm enhanced VFAs and propionate at 39.0 °C but showed reduced activity at high temperature. Protected fat and bentonite clay resulted in lower gas production with minimal influence on other parameters. The protozoa counts were not affected by temperature and showed statistically detectable differences among additives. Overall, betaine and yeast exhibited the highest thermal stability and appear to be suitable candidates for inclusion in feeding strategies aimed at supporting rumen fermentation during periods of HS.

Source: Dairy

DOI: 10.3390/dairy7030040