Abstract
Background:
Ruminant animals are essential food resources, but they can lead to nutrient loss and greenhouse gas emissions. Feeding tannin-containing plants has been shown to increase digestion efficiency and affect rumen fermentation. The application of pomegranate peel (PP) feed supplements can provide suitable prebiotic substances that increase animal productivity and reduce its environmental consequences.

Aim:
This study combined in vivo feeding experiments and in situ rumen degradability of PP as a natural condensed tannin (CT) source on digestibility, rumen fermentation, nitrogen balance, microbial populations quantitative-PCR (qPCR), and methane (CH4) production.

Methods:
This study used three fistulated goats with an average weight of 28.2 ± 1.7 kg to investigate the influence of three different levels (0, 114 g PP equivalent to 30 g CT, and 222 g PP equivalent to 60 g CT) of PP in their diets as sources of CT. Treatments were formulated according to the measured concentration of CT in the peel and labeled T1, T2, and T3, respectively. The same diet treatments were used in the in situ trials. The experimental design used a repetitive 3 × 3 Latin square with 10-day phases, comprising 7 days for diet adaptation and 3 days for sample collection.

Results:
Feed intake (p < 0.009) was significantly higher in the CT-supplemented treatments (T2 and T3) than in the control (T1). Incubation time influenced the disappearance of dry matter and protein, indicating that CT decreased immediate loss while protecting protein against rumen overdegradation. CT improved rumen fermentation as shown by lower Ammonia-N concentration (p < 0.001) and higher volatile fatty acid contents. This decreases the acetate/propionate ratio in T2 and T3. Results showed an increase in CH4 emissions, with T3 showing the largest increase at 53.32% compared to the control. qPCR showed decreased protozoa and methanogen populations in the CT groups, whereas moderate levels of Ruminobacter amylophilus were stimulated.

Conclusion:
Overall, this study indicates that moderate CT inclusion improves rumen fermentation characteristics without affecting nutrient digestibility (except crude protein) and may represent a sustainable dietary intervention for goats.

Key words: Condensed tannins; Digestibility; Methane; Nitrogen balance; Rumen fermentation.