Exacerbated conceptus signaling does not favor establishment of pregnancy in beef cattle

Table 1 Effect of iP4 supplementation and/or embryo transfer on the CL regression in beef cows

Variable	Non-iP4		iP4		P value
Variable	0-ET (n = 24)	5-ET (n = 27)	0-ET (n = 26)	5-ET (n = 27)	iP4	ET	iP4×ET
Number of cows having functional CL on D20^a	4 (16.7%)	21 (77.8%)	2 (7.7%)	16 (59.3%)	.	.	.
Estrus to structural luteolysis, d^b	17.58 ± 0.35	17.00 ± 0.63	17.92 ± 0.31	16.91 ± 0.46	0.79	0.09	0.64
Estrus to functional luteolysis, d^c	17.11 ± 0.31	16.50 ± 0.56	16.96 ± 0.28	16.09 ± 0.41	0.50	0.08	0.75
Estrus to P4 < 1.0 ng/mL, d^d	17.79 ± 0.35	16.83 ± 0.62	17.83 ± 0.31	16.91 ± 0.46	0.90	0.04	0.97
Number of pregnant cows on D30^e	.	15 (55.6%)	.	10 (37.0%)	0.16	.	.
Number of non-pregnant cows having functional CL on D30^f	.	6 (22.2%)	.	5 (18.5%)	0.74	.	.

Beef cows detected in estrus (D0) were assigned randomly to receive a single injection of vehicle (Non-iP4) or 150 mg of long acting progesterone (iP4) on D4 and transfer of none or 5 in vitro-produced blastocysts on D7;
^aCows that did not present any of the characteristics described in items 2, 3 and 4, below;
^bStructural luteolysis was defined as the day between D11 and D21 when the maximum CL area (cm²) and the luteal blood flow decreased by 25% and 50%, respectively, from the mean of D10 and D11;
^cFunctional luteolysis was defined as the day when plasma P4 concentrations decreased > 2 ng/mL between samples collected from D14 to D20, and was followed by a progressive decrease in plasma P4 concentrations to < 1 ng/mL;
^dDay when plasma P4 concentrations first reached < 1.0 ng/mL;
^e,fPregnancy status for each animal was determined by detection of at least one conceptus with heartbeat using transrectal B-mode ultrasonography on D30. In non-pregnant cows, the functionality of the CL from D20 was checked according to criteria established for detection of structural luteolysis

ISSN: 2049-1891