Relationship of semen quality, number of sperm inseminated, and fertility in rabbits.

ABSTRACT The relationship between the total number of sperm inseminated, semen quality, and fertility in rabbits was investigated, using fractionated or unfractionated semen and different diluting fluids. Semen was from Dutch-belted males collected twice weekly with an artificial vagina. All does were superovulated except in Experiment 3. In Experiment 1, sperm were fractionated on discontinuous 4% and 10% bovine serum albumin columns. Sperm from each portion of the gradient, along with unfractionated controls, were diluted to give 0.25 × 106, 0.5 × 106, 1.0 × 106, and 2.0 × 106 total sperm per insemination. In Experiment 2, sperm were diluted with Dulbecco's phosphate-buffered saline to provide 0.10 × 106, 0.50 × 106, and 1.0 × 106 total sperm per insemination, with minimal processing time. In Experiment 3, does were allowed to kindle after inseminating 0.1 × 106 or 1.0 × 106 sperm. In Experiment 4, sperm were diluted with TALP buffer: seminal plasma 1:1 to 0.025 × 106, 0.05 × 106, and 0.10 × 106 total sperm per insemination. Over 2,800 embryos or unfertilized oocytes were obtained either 24 or 48 hours after insemination to measure fertility. Sperm numbers required for normal fertility were 0.50 × 106 in Experiment 1 and only 0.05 × 106 in Experiment 4. This reduction presumably was due primarily to reduced processing time and diluent change. Litter size was normal with 0.1 × 106 sperm (Experiment 3). In Experiment 4, computer-assisted sperm analysis (HTM 2030 system; Beverly, Massachusetts) was adapted to successfully screen out some of the “inter-fering” granules in rabbit semen. The correlation between multiple characteristics of semen quality and fertility was 0.53 (P < 0.01). This correlation likely will be increased with refinements in instrumentation and reduced sperm numbers per insemination.