216 EFFECTS OF DIFFERENT POLYUNSATURATED FATTY ACID SUPPLEMENTATION DURING THE POSTPARTUM PERIODS OF EARLY LACTATING DAIRY COWS ON INSULIN RESISTANCE AND SOMATOTROPIC AXIS

Abstract

During periods of negative energy balance, GH cannot stimulate hepatic IGF-1; the condition is termed GH resistance (Donaghy and Baxter, 1996). Studies show that insulin may be a key metabolic signal that regulates the coupling of the somatotropic axis (Butler et al., 2003). The objectives were to test the hypothesis that α-linoleic acid (n-3), or linoleic acid (n-6) could promote insulin resistance in dairy cows. For this goal, Holstein cows were assigned randomly to be fed either 1-soybean whole roast (S, n = 4), or 2-linseed extruded (L, n = 4), or 3-palm oil use a source of saturated fatty acid (C, n = 4), respectively, from calving to 60 DIM. Three diets were formulated to have equal concentrations of DM, ME, and CP, but to differ in ratio of n-3/n-6 PUFA (4.2, 1.2, and 3.2 for S, L, and C treatments, respectively). Supplementation of FA was at 1.5% of dietary dry matter. There was no difference between groups (mean ± SEM) in parity (3.0 ± 1.90) or BCS at calving day (3.2 ± 0.07). At Day 60 postpartum, liver tissues (~100 mg) were collected by needle biopsy as described by Rhoads et al. (2008) with minor modifications. Liver tissue was washed with sterile PBS, placed in a screw-cap micro centrifuge tube, snap-frozen in liquid nitrogen, and stored at –80°C until RNA extraction. We applied real-time PCR for measurement of mRNA abundance. Real-time PCR was executed in triplicate. Reaction mixtures for real-time PCR included 1.5 µL of cDNA as template, 7.5 µL of SYBRR Green PCR Master Mix (ABI, USA), 1 µL of forward primer, 1 µL of reverse primer, and 4 µL of double distilled water. The efficiencies for GHR1A, insulin receptor (IR), IGF-I, and IGFBP-2 were 1.22, 0.99, 1.02, and 1 with an R² of 0.99 or above for the regression. We used the 2–ΔΔCt method in this model. Rotor Gene analysis software (version 6.0) was used to analyse all the results from the PCR assays. Data were analysed using the MIXED procedure of SAS (2000, SAS Institute Inc., Cary, NC, USA), in a completely randomised design. Results showed that supplementation with a high level of flaxseed on treatment L for 2 months increased levels of IR mRNA compared with S and C treatments (P < 0.05). The levels of IR mRNA were not different between S and C treatments (P = 0.202). There was also a strong tendency towards a 2.2-fold increase (P = 0.06) in GHR1A gene expression in cows on the flaxseed diet compared with the other diets, also there were no significant difference between S and C treatments. The IGF-I and IGFBP mRNA were not different between the treatments (P > 0.05). In conclusion, n-3 fatty acids promoted insulin resistance via increasing insulin receptor signalling that could improve milk production and specifically fertility in lactating dairy cows.