Contribution of Ruminal Protoza to Duodenal Flow of PUFA

Feeding fresh grass to dairy cows increases the polyunsaturated fatty acids (PUFA) concentration of rumen protozoa, but the flow of these PUFA to the duodenum is minimal.
calendar icon 15 May 2012
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Animal Bytes

Feeding fresh grass compared with straw:concentrate increased the 18:3 n-3 concentration of rumen protozoa as a consequence of chloroplast engulfment. Protozoal flow to the duodenum was minimal on the fresh grass diet, resulting in little contribution of protozoa to duodenal PUFA flow.

“So we know, conclusively, that we have the ability to increase the chloroplast content of protozoa, thus increasing 18:3 n-3 content,” said Aberystwyth University’s Sharon Huws, who presented her team’s findings to delegates at last year’s British Society of Animal Science’s annual conference, held at the University of Nottingham.

Rumen protozoa contain 75% of the total microbial lipids – 90% of which are unsaturated fatty acids – maybe due to engulfment of chloroplasts, which are rich in polyunsaturated fatty acids (PUFA) and in particular 18:3 n-3.

“So we decided to evaluate protozoal contribution to duodenal n-3 PUFA flow as a result of their intracellular chloroplast content,” said Dr Huws.

The experiment took eight Holstein cross Friesian steers and used a two-period change-over design with two diets; straw:concentrate (low chloroplast, hence low 18:3 n-3) and fresh grass (high chloroplast, hence high 18:3 n-3).

Following 14-day diet adaptations, duodenal fatty acid flow were monitored using chromium and ytterbium as markers. On the final day of diet adaptations, rumen protozoal samples were taken and purified by centrifugation. Duodenal samples were also taken at the same time.

Fatty acid content of rumen protozoal samples were assessed and protozoal qPCR was performed on rumen protozoal and duodenal samples, enabling calculation of the ratio of protozoal DNA:individual fatty acid.

“And protozoal fatty acid data, coupled with microscopic observations, revealed that protozoa were enriched with 18:3 n-3 due to an abundance of intracellular chloroplasts on the grass diet compared with the straw:concentrate diet,” said Dr Huws.

“However, protozoal 18S rDNA based qPCR data for duodenal samples obtained post-grass feeding of steers were low indicating retention of the protozoa within the rumen on the grass diet. The relatively low abundance of protozoal 18S rDNA at the duodenum following perennial ryegrass feeding represented protozoal contribution to the flow of all fatty acids being exceptionally low on this diet.

“The challenge is to develop strategies to increase protozoal flow to the small intestine, while maintaining sustainable rumen densities, in order to increase the n-3 content PUFA availability to tissues,” she added.

May 2012

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