No seasonal effect on embryo donor performance in the southwest region of the USA

Detailed superovulation and embryo collection records from this commercial transplant unit were statistically analyzed to evaluate seasonal effects, if any, on embryo donor performance. The raw data set included all the superovulation-collection attempts (n=1,029) by this unit on beef donor females during a 12-month interval (1982). Seasons (fall, winter, spring and summer), breed types (European and Brahman), FSH treatment schedules (A, B and C) and two-way interactions were evaluated by analysis of variance for an effect on mean corpora lutea (CL), ova collection rate, ova collected, fertilized ova, fertilization rate, embryo degeneration rate, transferable embryos and transferable embryo rate. Parameters were analyzed in two different data sets. First, Data Set I included records from all cows started on superovulatory treatments during a 12-month period whether or not they responded to treatment and whether or not ova were recovered at the time of collection. Mean values from this data set would be for all females started on superovulatory treatments and should be viewed only for their economic implications. A more realistic approach was made with Data Set II, which includes only those records from donors responded to superovulatory treatment and where at least one ovum was recovered at the time of non-surgical collection. Results showed that there was no season effect on superovulatory responses and ova parameters for beef donors in Data Sets I and II. When parameters were evaluated by breed type, European breed types produced more transferable embryos per donor (P<.05) and had a greater fertilization rate and transferable embryo rate (P<.001) than Brahman-type donors in both Data Sets I and II. However, Brahman-type donor animals produced more ova per collection (P<.05) than European donors in Data Set II. Season × Breed Type interaction was not different for superovulatory response or embryo parameters. This information further establishes a data base for stating that season does not affect embryo donor performance in the southwestern region of the USA.