Abstract
The aim of this paper was to investigate the effects of soybean oil, an oilseed rich in the polyunsaturated fatty acid C18:2, on dry matter intake (DMI), milk yield (MY) and milk composition (including fatty acid profile) of dairy cows by using a meta-analysis approach. In the meta-analysis, effect size for all outcomes was reported as standardised means difference with 95% confidence intervals. Q test and I2 were calculated to detect the heterogeneity, with a meta-regression also used to investigate sources of heterogeneity. Results of the meta-analysis indicated that adding soybean oil to the diet of dairy cows decreased DMI, milk fat percentage (MFP), milk fat yield (MFY) and milk protein percentage (MPP), whilst significantly increasing MY. Unsaturated fatty acids C18:2, C18:1 trans-11 and C18:2 cis-9 trans-11 conjugated linoleic acid (CLA) all significantly increased with soybean oil inclusion in the diet, whereas C18:3 was numerically higher but not significantly different. Milk composition, including MFP, MFY, MPP, short-chain and medium-chain fatty acids (C4–C20) and unsaturated fatty acids showed a significant percentage of heterogeneity. Results of the meta-regression indicated that dose of soybean oil, total fatty acids in the diet, and the concentration of C18:2 between groups receiving soybean oil and control are the most important factors affecting this heterogeneity. By performing meta-analysis and meta-regression it can be concluded that dietary supplementation of soybean oil to lactating dairy cows decreased DMI, and increased MY and the amount of unsaturated fatty acids in milk.HighlightsSoybean oil dietary supplementation to dairy cows increased milk yield but reduced milk fat content.Milk fat in soybean oil dietary supplemented cows has a lower content of short-chain fatty acids, associated with de novo synthesis.Milk fat in soybean oil dietary supplemented cows has a higher content of C18:1 trans-11, C18:2 and CLA.
Highlights
Nutrition plays an important role in human health with significant interest shown towards the composition of animal-based products, including dairy, in certain diseases such as: cancer, cardiovascular disease and diabetes (Conto et al 2017)
The purpose of this study was to use a meta-analysis approach to determine the effect of soybean oil supplementation on milk yield (MY), dry matter intake (DMI), milk composition and fatty acid profile in lactating dairy cows and further examine the reasons for the heterogeneity of responses observed using meta-regression
For the meta-analysis, papers were included, as Dhiman et al (2000) reported two studies studies were used in total
Summary
Nutrition plays an important role in human health with significant interest shown towards the composition of animal-based products, including dairy, in certain diseases such as: cancer, cardiovascular disease and diabetes (Conto et al 2017). Studies have shown that the presence of saturated fatty acids C14 and C16, as well as certain trans fatty acids (trans isomers of C18:1) increase the risk of cardiovascular disease. Siri-Tarino et al (2010) reported in a metaanalysis study that there is no significant evidence for concluding that dietary saturated fat is associated with an increased risk of cardiovascular disease. Other fatty acids have been shown to have beneficial effects for human health, e.g. mono- and polyunsaturated fatty acids and certain trans fatty acids such as conjugated linoleic acid (CLA cis-9 trans-11, Givens 2010; Shingfield et al 2013). CLA refers to the local and geometric isomers of linoleic fatty acids, which within milk 82% are the isomer cis-9 trans-11
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