Dose and time response of ruminally infused algae on rumen fermentation characteristics, biohydrogenation and Butyrivibrio qroup bacteria in qoats

Background： Micro-algae could inhibit the complete rumen BH of dietary 18-carbon unsaturated fatty acid （UFAs）. This study aimed to examine dose and time responses of algae supplementation on rumen fermentation, biohydrogenation and Butyrivibrio group bacteria in goats. Methods： Six goats were used in a repeated 3 x 3 Latin square design, and offered a fixed diet. Algae were infused through rumen cannule with 0 （Control）, 6.1 （L-AIg）, or 18.3 g （H-AIg） per day. Rumen contents were sampled on d 0, 3, 7, 14 and 20. Results： H-AIg reduced total volatile fatty acid concentration and acetate molar proportion （P 〈 0.05）, and increased propionate molar proportion （P 〈 0.05）, whereas L-AIg had no effect on rumen fermentation. Changes in proportions of acetate and propionate in H-AIg were obvious from d 7 onwards and reached the largest differences with the control on d 14. Algae induced a dose-dependent decrease in 18：0 and increased trons-18：1 in the ruminal content （P 〈 0.05）. H-AIg increased the concentrations of t9, t] 1-18：2 and tl 1, cl 5-18：2 （P 〈 0.05）. L-AIg only seemed to induce a transient change in 18-carbon isomers, while H-AIg induced a rapid elevation, already obvious on d 3, concentrations of these fatty acid rose in some cases again on d 20. Algae had no effect on the abundances of Butyrivibfio spp. and Butyrivibrio proteoclosdcus （P 〉 0.10）, while H-AIg reduced the total bacteria abundance （P 〈 0.05）. However, this was induced by a significant difference between control and H-AIg on d 14 （-4.43 %）. Afterwards, both treatments did not differ as increased variation in the H-AIg repetitions, with in some cases a return of the bacterial abundance to the basal level （d 0）. Conclusions： Changes in rumen fermentation and 18-carbon UFAs metabolism in response to algae were related to the supplementation level, but there was no evidence of shift in ruminal biohydrogenation pathways towards t1 0-18：1 L-AIg mainly induced a transient effect on rumen biohydrogenation of 18-carbon UFAs, while H-AIg showed an acute inhibition and these effects were not associated with the known hydrogenating bacteria.