Scarce Evidence of Heterosis for Growth Traits in Peruvian Guinea Pigs.

This study aimed to estimate the heterosis for productive traits in a two-way crossbreeding scheme. Four guinea pig lines were originally selected for the following traits: line P1 for the growth rate, P2 for the partial feed conversion rate, M1 for the growth rate of the litter at 10 days of age, and M2 for the litter size at birth. The comparison included 176 purebreds (P1: 46, P2: 43, M1: 54 and M2: 33) and 150 crosses (P1P2: 42, P2P1: 38, M1M2: 11 and M2M1: 59); body weights at birth, 10 days, weaning and 60 days of age were analyzed. A linear fixed-effect model was used, and heterosis was estimated as the difference between the average performance of the crossbred and pure-line animals. The pure line comparisons showed that P2 was lower than P1 for weight at 10 days and weaning weight, while all other comparisons between the paternal and maternal pure lines were not significant. The results indicated significant positive heterosis effects for both types of crosses, but only for birth weight: 3.7% for paternal crosses and 12.7% for maternal crosses. The heterosis estimates were mostly positive but not significant for all other traits. A reason for the low levels of heterosis could be that the lines are not very genetically differentiated. These results suggest that applying a two-way crossbreeding scheme within paternal and maternal guinea pig lines for meat production is not recommended due to the absence of heterosis for growth traits.

Cryosurvival of rabbit embryos obtained after superovulation with corifollitropin alfa with or without LH.

The efficiency of an embryo bank depends on provision of optimal conditions for recovery, cryopreservation and transfer to a breed or strain. In this sense, increasing the number of embryos available using superovulation should improve the cryobank efficiency. However, vagueness of response to conventional protocols to control or increase ovarian response and the quality of oocytes and embryos and their cryotolerance remain a challenge. The aim of our study was to evaluate the effect of corifollitropin alpha (CTP) and a recombinant human FSH (rhFSH), alone or supplemented with rhLH, on embryo cryosurvival by in vitro development and OCT4 and NANOG mRNA abundance at blastocyst stage and offspring rate. In vitro development of vitrified embryos was not significantly affected by superstimulation with or without rhLH supplementation, resulting in similar development rates to those of the control groups (fresh and vitrified embryos from non-superstimulated donor does). Blastocysts developed from vitrified embryos showed higher levels of OCT4 transcript abundance than fresh control, while NANOG transcript abundance was only higher in the blastocysts developed from vitrified embryos after superstimulation treatment in comparison with control groups. The implantation and offspring rates at birth were negatively affected by supplementation with rhLH. Both rhFSH or CTP vitrified embryo groups showed an implantation rate similar to those of the control groups, but an offspring rate lower than control. In conclusion, embryos produced using corifollitropin alpha did not compromise the cryosurvival of vitrified embryos in the rabbit. In addition, this study points out the negative effect of rhLH supplementation in terms of offspring rate on embryo vitrification.

Effect of corifollitropin alfa supplemented with or without LH on ovarian stimulation and embryo viability in rabbit.

There is increasing interest in using rabbits for research as a laboratory model as well as for industrial production of meat, wool and fur. Superovulation in animals is used to produce a maximum number of transferable embryos per donor, in order to either support genetic improvement programs, ex situ conservation or to optimize other biotechnologies. Over time, the use of this biotechnology has shown variable outcomes as a consequence of several factors, such as the origin of exogenous hormone, posology and the effect of gonadotropins used simultaneously, the donor and the environment. The aim of this study was to compare the efficacy of a single injection of corifollitropin alfa (CTP), alone or supplemented with LH, versus a FSH standard protocol of five equal doses administered twice daily to superovulate rabbit does (20 per group and 29 control females). We determined: 1) the impact of this stimulation on in vitro development and mRNA expression at blastocyst stage and 2) in vivo embryo development and viability rate at birth of transferred embryos. Our outcomes showed that the ovulation rate was similar among the different ovarian stimulation groups, reaching more than fourfold the ovulation rate of a control doe. While rates of embryos developing to the blastocyst stage after 48 h of in vitro culture were similar between groups, the hatched blastocyst rate was higher for superovulated embryos from CTP group. Moreover, no significant differences among mRNA expression of OCT4, SOX2 and NANOG genes were detected. Nevertheless, embryos from ovarian stimulated does with CTP + LH showed significantly higher implantation rates and survival at birth among the different ovarian stimulation groups and similar to those in the control group. In conclusion, the results of this study suggest that a single injection of long acting corifollitropin alfa can be effectively used in rabbits to elicit a more than fourfold increase in ovulation rate compared to control animals. In addition, the LH supplementation allows us to obtain similar in vivo embryo development results as in the control group.