Variations in the milk lipidomic profile of lactating dairy cows fed the diets containing alfalfa hay versus alfalfa silage

Abstract

Alfalfa is primarily stored as silage or hay in livestock production. Previous research has shown that the storage method of grass significantly influences milk composition. This study aimed to investigate milk production performance and lipid composition in dairy cows fed diets consisting of alfalfa hay or alfalfa silage as roughage. Forty-two mid-lactation Holstein dairy cows were selected and randomly divided into three groups, each receiving a total mixed ration consisting of alfalfa hay (AH), 50% alfalfa silage + 50% alfalfa hay (AHAS), or alfalfa silage (AS). The results showed that milk fat content (P = 0.049) and milk fat yield (P < 0.001) were significantly higher in the AH and AHAS groups compared to the AH group. With increased supplementation of alfalfa silage in the diet, ω-3 polyunsaturated fatty acid content increased significantly (P < 0.001), while ω-6 polyunsaturated fatty acid content (P = 0.007) and the ratio of ω-6 to ω-3 polyunsaturated fatty acids decreased (P < 0.001). The contents of sphingomyelins, phosphatidylserines, phosphatidylethanolamines, and phosphatidylglycerols in the AHAS and AS samples were higher than in the AH samples, although the differences were not statistically significant. Additionally, the content of phosphatidylcholines was significantly higher in the AS group compared to the AH group (P = 0.032). In conclusion, feeding dairy cows a diet consisting of alfalfa silage can increase the major phospholipid content and polyunsaturated fatty acid composition in raw milk, which is more conducive to human health. These findings provide valuable insights into the benefits of alfalfa silage for dairy cows.

Keywords: Alfalfa hay; Alfalfa silage; Dairy cow; Fatty acid; Lipidomic profile; Milk fat.

Fig. 1

The fatty acid (FA) concentrations among three groups. AH, the diet containing alfalfa hay; AHAS, the diet containing 50% alfalfa hay and 50% alfalfa silage; AS, the diet containing alfalfa silage. (A, B and C) Percentages of FA < C10, C11 to C16, and > C17, respectively. The different letters on the bars indicate significant differences between the three groups (P < 0.05).

Fig. 2

Lipid subclasses and molecules in the milk of dairy cows. AH, the diet containing alfalfa hay; AHAS, the diet containing 50% alfalfa hay and 50% alfalfa silage; AS, the diet containing alfalfa silage. (A) The number of lipids in each subclass. (B) The percentage distribution map of lipid subclasses. (C) The principal component analysis (PCA) plot of individual lipid molecules among the three treatments. (D) The heatmap of differential lipid molecules. (E) The differences of each lipid subclass of AHAS and AS compared to AH group. ∗, P < 0.05; ∗∗, P < 0.01. Cer = ceramides; DAG = diacylglycerols; Hex1Cer = monohexosylceramide; Hex2Cer = dihexosylceramide; LPC = lysophosphatidylcholine; LPE = lysophosphatidylethanolamine; LPG = Lysophosphatidylglycerols; LPI = lysophosphatidylinositol; LPS = lysophosphatidylserine; PA = phosphatidic acids; PC = phosphatidylcholines; PE = phosphatidylethanolamines; PG = phosphatidylglycerols; PI = phosphatidylinositols; PS = phosphatidylserines; SM = sphingomyelins; SPH = sphingosine; TAG = triacylglycerol.

Fig. 3

Pair-wise comparisons of lipid molecules among three dietary treatments. (A, B, and C) The differential lipids between AH and AHAS, AH and AS, and AHAS and AS, respectively. (D) The number of differential lipids in each subclass. AH mean the diet containing alfalfa hay; AHAS means the diet containing 50% alfalfa hay and 50% alfalfa silage; AS means the diet containing alfalfa silage. DE_Meta means the differential metabolites; DW means down; NoDiff means the undeferential metabolites. Cer = ceramides; DAG = diacylglycerols; Hex1Cer = monohexosylceramide; Hex2Cer = dihexosylceramide; LPC = lysophosphatidylcholine; LPE = lysophosphatidylethanolamine; LPG = lysophosphatidylglycerols; LPI = lysophosphatidylinositol; LPS = lysophosphatidylserine; PA = phosphatidic acids; PC = phosphatidylcholines; PE = phosphatidylethanolamines; PG = phosphatidylglycerols; PI = phosphatidylinositols; PS = phosphatidylserines; SM = sphingomyelins; SPH = sphingosine; TAG = triacylglycerol.

Fig. 4

Differences in milk lipid molecules among the three dietary treatments. AH, the diet containing alfalfa hay; AHAS, the diet containing 50% alfalfa hay and 50% alfalfa silage; AS, the diet containing alfalfa silage. (A, B, C, D, E, and F) The differential lipids in TAG, DAG, PC, PE, Hex1Cer, Hex2Cer, respectively. (G) The differential lipids in PS, PI and PG. (H) The differential lipids in SM and Cer. (I) The differential lipids in LPC, LPE, LPS, LPG, LPI, AcCa, and PA. ∗, P < 0.05; ∗∗, P < 0.01; ∗∗∗, P < 0.001. Cer = ceramides; DAG = diacylglycerols; Hex1Cer = monohexosylceramide; Hex2Cer = dihexosylceramide; LPC = lysophosphatidylcholine; LPE = lysophosphatidylethanolamine; LPG = lysophosphatidylglycerols; LPI = lysophosphatidylinositol; LPS = lysophosphatidylserine; PA = phosphatidic acids; PC = phosphatidylcholines; PE = phosphatidylethanolamines; PG = phosphatidylglycerols; PI = phosphatidylinositols; PS = phosphatidylserines; SM = sphingomyelins; SPH = sphingosine; TAG = triacylglycerol.