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

SIMPLE SUMMARY: Neem leaves are a rich source of tannin, may prevent protein degradation in the rumen, and may increase growth performance because they are natural substances; thus, they are appealing as rumen modifiers. Animal nutritionists must manipulate ruminal ecology and fermentation to improve feed intake in ruminants. Therefore, the purpose of this study was to evaluate the effect of neem leaf supplementation on digestibility, growth performance, rumen fermentation, and ruminal microbial population in goats. The findings indicated that goats fed 6% neem leaf (NL) + 15% (polyethylene glycol (PEG)) in the concentrate had the highest values of feed intake, nutrient digestion, and nitrogen utilization increased growth performance; the highest values of Butyrivibrio fibrisolvens and Streptococcus gallolyticus; and reduced protozoa and methanogens. Our results suggest that neem leaf could be an interesting substitute supplement for goat feed. We believe that neem leaf has the potential to help the goat meat industry meet the demands of health-conscious consumers. ABSTRACT: This study aims to investigate the effect of neem leaf supplementation on the feed intake, digestibility, performance, fermentation characteristics, and ruminal microbes in goats. We included 24 Anglo-Nubian Thai native male goats with a body weight of 20 ± 2.0 kg, using 2 × 2 factorial in a completely randomized design for the following four treatments: (1) control, (2) control + 15% PEG in the concentrate, (3) 6% NL in concentrate, and (4) 6% NL + 15% PEG in concentrate. The results show that supplementation with 6% NL + 15% PEG in the concentrate had a higher (p < 0.05) feed intake gDM/d, % BW, g/kgBW(0.75), nutrient intake, nutrient digestion, weight change, and ADG than did the goats that were fed with 0% NL + 0% PEG, 0% NL + 15% PEG, and 6% NL + 0% PEG in concentrate, respectively. The feeding with 6% NL + 15% PEG had a higher (p < 0.05) level of propionic acid at 2 and 4 h post feeding compared to the other treatments. Supplementation with 6% NL + 15% PEG in the concentrate had the lowest (p < 0.05) methanogen, protozoa, blood urea nitrogen, ammonia nitrogen, acetic acid, and butyric acid, as well as a lower ratio of acetic acid to propionic acid at 2 and 4 h post feeding than the other treatments. However, supplementation with 6% NL + 15% PEG in concentrate had the highest values of Butyrivibrio fibrisolvens and Streptococcus gallolyticus at 2 and 4 h post feeding compared to the other treatments (p < 0.05). Collectively, this study indicates that neem leaf supplements can increase growth performance and propionic acid and can modulate the abundance of Butyrivibrio fibrisolvens and Streptococcus gallolyticus. Thus, neem leaf could potentially be a good supplement for goat feed.