Abstract
The effect of dose of pregnant mare serum gonadotropin (PMSG) was determined on the superovulatory response and follicular development in 50 cycling, mature Pelibuey ewes following treatment with Syncro-mate-B (SMB) implants. A randomized complete block design with five treatments was utilized; all ewes were treated for 10 days with SMB implants and at the end of the treatment, groups of 10 ewes each were randomly allocated and treated with 1-500, 2-1000, 3-2000, 4-3000 or 5-4000 IU of PMSG, 24 h prior to SMB removal. Ovarian responses were recorded as the number of corpora lutea (CL) and the number and size of follicles present 5–6 days after estrus, by means of a midventral laparotomy. The percentage of ewes responding to treatment, determined by the presence of unovulated follicles, was significantly different ( p<0.01) among treatments, these values were 50, 60, 90, 80 and 100%, respectively, for the groups 1–5. The number of unovulated follicles was also different ( p<0.05), among the treatment groups, the corresponding means (±SEM) were 0.7±0.63, 2.4±4.07, 8.0±4.7, 9.4±7.03 and 9.0±5.6 follicles per ewe, respectively, for the treatment groups 1–5. The overall percentage of ewes ovulating was 80%. The percentage of ewes ovulating at least once per group was also different ( p<0.01) among the treatment groups, the corresponding values per group were 70, 60, 100, 80 and 90%; whereas the percentage of ewes ovulating at least twice was 48% and the corresponding treatment group values were 30, 20, 80, 60 and 50%, respectively. These values were significantly different ( p<0.01). The mean number of CL for the ewes with two or more CL among the treatment groups was different ( p<0.05); the values being 1.5±2.4, 1.0±2.1, 6.9±6.1, 4.4±4.2 and 4.6±5.4 CL per ewe. It is concluded from these results, that Pelibuey ewes can be effectively superovulated with a dose of PMSG of 2000 IU.
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