Abstract
BackgroundNutritional 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.ResultsMilk 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.ConclusionThis 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2423-x) contains supplementary material, which is available to authorized users.
Highlights
Nutritional strategies can decrease saturated fatty acids (SFAs) and increase health beneficial fatty acids (FAs) in bovine milk
This study shows that rich α-linolenic acid linseed oil (LSO) has a greater impact on mammary gland transcriptome by affecting more genes, pathways and processes as compared to safflower oil (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 polyunsaturated fatty acid (PUFA) 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
Summary
Nutritional strategies can decrease saturated fatty acids (SFAs) and increase health beneficial fatty acids (FAs) in bovine milk. Nextgeneration RNA-sequencing was used to investigate the bovine mammary gland transcriptome following supplemental feeding with 5 % linseed oil (LSO) or 5 % safflower oil (SFO). Nutritional strategies include feeding high grain/low forage and feed supplements rich in unsaturated fatty acids (USFAs) (e.g. soybean oil, corn oil, safflower oil, linseed oil, canola oil, marine algae, and fish oil) to dairy animals. These strategies have shown reduced yields of milk fat and milk saturated fatty acids (SFAs) of all chain lengths [4, 5]. Milk fat synthesis under regulation by dietary factors and feed ingredients high in USFAs cause a phenomenon known as milk fat depression whereby milk fat yield can be reduced by up to 50 % while other milk components are unaffected [6, 7]
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