Abstract

    The objective of this study was to evaluate the effect of reducing sperm numbers per insemination dose on fertility of cryopreserved buffalo bull semen. For this purpose, semen was collected at weekly intervals from a Nili-Ravi buffalo bull (Bubalus bubalis) using an artificial vagina in two batches. The ejaculates were split-sampled and diluted at 37°C with tris-citric acid extender having 15x10⁶ or 30x10⁶ motile spermatozoa/0.5 ml. After dilution, the semen was cooled to 4°C, equilibrated for 4 hours, packaged in 0.5 ml straws and frozen in programmable cell freezer. Fertility test based on 75-days first service pregnancy rate was determined under field conditions. A total of 500 buffaloes were inseminated with frozen semen and out of these 431 could be followed, 209 for semen straws packaged with 15x10⁶ spermatozoa/straw and 222 for doses filled with 30x10⁶ spermatozoa/straw. The inseminations were performed in two batches and each batch was spread over a period of three months. The fertility rate for sperm concentration of 15x10⁶ spermatozoa/0.5 ml vs. 30x10⁶ spermatozoa/0.5 ml (49.28 vs. 56.75%) was similar (P>0.05).  The fertility rates were also similar (P>0.05) in the first and second batch of inseminations performed with  15x10⁶ or 30x10⁶ spermatozoa/0.5 ml straw of cryopreserved semen. In conclusion, reduction of sperm number from 30x10⁶ to 15x10⁶ spermatozoa/0.5 ml dose of insemination did not affect fertility of cryopreserved buffalo bull semen.

Key words: Sperm number, frozen semen, fertility, AI, buffalo.