Effects of dietary supplements rich in docosahexanoic acid on in vitro fermentation and microbial composition of lamb rumen fluid

Introduction – Microalgae is a potential alternative dietary source of polyunsaturated fatty acids (PUFA), especially omega-3, that could improve meat quality of the ruminants (Meale et al.,2014). However, the impact of that dietary supplementation on the ruminal microbiota is still unclear. This study aims to evaluate the impact of the supplementation of a DHA rich microalgae and oil extracted from the microalgae on the in vitro fermentation patterns and microbial composition of lamb’s rumen fluid

Material and methods – The rumen fluid of three 8-month old Texel-cross lambs fed a 50:50 energy-based control diet of grass silage and balanced concentrates was sieved and mixed with Van Soest buffer in a 1:3 ratio (v/v). The preparation was anaerobically incubated in triplicates with milled silage (0.8%) (control treatment), milled silage (0.8%) + microalgae (0.6%) (algae treatment) and milled silage (0.8%) + oil (0.5%) (oil treatment) into ANKOM gas pressure monitor jars for 48h (39oC – 25RPM). Samples jars were collected at four time points (0, 7, 24, 48h) and analysed as follows: pH – each incubation time, ammonia concentration – Chaney and Marbach method (1961), microbial protein – Bradford method (1976), gas pressure - automatically, volatile fatty acid – gas chromatography, protozoa counts – Sedgewick rafter counting slide and DNA 16S sequences – MGnify pipeline (ENA). Statistical tests (ANOVA and pairwise T test or Kruskal Wallis and pairwise Wilcoxon test according to the data distribution) for each parameter, potential correlations and graphics were run on R (4.0.3).

Results – The pH remained similar amongst the treatments (P=0.99) and decreased over time (6.40 to 6.05). The ammonia concentration increased over time (109mg/L, 130mg/L, 138mg/L to 521mg/L, 556mg/L, 516mg/L for control, algae and oil respectively) but no significant treatment effect was observed (P=0.96). A tendency for higher microbial protein was observed for the algae and oil compared to the control treatment (P=0.06). Total gas production increased over time but was not statistically different between treatments (P=0.86). Volatile fatty acids concentration increased over time but were similar between treatments (P=0.82). Shannon diversity index ranged from 1.95 at 0h to 2.31 at 48h regardless of the treatment. The protozoa count decreased over time and was similar amongst the treatments (P=0.95). The most predominant families were Christensenellaceae, Prevotellaceae, Lachnospiraceae and Ruminococcaceae, with a significantly higher presence of Prevotellaceae (P=0.02) but a significantly lower presence of Lachnospiraceae (P=0.01) in the control compared to the supplemented treatments.