ENDOMETRIAL GENE EXPRESSION IN PRIMIPAROUS DAIRY COWS GRAZING DIFFERENT SWARD HERBAGE ALLOWANCES

Abstract Text: Primiparous Holstein dairy cows (n = 44, 595 ± 41 kg of BW, 3.7 ± 0.3 of BCS) were used in a randomized block design to study the effect of different herbage allowances on endometrial gene expression at day 7 of the estrous cycle. Cows were assigned to three grazing treatments (TREAT; n=11 each): high (HA, 30 kgDM/cow/d), medium (MA, 15 kgDM/cow/d) and low (LA, 7.5 kgDM/cow/d) herbage allowance (mixed pasture, 2600 kgDM/ha) or to a total mixed ratio (55% forage, 45% concentrate) fed ad-libitum (TMR) from calving to 56 days postpartum (DPP). At 57 DPP, estrous cycles were synchronized (intravaginal progesterone insert and PGF2alpha injection) and estrus was detected twice a day. At day 7 of the estrous cycle uterine biopsies were obtained to measure mRNA expression of insulin, leptin and adiponectin receptors (INSR, LEPR-long isoform, ADIPOR1 and ADIPOR2, respectively) by SYBR-Green real time RT-PCR. Data were normalized to the expression of three internal control genes and analyzed in a mixed model using TREAT and occurrence of ovulation (yes/no) as fixed effects and block as a random effect. All cows mobilized BCS after calving (0.5 units for TMR and HA and 1 unit for MA and LA cows). Ovulation rate after synchronization (55%) did not differ among treatments. Endometrial expression of INSR, LEPR-long and ADIPOR1 mRNA were not different between treatments. However, ADIPOR2 mRNA expression, which was 2 to 15-fold more abundant than ADIPOR1 mRNA, was affected by TREAT (P<0.01). Endometrial ADIPOR2 mRNA was the greatest in TMR, the lowest in HA and MA, and intermediate in LA cows (1.0^a, 0.3^b, 0.2^b, 0.7^ab± 0.02, respectively). In addition, INSR mRNA had a 2-fold and ADIPOR2 mRNA had a 5-fold decrease (P<0.03) in ovulated than non-ovulated cows. We have not found reports of adiponectin receptors in the ruminant uterus, but in other species it has been implicated in endometrial changes in preparation to embryo implantation and reduced ADIPOR2 mRNA has been associated with decreased uterine receptivity. Interestingly, both INSR and ADIPOR2 were downregulated suggesting the interdependence of these two factors as has been suggested for insulin/adiponectin. Thus, taking into account that adiponectin is a metabolic signal, these results suggest a direct role of this hormone in uterus moderating the success of pregnancy and ADIPOR2 mRNA could be, among others, one of the molecules linking a better nutrition and metabolic status with reduced embryo mortality.

Keywords: nutrition, reproduction, dairy cows