Pregnancy rate and birth rate of calves from a large-scale IVF program using reverse-sorted semen in Bos indicus, Bos indicus-taurus, and Bos taurus cattle

Obtaining sexed sperm from previously frozen doses (reverse-sorted semen [RSS]) provides an important advantage because of the possibility of using the semen of bulls with desired genetic attributes that have died or have become infertile but from whom frozen semen is available. We report the efficiency of RSS on the pregnancy rate and birth rate of calves in a large-scale program using ovum pick-up and in vitro embryo production (IVEP) from Bos indicus, Bos indicus-taurus, and Bos taurus cattle. From 645 ovum pick-up procedures (Holstein, Gir, and Nelore), 9438 viable oocytes were recovered. A dose of frozen semen (Holstein, Nelore, Brahman, Gir, and Braford) was thawed, and the sperm were sex-sorted and cooled for use in IVF. Additionally, IVF with sperm from three Holstein bulls with freeze-thawed, sex-sorted (RSS) or sex-sorted, freeze-thawed (control) was tested. A total of 2729 embryos were produced, exhibiting a mean blastocyst rate of 29%. Heifers and cows selected for adequate body condition, estrus, and health received 2404 embryos, and 60 days later, a 41% average pregnancy rate was observed. A total of 966 calves were born, and 910 were of a predetermined sex, with an average of 94% accuracy in determining the sex. Despite the lower blastocyst rate with freeze-thawed, sex-sorted semen compared with sex-sorted semen, (P < 0.05), the pregnancy rate (bull I, 45% vs. 40%; II, 35% vs. 50%; and III, 47% vs. 48% for RSS and control, respectively; P > 0.05) and sex-sorted efficiency (bull I, 93% vs. 98%; II, 96% vs. 94%; and III, 96% vs. 97% for RSS and control, respectively; P > 0.05) were similar for each of the three bulls regardless of the sperm type used in the IVF. The sexing of previously frozen semen, associated with IVEP, produces viable embryos with a pregnancy rate of up to 40%, and calves of the desired sex are born even if the paternal bull has acquired some infertility, died, or is located a long distance from the sexing laboratory. Furthermore, these data show the feasibility of the process even when used in a large-scale IVEP program.

Birth of offspring after artificial insemination of heifers with frozen-thawed, sex-sorted, re-frozen-thawed bull sperm

Two field trials were conducted to determine the fertilising capacity of (i) frozen-thawed, sex-sorted re-frozen-thawed (FSF) dairy bull sperm inseminated close to the time of ovulation, (ii) FSF sperm following large dose insemination, and frozen-thawed, sex-sorted (FS) sperm inseminated within 12h after sorting. In Trial 1, 24 heifers in synchronised oestrus were observed for standing heat over a 30-min period once every 3h. Upon observation of standing heat, the size of the pre-ovulatory follicle was tracked by ultrasound every 6h until ovulation was judged to be imminent. Heifers were inseminated with 4 x 10(6) X-bearing FSF or Control sperm within 6h of ovulation. Ovaries were scanned 6h after AI to ensure ovulation had occurred. All 24 heifers displayed standing oestrus and 20 of these subsequently ovulated. The mean length of standing oestrus was 16.8+/-0.4h and ovulation occurred 27.6+/-1.1h after the onset of standing heat from a pre-ovulatory follicle with a diameter of 16.1+/-0.3mm. All 12 heifers that received FSF sperm returned to oestrus<26d after AI. Of 8 heifers that received Control sperm, 6 (75%) were confirmed pregnant by ultrasound 7 wk after AI, confirming that the method of AI and herd fertility were sound. In Trial 2 the number of sperm inseminated and the effect of eliminating the post-sort cryopreservation step were investigated. Heifers (n=21) were synchronised for oestrus, and inseminated 24h after the onset of standing oestrus with 10 x 10(6) X-bearing FSF, 4 x 10(6) X-bearing FS, or 10 x 10(6) non-sorted frozen-thawed (Control) sperm. Heifers were observed for return to oestrus from 21d, and diagnosed for pregnancy 7 wk after AI. Of the 7 heifers that received FSF sperm, one was confirmed pregnant (14.3%) and delivered a female calf. Four heifers inseminated with control sperm became pregnant and calved, but no pregnancies were obtained using FS sperm. The birth of a calf following AI with FSF sperm demonstrates the potential of sorting from frozen-thawed semen, and with further work, may be a promising technique that will give producers access to sexed sperm from a greater range of bulls.