Impacts of estradiol use on super early resynchronization at 14 days post IATF in beef heifers

Author(s)

Igor Garcia Motta

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina Veterinária e Zootecnia (FMVZ/SBD)
• Defense date: 2019-09-27

Examining board members

Guilherme Pugliesi; Alan Maia Borges; Luciano Andrade Silva

• Advisor: Guilherme Pugliesi

Abstract

The aim of this study was to evaluate the use estradiol benzoate (EB) or 17β-estradiol (E2) associated with progesterone (P4) for resynchronization of ovulation at 14 days after timed artificial insemination (TAI) and its effect on the maintenance of pregnancy in beef heifers. In Experiment 1 (Exp1), Nelore heifers were submitted to TAI (D0). On D14, the animals received an intravaginal P4 device and were allocated in three groups: control (no treatment; n=17); EB (1mg EB; n=17); and E2+P4 (1mg E2 + 9mg P4; n=18). Ultrasonography evaluations (B mode and Doppler) were performed daily from D14 to D22 for follicular and luteal dynamics. On D22, the devices were removed and pregnancy diagnosis was performed with Doppler ultrasonography to for luteolysis detection. In Exp2, 1178 Nelore heifers and 117 cross beef heifers (Nelore x Angus) were resynchronized according to Exp1 and ramdoly allocated in the same three groups. On D22, the dominant follicle (DF) was measured in non-pregnant (NP) and the second TAI was performed on D24. In a subgroup of NP heifers (n=337), an oestrus detection patch was used between D22 and D24 and the DF was measured at D24. Confirmatory diagnoses were performed between D37-67 and D43-47 after first and second TAI, respectively. In Exp1, the proportion of heifers with a synchronized follicle wave emergence (from 3 to 5 days after treatment) was greater (P<0.05) in the EB group (93.8%) than in the control (62.5%) and E2+P4 (64.7%) groups. Luteolysis occurred earlier (P<0.05) in the EB (18.6±0.5) and E2+P4 (19.1±0.5) groups than in the controls (20.6±0.4). The pregnancy rate after first TAI did not differ (P>0.1) among the control, EB and E2+P4 groups in DG22 and confirmatory diagnosis in both experiments. In Exp2, the pregnancy loss between D22 and D37-67 was similar (P>0.1) and in the control group (19% [36/185]), EB (15% [28/182]) and E2+P4 (15% [28/184]). The DF on D22 was greater (P<0.05) in the control group (11.9±0.14) than in EB (11.3±0.1) and E2+P4 (11.5±0.1). No difference (P>0.1) was observed in the proportion of heifers detected in estrus on D24, but DF growth rate (mm/day) was greater (P<0.05) in the EB group (0.89±0.08) than in the control (0.59±0.07) and E2+P4 (0.66±0.09) groups. The pregnancy rate for the second TAI was greater (P<0.05) in the EB group (47% [94/200]) than in the control group (37% [76/203]), but did not differ (P>0.1) from the E2+P4 group (43% [93/214]). Cumulative pregnancy (first and second TAIs) did not differ (P>0.1) between control (59% [204/344]), EB (65% [227/349]) and E2+P4 (64% [220 / 342]). It is concluded that the administration of 1 mg EB or 1 mg E2 + 9 mg P4 at 14 days post-TAI anticipates luteolysis in NP heifers but does not compromise pregnancy. The treatment with EB induces a new synchronized follicle wave emergence and improves the pregnancy rate of resynchronized NP heifers. (AU)

• FAPESP's process: 17/18613-0 - Effects of ressynchronization of estradiol on day 14 after timed-AI on morphofunctional characteristics of corpus lute and uterus in Nelore females
• Grantee: Igor Garcia Motta
• Support Opportunities: Scholarships in Brazil - Master