Effect of Ocimum basilicum extracts on in vitro rumen fermentation and subsequent in vivo apparent total tract digestibility and methane emission of young calves

This study determined the in vitro and in vivo rumen fermentation patterns and nutrient digestibility during the pre-weaning period of Holstein crossbreed (Baladi × Holstein) dairy calves supplemented with different levels of aqueous, ethanol, and a combination of aqueous and ethanol extracts of the basil (Ocimum basilicum) leaves. In an in vitro study, a basal diet (80% starter feed: 20% Trifolium alexandrinum hay) was incubated without additives (control) and with aqueous extract, solvent extract, or a combination of both extracts of basil leaves [1 and 2 mL/kg dry matter (DM)], for 24 h to assess their effects on in vitro ruminal fermentation, feed degradability, and gas and methane (CH4) production. Thirty Baladi × Holstein crossbred dairy calves aged 4 or 5 days were divided into three experimental groups: the control group (without additive, n = 10) and two supplemented groups (n = 10 per group) with 1 mL and 2 mL of Ocimum basilicum extract (OBE)/calf for the apparent total-tract digestibility for 90 days. The gas chromatography–mass spectrometry (GC-MS) spectrum of OBE showed that the main components of OBE varied with the extraction method. 9-Octadecenoic acid (Z)-methyl ester was detected in all three extraction methods with varying concentrations: aqueous (39.28%), ethanol (9.75%), and mixed aqueous-ethanol (17.99%). Despite these variations, the characteristics of gas production and rumen fermentation did not differ significantly. However, the solvent OBE extract, particularly at lower doses, numerically reduced CH4 production, with the low-dose solvent treatment showing a 5.2% decrease in CH4 relative to the control. Supplementation with OBE increased the concentrations of acetic acid and total volatile fatty acids and enhanced total gas production compared to the control. Suckling calves fed an OBE-supplemented diet exhibited a reduced intake of calf starter, clover hay, and total DM compared with the control group. The digestibility coefficients of DM, crude protein, neutral detergent fiber, and acid detergent fiber were higher (P