T392
Hepatic expression of genes related with fatty acid metabolism in Holstein cows with different feeding strategies in early lactation
Multiparous cows (n=25) were used in a randomized complete block design to study the effects of nutrition during the first 60 d postpartum (DPP) on hepatic expression of genes associated with fatty acid oxidation. Cows were assigned to 3 treatments (TREAT): TMR= total mixed ration (30 kg DM/d offered; 45% forage, 55% concentrate); G1= 50% pasture in one (am) grazing session (6 h; pasture allowance =15 kg DM/d) + 50% TMR (15 kg DM/d offered) and G2= 50% pasture in two (am/pm) grazing sessions (9 h; pasture allowance =15 kg DM/d) + 50% TMR (15 kg DM/d offered). Liver biopsies were collected at -40, -20, +10 and +55 DPP to measure the abundance of mRNA of pyruvate dehydrogenase (PDH1A) and pyruvate dehydrogenase kinase (PDK), acyl-CoA dehydrogenase, very long chain (ACADVL), acyl-CoA oxidase (ACoAoX), carnitine palmitoyltransferase-1A (CPT1A), β- hydroxy-β-methylglutaryl-coenzyme A (HMGCOA) and citrate synthase (CS) by SYBR-Green real time RT-PCR. Data were analyzed in a mixed model using a repeated measures analysis. Milk energy output did not differ among TREAT (27.8, 26.4 and 23.4 ± 1.4 Mcal/d for TMR, G1 and G2, respectively) while BCS decreased (P<0.05) during the postpartum and at +55 DPP was greater (P=0.02) in TMR than G1 and G2 cows. Hepatic expression of ACADVL, ACOX, and CPT1A and HMGCOA mRNA increased (P<0.03) from pre to postpartum. The PDK mRNA tended (P=0.06) to increase from pre to postpartum. Expression of ACADVL mRNA tended (P=0.06) to be affected by the TREAT by DPP interaction, being greater in G2 than TMR cows at +55 DPP (1.18, 1.50 and 2.19 ± 0.2 for TMR, G1 and G2, respectively). The CPT1A mRNA was greater (P=0.03) in G1 than G2 cows (1.83 and 1.30 ± 0.3 for G1 and G2, respectively) and HMGCOA mRNA was greater (P=0.05) in G2 than TMR cows (0.90 and 1.35 ± 0.2 for TMR, and G2, respectively) during the postpartum period. Hepatic AOX, PDK, PDH1A and CS mRNA were not affected by TREAT. Results indicate that hepatic expression of fatty acid oxidation and ketogenesis genes increased in early lactation to cope with negative energy balance. This increase was greater in G2 than TMR cows which could be associated to the greater energy requirement for maintenance due to the activity of walking and grazing in the former ones
Keywords: nutrition, hepatic expression, dairy cows.