title: Ruminal protozoal contribution to the duodenal flow of fatty acids following feeding of steers on forages differing in chloroplast content.
abstract: Ruminant products are criticised for their SFA content relative to PUFA, although n-6:n-3 PUFA is desirable for human health ( < 4). Rumen protozoa are rich in unsaturated fatty acids due to engulfment of PUFA-rich chloroplasts. Increasing the chloroplast content of rumen protozoa offers a potentially novel approach to enhance PUFA flow to the duodenum and subsequent incorporation into meat and milk. We evaluated protozoal contribution to duodenal n-3 PUFA flow due to intracellular chloroplast content. A total of six Holstein × Friesian steers were fed, in a two-period changeover design, either straw:concentrate (S:C, 60:40; DM basis; S:C, low chloroplast) or fresh perennial ryegrass (PRG; high chloroplast). Following 12 d adaptation to diet, ruminal protozoal and whole duodenal samples were obtained. N and fatty acid content of whole duodenum and rumen protozoal samples were assessed and protozoal 18S rDNA quantitative PCR performed, enabling calculation of protozoal N flow. The ratio of individual fatty acids:N in rumen protozoal samples was calculated to obtain protozoal fatty acid flows. Based on total fatty acid flow, contribution (%) of protozoa to individual fatty acid flows was calculated. Protozoal fatty acid data and microscopical observations revealed that protozoa were enriched with 18 : 3n-3 following PRG feeding, compared with the S:C diet, due to increased intracellular chloroplast content. However, duodenal protozoal 18S rDNA concentration post PRG feeding was low, indicating rumen retention of the protozoa. Nutrition influences the 18 : 3n-3 content of protozoa; the challenge is to increase protozoal flow to the small intestine, while maintaining sustainable rumen densities.
authors.affiliation: Animal and Microbial Sciences, Institute of Biological, Environmental and Rural Sciences (IBERS), Aberystwyth University, Gogerddan, Aberystwyth              SY23 3EB, UK.
authors.forename: S A
authors.initials: SA
authors.lastname: Huws
authors.forename: M R F
authors.initials: MR
authors.lastname: Lee
authors.forename: A H
authors.initials: AH
authors.lastname: Kingston-Smith
authors.forename: E J
authors.initials: EJ
authors.lastname: Kim
authors.forename: M B
authors.initials: MB
authors.lastname: Scott
authors.forename: J K S
authors.initials: JK
authors.lastname: Tweed
authors.forename: N D
authors.initials: ND
authors.lastname: Scollan
mesh_terms: D000818:Animals; D002417:Cattle; D002736:Chloroplasts / Q000737:chemistry / Q000648:ultrastructure; D016054:DNA, Protozoan / Q000032:analysis*; D004032:Diet / Q000662:veterinary; D004386:Duodenum / Q000378:metabolism* / Q000382:microbiology; D005227:Fatty Acids / Q000032:analysis / Q000378:metabolism*; D008297:Male; D012417:Rumen / Q000469:parasitology*
chemical_list: D016054:DNA, Protozoan; D005227:Fatty Acids