Determining the Effects of Nerve Growth Factor Supplemented In-vitro Fertilization Media on Bovine Embryo Development

Scientists have developed techniques like ovum pick up (OPU) and follicular ablation as a large source of oocytes for creating IVP bovine embryos. These techniques have allowed for more efficient dissemination of valuable female genetics compared to traditional artificial insemination or embryo flushing. IVP embryos have lower embryo development rates and quality, leading to lower pregnancy rates. Nerve growth factor-beta (NGF), however, has been previously shown to improve 48-hour cleavage rates and the number of hatching/ hatched blastocysts out of total presumptive zygotes. We hypothesize that NGF will improve IVP embryo development by positively influencing cleavage and blastocyst rates. The first two experiments' objectives were to determine the effect of recombinant bovine (60 or 90% purity) and human NGF (97% purity) supplementation during in vitro fertilization on 24- and 48-hour cleavage and day 8 blastocyst development rates. The objective of the third experiment was to assess the effect of the supplementation of bovine NGF (90% purity) on heat shocked and non-heat shocked in vitro-matured cumulus-oocyte complexes, assessing cleavage rates at 48 and 72 hours post insemination and blastocyst development rates. The results of experiment 1 show there were no differences between any of the three treatment groups (bNGF60, hNGF95, and control) for 24 hour (P = 0.66) or 48 hour (P = 0.33) embryonic cleavage rates. Additionally, there were no differences between treatments in the total percentage of blastocysts per oocyte (P = 0.91) or the percentage of blastocysts per cleaved embryo (P = 0.32). The results of experiment 2 also showed no differences between any of the three treatment groups (bNGF90, hNGF95, and control) for 24 hour (P = 0.16) or 48 hour (P = 0.18) embryonic cleavage rates. Additionally, there were no differences between treatments in the total percentage of blastocysts per oocyte (P = 0.42) or the percentage of blastocysts per cleaved embryo (P = 0.57). In the 3rd experiment, there was not a significant effect of treatment (P ≤ 0.05) at all stages of embryonic development assessed. On the contrary, in the third experiment, non-heat stressed NGF treatment had an interestingly detrimental effect on early cleavage rates of embryos compared to the non-treated control embryos. These results showed that NGF could not improve in vitro embryonic development rates in standard conditions; however, this negative impact of NGF on early cleavage was not observed in heat-shocked embryos. Suggesting that there could be a protectant factor in NGF that warrants further investigation.