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 12 h after sorting. In Trial 1, 24 heifers in synchronised oestrus were observed for standing heat over a 30-min period once every 3 h. Upon observation of standing heat, the size of the pre-ovulatory follicle was tracked by ultrasound every 6 h until ovulation was judged to be imminent. Heifers were inseminated with 4 × 106 X-bearing FSF or Control sperm within 6 h of ovulation. Ovaries were scanned 6 h 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 ± 0.4 h and ovulation occurred 27.6 ± 1.1 h after the onset of standing heat from a pre-ovulatory follicle with a diameter of 16.1 ± 0.3 mm. All 12 heifers that received FSF sperm returned to oestrus < 26 d 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 24 h after the onset of standing oestrus with 10 × 106 X-bearing FSF, 4 × 106 X-bearing FS, or 10 × 106 non-sorted frozen-thawed (Control) sperm. Heifers were observed for return to oestrus from 21 d, 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.