123 Induction of ovulation after artificial insemination in rabbits: intramuscular injection of gonadotrophin-releasing hormone analogue versus intravenous administration of mated doe serum

Rabbits are reflex ovulators with the ovulatory process triggered by neurohormonal impulses generated during natural mating. When applying AI, an array of biostimulation methods and/or exogenous hormones (e.g. gonadotrophin-releasing hormone (GnRH) or its analogues) must be used to induce ovulations in female rabbits. However, the effectiveness of various biostimulation techniques and exogenous hormones is not always satisfactory and the use of GnRH analogues is additionally associated with high production costs. Therefore, developing an inexpensive, efficient, and safe treatment for ovulation induction in AI does is urgently needed. In the present study, we examined and compared the effects of mated doe serum (MDS) and GnRH analogue (Gonadorelin) given immediately after AI on circulating concentrations of LH and fertility in New Zealand does. Mated doe serum was obtained from 40 donor females bled at 0, 1, 2, and 3 h after successful mating, and all blood samples were pooled and centrifuged at 3000 × g for 10 min. After centrifugation, the supernatant was separated and filtered under the sterile conditions, and then stored at 4°C for up to 24 h before use. Forty AI does were allocated to four equinumerous groups that received 0.2 mL of saline IM (Control G), 0.8 µg of Gonadorelin dissolved in 0.2 mL of saline IM (Treatment G), 2.5 mL of mixed-sex normal rabbit serum IV (Control M), or 2.5 mL of MDS/doe IV (Treatment M). Reproductive end points were analysed by the Pearson chi-squared test. A comparison of single time-point observations was done using one-way ANOVA at a 95% confidence level. Two-way repeated-measures ANOVA (RM-ANOVA) was used to compare circulating LH over time and among the four groups of does studied. A peak in systemic LH concentrations occurred earlier in treatment m than in treatment G does (71 ± 3 vs. 107 ± 6 min post-AI, respectively; mean ± s.e.m.; P < 0.05); mean LH concentrations did not vary (P > 0.05) from the pre-AI values in both control groups. Serum LH concentrations remained higher (P < 0.05) in treatment m compared with treatment G does from 30 to 90 min post-AI but they were greater (P < 0.05) in treatment G than in treatment m at 120 and 160 min after AI. Gonadorelin and MDS injections both resulted in the same kindling rate of 80% at each of the four consecutive AIs (last three AIs starting 30 days postpartum) and it was significantly greater than that recorded in control animals (20%). We concluded that MDS administration is an effective treatment to induce ovulations in rabbits, with the repeatability similar to that achieved with a GnRH analogue. We demonstrated that a relatively simple, drug-free, and inexpensive method could be used by rabbit breeders to induce ovulations after AI using the serum of pregnant rabbits. This novel approach could significantly reduce production costs and help provide lower-cost protein for the world’s growing population.