25 TIMED ARTIFICIAL INSEMINATION ENABLES HIGH FERTILIZATION RATES IN NORMAL CYCLING AND IN SUPEROVULATED CATTLE WITH REDUCED DOSAGES OF UNSORTED SPERMATOZOA AND WITH SEXED SPERMATOZOA

Abstract

Different factors determine the effectiveness of the use of sires in AI. Most important factors are the number of inseminated spermatozoa, the quality of spermatozoa, and the time of insemination. Especially in superovulated animals, the insemination scheme plays in important role to cover the whole ovulation period. The influence of 3 different dosages of spermatozoa (15 × 10⁶, 5 × 10⁶, and 1 × 10⁶) on fertilization rate was examined in experiment A. In experiment B, one dosage of female and male spermatozoa of 3 different bulls was used for timed AI in 31 heifers. Timed AI in normal-cycling cattle [13 h after gonadotropin-releasing hormone (GnRH) application] with detected corpus luteum (Days 8 to 13 of cycle) was carried out after induction of luteolysis and induction of ovulation [GnRH application 60 h after prostaglandin F_2α (PGF2) application]. Embryos and oocytes were flushed from the oviduct of 116 hemicastrated or slaughtered heifers on Day 4 after insemination. The ovulation rate in heifers was 95.4%. Eighty percent of the oocytes or embryos were recovered. The influence of the factors sire, ejaculate, and dosage were tested by GLM analyses of SAS^® (SAS Institute Inc., Cary, NC, USA). There was no significant difference in the fertilization rate (93.3, 96.2, and 78.8%) and in the proportion of normally developed embryos (84.6, 80.7, and 75.8%) between groups. Significant differences were found in the mean number of accessory sperms/embryo and in the proportion of embryos with >10 accessory sperms/embryo or without accessory sperms; however, the proportion of intact embryos was similar. Using sexed semen in experiment B, similar results were obtained after flushing of the oviducts on Day 4 after insemination of hemicastrated or slaughtered animals. In total, an ovulation rate of 91.7%, a recovery rate of 70%, and a fertilization rate of 86.8% were obtained. There were no differences between female- and male-sorted spermatozoa and the control group. In experiment C, altogether 13 heifers were treated 8 times with FSH for 4 days starting between Day 8 to 12 of estrous cycle. Prostaglandin F_2α was given 48 and 60 h after the first FSH injection. Insemination with sexed semen (n = 5 heifers) and with unsorted semen (n = 8; 15 × 10⁶ and 1 × 10⁶) was done at 55 and 71 h after induction of luteolysis. Flushing of the uterus was performed on Day 7. Using the time-oriented insemination after superovulation of animals, fertilization rates varied between 65 and 85%. There was no difference between groups regarding the number of transferable embryos (5.5, 4.9, and 4.8). The results demonstrate that the application of an approved insemination schedule may accomplish high fertilization rates after insemination with sexed or reduced dosages of spermatozoa in normal-cycling as well as superovulated cattle.