80 The role of maternal progesterone in embryonic attachment and pregnancy loss in cows
F. P. J. da Silva Junior A , E. G. Kidwell A , C. G. Hubbard A , A. C. Gaines A , J. P. N. Andrade B and R. R. Domingues AA
B
Adequate concentrations of progesterone (P4) are essential to prepare the uterine environment for embryonic development and attachment to the endometrium. Insufficient P4 may impair embryonic attachment and cause pregnancy loss. This study aimed to investigate the risk for pregnancy loss (RPL) in cows based on the day of embryonic attachment (exp. 1) and investigate the impact of P4 supplementation on the timing of embryo attachment (exp. 2). In exp. 1, lactating dairy cows (n = 86) were artificially inseminated using a double-ovsynch protocol (d0 = day of AI). Blood samples were collected from d16 to d30 to determine circulating pregnancy-associated glycoproteins (PAGs) as a marker for embryonic attachment. Each cow’s embryonic attachment day was determined as the day of a 10% increase from baseline followed by a continuous increase for 2 days. Pregnancy was confirmed via ultrasonography on d30, d45, and d60. Cows were categorized into two groups: those that remained pregnant until d60 (P, n = 41) and those with pregnancy loss (PL, n = 13) as determined by a decrease in PAGs after pregnancy establishment or no embryonic heartbeat on d30, d45, or d60. In exp. 2, primiparous lactating beef cows were artificially inseminated following a (G6G) synchronization protocol. Cows were randomly assigned to either remain untreated (control, n = 15) or receive an intravaginal device containing 1.38 g of progesterone (CIDR; sP4, n = 15) from d3 to d12. Blood samples were collected on d3 to d24 to determine concentrations of P4 and PAGs. Pregnancy status was determined based on PAGs and on evaluation of the corpus luteum and uterus ultrasonography on d24. Only pregnant cows were used in the analysis (control, n = 7; sP4, n = 8). Data were analyzed using the GLIMMIX and MIXED procedures of SAS. The analysis included adjustments for multiple comparisons using the Dunnett method to assess the RPL. In exp. 1, embryonic attachment occurred earlier (P = 0.0001) in P cows (d20.2 ± 0.1) compared with PL cows (d21.8 ± 0.4). The RPL increased as the day of attachment was delayed (P = 0.02). Specifically, cows with attachment on d22 or later had higher RPL (85.7%) compared with those with attachment on d19 (11.1%, P = 0.03), d20 (7.1%, P = 0.01), and d21 (20.8%, P = 0.02). In exp. 2, P4 was greater in the sP4 group from d4 to d14 (P < 0.05). There was no difference in P4 between the control and sP4 groups on d3 and from d16 to d24 (P > 0.1). The day of embryonic attachment occurred earlier (P = 0.04) in the sP4 group (d19.1 ± 0.4) compared with the control (d20.1 ± 0.3). The first significant increase in circulating PAGs occurred a day earlier (P < 0.0001) in the sP4 (d20) compared with the control (d21). Lastly, there was a negative correlation (−0.64; P = 0.009) between the average P4 concentrations from d4 to d12 and the day of attachment; that is, greater P4 during this period hastened embryonic attachment. In conclusion, exp. 1 demonstrated that delayed embryonic attachment increases the risk of pregnancy loss. From exp. 2, we ascertained that P4 supplementation from d3 to d12 promoted earlier embryonic attachment. Further studies are needed to evaluate whether earlier embryonic attachment caused by P4 supplementation reduces the RPL and improves pregnancy rates in cattle.
