Body condition score and day of lactation regulate fatty acid metabolism in milk somatic cells and adipose tissue of beef cows

We hypothesized that body condition score (BCS) at parturition and day of lactation will alter transcript abundance of mammary and adipose tissue lipogenic enzymes, as well as adipose tissue protein concentrations of lipogenic and transcription factors during early lactation in beef cows fed supplemental fat. Beginning 3 d postpartum three-year-old Angus × Gelbvieh beef cows nutritionally managed to achieve a BCS of 4 ± 0.07 (BW = 479 ± 36 kg; n = 18) or 6 ± 0.07 (BW = 579 ± 53 kg; n = 18) at parturition were assigned to a hay diet plus low-fat control supplement or high-fat supplements (isonitrogenous and isocaloric with 5% of DMI as fat) until day 60 of lactation. At day 30 and day 60 of lactation, somatic cells from 300 mL of milk were collected for ribonuclease protection assay as a measure mammary transcript abundance for lipoprotein lipase (LPL), acetyl-CoA carboxylase (ACC), fatty acid synthase (FAS), and stearoyl-CoA desaturase (SCD). Abundance of mRNA was greater for FAS (P = 0.02) and SCD (P = 0.04) in cows of BCS 4 compared with 6. By using RT-PCR to quantify mRNA in biopsies of adipose tissue we determined that BCS 4 cows had less mRNA for LPL (P < 0.001) and hormone sensitive lipase (HSL) (P = 0.05) compared with BCS 6 cows. Abundance of LPL mRNA was lower (P = 0.001) at day 30 postpartum compared to day 60; whereas, HSL mRNA was greater at day 30 (P < 0.001). Concentration of CD36 protein was greater (P = 0.03) in the BCS 6 cow adipose tissue. Both signal transducer and activator of transcription-subtype 5 (STAT-5) (P < 0.001) and peroxisome-proliferator activated receptor-subtype gamma (PPAR-λ) (P = 0.05) were greater at day 30 compared to day 60 postpartum. We conclude that abundance of mammary gland lipogenic enzyme mRNA was mainly affected by BCS at parturition; whereas, in adipose tissue, mRNA for enzymes for fatty acid uptake and mobilization, as well as fatty acid transport were affected by both BCS and day of lactation. Also, data suggest there was a shift in nutrient partitioning away from the mammary gland to subcutaneous adipose tissue at 60 d postpartum in beef cows.