title: Transcriptome adaptation of the bovine mammary gland to diets rich in unsaturated fatty acids shows greater impact of linseed oil over safflower oil on gene expression and metabolic pathways.
abstract: BACKGROUND
  Nutritional strategies can decrease saturated fatty acids (SFAs) and increase health beneficial fatty acids (FAs) in bovine milk. The pathways/genes involved in these processes are not properly defined. Next-generation RNA-sequencing was used to investigate the bovine mammary gland transcriptome following supplemental feeding with 5% linseed oil (LSO) or 5% safflower oil (SFO). Holstein cows in mid-lactation were fed a control diet for 28 days (control period) followed by supplementation with 5% LSO (12 cows) or 5% SFO (12 cows) for 28 days (treatment period). Milk and mammary gland biopsies were sampled on days-14 (control period), +7 and +28 (treatment period). Milk was used to measure fat(FP)/protein(PP) percentages and individual FAs while RNA was subjected to sequencing.
  
  
  RESULTS
  Milk FP was decreased by 30.38% (LSO) or 32.42% (SFO) while PP was unaffected (LSO) or increased (SFO). Several beneficial FAs were increased by LSO (C18:1n11t, CLA:10t12c, CLA:9c11t, C20:3n3, C20:5n3, C22:5n3) and SFO (C18:1n11t, CLA:10t12c, C20:1c11, C20:2, C20:3n3) while several SFAs (C4:0, C6:0, C8:0, C14:0, C16:0, C17:0, C24:0) were decreased by both treatments (P < 0.05). 1006 (460 up- and 546 down-regulated) and 199 (127 up- and 72 down-regulated) genes were significantly differentially regulated (DE) by LSO and SFO, respectively. Top regulated genes (≥ 2 fold change) by both treatments (FBP2, UCP2, TIEG2, ANGPTL4, ALDH1L2) are potential candidate genes for milk fat traits. Involvement of SCP2, PDK4, NQO1, F2RL1, DBI, CPT1A, CNTFR, CALB1, ACADVL, SPTLC3, PIK3CG, PIGZ, ADORA2B, TRIB3, HPGD, IGFBP2 and TXN in FA/lipid metabolism in dairy cows is being reported for the first time. Functional analysis indicated similar and different top enriched functions for DE genes. DE genes were predicted to significantly decrease synthesis of FA/lipid by both treatments and FA metabolism by LSO. Top canonical pathways associated with DE genes of both treatments might be involved in lipid/cholesterol metabolism.
  
  
  CONCLUSIONS
  This study shows that rich α-linolenic acid LSO has a greater impact on mammary gland transcriptome by affecting more genes, pathways and processes as compared to SFO, rich in linoleic acid. Our study suggest that decrease in milk SFAs was due to down-regulation of genes in the FA/lipid synthesis and lipid metabolism pathways while increase in PUFAs was due to increased availability of ruminal biohydrogenation metabolites that were up taken and incorporated into milk or used as substrate for the synthesis of PUFAs.
authors: Agriculture and Agri-Food Canada, Research and Development Centre, Sherbrooke, Quebec, J1M 0C8, Canada. eveline.ibeagha-awemu@agr.gc.ca.
authors: Eveline M
authors: EM
authors: Ibeagha-Awemu
authors: Agriculture and Agri-Food Canada, Research and Development Centre, Sherbrooke, Quebec, J1M 0C8, Canada. ran.li1986@hotmail.com.
authors: Ran
authors: R
authors: Li
authors: Agriculture and Agri-Food Canada, Research and Development Centre, Sherbrooke, Quebec, J1M 0C8, Canada. Ammah.Adolf@AGR.GC.CA.
authors: Adolf A
authors: AA
authors: Ammah
authors: Agriculture and Agri-Food Canada, Research and Development Centre, Sherbrooke, Quebec, J1M 0C8, Canada. Pier-Luc.dudemaine@agr.gc.ca.
authors: Pier-Luc
authors: PL
authors: Dudemaine
authors: Agriculture and Agri-Food Canada, Research and Development Centre, Sherbrooke, Quebec, J1M 0C8, Canada. nathalie.bissonnette@agr.gc.ca.
authors: Nathalie
authors: N
authors: Bissonnette
authors: Agriculture and Agri-Food Canada, Research and Development Centre, Sherbrooke, Quebec, J1M 0C8, Canada. chaouki.benchaar@agr.gc.ca.
authors: Chaouki
authors: C
authors: Benchaar
authors: Department of Animal Science, McGill University, Ste-Anne-de-Bellevue, Quebec, H9X 3 V9, Canada. xin.zhao@mcgill.ca.
authors: Xin
authors: X
authors: Zhao
mesh_terms: D000220:Adaptation, Biological; D000821:Animal Feed; D000818:Animals; D001835:Body Weight; D002417:Cattle; D005231:Fatty Acids, Unsaturated / Q000378:metabolism*; D005786:Gene Expression Regulation; D053263:Gene Regulatory Networks; D059014:High-Throughput Nucleotide Sequencing; D006801:Humans; D008043:Linseed Oil; D042361:Mammary Glands, Human / Q000378:metabolism*; D053858:Metabolic Networks and Pathways; D015203:Reproducibility of Results; D012450:Safflower Oil; D059467:Transcriptome
chemical_list: D005231:Fatty Acids, Unsaturated; D012450:Safflower Oil; D008043:Linseed Oil