# Effects of Variable Dietary Sorghum Proportions on the In Vitro Digestibility of Nutrients for Ruminants

## TL;DR

This study shows how varying sorghum levels in ruminant diets affects digestion and fermentation, with tannins playing a key role.

## Contribution

The study introduces new insights into the impact of sorghum tannins on ruminant digestion and the effectiveness of PEG as a tannin binder.

## Key findings

- Higher sorghum inclusion reduced dry matter digestibility but increased fiber digestibility.
- PEG supplementation enhanced protein degradation by neutralizing tannins.
- Sorghum altered volatile fatty acid profiles without affecting methane production.

## Abstract

In regions facing recurrent feed shortages, identifying locally available, drought-resistant forage resources is essential for sustainable ruminant production. Sorghum (Sorghum bicolor L. Moench) represents a promising alternative to conventional forages. However, its nutritional value may be limited by the presence of condensed tannins. Tannins are polyphenolic compounds with well-documented antinutritional effects, mainly due to their negative impact on feed digestibility in ruminants. This study investigated the effects of different dietary proportions of sorghum forage on in vitro rumen fermentation, as well as the role of polyethylene glycol as a tannin-binding agent. The results showed that higher sorghum inclusion altered rumen fermentation patterns, particularly volatile fatty acid profiles, and affected dry matter and fiber digestibility. In contrast, methane production remained unchanged. Polyethylene glycol supplementation further revealed the biological activity of tannins, particularly with regard to rumen protein degradation. Overall, sudangrass sorghum appears to be a viable forage option for ruminants in arid regions if its inclusion level and the effects of condensed tannins are appropriately managed.

This study evaluated the effects of increasing proportions of sudangrass sorghum forage in ruminant diets, with or without polyethylene glycol (PEG), on rumen fermentation, gas and methane production, nutrient digestibility, and protein fermentation metabolites. Three experimental diets containing 20%, 40%, or 60% sorghum forage (S20, S40, and S60) were incubated in vitro with cattle rumen fluid. Incubations were performed with or without PEG used as a tannin-binding agent. After 24 h of incubation, gas and methane production, in vitro dry matter digestibility (DMD), neutral detergent fiber digestibility (NDFD), ammonia nitrogen concentration (N-NH3), and volatile fatty acid (VFA) production and profiles were measured. Increasing sorghum inclusion resulted in a significant reduction in DMD (p = 0.0012). In contrast, NDFD increased (p = 0.0005), likely due to differences in lignin content among diets. Methane production was unaffected by the proportion of sorghum, despite the increasing tannin content. PEG supplementation significantly increased N-NH3 concentration (p = 0.042) and isobutyric molar proportion (p < 0.0001), indicating enhanced rumen protein degradation following tannin neutralization. The total VFA concentration was not influenced by either sorghum level or PEG treatment. However, higher sorghum inclusion was associated with shifts in the VFA profiles toward higher acetate (p = 0.0023) and lower butyrate proportions (p = 0.0114). Overall, the results suggest that moderate levels of condensed tannins (CTs) in sorghum forage may alter rumen fermentation patterns without markedly reducing methane production. PEG supplementation further confirmed the biological activity of tannins, especially regarding protein metabolism. Therefore, sudangrass sorghum may be considered a viable forage option for ruminant diets, provided its inclusion level and tannin effects are carefully managed.