Oilseed Supplementation Improves Milk Composition and Fatty Acid Profile of Cow Milk: A Meta-Analysis and Meta-Regression

Abstract

Oilseed supplementation is a strategy to improve milk production and milk composition in dairy cows; however, the response to this approach is inconsistent. Thus, the aim of this study was to evaluate the effect of oilseed supplementation on milk production and milk composition in dairy cows via a meta-analysis and meta-regression. A comprehensive and structured search was performed using the following electronic databases: Google Scholar, Primo-UAEH and PubMed. The response variables were: milk yield (MY), atherogenic index (AI), Σ omega-3 PUFA, Σ omega-6 PUFA, fat, protein, lactose, linoleic acid (LA), linolenic acid (LNA), oleic acid (OA), vaccenic acid (VA), conjugated linoleic acid (CLA), unsaturated fatty acid (UFA) and saturated fatty acid (SFA) contents. The explanatory variables were breed, lactation stage (first, second, and third), oilseed type (linseed, soybean, rapeseed, cottonseed, and sunflower), way (whole, extruded, ground, and roasted), dietary inclusion level, difference of the LA, LNA, OA, forage and NDF of supplemented and control rations, washout period and experimental design. A meta-analysis was performed with the “meta” package of the statistical program R. A meta-regression analysis was applied to explore the sources of heretogeneity. The inclusion of oilseeds in dairy cow rations had a positive effect on CLA (+0.27 g 100 g−1 fatty acids (FA); p < 0.0001), VA (+1.03 g 100 g−1 FA; p < 0.0001), OA (+3.44 g 100 g−1 FA; p < 0.0001), LNA (+0.28 g 100 g−1 FA; p < 0.0001) and UFA (+8.32 g 100 g−1 FA; p < 0.0001), and negative effects on AI (−1.01; p < 0.0001), SFA (−6.51; p < 0.0001), fat milk (−0.11%; p < 0.001) and protein milk (−0.04%; p < 0.007). Fat content was affected by animal breed, lactation stage, type and processing of oilseed and dietary NDF and LA contents. CLA, LA, OA and UFA, desirable FA milk components, were affected by type, processing, and the intake of oilseed; additionally, the concentrations of CLA and VA are affected by washout and design. Oilseed supplementation in dairy cow rations has a positive effect on desirable milk components for human consumption. However, animal response to oilseed supplementation depends on explanatory variables related to experimental design, animal characteristics and the type of oilseed.

Keywords: CLA; atherogenic index; experimental design; milk fatty acid; roasted; washout.

Figure 1

Flowchart of the systematic review (PRISMA) from the initial search to the selection of the articles included in this review.

Figure 2

Forest plot of fat content (g 100 g⁻¹) for trials with the inclusion of oilseeds in dairy cow diets, grouped by type of oilseed. Point size reflects the relative weighting of the study to the overall effect size estimated, where a larger point size represents a greater weight and the combined effect size estimated, including the confidence intervals. The diamond represents the overall effect. RMD, raw mean difference.

Figure 3

Forest plot of vaccenic fatty acid (VA; g 100 g⁻¹ FA) for trials with the inclusion of oilseeds in dairy cow diets, grouped by type of oilseed. Point size reflects the relative weighting of the study to the overall effect size estimated, where a larger point size represents a greater weight and the combined effect size estimated, including the confidence intervals. The diamond represents the overall effect. RMD, raw mean difference.

Figure 4

Forest plot of conjugated linoleic acid (CLA; g 100 g⁻¹ FA) for trials with the inclusion of oilseeds in dairy cow diets, grouped by type of oilseed. Point size reflects the relative weighting of the study to the overall effect size estimated, where a larger point size represents a greater weight and the combined effect size estimated, including the confidence interval. The diamond represents the overall effect. RMD, raw mean difference.

Figure 5

Forest plot of Σ omega-3 PUFA (g 100 g⁻¹ FA) for trials with the inclusion of oilseeds in dairy cow diets, grouped by oilseed processing. Point size reflects the relative weighting of the study to the overall effect size estimated, where a larger point size represents a greater weight and the combined effect size estimated, including the confidence intervals. The diamond represents the overall effect. RMD, raw mean difference [25,29,33,35,37,38,40,41,43,48,50,53].

Figure 6

Bubble plot of UFA (g 100 g⁻¹ FA) of the raw mean difference. Inclusion level of oilseeds is represented by the size of the point with the value to the left (%); the color of the point indicates the type of oilseed.

Figure 7

Bubble plot of AI of the raw mean difference. Inclusion level of oilseeds is represented by the size of the point with the value to the left (%); the color of the point indicates the type of oilseed.