The onset of lactation in dairy cows is characterized by severe negative energy and protein balance. Methionine availability during this time for milk production, hepatic lipid metabolism, and immune function may be limiting. Supplementing Met to peripartal diets with adequate Lys in metabolizable protein (MP) to fine-tune the Lys:Met ratio may be beneficial. Fifty-six multiparous Holstein cows were fed the same basal diet from 50 d before expected calving to 30 d in milk. From -50 to -21 d before expected calving, all cows received the same diet [1.24 Mcal/kg of dry matter (DM), 10.3% rumen-degradable protein, and 4% rumen-undegradable protein] with no Met supplementation. From -21 d to expected calving, the cows received diets (1.54 Mcal/kg of DM, 10% rumen-degradable protein, and 5.1% rumen-undegradable protein) with no added Met (control, CON; n=14), CON plus MetaSmart (MS; Adisseo Inc., Antony, France; n=12), or CON plus Smartamine M (SM; Adisseo Inc.; n=12). From calving through 30 d in milk, the cows received the same postpartum diet (1.75 Mcal/kg of DM and 17.5% CP; CON), or the CON plus MS or CON plus SM. The Met supplements were adjusted daily and top-dressed over the total mixed ration at a rate of 0.19 or 0.07% (DM) of feed for MS or SM. Liver tissue was collected on -10, 7, and 21 d, and blood samples more frequently, from -21 through 21 d. Data were analyzed using the MIXED procedure of SAS (SAS Institute Inc., Cary, NC) with the preplanned contrasts CON versus SM + MS and SM versus MS. No differences in prepartal DM intake (DMI) or body condition score were observed. After calving, body condition score was lower (2.6 vs. 2.8), whereas DMI was greater (15.4 vs. 13.3 kg/d) for Met-supplemented cows. Postpartal diet × time interactions were observed for milk fat percentage, milk fat yield, energy-corrected milk:DMI ratio, and energy balance. These were mainly due to changes among time points across all treatments. Cows supplemented with either Met source increased milk yield, milk protein percentage, energy-corrected milk, and milk fat yield by 3.4 kg/d, 0.18% units, 3.9 kg/d, and 0.18 kg/d, respectively. Those responses were associated with greater postpartum concentration of growth hormone but not insulin-like growth factor 1. There was a diet × time effect for nonesterified fatty acid concentration due to greater values on d 7 for MS; however, liver concentration of triacylglycerol was not affected by diet or diet × time but increased postpartum. Blood neutrophil phagocytosis at 21 d was greater with Met supplementation, suggesting better immune function. Supplemental MS or SM resulted in a tendency for lower incidence of ketosis postpartum. Although supplemental MS or SM did not decrease liver triacylglycerol, it improved milk production-related traits by enhancing voluntary DMI.

Osorio JS, Lohakare J, Bionaz M. Biosynthesis of milk fat, protein, and lactose: roles of transcriptional and posttranscriptional regulation.

Mechanisms regulating subcutaneous adipose tissue (SAT) insulin sensitivity and gene network expression during the peripartal period were evaluated in cows fed to meet or exceed prepartal energy requirements. Holstein cows were dried off at -50 d relative to expected parturition and fed a controlled-energy diet [CON; net energy for lactation=1.24 Mcal/kg of dry matter (DM); 36% of DM as wheat straw] until -21 d. Cows were then randomly assigned (n=7/diet) to either the same CON diet or a moderate-energy close-up diet (OVE; net energy for lactation=1.47 Mcal/kg of DM) until parturition. Biopsies of SAT were harvested at -10, 7, and 21 d for mRNA expression of 48 genes associated with insulin signaling, adipogenesis, and lipolysis. In vitro basal and insulin-stimulated insulin receptor substrate 1 tyrosine phosphorylation (IRS1-PY) was assessed at -10 and 7 d. The OVE led to more positive energy balance and greater serum insulin concentration prepartum. Compared with CON, OVE led to a more drastic increase in serum NEFA and also greater overall serum BHBA postcalving, both of which were associated with greater hepatic total lipid and triacylglycerol concentration. Close-up OVE did not improve any aspect of performance. In prepartal SAT, insulin-stimulated IRS1-PY was greater in OVE than in CON. However, IRS1-PY, serum insulin, and GLUT4 expression decreased postpartum regardless of prepartal treatment, suggesting a more severe state of insulin resistance. The expression of all genes encoding adipogenic regulators (PPARG and ZFP423), most lipogenic enzymes/inducers (FASN, SCD, DGAT2, and INSIG1), and basal-lipolysis regulators (ATGL and ABDH5) was greater at -10 d in OVE than in CON. Whereas adipogenic and basal lipolysis regulator expression remained greater in cows fed OVE by 7 d postpartum, expression of all lipogenic enzymes decreased regardless of diet. Despite those responses, the approximately 3-fold increase in expression of IRS1 and ZFP423 between 7 and 21 d suggested that insulin responsiveness and adipogenic capacity of SAT were partially restored. Expression of the preadipocyte marker DLK1, adiponutrin (PNPLA3), and fibroblast growth factor 21 (FGF21) was undetectable. Results suggested that close-up energy overfeeding did not exacerbate insulin resistance in SAT. Signs of restored insulin responsiveness (upregulation of IRS1, INSIG2, SREBF1, and ZFP423) were apparent as early as 3 wk postpartum. Thus, identifying specific nutrients capable of activating PPARγ after calving in AT might help accelerate its replenishment. A regulatory network encompassing the genes and physiological measurements obtained is proposed.