No abstract

Periparturient dairy cattle are susceptible to metabolic disease due to immense physiological stress caused by calving and the onset of lactation. Susceptibility to disease is related to the cow’s ability to maintain metabolic homeostasis and mount a proper immune response, despite high demand for glucose to support fetal growth and milk synthesis, and as a fuel for increased circulating levels of white blood cells (WBC). This study was conducted to determine if there was a correlation among white blood cell percentages, blood glucose, and the levels of the ketone betahydroxybutyrate (BHBA) on the days immediately around parturition, and to determine if the variables exhibited circadian rhythms. We hypothesized that glucose levels would vary inversely with WBC, and BHBA levels would vary directly with glucose levels. Blood was sampled from the tail vein of multiparous Holstein cows (n=12) at 0600 from 4 days prepartum to 4 days postpartum, and every 4 hr over a 24-hr period (n=6) starting at 0600 on postpartum day 3.  Blood glucose and BHBA levels were measured using a CentriVet™, and WBC percentage was calculated by measuring packed cell volume. Glucose was higher (p<0.05) before (73.77 mg/dL±4.65) versus after (68.85 mg/dL±6.15) parturition, whereas BHBA was higher (p<0.05) after calving (0.53 mg/dL±0.39) versus before (0.20 mg/dL±0.16). WBC percentages did not vary significantly by day. None of the variables exhibited circadian rhythms according to cosinor analysis. Pearson’s correlation analysis revealed an inverse relationship (r= -0.23, p=0.04) between glucose and BHBA levels, and a direct relationship between WBC percentage and BHBA (r= 0.25, p=0.03).  This finding supported our hypothesis, and suggests that immune responses during the periparturient period may affect metabolic homeostasis.

Milk is an easily digestible source of nutrients and bioactive factors, 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 ± 0.3) were higher (P&lt;0.05) than on D0 (10 ± 3.9, and 1.5 ± 0.3; respectively). Levels of fat and lactose were not different between D3 and D14. Percent total protein decreased (P&lt;0.05) between D0 (11 ± 2.1) and D3 (5 ± 0.7), but there was no significant change in percent protein between D3 and D14. Total carbohydrates increased (P&lt;0.05) between D3 (944 ± 353 µg/ml) and D14 (1150 ± 462 µg/ml). Quantitative proteomic analysis using liquid chromatography tandem mass spectrometry (LC-MS/MS) of homogenate D0, D3, and D14 milk samples (n=6) identified 772 protein groups which corresponded to 501 individual protein-coding genes. A total of 207 high confidence proteins were detected in n=3 sows/day. Of the high confidence proteins, 81 proteins were common amongst all three days of lactation. Among the proteins that decreased between the days (FDR &lt; 0.05) were multiple apolipoproteins and XDH which decreased between D0 to D3. Proteins that increased across the days (FDR &lt; 0.05) were complement factors and14-3-3 proteins (YWHAQ, YWHAE). 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.

Sow milk fat content is crucial to neonatal survival, as it is utilized for thermogenesis and nutrition. However, fat is the most variable component of milk in concentration and lipid species. Characterizing lipid changes across the course of a sow’s lactation may help identify molecules or systems to target to help enhance milk fat quality and quantity for neonatal survival and growth. Percent fat variation is greatest in colostrum, the first milk. Little is known regarding colostrum synthesis, other than it accumulates in the gland beginning in mid-late pregnancy, which is prior to the initiation of fatty acid synthesis in lactocytes. The objective of this study was to characterize changes in lipid composition of milk across the course of lactation and determine if there was a relationship between fat percent and lipid species in colostrum and mature milk. Milk was collected from 9 multiparous sows on days 0, 3, 7, and 14 relative to birth. Percent fat was determined by creamatocrit, and found to be different (p&lt; 0.05) between day 0 (12.36 ± 5.90%) and day 3 (16.22 ± 3.65%) but not between day 7 (13.13 ± 2.19%) and 14 (12.13 ± 2.45%). Fat was extracted from milk using the Bligh-Dyer method and profiled using multiple reaction monitoring. Amounts of lipid species were calculated relative to standards and data analysis was performed using Metaboanalyst 4.0. Principle component analysis revealed lactation day had a significant effect on distribution of fats. Triacylglycerides (TAG), phosphatidylglycerol (PG), and plasma membrane lipids were modified from colostrum to mature milk, with a significant increase in PGs and TAGs across the course of lactation. Correlation analysis of percent fat with lipid concentration indicated strong relationships (P &lt; 0.05; |r| &gt;0.80) with eight lipids. No differences are found in the abundance of plasma membrane phospholipids, sphingomyelin, or cholesterol esters across lactation days.