Development of rabbit embryos during a 96-h period of in vitro culture after superovulatory treatment under conditions of elevated ambient temperature

High temperature impairs rabbit viability, feed consumption, growth and fecundity: examination of endocrine mechanisms

The aim of the present study was to examine the effect of high ambient temperature on rabbit feed consumption, growth, viability, and fecundity, as well as the morphology and endocrine function of gonadal and adrenal cells. Adult does and their offspring were kept at either a comfortable (20°C; control) or high (36°C) temperature throughout pregnancy and up until weaning of pups. Doe mortality and fecundity, and plasma concentrations of hormones were evaluated. In addition, granulosa cells were cultured with and without FSH to assess progesterone production. In the offspring, we assessed mortality, total feed consumption, feed efficiency, growth, plasma hormone concentrations, as well as the microstructure in ovarian granulosa cells, testicular Leydig cells, and adrenocortical cells. We observed greater mortality of both adult animals and offspring at the higher ambient temperature compared with the control. The higher ambient temperature suppressed feed consumption, feed efficiency, and growth of pups. Adult and young females exposed to a high temperature had lower circulating concentrations of progesterone, but not of estradiol, compared with controls. Young males exposed to a high ambient temperature had greater circulating concentrations of testosterone, but not progesterone, compared with controls. High ambient temperature reduced circulating IGF-I concentrations in all the animals. Corticosterone level was increased in plasma of young but not of adult animals. Granulosa cells isolated from the ovaries of does subjected to high temperatures released less progesterone, and they had poorer response to the stimulatory action of FSH than the cells from control does. High temperatures induced fragmentation of nucleoli in ovarian granulosa cells, but they did not alter the state of other organelles in ovarian, testicular, or adrenocortical cells. A negative influence of high temperature on rabbit feed consumption, growth, viability, and fecundity was observed. Taken together, these changes could be due to a decrease in IGF-I and/or progesterone secretion, destruction of ovarian cell nucleoli, and/or impaired ovarian cell response to FSH.

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 exposure to heatwave during blastocyst formation on reproductive performance of female rabbits

We examined the effect of female exposure to heatwave during blastocyst formation on their reproductive performance and its effect on transcriptome in blastocyst and endometrial tissue. In this study, a total of 72 rabbit does were artificially inseminated and divided into two environmental groups 2 days later: does under conventional conditions (maintained between 14-22°C, n = 29) and does heat stressed in a climatic chamber (maintained between 32-37°C, n = 43). The heat-stressed group were kept under these conditions for 3 days and returned to conventional conditions thereafter. Five days post-insemination, 48 does were slaughtered to collect blastocyst and endometrium samples. mRNA transcripts from OCT-4, VEGF, erbB3, Ifn-ɣ, HSP70 and HSP90 were analysed by qRT-PCR. At day 12 of gestation, 24 females were examined by laparoscopy to evaluate implanted embryos and at birth the total kits born and individual weights were recorded. Results revealed no gene expression changes in blastocyst and endometrial tissue under heatwave exposure. Moreover, our results demonstrated that rabbit embryos developed from 8-16 cells to blastocyst during a heatwave did not affect implantation rates, total number of kits born and foetal losses. In summary, these results demonstrate that heatwave period is not a critical point in the reproductive performance of rabbits during blastocyst formation.

Using the product threshold model for estimating separately the effect of temperature on male and female fertility

Animals under environmental thermal stress conditions have reduced fertility due to impairment of some mechanisms involved in their reproductive performance that are different in males and females. As a consequence, the most sensitive periods of time and the magnitude of effect of temperature on fertility can differ between sexes. The objective of this study was to estimate separately the effect of temperature in different periods around the insemination time on male and on female fertility by using the product threshold model. This model assumes that an observed reproduction outcome is the result of the product of 2 unobserved variables corresponding to the unobserved fertilities of the 2 individuals involved in the mating. A total of 7,625 AI records from rabbits belonging to a line selected for growth rate and indoor daily temperature records were used. The average maximum daily temperature and the proportion of days in which the maximum temperature was greater than 25°C were used as temperature descriptors. These descriptors were calculated for several periods around the day of AI. In the case of males, 4 periods of time covered different stages of the spermatogenesis, the transit through the epididymus of the sperm, and the day of AI. For females, 5 periods of time covered the phases of preovulatory follicular maturation including day of AI and ovulation, fertilization and peri-implantational stage of the embryos, embryonic and early fetal periods of gestation, and finally, late gestation until birth. The effect of the different temperature descriptors was estimated in the corresponding male and female liabilities in a set of threshold product models. The temperature of the day of AI seems to be the most relevant temperature descriptor affecting male fertility because greater temperature records on the day of AI caused a decrease in male fertility (-6% in male fertility rate with respect to thermoneutrality). Departures from the thermal zone in temperature descriptors covering several periods before AI until early gestation had a negative effect on female fertility, with the pre- and peri-implantational period of the embryos being especially sensitive (from -5 to -6% in female fertility rate with respect to thermoneutrality). The latest period of gestation was unaffected by the temperature. Overall, magnitude and persistency of the temperatures reached in the conditions of this study do not seem to be great enough to have a large effect on male and female rabbit fertility.