Efecto de la bST aplicada al inicio de un programa superovulatorio con FSHp y al momento de la inseminación artificial sobre la respuesta ovárica y la producción de embriones transferibles en vacas mestizas

Abstract

Application of bovine recombinant somatotropin (bST) at the beginning of a superovulation treatment (SOV) increased the number of antral follicles that emerged in a follicular wave, improved the SOV response and increased the rate of embryos recovered. A study was conducted with the objective of evaluate the quantity and quality of embryos obtained in response to the application of bST in two strategic moments of an ovarian super stimulation treatment. A total of 40 crossbred cows with a body condition between 2.75 and 3 on the scale of 1 to 5, clinically healthy and without apparent reproductive alterations were used. The cows were treated with an intravaginal progesterone device for 6 days (Day 0, beginning of the treatment) and with 4 daily decreasing doses of FSH-p from day 4, divided into two daily IM injections (50, 40, 30, 20 mg of FSH  2). The females were randomly assigned to one of the following treatments: GH0 (control group; n=10) without bST; GH1 (n=10) a dose of 500 mg bST at day 0; GH2 a dose of rbST at the time of the first insemination (IA) (day 8); GH3 two doses of 500 mg bST, at day 0 and 8 of the treatment. The embryos were recovered by a non-surgical method, 7 days after the first AI (day 15). Ultrasonography showed that the control group had a greater number of corpora lutea than the groups treated with rbST (13.9 ± 9.2 versus 8.0 ± 4.0, 7.1 ± 3.6 and 9.0 ± 4.4 for GH1, GH2 and GH3 respectively, P>0.05). The total number of structures recovered (oocytes and embryos), degenerate embryos and unfertilized oocytes did not differ between treatments, although in all cases the coefficient of variation was considerably lower in GH3 and GH2 than in the other groups. The percentage of transferable embryos was statistically similar between treatments, ranging from 74.1% in GH0 to 80.2% in GH1, with intermediate figures in the other experimental groups. It was concluded that the application of bST at the start of treatment with SOV and / or at the time of AI did not improve the superovulatory response nor the number of transferable embryos recovered.