Reproductive performance of goats treated with free gonadorelin or nanoconjugated gonadorelin at oestrus

Abstract The reproductive performance of goats that received a GnRH analogue (gonadorelin) fabricated with or without chitosan-TPP nanoparticles on the day of oestrus (day 0) was evaluated. The chitosan-TPP polymer was conjugated with gonadorelin using an ionic gelation method. Thirty-three multiparous Zaraiebi goats were synchronized for oestrus with two intramuscular (im) injections of 125 μg PGF2α 14 days apart. Goats showing signs of oestrus were divided equally into three experimental groups and received a single im injection of 1 mL physiological saline (placebo; control), 50 μg/mL gonadorelin (GnRH) or 12.5 μg (quarter of GnRH dose)/mL chitosan-TPP-conjugated gonadorelin nanoparticles (NGnRH). Each goat underwent ultrasound imaging of their ovaries at day 0 and at day 10 post-mating, and pregnancy was diagnosed 28 and 45 days post-mating. The concentrations of oestradiol (E2) and progesterone (P4) were determined at day 0 and at days 0, 7, 14, 21, and 42 postmating. NGnRH size, polydispersity (PdI) and zetapotential were 93.91nm, 0.302 and 11.6 mV, respectively. Chitosan-TPP nanoparticles showed 91.2% entrapment efficiency for GnRH. No differences in oestrous rate, interval to oestrus or ovarian structure at day 0 were observed among the experimental groups, but the GnRH and NGnRH treatments significantly decreased the duration of oestrus compared to the control. At day 10 post-mating, both GnRH and NGnRH increased (P = 0.011) the number of corpora lutea (CL) compared with the control. Treatment with GnRH increased (P = 0.023) serum E2 concentrations from day 7 to 42 post-mating compared to NGnRH and control treatments. The highest (P = 0.043) serum P4 concentration was observed in the GnRH-group, followed by the NGnRH and control groups. The increase in serum P4 concentration started earlier at day 7 in the GnRH-group but later at day 14 in the NGnRH-group. Compared to the control, GnRH resulted in a higher (P = 0.041) P4 to E2 ratio, followed by NGnRH. Both gonadorelin treatments significantly increased the twinning rate, the number of embryos at days 28 and 42 and prolificacy and decreased pregnancy losses compared to the control. In conclusion, the administration of GnRH at the time of oestrus improved the prolificacy of goats by increasing both the ovulation rate and the number of embryos. In addition, the nanoformulation developed in this study allowed a 75% reduction in the conventional dose of gonadorelin without affecting the fertility and prolificacy of goats, indicating the bioavailability of the reduced GnRH dose after conjugation with developed nanoformula.