Abstract
Data on 1,294 superovulations of Brahman, Gyr, Guzerat and Nellore females were used to evaluate the effects of: breed; herd; year of birth; inbreeding coefficient and age at superovulation of the donor; month, season and year of superovulation; hormone source and dose; and the number of previous treatments on the superovulation results. Four data sets were considered to study the influence of donors’ elimination effect after each consecutive superovulation. Each one contained only records of the first, or of the two firsts, or three firsts or all superovulations. The average number of palpated corpora lutea per superovulation varied from 8.6 to 12.6. The total number of recovered structures and viable embryos ranged from 4.1 to 7.3 and from 7.3 to 13.8, respectively. Least squares means of the number of viable embryos at first superovulation were 7.8 ± 6.6 (Brahman), 3.7 ± 4.5 (Gyr), 6.1 ± 5.9 (Guzerat) and 5.2 ± 5.9 (Nellore). The numbers of viable embryos of the second and the third superovulations were not different from those of the first superovulation. The mean intervals between first and second superovulations were 91.8 days for Brahman, 101.8 days for Gyr, 93.1 days for Guzerat and 111.3 days for Nellore donors. Intervals between the second and the third superovulations were 134.3, 110.3, 116.4 and 108.5 days for Brahman, Gyr, Guzerat and Nellore donors, respectively. Effects of herd nested within breed and dose nested within hormone affected all traits. For some data sets, the effects of month and order of superovulation on three traits were importants. The maximum number of viable embryos was observed for 7-8 year-old donors. The best responses for corpora lutea and recovered structures were observed for 4-5 year-old donors. Inbreeding coefficient was positively associated to the number of recovered structures when data set on all superovulations was considered.
Highlights
Multiple ovulation and embryo transfer technique (MOET) has been carried out in central units (CU) located in several regions of Brazil
According to Brazilian Society for Embryo Transfer (SBTE), since 1995, the number of transferred and frozen embryos has increased by 20% and 60%, respectively
The viable embryos average values ranging from 4.1 to 7.3, can be considered excellent for Zebu cattle, compared to 1.7 to 5.8 viable embryos per superovulation reported by Herrera-Alvarez et al, 1987; Coelho and Azevedo, 1991; Penna et al, 1998; Evangelista and Sousa, 1999
Summary
Multiple ovulation and embryo transfer technique (MOET) has been carried out in central units (CU) located in several regions of Brazil. With the introduction of breeding and conservation MOET nucleus schemes (Nicholas and Smith, 1983), in Brazilian Zebu cattle (Penna et al, 1998), these studies became more important. The reduction in generation interval when selection is carried out in MOET nucleus is important to genetic gain (Nicholas and Smith, 1983). MOET practice allows the birth of a broad number of progenies and the sire genetic evaluation earlier than usually obtained. When considering Zebu and crossbred donors, means of 1.7 to 5.8 viable embryos per superovulation were found (Coelho and Azevedo, 1991; Penna et al, 1998; Evangelista and Sousa, 1999)
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