Lipogenic enzyme mRNA of milk and adipose tissue of lactating beef cows and their calves: Influence of day of lactation, maternal dietary fat supplementation, and body condition score

Initially, it was determined that beef cow milk somatic cells could be used as reliable source of mRNA to study mammary gland lipogenesis. Significant, positive correlation coefficients (r = 0.68 to 0.90; P = 0.001 to 0.05) allowed the use of a non-invasive method to obtain mRNA for quantification of lipogenic enzymes in mammary tissue during lactation in beef cows. Following validation of beef cow milk somatic cells as a reliable source of lipogenic mRNA, our objective was to measure lipogenic mRNA in milk somatic cells of three-year-old Angus x Gelbvieh beef cows nutritionally managed to achieve a BCS of 4 or 6 at parturition. Our second objective was to determine suckling calf adipose tissue lipogenic enzyme mRNA abundance at d 60 of lactation. Cows within each BCS were assigned to a hay diet plus low-fat control supplement or supplements with either cracked high-linoleate or cracked high-oleate safflower seeds until d 60 of lactation. At d 30 and d 60 of lactation, milk somatic cells were collected to measure mRNA abundance for lipoprotein lipase (LPL), acetyl-CoA carboxylase ( ACC), fatty acid synthase (FAS), and stearoyl-CoA desaturase (SCD). Western blot analysis was used quantify cow adipose tissue signal transducer and activator of transcription-subtype 5 (STAT-5) and peroxisome-proliferator activated receptor-subtype gamma (PPAR-gamma ). Milk somatic cell mRNA was greater for FAS (P = 0.02) and SCD (P = 0.04), and tended to be greater for LPL (P = 0.13) and ACC (P = 0.16) in cows of BCS 4 compared with 6. From d 30 to d 60 of lactation, milk somatic cell LPL mRNA increased (P = 0.002), whereas FAS mRNA decreased ( P = 0.004). Adipose tissue of BCS 4 cows had less mRNA for LPL ( P = 0.001) and hormone-sensitive lipase (HSL; P = 0.10) compared with BCS 6 cows. Protein abundance of PPAR-gamma was lower (P = 0.001) in adipose tissue BCS 4 cows compared to BCS 6. Abundance of LPL mRNA was lower (P = 0.002) at d 30 postpartum compared to d 60; whereas, HSL mRNA was greater ( P < 0.001) at d 30 in cow adipose tissue. Both STAT-5 ( P < 0.0001) and PPAR-gamma (P = 0.05) were greater in adipose tissue at d 30 compared to d 60 of lactation. Neither maternal dietary treatment nor maternal BCS affected lipogenic enzyme mRNA abundance in suckling calf adipose tissue. Quantification of lipogenic mRNA in milk somatic cells and adipose tissue of beef cows during lactation will provide valuable information regarding nutrient partitioning. Furthermore, this information will allow the producer to make sound decisions regarding dietary fat supplements to offset the nutritional demands of lactation and help subsequent reproduction.