Abstract
The aim of this study was to quantify the pregnancy rate after implantation of two embryos after FTET protocols, as well as to monitor pregnancy losses until parturition, evaluating, mainly, if this strategy results in more number of animals born. Therefore, 423 multiparous recipients were selected, standardized in terms of body score, who had high-quality corpora lutea. Animals were randomly divided into two groups according to one or two embryos transferred (1 embryo = Control, n = 237; 2 embryos = Group 1, n = 186). All recipients received the same hormonal treatment, which consisted of administering, on Day 0, 2 mL of estradiol benzoate (Gonadiol, ZOETIS) + 1.9 g multidose 1st use progesterone implant (CIDR, ZOETIS); on Day 8 the implants were removed + injected 0.4 mL of estradiol cypionate (E.C.P, ZOETIS) + 1.5 mL of eCG (Novormon, ZOETIS) + 1 mL of dinoprost tromethamine (Lutalyse, ZOETIS). The animals were evaluated by ultrasonography at 30 and 60 days after embryo transfer, to diagnose the success rate and embryo losses during this period. Furthermore, information was collected on births, length of gestation, number of twin births, number of childbirth assistance and the weight of the calves. The results showed that Group 1 had better success than the Control, with higher conception rates at 30 days (68.3% vs. 53.2%, P<0.001) and at 60 days (62.9% vs. 52.3%; P<0 .05). The number of animals born was also higher for Group 1 (53.3% vs. 43.3%, P<0.01). The percentage of twins born in Group 1 was 17.9%, and the animals had lower weight compared to the Control (34.29 + 7.36 vs 37.63 + 5.73, P<0.05). The length of pregnancy and the number of assistances were similar between groups. In conclusion, the strategy adopted in this experiment suggests a considerable increase in the calf birth rate, but losses during pregnancy and their mechanisms need to be elucidated.
Highlights
The search for improvement in reproductive efficiency is an effective tool for the economic maintenance of economic development in beef cattle
The aim of this study was to quantify the pregnancy rate after implantation of two embryos after fixed-time transfer (FTET) protocols, as well as to monitor pregnancy losses until parturition, evaluating, mainly, if this strategy results in more number of animals born
Diversification in the use of fixed-time insemination (TAI) and fixed-time transfer (FTET) protocols has been common since the early 2000s, as it increases the number of animals inseminated and facilitates large-scale embryo innovation (Bo et al 2004; Aguiar et al, 2019; Pinto Neto et al, 2018; Baruselli et al, 2004)
Summary
The search for improvement in reproductive efficiency is an effective tool for the economic maintenance of economic development in beef cattle. Diversification in the use of fixed-time insemination (TAI) and fixed-time transfer (FTET) protocols has been common since the early 2000s, as it increases the number of animals inseminated and facilitates large-scale embryo innovation (Bo et al 2004; Aguiar et al, 2019; Pinto Neto et al, 2018; Baruselli et al, 2004). Another alternative to increase profit is the dissemination of the genetics of superior animals through biotechniques with the production of donor embryos, either in vivo or in vitro, in order to increase the number of products (Hansen 2020; Mebratu et al 2020; Bo et al, 2019). Synchronization of the recipients can be done in a similar manner and at the same working time as the donor cows (Galina & Orihuela, 2007)
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