Shotgun proteome analysis of homogenate milk samples reveals dynamic changes in milk proteins across sow lactation and relative abundance of proteins to each other.

Milk is an easily digestible source of nutrients and bioactive factors, and its composition reflects the neonate's needs and changes from colostrum to transitional and mature milk. Our objective was to measure milk fat, lactose, total carbohydrate, and protein content in parallel with global proteome of homogenate milk samples to characterize changes across the three phases of swine lactation. Milk samples were collected from multiparous sows (n=9) on postnatal day 0 (D0; colostrum), 3 (D3; early transitional), 7 (D7; late transitional) and 14 (D14; mature). On D3 percent fat (16 ± 2.1) and lactose (3.8 ± 0.27) were higher (p<0.05) than on D0 (10 ± 3.9, and 1.5 ± 0.30; respectively). Levels of fat and lactose were not different between D3 and D14. Percent protein decreased (p<0.05) between D0 (11 ± 2.11) and D3 (5 ± 0.74), but there was no significant change in percent protein between D3 and D14. Total carbohydrates increased (p<0.05) between D3 (944 ± 353 µg/ml) and D14 (1150 ± 462 µg/ml). Liquid chromatography tandem mass spectrometry proteomic analysis of homogenate D0, D3, and D14 milk samples (n=6) identified 772 proteins corresponding to 501 non-redundant protein-coding genes, of which 207 proteins were high confidence (detected in n=3 sows/day). Of the high confidence proteins, 81 were common to all days. Among the proteins that changed between the days was the decrease in multiple apolipoproteins and the milk fat globule membrane protein XDH. There were variable changes in complement factors, whereas14-3-3 proteins (YWHAQ, YWHAE) increased across the days (FDR < 0.05). Our data provide a good characterization of milk proteome changes that likely reflect mammary function as well as the neonate's phase-specific developmental needs. This data may be useful in developing approaches to enhance the health and welfare of swine.