Association Analysis Of Fatty Acid Synthase (FASN) And Stearoyl- Coa Desaturase-1 (SCD1) Genes Polymorphisms With Milk Fatty Acid Composition In Xinong Saanen Dairy Goats

Fatty acid synthase (FASN) and Stearoyl-CoA desaturase-1 (SCD1) are genes involving in catalyzing the de novo fatty acid synthesis and desaturation of saturated FAs to MUFAs, respectively. High mRNA expression of the genes in goat mammary epithelial cells (GMECs) substantiated by the medium to high heritability of milk fat, reinforced their role as candidates for association analysis with milk fat profile. Two,1241,45mLs pooled,2/3 morning and 1/3 evening, milk samples were collected 30,60,90 and 120 days postpartum, from 321 Saanen does, from 2 herds sired by 73 bucks, and each was analyzed by MilkoScan FT-FOSS and GC (gas-chromatography), respectively.The first objective of the study was:-1. To conduct association analysis of capra hircus FASN and SCD1 genes with milk fat profile to develop markers to improve healthfulness of goat milk.A linear mixed model for longitudinal data, that considered the effects of herd, herd test day (HTD), DIM (days in milk), parity, doe, sire and allele and haplotype substitution effects and interaction of alleles and haplotypes with DIM was used to investigate the associations of 3 FASN SNPs (-911 C/T intron1 SNP1,852 A/G intron2 SNP2 and 14420 T/C exon37 SNP3), two SCD1 SNPs(5205 A/G Exon 3 and 5311 C/T intron 3) and two haplotypes of FASN (HI, C1-A2-T3 and H2, T1-G2-C3, constructed from the three SNPs) with 37 individual FAs,11 FA groups, and 7 FA indices, by SPSS 20, REML function. All the SNPs, except SNP 5205 A/G, were consistent with HWE (Hardy Weinberg Equilibrium). A single test per SNP and haplotype was performed to avoid the effect of multiple testing. SNP1 and SNP2 had not shown any significance effects, where as SNP 3 and SNP4 had shown tendencies of significances on C16:1 fatty acid. The interaction of the 3 FASN SNPs and DIM had shown significant effects on C6:0, C8:0, C10:0 and C14:0 de novo fatty acids, in which the major alleles had shown lower levels of the fatty acids, implying differential effects of SNPs across DIM. Interaction of Haplotype1 (C1A2T3) with DIM had also shown significant effects in similar fashion to the FASN SNPs major alleles. Furthermore, H2 (T1G2C3) and its interaction with DIM had shown significant effects, but in an opposite manner to H1. H2 had shown significant effects on C18:1 n9 trans and rumenic CLA. SNP4 intron 3,5311 C/T had shown significant effects on C16:1 fatty acid, while its interaction with DIM had shown effects on protein, C13:0 and C14:1. Although not consistent with HWE SNP5 had shown significant effects on C4:0, C11:0, C12:0, C16:1, C17:1 and C18:0 fatty acids. The markers developed in this study could assist in improving healthfulness of goat milk.The second objective of the study was2. To investigate the effects of herd, TD, parity and DIM on milk composition and to decipher correlation patterns of FAs in Saanen dairy goats.A linear mixed model, for longitudinal unbalanced data, that considered the fixed effects of TD (nested within DIM and herd to avoid confounding effects), herd, parity and random effects of doe and sire was used to investigate 27 individual FAs,5 major milk components,3 milk physical characteristics,11 FA groups, and 7 FA ratios and indices, by SPSS 20, REML function. TD and Herd were the predominant factors affecting FA variations, indicating the leading role of nutrition, environment and management on milk proximate components and FA composition variations. SFAs levels were significantly increasing with parity, lowest levels were scored in parity group 1, accompanied with higher levels of MUFA (Monounsaturated FAs) and PUFA (Polyunsaturated FAs), indicating the increasing indigenous metabolic activity of mammary tissue with age, hence, the quality of milk fatty acids should be given attention while efforts are being made to increase longevity of the animal. FPratio deviation decreases significantly across DIM, revealing the existence of fat mobilization in the early days of lactation in goats. Lower levels of de novo and higher levels of MUFA were observed in the early days of lactation, which dissipates as lactation progress. Rumenic CLA was increasing across DIM, supposedly due to the increasing activity of delta 9 desaturase and/or supply of rumenic vaccenic acid. There was an observed negative correlation patterns between de novo fatty acids and C18 MUFAs demonstrating inhibiting effects of long chain fatty acids on de novo. Although considered as de novo, butyric acid had shown negative correlations with the other de novo FAs, suggesting other sources of origin. Majority of the odd chain fatty acids (OCFAs) are originated from rumen bacteria, hence their quantity and patterns of correlation may reflect rumen microbial activity. In our study positive correlations of all OCFAs with rumenic CLA (supposedly through its precursor C18:1 trans-11) and some trans-FAs was observed, which indicates that OCFAs could serve as diagnostic tool for rumen microbial activity in caprine. This investigation, the first in goat to our knowledge, will help to decipher the main factors of variation and develop means of modulating to meet quality and health standards.