Impact of estradiol cypionate prior to TAI and progesterone supplementation at initial diestrus on ovarian and fertility responses in beef cows

Abstract

In cattle, early diestrus progesterone (P4) supplementation modulates endometrial function to exert pro- and anti-pregnancy establishment effects; specifically, P4 stimulates conceptus growth, but also induces early onset of luteolysis. This paradoxical effect is frequently related to the inconsistent fertility outcomes that result from P4 supplementation experiments. Aim was to investigate the impact of exogenous estradiol (E2) treatment at the end of timed fixed AI (TAI) on frequency of early luteolysis and pregnancy of beef cows supplemented with P4. Ovulations (D0 of study) of suckled multiparous (n = 643) and primiparous (n = 193) Nelore cows (Bos indicus) were synchronized with an E2/P4-based protocol for TAI and assigned to receive 1.0 mg of estradiol cypionate (CP) or nothing (NoCP) on D-2 and 150 mg of injectable long-acting P4 (iP4) or Placebo (NoiP4) on D4 on a 2 × 2 factorial arrangement. On D15, the iP4 supplementation increased (P < 0.05) the frequency of early luteolysis (NoCP + iP4: 26.0%; [13/50] vs. NoCP: 8.0% [4/50]), but CP prevented this effect (CP + iP4: 8.3% [4/48] and CP: 6.4% [3/47]). The CP improved pregnancy/AI (P/AI) of multiparous (CP: 51.6% [165/320] and NoCP: 35.0% [113/323]; P < 0.001) and primiparous cows (CP: 40.4% [40/99] and NoCP: 24.5% [23/94], P < 0.05), regardless of iP4 treatment. The iP4 supplementation affected P/AI of CP and NoCP treated cows according to follicle size at TAI. For the CP treated cows, the iP4 supplementation improved P/AI of sub-populations of cows with follicles <12.35 mm (42.0% [34/81] vs. 53.1% [34/64]), while for NoCP treated cows, the improvements occurred in subpopulations of cows with follicles ≥12.35 mm (46.1% [35/76] vs. 58.7% [37/63]). In conclusion, strategies associating E2 and P4 supplementation decrease the incidence of early onset of luteolysis and improve P/AI of suckled beef cows with smaller follicles.

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

“…Such changes both benefitted (i.e., stimulated ISG15 abundance) and impaired (greater EEM) embryo survival, but reasons for such contrasting outcomes to the same stimulus are unknown currently. We and others reported previously that early elevation of P4 concentrations during diestrus have increased the incidence of early luteolysis [ 11 , 25 , 27 , 37 ]. However, in the present study, iP4 treatment did not reduce luteal lifespan of any animal.…”

“…This dose was chosen because cycling, multiparous, non-lactating Nelore cows injected with this formulation on D3 after ovulation presented greater plasma P4 concentrations from D3.5–D5.5 than controls [ 25 ]. This regime of P4 supplementation has produced both embryotrophic and luteolytic stimuli [ 25 – 27 ]. We used five blastocysts because a greater number of blastocysts could reduce pregnancy rates and growth of conceptuses [ 20 ].…”

Efectos Del Cipionato Y Benzoato De Estradiol en Vaquillas Mestizas Sobre El Porcentaje De Preñez

“…Al respecto, uno de los factores que limita su introducción en los rebaños de pequeños y medianos productores en el trópico, es la baja eficiencia en la detección del estro y la realización en el tiempo óptimo de los servicios de inseminación artificial (Pedroso, 2003). "Por consiguiente, en las últimas décadas se han desarrollado múltiples esfuerzos por desarrollar procedimientos biotécnicos, que permitan sincronizar el celo, la ovulación con el objetivo de realizar la inseminación en tiempo fijo garantizando una adecuada fertilidad" (Martins et al, 2017).…”

Evolution of knowledge on ovarian physiology and its contribution to the widespread application of reproductive biotechnologies in South American cattle

“…This permitted FTAI with acceptable pregnancy rates. As an alternative, administration of 0.5 to 1.0 mg of estradiol cypionate (ECP; Colazo et al ., 2003 ) at the time of progestin removal with FTAI 48 to 52 hours later is often used in South America ( Sales et al ., 2012 : Martins et al ., 2017 ). Pregnancy rates following FTAI have been shown to be improved in suckled beef cows and heifers, especially B. indicus crosses, when 300 to 400 IU of eCG is administered at the time of progestin removal ( Baruselli et al ., 2004 ; Bó et al ., 2012 ; 2016).…”