Abstract
The objective of this study was to investigate whether the use of rbST and eCG prior to ultrasound-guided follicular aspiration (OPU) improves oocyte yield and quality in Tabapua and Holstein heifers. The study was conducted in two phases, 20 days apart, in a change-over design. The dominant follicle was ablated two days (D-2) before two treatments: stimulation (6 Holstein and 8 Tabapua), 500 mg of rbST (Boostin®) on D0 and 500 IU of eCG (Folligon) on D2; and control (6 Holstein and 8 Tabapua), in which heifers received injections of the excipient. Heifers were aspirated on D4. Oocytes were subjected to a well established commercial in vitro embryo production protocol (Vitrogen®) and embryos were evaluated seven days after fertilization. There was an effect from the interaction of treatment and breed, so that hormonal stimulation increased antral follicle count (2-8 mm) in Tabapua (29.9±2.6 to 41.4±2.6), but not in Holstein heifers (14.4±2.6 to 15.5±2.6). Tabapua heifers had higher mean antral follicle count than Holsteins (35.6±1.8 vs. 15.0±2.1). The number of viable oocytes was not increased by stimulation in Tabapua (from 4.7±1.0 to 5.2±1.1 in control and simulation, respectively) or in Holstein heifers (1.3±1.9 to 2.0±1.6 in control and simulation, respectively). There was no difference in the percentage of heifers with more than five viable oocytes in the group treated (33 vs 27%). The number of blastocysts was not affected by treatment (1.75 vs. 1.00 in hormonal stimulation and control, respectively). The increase in antral follicle count in the stimulated Tabapua heifers did not reflect upon oocyte yield. The differential breed response to the hormonal treatment underscores the need for additional tests, especially for the Holstein breed, in order to enhance OPU efficiency.
Highlights
Oocyte yield obtained after bovine ovum pick up (OPU) and OPU-derived embryo yield after in vitro culture (IVP) are low, especially in relation to the antral follicle population available at the time of ultrasound-guided follicle aspiration (Blondin et al, 2002; Chaubal et al, 2007).Equine chorionic gonadotrophin, with its FSH-like action and growth hormone, with its effect on IGF-I (Moreira et al, 2002), are important regulators of antral follicle development and their actions are related to oocyte viability (Cushman et al, 2001; Murugavel et al, 2009)
The objective of this study was to investigate whether the use of recombinant bovine somatotropin (rbST) and equine chorionic gonadotropin (eCG) prior to ultrasound-guided follicular aspiration (OPU) improves oocyte yield and quality in Tabapuã and Holstein heifers
There was an effect from the interaction of treatment and breed, so that hormonal stimulation increased antral follicle count (2-8 mm) in Tabapuã (29.9±2.6 to 41.4±2.6), but not in Holstein heifers (14.4±2.6 to 15.5±2.6)
Summary
With its FSH-like action and growth hormone, with its effect on IGF-I (Moreira et al, 2002), are important regulators of antral follicle development and their actions are related to oocyte viability (Cushman et al, 2001; Murugavel et al, 2009). It is important to notice that the studies of Blondin et al (2002) and Rossa et al (2009) showed that increases in oocyte yield after follicle growth stimulation protocols may adversely affect in vitro oocyte developmental competence. Holsteins usually produce less OPU-derived oocytes in relation to Bos indicus cows. This is true for embryo production, either after superovulation (Sales et al, 2008) or OPU-derived oocyte culture (Merton et al, 2009)
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