Rumen fermentation, nitrogen utilization, blood metabolites, predicted greenhouse gas emission, and economic viability of crude glycerin-enriched Leucaena leucocephala pellets in growing tropical goats.

This study evaluated the effects of graded inclusion of crude glycerin (CG) in Leucaena leucocephala (LL) pellets on ruminal fermentation, growth performance, nutrient digestibility, nitrogen utilization, blood metabolites, predicted methane production and economic returns in growing goats. Thirty-two male Boer × Thai native crossbred goats (6 months old; 14.79 ± 1.31 kg) received diets containing 0, 5, 10 or 15% CG on a pellet dry matter basis for 90 days. Dry matter intake decreased from 1.19 to 1.12 kg/d (linear P = 0.014), whereas gain to feed ratio increased from 0.088 to 0.108 kg/kg (linear P = 0.001), with no effect on nutrient digestibility. Ruminal propionate increased from 18.3 to 28.1 mol/100 mol, while the acetate to propionate ratio decreased from 3.76 to 2.23 (P < 0.001). Ruminal pH increased linearly (P = 0.022), whereas ammonia nitrogen was unaffected. Nitrogen intake and fecal nitrogen excretion decreased (P ≤ 0.021), while nitrogen retention remained unchanged. Microbial nitrogen supply increased from 11.23 to 12.99 g/d, and blood glucose increased from 55.1 to 63.8 mg/dL (linear P = 0.009). Under a carbohydrate based stoichiometric model, predicted methane production decreased by 25%, while greenhouse gas emissions decreased from 35.69 to 27.17 kg CO₂ equivalent/kg gain (P < 0.001). Net profit increased by 87%, and return on investment increased from 12.9% to 25.4%. Overall, increasing CG inclusion in LL-based pellets was associated with improved feed efficiency, altered ruminal fermentation, lower predicted methane emissions and enhanced economic returns in growing goats.