Quispe QT, Zarco QL, Ortiz HA, Valencia MJ

Language: English/Spanish
References: 34
Page: 23-29
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ABSTRACT

The aim of this study was to evaluate the optimal dosis of a short treatment with melengestrol acetate (MGA) and the effect of oestradiol cipionate (ECP) for estrous synchronization in ewes. The experiment was performed during the reproductive season (August- October). Ninety six ewes were used. Estrous detection was done by using vasectomized males and was carried out twice a day, 18 days prior to the beginning of the experiment. It was found that 91% of the animals showed estrous during this period. Ewes were assigned to the following 5 groups: MGA22-ECP (n:19); MGA22 (n:19); MGA11-ECP (n:20); MGA11 (n:18) and the control (n:19). Females of the first two groups received in the concentrate 0.22 mg of MGA/ewe/day for 9 days; the third and fourth groups received 0.11 mg of MGA/ewe/day for 9 days. Additionally, the animals of the first and third groups were injected with 0.5 mg of oestradiol cipionate (ECP) at the beginning of the MGA administration, in order to induce the lysis of the corpus luteum. Percentage of ewes in estrous during the first 6 days after the end of the MGA treatment was significantly lower (P ‹ 0.05, chi square) in the control group (42%) than in the groups: MGA22-ECP (74%); MGA22 (90%); MGA11-ECP (65%) and MGA11 (67%). The highest incidence of estrous after 72 h was also significantly lower (P ‹ 0.05) in the control group (37%) than in the: MGA22-ECP (63%); MGA22 (79%); MGA11-ECP (50%) and MGA11 (56%) groups. Ewes were inseminated with extended fresh semen 12 h after the onset of estrous. Although conception rates between the groups were not different, they were lower in groups: MGA22-ECP (22%) and MGA11-ECP (15%), than in groups MGA22 (53%), MGA11 (65%) and the control (42%), suggesting a detrimental effect of ECP upon fertility. It is concluded that an oral administration of MGA for 9 days is an efficient, practical and low cost method for estrous synchronization in ewes. The addition of ECP to the MGA treatment does not improve the degree of synchronization, and even seems to depress fertility.

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