Long interval prostaglandin-based treatment regimens do not affect ovulatory or prolificacy rates of multiparous ewes after cervical fixed timed AI

Highlights

• Long interval PG FTAI-based treatments do not affect ovulation rate and prolificacy.

• Long interval PG FTAI-based treatments decrease conception and fecundity rate.

Abstract

To evaluate effects of a longer, than conventional, interval between time of prostaglandin F_2α (PG)-based administrations in a PG-based treatment regimen for fixed timed AI (FTAI) on ovulation rate (OR), non-estrous return rate on Day 21 subsequent to the time of AI (NRR21), as well as conception, prolificacy and fecundity rates, ewes were assigned to two groups. Ewes of treatment group (PG15) were estrous-synchronized using two PG doses 15 days apart and FTAI was conducted at 56 h after the second PG administration (Day 0). Ewes of the Control group (SE) had imposed a pre-estrous synchrony treatment regimen with two PG doses 7 days apart and AI was conducted after detection of spontaneous estrus from 17 to 19 days after the second PG administration (Day 0). Ovulation rate on Day 8, NRR21, conception, prolificacy and fecundity rates on Day 60 were evaluated. There were no differences (P > 0.05) between ewes of the PG15 and SE groups in OR (1.47 ± 0.50 and 1.54 ± 0.50, respectively) or prolificacy (1.42 ± 0.80 and 1.33 ± 0.62, respectively), however, there were lesser values (P < 0.05) in the PG15 than SE group for NRR21 (65.2% and 91.3%, respectively), conception (59.8% and 91.3%, respectively) and fecundity (84.8% and 120%, respectively). The longer interval with the PG-based treatment regimen does not affect OR and prolificacy, but there is a lesser NRR21, conception and fecundity rate in comparison to ewes of the Control group.

Introduction

Fixed timed artificial insemination (FTAI) in sheep represents a practical technique in commercial flocks that shorten the AI breeding period, because there is no estrous detection and there is greater use of genetically superior rams, access to nutritional resources and more effective use of labor resources (Menchaca and Rubianes, 2004), however, it involves hormonal treatments to ensure synchronization of timing of ovulation among ewes and acceptable pregnancy rates (Abecia et al., 2012). The application of these biotechnologies in commercial farming enterprises requires ease in implementation of procedures, acceptable reproductive outcomes and a lack of effects on the environment as a result of imposing treatments (Martin and Ferasyi, 2016). Because of the rapid rate of metabolization (Piper et al., 1970; Davis et al., 1980), ease of application and relatively lesser cost, the use of prostaglandin F2α represents a more desirable option than treatment regimens including intravaginal devices impregnated with progesterone or progestogens plus an i.m. dose of equine chorionic gonadotrophin at time of device withdrawal (P4-eCG) for the reproductive management of sheep (Martemucci and D’Alessandro, 2011; Viñoles et al., 2011; Abecia et al., 2012; González-Bulnes et al., 2020).

Prostaglandin F2α and its synthetic analogues (PG) are potent luteolytic agents in ruminants when there is FTAI (Fierro et al., 2013), however, lesser than desirable reproductive outcomes have occurred when there was use of short-interval (7–8 days) or conventional PG-based regimens (9–12 days apart between doses) are used, have resulted in a lack of use of these treatment regimens (Gordon, 1983; Menchaca and Rubianes, 2004; Olivera-Muzante et al., 2011a). Extending the interval between PG administration times for as long as 14–16 days between administrations (“long interval” treatment regimens), increase the time that pre-ovulatory follicles develop when there are luteal-phase progesterone concentrations, resulting in more desirable reproductive outcomes after FTAI (Fierro et al., 2016, 2017). Furthermore, the use of these treatment regimens with longer, than conventional, periods between PG administrations resulted in non-estrous return rates by Day 21 following AI (NRR21) and conception rates comparable to what occurs with use of P4-eCG based treatment regimens (Fierro and Olivera-Muzante, 2017). The ovulation rate (OR), prolificacy and conception rate, however, when there is use of PG FTAI-based treatment regimens may be less than those when there is AI of ewes after detections of a spontaneous estrus, an important factor to be considered in flocks where there is commercial lamb production or in those focused on genetic improvement.

Results from studies in which there were evaluations of OR, prolificacy and conception rate after the use of PG are inconsistent. There was no detrimental effect on OR when PG was administered during the mid-luteal phase of the estrous cycle (Bindon et al., 1979; Houghton et al., 1995), however, Fierro et al. (2011) reported there was a decrease in OR, prolificacy and conception rate when PG was administered during the early luteal phase of the estrous cycle when treatments were imposed on multiparous Corriedale ewes. The OR in multiparous Corriedale ewes tended to be greater when there was a relatively longer, as compared with a shorter or conventional interval between PG administrations in the estrous synchrony treatment regimen (Fierro et al., 2017). When there was a focused feeding regimen imposed on multiparous Merino ewes using a relatively longer, than conventional, interval between PG administrations or when there was AI after a detection of a spontaneous estrus there was a lesser OR, NRR21 and conception rate, but no difference in prolificacy in pregnant ewes of control and treated groups (Errandonea et al., 2018). The result from this previous study leads to the question of whether the problem related to fertility when there is imposing of the relatively longer, that conventional, interval between PG administrations is the lesser variability in OR and prolificacy of the breed of sheep or when there is a PG-based treatment regimen used in the comparison to what occurs when ewes are AI after detection of a spontaneous behavioral estrus.

The aim of the present experiment, therefore, was to evaluate the effect of a relatively longer, than conventional, interval between PG administrations in a PG-based treatment regimen when there was cervical semen placement with FTAI on OR, NRR21, conception, prolificacy and fecundity rate in multiparous Corriedale ewes. It was hypothesized that OR and prolificacy of ewes would not be affected, however, NRR21, conception and final fecundity rates would be less with use of this treatment regimen.