202 SEX PRE-SELECTION IN RABBITS: AN ATTEMPT TO SKEW OFFSPRING SEX THROUGH PERCOLL AND SWIM-UP SPERM PREPARATION TECHNIQUES

Abstract

Sperm preparation techniques could have an effect on the birth ratio (male vs female offspring) through enrichment of either X- or Y-bearing sperm populations, although studies have been poorly controlled and results have been inconclusive. In the rabbit, producers may be interested in producing a majority of males (meat producing systems) or females (hybrid producing systems). The objective of this study was to evaluate the effect of modified Percoll and Swim-up protocols on the enrichment of the male and female birth ratios in rabbits. Four hybrid mature bucks of adequate body condition score and proven fertility were used. The same four bucks were used throughout the study (8 replicates). Ejaculates were collected using a warmed, solid, artificial vagina. Progressive motility was assessed at 200× magnification under brightfield microscopy on a heated (37°C) stage. Sperm concentration for each buck was determined using a Neubaur chamber and adjusted (350 × 10⁶ total spermatozoa mL^–1); they were then combined (1 mL/buck) to form a heterospermic sample (final heteropsermic sample volume = 4 mL). The heteropsermic sample was then divided into 3 sperm preparation treatments: (1) diluted in commercial tri-buffered extender followed by immediate AI (control); (2) modified Percoll centrifugation in a 90 to 45% density gradient (diluted in human tubal fluid medium); and (3) Swim-up (in human tubal fluid medium). In total, 125 females were inseminated. Does were treated with PMSG (20 UI/doe, 48 h before AI) and inseminated with 30 to 40 × 10⁶ spermatozoa; ovulation was induced with 20 μg of gonadotropin-releasing hormone (GnRH)/doe immediately after AI. Sex of newborn kits was determined 35 days after birth by an experienced technician through external visualization of genitalia. Results were statistically analyzed using ANOVA and Tukey test (Infostat). The insemination of does with heterospermic ejaculates (control) resulted in a progeny distribution of 49 ± 2% males and 51 ± 2% females, which is in good agreement with the expected theoretical 50:50 ratio. Sex ratios from modified Percoll and Swim-up treatments deviated significantly from the control (P < 0.01). Percoll gradient resulted in a progeny distribution of 32 ± 2% males and 68 ± 2% females; Swim-up resulted in a 64 ± 2% male and a 36 ± 2% female distribution (P < 0.01), whereas prolificacy, perinatal mortality and birth weight were not affected by treatment (Table 1). Our results indicate sperm preparation techniques could be used to skew birth ratios towards male or female offspring in rabbits; Percoll preparation could be used to increase proportion of female kits whereas Swim-up could be used to increase the proportion of males. Further studies are needed to determine the underlying mechanisms of action.

Table 1.  Progeny distribution after Percoll or Swim-up sperm preparation in rabbits