Abstract
ABSTRACT Estradiol benzoate (EB), estradiol cypionate (EC), and gonadotrophin releasing hormone (GnRH) were evaluated as ovulation inducers for TAI of crossbred lactating cows. In experiment I (n = 45), the follicular dynamics was evaluated, while in experiment II (n = 171) the reproductive efficiency was evaluated. All females were submitted to a synchronization protocol: insertion on day 0 (D0) of intravaginal progesterone -release intravaginal device (PRID; 1g) plus administration of EB 2mg; D8, PRID removal, administration of 0.150mg PGF2α and 400 IU of eCG, and cows were allocated into three treatments: 1) TEB9 - IM administration of 1mg EB on D9 and AI performed 52 hours after PRID removal; 2) TEC - IM administration of 1mg EC on D8 and AI performed 48 hours after withdrawal of PRID; and 3) TGnRH - administration of 100pg GnRH on D10 and AI performed 52 hours after removal of PRID. The follicular growth rate was lower in the EC group (p <0.05). There was no effect of treatments on ovulation and pregnancy rates (p >0.05). The use of EB, EC, and GnRH as ovulation inducers in the TAI protocol did not show marked differences in the evaluated patterns of follicular dynamics and pregnancy.
Highlights
The tropical dairy herd is basically composed of crossbred cattle, mainly because it is a viable alternative for many production systems that seek to reduce the cost of production from animals kept under grazing conditions
Estradiol benzoate (EB) has been commonly used as an ovulation inducer in association with synchronization treatment based on progesterone and estrogen for Bos taurus taurus (MARTINEZ et al, 2002; COLAZO et al, 2013; MELO et al, 2016), Bos taurus indicus (SÁ FILHO et al, 2009), and Bos taurus taurus x Bos taurus indicus (ALMEIDA et al, 2016a)
This study aimed to evaluate the efficiency of EB, Estradiol cypionate (EC), and gonadotropin releasing hormone (GnRH) as ovulation inducers in timed artificial insemination (TAI) protocols for crossbred dairy cattle
Summary
The tropical dairy herd is basically composed of crossbred cattle, mainly because it is a viable alternative for many production systems that seek to reduce the cost of production from animals kept under grazing conditions. Synchronization treatments of ovulation based on the use of progesterone simultaneous to the use of estrogen have presented improvements in the pregnancy rate in both anestrous and cycling cows (AYRES et al, 2008; SÁ FILHO et al, 2009; COLAZO et al, 2013; VASCONCELOS et al, 2018). These protocols have been successfully used to control the follicular and luteal dynamics, and in ovulation synchronizing, allowing artificial insemination (AI) without estrus detection (SÁ FILHO et al, 2009; BÓ et al, 2016). EB is administered 24 h after removal of the progesterone device; requiring to submit females to four managements during the synchronization protocol
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