Effect of replacement of berseem clover by almond hulls from Palestine or Tunisia with Pichia manshurica yeast as feed additives in mixed diet on rumen fermentation, methane emissions, and protozoa counts, in vitro

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Abstract

This study was conducted to evaluate the effects of combined supplementation of two rumen-isolated Pichia manshurica yeast strains (FFNLYFC1and FFNLYFC2), which were combined 1:1 and dosed at 1.4 × 10⁸ CFU/g dry matter (DM) from each strain on in vitro ruminal fermentation of diets in which almond hulls from Palestine (AHP) or Tunisia (AHT) replaced berseem clover (Trifolium alexandrinum) as the primary forage source. Five experimental treatments were evaluated at a 60:40 forage-to-concentrate ratio: a control diet (berseem clover hay); AHP without yeast (AHP–); AHP with yeast (AHP+); AHT without yeast (AHT–); and AHT with yeast (AHT+). Three independent biological runs were performed using rumen fluid from three water buffalo males. The asymptotic gas production potential (b) was highest in the control and AHP+ (149.3 and 149.2 mL/g DM, respectively; P = 0.016) and significantly lower in AHT diets (140.4–141.1 mL/g DM). True dry matter digestibility was highest in AHP+ (81.4%) and lowest in AHT– (77.9%). The AHP+ diet yielded the highest total volatile fatty acid (VFA) concentration (129.6 mmol/L), representing a 37.6% increase over the control (94.2 mmol/L), alongside the greatest propionate proportion (35.4% vs. 21.1% in the control; P = 0.001). Microbial biomass production was highest in AHP+ (523.3 mg/g DM; P = 0.003). True digestible organic matter was significantly greater in AHT– and AHT+ (812.9 and 813.8 g/kg DM, respectively) than in the control (786.4 g/kg DM), reflecting lower lignification in Tunisian hulls. The true neutral detergent fiber degradability (TNDF) was markedly higher in the control (539.1 g/kg DM NDF than in all almond hull diets (357.4–421.5 g/kg NDF; P < 0.001), though yeast supplementation improved TNDF in AHP diets by 17.9%. Methane production per gram of DM was highest in AHP+ (32.6 mL/g DM; P = 0.039), though methane (CH₄) per unit of truly digested organic matter did not differ significantly among treatments (P = 0.059), indicating that the elevated absolute CH₄ in AHP+ reflects greater total fermentation activity rather than enhanced methanogenesis per se. Ruminal pH and protozoal counts were not significantly different among treatments. These findings indicated that P. manshurica yeast supplementation substantially enhanced fermentation efficiency and VFA output in Palestinian almond hull diets and exerted a meaningful but more modest benefit in Tunisian hull diets, with the geographic origin of the almond hulls appearing to modulate the fermentation response to yeast inclusion. P. manshurica-supplemented Palestinian almond hull diets (AHP+) produced the best combined fermentation outcome among the almond hull treatments evaluated.

Keywords

P. manshurica / almond hulls / in vitro rumen fermentation / volatile fatty acids / methane

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