Minimum Number of Sex-Sorted Frozen Sperm per dose in Sahiwal (Bos indicus) Cattle

The aim of this study was to determine the minimum number of sex-sorted frozen sperm required for reasonable pregnancies in Sahiwal cow and heifers. Ejaculates from six Sahiwal bulls were processed according to Beltsville sperm sorting technology using a high speed cell sorter and sorted sperm were packaged in 0.25 ml straws with 1.5 million sperm per straw. Non-synchronized Sahiwal heifers (n= 82) and cow (n= 67) were inseminated with unsexed frozen semen (20 million) and sex-sorted frozen semen with 1.5, 3.0 and 4.5 million sperm per dose. Significantly (P < 0.05) lower pregnancy rate was recorded at 1.5 million (25.3%) and 3.0 million (32.5%) sperm compared to unsexed semen (45.4%) and sexed semen of 4.5 million (60%) sperm. No significant difference was found between sexed semen of 4.5 million sperm and unsexed semen. Pregnancy rates of 1.5 and 3 million sexed sperm were 56% and 72% of unsexed semen, respectively. Significantly (P < 0.05) lower pregnancy rates were observed in sorted X- semen (31.32%) and Y- semen (27.30%) compared to unsexed semen (45.40%). Pregnancy rates were significantly (P < 0.05) affected by the sire. The present work indicates that sexed semen as low as 3 million represents an optimal insemination dose and can be used to achieve reasonable pregnancy rates in Sahiwal cattle.