Fertility of fresh and frozen sex-sorted semen in dairy cows and heifers in seasonal-calving pasture-based herds

摘要

Our objective in this study was to evaluate the reproductiveperformance of dairy heifers and cows inseminatedwith fresh or frozen sex-sorted semen (SS) inseasonal-calving pasture-based dairy herds. Ejaculatesof 10 Holstein-Friesian bulls were split and processed toprovide (1) fresh conventional semen at 3 × 10~6 spermper straw (CONV); (2) fresh SS at 1 × 10~6 sperm perstraw (SS-1M); (3) fresh SS semen at 2 × 10~6 spermper straw (SS-2M); and (4) frozen SS at 2 × 10~6 spermper straw (SS-FRZ). Generalized linear mixed modelswere used to evaluate the effect of semen treatment andother explanatory variables on pregnancy per artificialinsemination (P/AI) in heifers (n = 3,214) and lactatingcows (n = 5,457). In heifers, P/AI was greater forinseminations with CONV (60.9%) than with SS-FRZ(52.8%) but did not differ from SS-1M (54.2%) or SS-2M (53.5%). Cows inseminated with CONV had greaterP/AI (48.0%) than cows inseminated with SS, irrespectiveof treatment (SS-1M, SS-2M, and S-FROZEN;37.6, 38.9, and 40.6%, respectively). None of the SStreatments differed from each other with regard to P/AI in either heifers or cows. The relative performance ofSS compared with CONV was also examined [i.e., relativeP/AI = (SS P/AI)/(CONV P/AI) × 100]. FrozenSS achieved relative P/AI >84%. Bull affected P/AI inboth heifers and cows, but no bull by semen treatmentinteraction was observed. In heifers, P/AI increasedwith increasing predicted transmitting ability for milkprotein percentage. In cows, P/AI increased with increasingEconomic Breeding Index (EBI) and with daysin milk (DIM) at AI but decreased with increasing EBImilk subindex, parity and with DIM~2. Cows in parity≥5 had the lowest P/AI and differed from cows in parities1, 2, or 3. Dispatch-to-AI interval of fresh semen didnot affect P/AI in lactating cows, but a dispatch-to-AIinterval by bull interaction was detected whereby P/AIwas constant for most bulls but increased with greaterdispatch-to-AI intervals for 2 bulls. In conclusion, frozenSS achieved greater P/AI relative to conventionalsemen than was previously reported in lactating cows.Fresh SS did not achieve greater P/AI than frozen SS,regardless of whether the sperm dose per straw was 1 ×10~6 or 2 × 10~6. A bull effect for all semen treatments, aswell as a dispatch-to-AI interval by bull interaction forfresh semen, highlights the importance of using a largeteam of bulls for breeding management.