Short communication: heritability of milk fatty acid composition and stearoyl-CoA desaturase indices in dairy cows.

Activity of stearoyl-CoA desaturase (SCD) in the mammary gland is important for determining the relative proportions of saturated and monounsaturated fatty acids in milk and the concentration of the conjugated linoleic acid isomer rumenic acid (RA; cis-9,trans-11 18:2). Previous studies identified a large degree of between-cow variation in SCD activity, which was consistent across diets and suggests a genetic influence. The objectives of this study were to quantify genetic and phenotypic variations in fatty acid concentrations and SCD indices in milk fat and to estimate their heritabilities in a population of United Kingdom dairy cows. Milk samples were collected from 2,408 daughters of 597 Holstein-Friesian sires on 325 commercial farms for determination of fatty acid profiles. Indices of SCD activity were calculated by expressing each SCD product (cis-9 14:1, cis-9 16:1, cis-9 18:1, and RA) as a proportion of the precursor plus product [e.g., SCDI(14)=cis-9 14:1/(14:0+cis-9 14:1)]. For individual fatty acids, phenotypic variance was considerably greater than additive genetic variance, resulting in small and nonsignificant heritability estimates (+/- standard error) for all except 6:0 (h(2)=0.27+/-0.10), 8:0 (h(2)=0.27+/-0.09), 12:0 (h(2)=0.13+/-0.07), cis-9 14:1 (h(2)=0.28+/-0.10), and cis-9 18:1 (h(2)=0.12+/-0.07). Heritability estimates of desaturase indices were significant for SCDI(14) (h(2)=0.38+/-0.11), SCDI(18) (h(2)=0.19+/-0.09), and SCDI(RA) (h(2)=0.21+/-0.09), but not for SCDI(16) (h(2)=0.05+/-0.06). This study provides evidence that additive effects are responsible for a significant proportion of the phenotypic variation in SCD activity in dairy cows. It is concluded that because heritability of desaturase indices is moderate and significant in many cases, these indices could be investigated further for use in future breeding programs to increase concentrations of monounsaturated fatty acids and RA while decreasing concentrations of saturated fatty acids in milk fat.

Garnsworthy PC ，Feng S ，Lock AL ，Royal MD ... -  《-》

Variation of Delta 9-desaturase activity in dairy cattle.

The endogenous production of unsaturated fatty acids (FA), particularly some monounsaturated FA (%MONO) and nearly all conjugated linoleic acids, is regulated by the Delta(9)-desaturase activity. The aims of this study were to assess the variation of this enzymatic activity within lactation, across dairy breeds, and to estimate its genetic parameters. The ratios of C14:1 cis-9 to C14:0, C16:1 cis-9 to C16:0, and C18:1 cis to C18:0 were calculated from FA contents predicted by mid-infrared spectrometry. Variance components and standard errors were estimated using average information REML. The multitrait mixed model included as fixed effects herd x test date x class of lactation number, class of days in milk x class of lactation number, class of age x class of lactation number, and regressions on breed composition. Four random effects were also included: animal genetic effect, 2 permanent environments (within and across lactations), and residual effect. Under the assumption that the calculated ratios are an approximate measurement of Delta(9)-desaturase activity, this study showed different sources of variation for this enzymatic activity. A slight difference was observed within lactation. The ratios of C14:1 cis-9 to C14:0 and C16:1 cis-9 to C16:0 increased as a function of days in milk. Differences across 7 dairy breeds were observed. The values of Delta(9)-desaturase indices observed for Jersey and Brown-Swiss cows were lower compared with Holstein. The opposite was observed for dual-purpose Belgian Blue cows. Values of heritability for the ratios of C14:1 cis-9 to C14:0, C16:1 cis-9 to C16:0, and C18:1 cis to C18:0 were 20, 20, and 3%, respectively. Negative genetic correlations observed between fat or protein contents and the 3 indices suggested that an increased activity of Delta(9)-desaturase could inhibit the synthesis of fat and protein in bovine milk. Negative correlations were also observed between fat or protein contents and the contents of 3 studied unsaturated FA in milk fat (C14:1 cis-9, C16:1 cis-9, and C18:1 cis). The positive genetic correlations observed between %MONO and the ratios of C14:1 cis-9 to C14:0 (0.72), C16:1 cis-9 to C16:0 (0.62), and C18:1 cis to C18:0 (0.97) showed that %MONO is linked to the Delta(9)-desaturase activity.

Soyeurt H ，Dehareng F ，Mayeres P ，Bertozzi C ，Gengler N ... -  《-》

Analysis of variation in cis-9, trans-11 conjugated linoleic acid (CLA) in milk fat of dairy cows.

Peterson DG ，Kelsey JA ，Bauman DE 《JOURNAL OF DAIRY SCIENCE》

Stearoyl-coenzyme A desaturase gene polymorphism and milk fatty acid composition in Italian Holsteins.

Mele M ，Conte G ，Castiglioni B ，Chessa S ，Macciotta NP ，Serra A ，Buccioni A ，Pagnacco G ，Secchiari P ... -  《-》

Effects of intravenous infusion of trans-10, cis-12 18:2 on mammary lipid metabolism in lactating dairy cows.

Gervais R ，McFadden JW ，Lengi AJ ，Corl BA ，Chouinard PY ... -  《-》