Cow’s milk and dairy products are the primary sources of OBCFAs, which have beneficial health properties. The goal of this study was to identify the factors that influence the content of OBCFAs in cow’s milk and to indicate which OBCFAs can serve as biomarkers for fermentation processes. The content of OBCFAs in milk depends on the species of ruminants, with studies showing that this varies between 3.33% (in goat’s milk) and 5.02% (in buffalo’s milk). These differences also stem from the animals’ energy balance, lactation phases, forage-to-concentrate ratio, and the presence of bioactive compounds in feeds, as well as management practices and environmental conditions. The OBCFAs in milk fat mainly come from rumen bacteria, but can also be synthesized de novo in the mammary gland, making them potentially useful noninvasive indicators of rumen fermentation. The concentration of BCFA is lower in colostrum and transitional milk than in full lactation milk. The proportions of total OBCFAs are higher in first- and second-parity cows. The most effective predictors of the biohydrogenation of fatty acids in the rumen are likely C18:2 cis-9, trans-11, iso-C16:0, and iso-C13:0. OBCFAs have been identified as potential biomarkers for rumen function, because their synthesis depends on specific bacteria. Strong predictors of subclinical ruminal acidosis include iso-C14:0, iso-C13:0, and C15:0. The concentration of ∑ OBCFA >C16 in milk is associated with fat mobilization and serves as a significant marker of the energy balance in cows.

This study aimed to evaluate the effects of essential oils (EOs) extracted from Cannabis sativa L. and Cannabis indica Lam. on in vitro ruminal fermentation characteristics, selected rumen microbial populations, and methane production. GC-MS analyses allowed us to identify 89 compounds in both EOs. It was found that E-β-caryophyllene predominated in C. sativa (18.4%) and C. indica (24.1%). An in vitro (Ankom) test was performed to analyse the control and monensin groups, as well as the 50 µL or 100 µL EOs. The samples for volatile fatty acids (VFAs), lactate, and microbiological analysis were taken before incubation and after 6 and 24 h. The application of EOs of C. indica resulted in an increase in the total VFAs of acetate and propionate after 6 h of incubation. The applied EOs had a greater impact on the reduction in methane production after 6 h, but no apparent effect was noted after 24 h. Lower concentrations of C. sativa and C. indica had a more pronounced effect on Lactobacillus spp. and Buryrivibrio spp. than monensin. The presented findings suggest that C. sativa and C. indica supplementation can modify ruminal fermentation, the concentrations of specific volatile fatty acids, and methane production.

This study aimed to quantitatively determine the composition of 25 essential oils (EOs) using gas chromatography–mass spectrometry (GC-MS) to assess their minimum inhibitory concentrations (MICs) against selected rumen microorganisms and to confirm their effects in in vitro tests on volatile fatty acid (VFA) formation. GC-MS analysis identified over 80 compounds across the tested oils. The MICs were determined for Butyrivibrio fibrisolvens, Prevotella albensis, Lactobacillus delbrueckii ssp. lactis, and Streptococcus bovis, revealing diverse sensitivities. The rumen bacteria’s sensitivity to essential oils varied by strain, with some microorganisms inhibited at low concentrations while others required higher doses, highlighting the potential for targeted modulation of the rumen microbiota. Amyris balsamifera and Zingiber officinale demonstrated strong inhibitory effects at low concentrations and simultaneously enhanced VFA production. In contrast, Lavandula officinalis showed inhibitory effects on VFAs. Amyris balsamifera and L. officinalis also exhibited methane reduction. These findings demonstrate that selected essential oils can modulate rumen microbiota and fermentation by either inhibiting or stimulating specific bacterial groups, highlighting their potential as natural modulators to improve rumen function and animal health.

Conifer-derived essential oils have gained attention as versatile natural additives with potential applications in animal production, including influencing microbial processes and supporting environmental sustainability. This study aimed to characterize the chemical composition of selected conifer essential oils (EOs), evaluate their antimicrobial activity against rumen microorganisms in vitro, and assess the effects of Pinus sylvestris essential oil on rumen fermentation and methane production under in vitro and in vivo conditions. EOs from Thuja occidentalis, Cupressus sempervirens, Juniperus communis, Picea mariana, Pinus sylvestris, and Pinus pinaster were analyzed by GC–MS, and their inhibitory activity against selected rumen bacteria was determined by MIC and IC₅₀ assays. Based on these results, P. sylvestris oil was selected for fermentation experiments. Ninety-two volatile compounds were identified, with monoterpenes as the dominant constituents and α-pinene as the major compound in P. sylvestris oil. In vitro, P. sylvestris oil influenced fermentation in a dose-dependent manner without affecting ruminal pH. In vivo, ruminal pH, ammonia-related parameters, and total VFA concentration were not significantly affected by treatment, whereas several variables showed a significant effect of time. Temporal changes in VFA profiles suggested a transient adaptation of ruminal fermentation. Methane concentration was significantly (p < 0.01) reduced by Pinus sylvestris essential oil supplementation, with a decrease of approximately 28.7% after 14 days. These findings indicate that P. sylvestris EOs may serve as a promising natural modulator of rumen fermentation, although further studies are needed to optimize dosage and confirm long-term effects.

Black soldier fly larvae (BSFL; Hermetia illucens) oil and flaxseed oil provide contrasting fatty acid profiles and may serve as alternative lipid feed materials in ruminant nutrition. This study assessed low-α-linolenic/high-linoleic flaxseed oil, BSFL oil, and their blends using an in vitro rumen fermentation screening with pooled bovine rumen inoculum and a randomized prepartum feeding trial in 32 twin- or triplet-bearing Olkuska ewes. In vitro, the single oils and a 1:1 blend were evaluated at two inclusion levels; total VFA concentration was unchanged, whereas propionate proportion, the acetate-to-propionate ratio, methane, ammonia, and incubation-fluid fatty acid profiles showed treatment-dependent responses. In vivo, an unsupplemented control was compared with flaxseed oil, BSFL oil, and a 2:1 blend supplied at 30 g/day for 21 days before expected parturition. Colostrum fat concentration differed among treatments (p = 0.036); the 2:1 blend group had a higher value than the control group (11.29% vs. 8.26%; Dunnett-adjusted p < 0.05), while major fatty acid classes did not differ. Supplementation was also associated with differences in selected minor colostrum fatty acids and several serum metabolic variables. Colostrum yield was not measured; therefore, this finding reflects fat concentration rather than total colostrum fat output. Serum total antioxidant status (TAS) was unaffected, while a treatment-by-time interaction was observed for γ-glutamyl transferase. The tested plant- and insect-derived oils therefore modified ruminal lipid transformations and selected maternal and colostrum traits without a detectable change in TAS.

The peripartum period in prolific ewes is associated with increased metabolic demands, and dietary lipid supplementation may increase the energy density of the prepartum diet. This study evaluated the effects of prepartum supplementation with alternative lipid matrices on the physicochemical characteristics and comprehensive fatty acid (FA) profiles of mature and transitional sheep milk. Thirty-two pregnant Olkuska ewes were randomly assigned to four cohorts (n = 8/group): Control (basal diet), flaxseed oil (low n-3/high n-6 variety; FO), black soldier fly larvae oil (BSFL oil), and Mix oil (2:1 ratio of FO to BSFL oil). Dietary treatments exerted no significant effects (p > 0.05) on transitional milk composition or lipid quality indices. In contrast, in mature milk, BSFL oil supplementation significantly increased milk fat content (6.09%) compared to the Control group (4.70%; p < 0.01). Furthermore, all oil treatments significantly reduced total saturated FAs (p < 0.01), while the BSFL oil and Mix oil supplementation significantly increased the monounsaturated FA fraction (p < 0.01). The differences, particularly the increase in cis-9, trans-11 CLA concentration and the significant reduction in both the atherogenic and thrombogenic indices (p < 0.01), were observed exclusively in mature milk. These findings suggest that the combination of sustainable insect lipids with high-linoleic plant oils may represent a viable strategy to transform sheep milk into a functional food with potential cardiovascular health benefits for consumers. These findings additionally indicate that prepartum lipid supplementation may exert a persistent carry-over effect into early lactation, influencing the fatty acid composition of mature sheep milk.