Metabolomic profiles of colostrum and milk from lactating sows

Survival and growth of suckling piglets is highly dependent on the nutrients, growth factors, and protective components provided by sow colostrum and milk. The macrochemical composition undergoes large alterations during the lactation period, but knowledge of the composition and variation of low molecular weight metabolites is presently lacking. Samples of colostrum at 0, 12, 24, and 36 h and milk samples on Day 3, 10, 17, and 24 relative to farrowing were collected from 4 s parity sows fed a standard lactation diet. Samples were analyzed using a nontargeted metabolomics approach. Sample preparation was done by eliminating fat through centrifugation and precipitation of proteins with trichloracetic acid and acetonitrile. Metabolite profiles were obtained with an ESI-QTOF mass spectrometer after separation on a C18 column. Principal component analysis (PCA) was used to observe data distribution and the variables responsible for separation. PCA revealed data clustering according to sample type, with differences observed between colostrum and milk for both ionization modes. Positive ionization revealed a number of highly influential metabolites, such as L-carnitine, acyl esters of carnitine (L-acetylcarnitine, 2-metylbutyroylcarnitine), glycerophosphocholine, and betaine. L-Acetylcarnitine and 2-metylbutyroylcarnitine, involved in the metabolism and transport of fatty acids, decreased in milk compared to colostrum, whereas L-carnitine presented an opposite trend (P < 0.05). Similarly, glycerophosphocholine and choline decreased from colostrum to milk, whereas betaine showed higher values in milk compared to colostrum. The use of liquid chromatography-mass spectrometry metabolomics as a hypothesis generator tool opens up new questions with regard to the origin and function of mammary gland metabolites and the changes that occur during lactation.