Abstract
ABSTRACTHigh milk production, heat, physiological status and management impair reproduction in Holstein cows. The use of in vivo-produced embryos has been reported as an alternative to enhance pregnancy outcome in the tropics; however there are several limitations for its production, especially from variations in superovulatory responses. The in vitro production of embryos would avoid such variations, but few studies have been reported. This study aims to verify the effects of variables related to recipients under a program of routine in vitro embryo transfer on a commercial dairy farm in southeastern Brazil. It was hypothesized that pregnancy rates after transfer of ovum pick up or OPUderived embryos (ET) to lactating Holstein recipients may be influenced by recipient GnRH-treatment at ET, parity, milk production and body condition score. Recipients (267) were allocated to one of three i.m. treatments given at ET: Control (92) - 2.5 ml saline; Buserelin (86) - 10 μg Buserelin acetate; Deslorelin (89) - 750 μg Deslorelin acetate. Ultrasound images and blood samples were taken at ET and seven days later. The first pregnancy diagnosis was performed between 30-40 days and the second between 60-80 days post ET. Data were analyzed by GENMOD (SAS(r)). The proportion of pregnant cows was greater (P<0.05) in Buserelin-treated recipients (38.3%) at the first pregnancy diagnosis than Controls (24.1%), but similar to Deslorelin and control cows at the second diagnosis (13.0, 20.9 and 14.6% in Control, Buserelin and Deslorelin, respectively). In conclusion, Buserelin improved pregnancy rate only transitorily, under the present conditions.
Highlights
Embryo transfer and GnRH agonists have been used to improve reproductive efficiency in Holstein cows
Another recent study (Carvalho et al, 2014) has clearly identified higher pregnancy rates per artificial insemination (AI) in primiparous compared to multiparous cows (52.7 vs 43.1%)
Overall pregnancy rates were relatively lower (13.04-38.27%) than those of other studies in Brazil, as reported in a review by Bó et al (2004), which ranged from 40-50% and by Galimbert et al (2001), which observed in zebu-crossbred recipients, pregnancy rates as high as 65%
Summary
Embryo transfer and GnRH agonists have been used to improve reproductive efficiency in Holstein cows. It is generally accepted that high milk production decreases circulating progesterone concentrations. Progesterone influences embryo development, stimulates interferon-tau production, and inhibits the luteolytic cascade (Shahneh et al, 2008). Suboptimal progesterone concentrations cause embryo loss and impair gestation. Agrotec., Lavras, v. 39, n. 5, p. 498-505, set./out., 2015
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