Abstract
The aim of this study was to investigate estrus synchronization in prepubertal and pubertal heifers (crossbred ½ Nelore x Red Angus - commercial herd) submitted to a long-term progesterone-based protocol for timed artificial insemination (TAI), as well as overall pregnancy rates. Four hundred forty-seven heifers underwent ultrasound examination of the ovaries and were assigned to one of 3 groups: (1) prepubertal heifers (PPNS; n = 114) with ovarian follicles <8 mm in diameter and no corpus luteum (CL) that were submitted to natural service (NS) by bulls for 10 days; (2) prepubertal heifers (PPTAI; n = 124) with follicles <8 mm in diameter and no CL that underwent estrus synchronization with injection of 4.0 mg estradiol benzoate (EB) and insertion of a controlled-release intravaginal progesterone (P4) device containing 0.558 g P4 on d 0, followed by P4 device removal and injection of 150 mg prostaglandin F2α and 0.6 mg estradiol cypionate (ECP) on d 8, and TAI on d 10; and (3) pubertal heifers (PTAI; n = 209) with follicles >8 mm in diameter and/or a CL that underwent the same protocol as PPTAI heifers. Overall pregnancy rate was determined by transrectal ultrasonography on d 45 after NS or TAI. Data were analyzed using the FREQ procedure of SAS (SAS Inst. Inc., Cary, NC). Pregnancy rates were as follows: 20.1% in PPNS, 37.0% in PPTAI, and 48.5% in PTAI (P < 0.05). In conclusion, TAI after estrus synchronization with a hormonal protocol using EB and ECP in prepubertal and pubertal heifers resulted in higher pregnancy rates than prepubertal heifers exposed to natural service, and exposure of prepubertal heifers to a long-term progesterone-based protocol effectively synchronized estrus.
Highlights
Brazil has the largest commercial herd in the world—approximately 200 million animals (IBGE, 2004)
The present study investigated synchronization of estrus in prepubertal and pubertal heifers submitted to a longterm progesterone-based protocol for timed artificial insemination (TAI)
TAI is influenced by several factors, such as stage of the estrous cycle at the beginning of the protocol, animal category, breed, body condition score, and semen quality (Gofert, 2008; Marques et al, 2008; Sá Filho et al, 2010; Soares and Araldi, 2011)
Summary
Brazil has the largest commercial herd in the world—approximately 200 million animals (IBGE, 2004). Low reproductive efficiency in herdsis the main cause of persistently low production rates. Animal factors, such as age, category, body condition score, reproductive health (ovaries and uterus), and calving season (Cunha, 2011), need to be taken into account when planning the reproductive strategy for each farm. According to Soares and Araldi (2011), a critical factor in the beef industry remains low fertility of the cows in breeding herds and consequent low calving rates. Taira et al (2010) concluded that efficiency in the calving period is a determining factor in the economic viability of production systems. The Brazilian beef cattle industry is still conducted as an extractive activity, with minimal use of inputs and biotechnology (Santos et al, 2011), which further limits economic viability
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