The Effect of Neem Leaf Supplementation on Growth Performance, Rumen Fermentation, and Ruminal Microbial Population in Goats

**Background:** Animal nutritionists seek natural feed additives to improve rumen fermentation and feed efficiency in ruminants. Neem (Azadirachta indica) leaves are rich in condensed tannins (CT), which may reduce protein degradation in the rumen and improve amino acid absorption in the small intestine. However, high tannin levels can also reduce feed intake and microbial activity. Polyethylene glycol (PEG) can bind tannins and reduce their negative effects. This study aimed to evaluate the effects of neem leaf supplementation, with and without PEG, on feed intake, digestibility, growth performance, rumen fermentation, and ruminal microbial populations in goats.

**Methods:** Twenty-four Anglo-Nubian Thai native male goats (body weight 20 ± 2.0 kg) were assigned to four treatments in a 2 × 2 factorial completely randomized design: (1) control (0% NL + 0% PEG), (2) 0% NL + 15% PEG, (3) 6% NL + 0% PEG, and (4) 6% NL + 15% PEG in the concentrate. Goats were fed pangola hay as roughage and a 16% crude protein concentrate at a 60:40 ratio for 60 days. Feed intake, nutrient digestibility (using acid-insoluble ash technique), nitrogen utilization, growth performance, rumen fermentation parameters (pH, ammonia nitrogen, blood urea nitrogen, volatile fatty acids), and ruminal microbial populations (total bacteria, methanogens, protozoa, Butyrivibrio fibrisolvens, Streptococcus gallolyticus) were measured. Real-time PCR was used for microbial quantification.

**Key Results:** Supplementation with 6% NL + 15% PEG resulted in the highest feed intake (495.87 gDM/d, 4.07% BW, 75.41 g/kgBW^0.75), nutrient intake (OMI 466.12 g/d, CPI 84.30 g/d, EEI 9.92 g/d), and nutrient digestion (DDM 82.03%, DOM 82.39%, DCP 60.70%, DEE 85.55%) compared to all other treatments (p < 0.05). This group also showed the highest weight change (5.54 kg) and average daily gain (61.56 g/d) (p < 0.05). Nitrogen utilization was significantly improved, with the highest N intake (45.72 g/d), N absorption (27.75 g/d, 60.70%), and N retention (22.37 g/d, 48.93%) (p < 0.05). Rumen fermentation analysis showed the 6% NL + 15% PEG group had the lowest blood urea nitrogen (mean 15.82 Mg%), ammonia nitrogen (mean 12.00 mg/dL), and the highest propionic acid at 2 h (32.13% molar) and 4 h (28.51% molar) post feeding (p < 0.05). This group also had the lowest acetic acid to propionic acid ratio at 4 h (1.79) and the lowest methanogen (mean 7.29 lg10 copies/mL) and protozoa (mean 3.59 lg10 copies/mL) populations. Butyrivibrio fibrisolvens (mean 8.41 lg10 copies/mL) and Streptococcus gallolyticus (mean 10.02 lg10 copies/mL) were highest in the 6% NL + 15% PEG group (p < 0.05).

**Clinical Implications:** This study demonstrates that supplementing goat feed with 6% neem leaf combined with 15% PEG can significantly improve growth performance, feed efficiency, and nitrogen utilization while favorably modulating the rumen microbiome—increasing beneficial bacteria (Butyrivibrio fibrisolvens and Streptococcus gallolyticus) and reducing methanogens and protozoa. These findings suggest neem leaf could serve as a natural, cost-effective feed additive for the goat meat industry, potentially improving productivity and reducing environmental methane emissions. However, the study was limited to 60 days in 24 male goats, and further research is needed to evaluate effects on meat quality, antioxidant activity, and long-term safety.