Abstract
Lactating beef cows previously synchronized for estrus (d 0) were assigned to four treatments to assess their effectiveness in increasing blood progesterone (P4) and its effects on tumor necrosis factor-α (TNF-α) and prostaglandin F2α (PGF2α) after the transfer of embryos. At the time of transfer (d 7), cows received no treatment (control; n = 16), a controlled internal drug releasing device (CIDR; n = 16), human chorionic gonadotropin (hCG; n = 15), or gonadotropin releasing hormone (GnRH; n = 15). Blood samples were taken on d 7, 14, and 21 for analysis of P4 and tumor necrosis factor-α (TNF-α). Blood was collected (every 15 min for 2 h) in half the animals in each treatment group on d 14 and the remaining half on d 21 for analysis of prostaglandin F2α metabolite (PGFM). Retention rates were 56.2, 62.5, 46.7, and 13.3% for cows in the control, CIDR, hCG, and GnRH groups, respectively. Progesterone was greater (P ≤ 0.05) in cows receiving hCG compared to others on d 14. Progesterone in all treatment groups increased from d 7 to d 14 and declined (P ≤ 0.05) from d 14 to d 21. Contrary to pregnant cows, P4 and TNF-α declined from d 7 to d 21 in nonpregnant cows (P ≤ 0.05). Although PGFM increased by d 21, there was no difference between pregnant and nonpregnant cows.
Highlights
Progesterone (P4) is abundantly reported in the literature as the primary and most intrinsic hormone associated with embryonic survival during early pregnancy [1, 2]
No significant differences were observed in body condition scores among cows in the human chorionic gonadotropin (hCG) (5.76 ± 0.21), control (5.47 ± 0.18), gonadotropin releasing hormone (GnRH) (5.68 ± 0.11), and controlled internal drug releasing device (CIDR) (5.67 ± 0.49) groups of this study
Pregnancy rates were not different between cows in the control, CIDR, and hCG groups (P > 0.05); percent pregnancy rate was lower (P < 0.05) in the GnRH group when compared to the control and CIDR groups
Summary
Progesterone (P4) is abundantly reported in the literature as the primary and most intrinsic hormone associated with embryonic survival during early pregnancy [1, 2]. Low concentrations of P4 are associated with retention of pregnancy in beef cows [4]. Several studies have been recently designed to examine the effects of supplementing exogenous P4 on embryonic retention after the transfer of embryos. At present, this is commonly done by inserting a controlled internal drug releasing device (CIDR) at the time of breeding. Our laboratory previously reported [5] that inserting a CIDR immediately after the transfer of embryos enhanced retention rates in recipient lactating and nonlactating beef cows. Purcell et al [5] did not detect beneficial effects on pregnancy rates by placing CIDR’s immediately subsequent to embryo transfer in dairy cows
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