Fertility and sex of calf results from a new commercial scale technology platform for producing sexed sperm

Abstract Text:

By 2016, sexed sperm constitutes ~8% of AI breedings in dairy and beef cattle.  Further growth in the application of sexed sperm is limited by the existing technology. We developed a novel technology for producing sexed sperm at commercial scale to better address current and future needs of genetics companies and their producer customers. For this new technology platform, purpose-built microfluidics and laser based cell destruction components were invented to enable accurate quantification of sperm DNA content and rapid and efficient destruction of unwanted cells while safeguarding sperm of the desired chromosomal content. To assess performance resulting from the sexed sperm, field trials were conducted in dairy herds across the U.S. Experiments compared sexed sperm (SEXED, 2×10⁶ motile sperm per straw) and non-sexed controls (CON, 10×10⁶ sperm) produced using split or contemporaneous collections from a total of 26 bulls (Holstein and Jersey). All treatments were packaged and cryopreserved in 0.25 ml straws. Quality checks for the new sexed sperm product were developed and included an estimate of numbers of progressively motile sperm per straw and a fluorescence in situ hybridization assay for determining sex chromosome content of live sperm. For experiment 1, post-thaw numbers of progressively motile sperm/straw ranged from 0.75 to 1.5 × 10⁶ for SEXED batches, 3.9 to 7.7 × 10⁶ for CON-Citrate, and 4.1 to 8.9 × 10⁶ for CON-Tris. Conception rates from virgin dairy heifers were 61.4%±1.5% (n=1091 pregnancy diagnoses) for citrate control, 60.7%±1.5% (n=1079) for CON-Tris, and 37.4%±1.5% (n=1082) for SEXED. For experiments 2 and 3, no Tris control was used.  Numbers of progressively motile sperm/straw ranged from 4.2 to 8.7 × 10⁶ for CON and from 0.74 to 1.6 × 10⁶ for SEXED batches. In experiment 2, conception rates in dairy heifers were 65.2%±1.5% (n=1005 pregnancy diagnoses) for CON and 46.2%±1.6% (n=1025) for SEXED. Conception rates for experiment 3 were equally favorable and were 64.1%±1.6% (n=900) for CON and 48.3%±1.7% (n=895) for SEXED. Sex chromosome content for live sperm was 87.2% X-bearing (weighted average) and ranged from 73% to 93% for individual batches of SEXED; as indicated by others, proportion of female calves as reported on-farm was somewhat lower at 84.6%±1.3% (n=775, experiments pooled) for SEXED. Proportion of female calves for CON was 50.5%±1.4% (n=1187, pooled). Our novel sexed sperm technology delivers a new platform enabling preselecting the sex ratio of offspring.

Keywords:

conception rate, sexed sperm, sex ratio