222 Effective donor selection before superovulation treatment for Japanese Black beef cattle

Abstract

Japanese Black beef cattle (JBBC) are a leading Wagyu breed in Japan. Embryo transfers are being used to improve JBBC, a sturdy, fast-maturing breed prized for its marbled beef; however, relevant donor selection techniques have not been fully established. Accordingly, in this study, in order to produce embryos efficiently, we aimed to investigate donor selection techniques based on follicle counts at different time points (Experiment 1) and an associated genetic marker (Experiment 2). Statistical differences were evaluated with Student's t-test or Welch's t-test, regarding P < 0.05 as significant. In Experiment 1, we initially targeted 57 JBBCs for evaluation. Their follicle counts were determined by ultrasound 3 days before the start of superovulation (pre), close to the time of follicular wave emergence, and they were grouped according to number of follicles (0-19, 20-29, 30-39, and ≥40). Each cow was administered a tapered dose of FSH-R (20 AU) for superovulation, and then subjected to AI with cryopreserved semen from bulls of proven fecundity. Embryos were collected 7 days after AI by non-surgical intrauterine reflux. Post-AI follicle counts were done before ovulation and did not differ significantly from pre-superovulation follicle count in any group (range: −1.09 to 0.61). We then targeted a further 12 JBBC undergoing superovulation and AI with the same procedures, for counting of follicles at 30 days before (Day −30) embryo recovery (ER), pre-superovulation, and AI, and counting of corpora lutea and large follicles at ER, to investigate correlations between counts. We used decision coefficient (R²), regarding R² ≥ 0.5 as significant. We found positive correlations (R²) at Day −30 with pre-superovulation (0.91), AI (0.63), and ER (0.63), and at pre-superovulation with AI (0.69) and ER (0.74). In Experiment 2, we targeted 69 JBBCs for detection of mutations in the GRIA1 gene, which encodes inotropic glutamate receptor AMPA1 with a known association with ovulation rate, and embryo yield measurements. DNA obtained from blood was subject to microsatellite polymorphism analysis, for mutations at base 917 of GRIA1 exon 7. We identified 33 cows (48%) as bearers of the wild-type allele (GG), 29 cows (42%) as bearers of the heterozygous mutation (GA), and seven cows (10%) as bearers of the homozygous mutation (AA). Average embryo yield was highest in wild-type cows, followed by heterozygous mutants and then homozygous mutants, and was significantly lower for homozygous mutants than for the other two types. Our study results demonstrated that follicle count before superovulation and GRIA1 gene analysis have utility for selecting donors for embryo transfer in JBBC. Furthermore, follicle counts at the early time point of 30 days before ER can be a useful indicator for this selection.