Table 1. Response to estrous synchronization treatment in heifers with high or low serum progesterone concentrations at treatment initiation.
Progesterone
Responders
Non responders
> 1 ng/ml
28
3
< 1 ng/ml
11
2
Both AM heifers that ovulate without showing estrus did not have an active CL at treatment initiation. In the PM heifers that were in heat but did not ovulate, 2 had a CL and the other did not have a CL at the beginning of treatment. When we looked at the serum progesterone concentrations of the heifers that did not respond to the estrous synchronization treatment after the 5-day observational period, we observed that 2 of them increased their serum progesterone concentrations above 1 ng/ml 11 days after CIDR-B withdrawal. This progesterone increase would show that these 2 heifers ovulated beyond the observational period. The 3 other non-responding heifers maintained serum progesterone concentrations below 1 ng/ml until 15 days after CIDR-B removal.
Time from CIDR-B withdrawal to estrus detection (P>0.4) or ovulation (P>0.1) and from estrus detection to ovulation (P>0,5) were not affected by treatment (Table 2) when all heifers were taken into account.