Is prostaglandin F2α administration at the beginning of a progesterone and estradiol-based treatment for FTAI an effective strategy in Bos taurus heifers?

Effect of calving to timed artificial insemination interval on fertility of beef cows

“…However, the effect of C‐TAI interval on the pregnancy rate was highly significant, regardless of genetic group. Several studies aimed to increase the efficiency of TAI protocols, especially with changes in the hormonal protocol (Madureira et al, 2020; Núñez‐Olivera et al, 2019; Tortorella et al, 2013; Uslenghi et al, 2014). However, these studies did not consider the interval between calving and initiation of the protocol, which in the present study we demonstrate has a significant effect on the efficiency of the TAI.…”

“…The pregnancy rate after TAI is generally between 50% and 60% of the cows subjected to the protocols (Madureira et al, 2020; Sá Filho et al, 2010; Sales et al, 2012). Several studies have been performed to improve the efficiency of TAI protocols, including modifications of ovulation inducers, the concentration of progesterone present in the vaginal device (Uslenghi et al, 2014), an extra dose of prostaglandin analogue F2alpha (Núñez‐Olivera et al, 2019) and the use of equine chorionic gonadotropin (eCG) at different times (Tortorella et al, 2013). These studies have the same partial objective, to change the combination of drugs to increase the pregnancy rate of beef cows submitted to TAI protocols.…”

Hormonal adjustments for fixed-time artificial insemination and physiologic variables influence in the reproductive performance of >i<Bos indicus>/i< heifers

“…As expected, the CL regression in the present study was significantly different in the grouped treated, achieving more than 2 times of CL regression than the heifers non treated, reflecting as well in a lower of CL presence on Day -2. Likewise, a reduce CL presence on Day -2, contributed to the higher LF diameter at progesterone implant withdrawal, found in an anterior study with Bos taurus heifers, where reported a positive association of the PGF treatment at the TAI protocol initiation, on the LF size at the P4 implant removal (With PGF: 12.2 ± 0.5 mm vs. without PGF: 9.6 ± 0.5 mm) [47] like found in the present study, where treated heifers presented a higher follicular diameter on Day -2 (difference of 0.7 mm) partially accepting the first hypothesis of the study, nonetheless, there was no influence of the PGF on Day -9 over the LF diameter at the TAI moment, differing from the previously reported by Carvalho et al…”

“…However, even with the increase of CL regression between Day -9 and Day -2 in the present study, those heifers with the PGF administration did not express more estrus until the TAI compared with the non-treated heifers for the overall result, on the other hand, when analyzed the PGF influence within the heifers with CL presence on Day -9, there was an increase on the expression of estrus of 10% points as expected, because of the higher CL regression, the positive effect of having no CL on Day -2 on the follicle size, producing a LF with a higher diameter and steroidogenic capacity, leading to an increased expression of estrus, in accordance of the described by Martins et al where the heifers with the smallest follicles had lower expression of estrus compared with the ones with the biggest follicles (Small follicle at AI: 12.4% vs. big follicle 46.7%) [15]. Nonetheless, the PGF administration at the beginning of the TAI protocol, had no impact on the general P/IA or within the heifers with CL presence on Day -9 even with a higher expression of estrus, differing of the positive effect of this hormonal strategy already reported in Bos taurus heifers and cows in an anterior study which presented a higher proportion of pregnant females in the group treated with PGF at the TAI protocol initiation [40], as well as Nuñez et al found a tendency in Bos taurus 14 months old heifers, of better a pregnancy per AI results in the group that received a half dose PGF treatment at the beginning of the TAI protocol (54.7%) compared with the heifers with no additional PGF treatment during the TAI protocol (48.5%), nonetheless, the same study found no association of that treatment in two years old heifers [47]. In the same way, the results of the present study do not differ from those results in the older heifers, having no difference on the P/AI of the heifers treated or not with PGF on Day -9, partially rejecting the study's first hypothesis, confirming the information described in another study, where there was no difference in two years old Nelore heifers, between those treated or not with PGF on the TAI protocol initiation (With PGF: 51.7% vs. without PGF: 57.7%) [50], especially explained by the support provided by the eCG treatment, which increase the probability of pregnancy of beef heifers [49], strategy that allowed the increase in fertility of the TAI programs in heifers, independent of the genetic group, either with Bos taurus (With eCG: 57.1% vs. without eCG: 53.1%) [51] or Bos indicus (With eCG: 50.0% vs. without eCG: 36.8%) [18].…”