Effect of feeding high or low portions of concentrate during the transition period on serum adiponectin concentrations and mRNA expression of adiponectin and its receptors in subcutaneous and retroperitoneal fat of dairy cows
The mRNA expression of adiponectin (ADIPOQ) and its receptors ADIPOR1/2 in adipose tissue (AT) decreases with the onset of lactation in dairy cows; the serum concentrations of ADIPOQ have also been demonstrated to drop during the lactation-induced negative energy balance (NEB) but not during feed-restriction induced NEB at later stages of lactation (Singh et al., 2014, doi:10.3168/jds.2013-7598). As to whether the extent of NEB during the lactation-induced NEB may affect ADIPOQ system was not known and we thus hypothesized that the ADIPOQ system will be affected by feeding different portions of concentrate in the diet throughout the transition period, and that visceral (VC) and subcutaneous (SCAT) respond concordantly. Twenty pluriparous German Holstein cows were fed with rations containing either 60% (HC) or 30% (LC) concentrate (DM basis, n=10 per group) from d 1-21 postpartum. The SCAT (tail head) and RPAT were biopsied at d −21, 1 and 21 relative to parturition. Blood samples were collected weekly. ADIPOQ and AdipoR1/2 mRNA abundances were quantified by qPCR, and serum ADIPOQ by ELISA. The statistical analyses were performed using SPSS 21.0 (P<0.05).
The NEB was more negative in LC than in HC animals (Δ=18.5 MJ/d, third week of lactation). Effects of diet were limited to ADIPOQ in SCAT, with 4.1-fold lower mRNA abundance in LC than in HC at d 21 (P<0.02). With the exception of AdipoR2 mRNA in RPAT, we detected time-related changes in SC and RPAT with higher abundances ante partum (P<0.05) for all target mRNAs, and for ADIPOQ in serum. AdipoR2 mRNA abundance in RPAT was highest at d 1. Irrespective of time, ADIPOQ and AdipoR2 expression was higher in RPAT than in SCAT (P<0.05), whereas AdipoR1 mRNA abundance was not different between both tissues. ADIPOQ and AdipoR1 mRNA abundance were positively correlated in SCAT (r=0.461, P<0.01) and RPAT (r=0.745, P<0.01). AdipoR1 and AdipoR2 were correlated in SCAT (r=0.422, P<0.01). The lower ADIPOQ mRNA abundance in SCAT of the LC group points to greater responsiveness towards dietary effects in this depot; however, this was apparently not reflected in serum ADIPOQ indicating that other fat depots might compensate the decrease. The observed time-related changes in SCAT and of serum ADIPOQ confirm earlier reports, whereas the likewise regulation in RPAT for ADIPOQ and AdipoR1 has not been previously investigated in cows. The correlation between ADIPOQ and AdipoR1 mRNA abundances points to a co-regulation of both genes in AT.