Effect of Nellore (Bos indicus) donor age on in vitro embryo production and pregnancy rate

Injectable progesterone in 13-month-old prepubertal Nellore heifers: effects on in vitro embryo production and pregnancy rate

The aim of this study was to evaluate the effect of injectable progesterone administration before ovum pick-up (OPU) on in vitro embryo production (IVEP) and pregnancy rate in prepubertal Nellore heifers. Twenty-three Nellore females, 13.04 ± 0.8 months of age, were randomly assigned to two groups: control group (no progesterone application) and progesterone group (intramuscular administration of 1 mL [150 mg/mL] progesterone 7 days before OPU). The second OPU was performed after 28 days (crossover between groups). After OPU, oocytes were selected for IVEP and a sample was fixed in 4% paraformaldehyde. Viable oocytes were subjected to immunofluorescence staining for IGFBP2 and caspase-3. For each oocyte, one image was generated per channel (A555 and A488 filters) and analyzed with the ImageJ program for the quantification of fluorescence intensity (in pixels). The produced embryos were transferred to multiparous Nellore cows and pregnancy was diagnosed by ultrasound 30 days after transfer. Data were analyzed using the MIXED and GLIMMIX procedure of SAS®. Treatment with injectable progesterone had no effect on the number or size of the antral follicles of heifers. No differences between the control and progesterone groups were observed for total number of aspirated oocytes (P = 0.78), viable oocytes (P = 0.80), cleavage rate (P = 0.60), or blastocyst rate (P = 0.56). There were no differences in pixel intensity between the two groups, nor in the levels of IGFBP2 or caspase-3. However, a difference was observed in the pregnancy rate of embryos produced from heifers of the progesterone group (42.1%; 32/76) when compared to the rate of embryos produced from control heifers (28.4%; 23/81) (P = 0.02). The use of injectable progesterone before OPU in prepubertal Nellore heifers does not improve IVEP but increases the pregnancy rate after transfer.

Livestock-Forest integrated system attenuates deleterious heat stress effects in bovine oocytes

Global warming poses significant challenges to the fertility of tropical dairy cattle. One promising approach to mitigate heat stress effects on reproductive function and reduce the carbon footprint is the use of integrated livestock-forest (ILF) systems. The aim of this study was to investigate the effects of two different systems, namely Full Sun (FS) and ILF, on maternal hyperthermia and oocyte quality of Holstein and Girolando heifers during the tropical summer season. The temperature-humidity index (THI) data revealed intense heat stress during the experiment. Both the system (P<0.01) and the breed (P<0.01) factors had a significant impact on vaginal temperature, being hyperthermia more pronounced in the FS system and in the Holstein breed. Over the five time points collected at a 33-day interval, we observed distinct patterns for ILF (P=0.65) and FS (P<0.001) systems, suggesting an adaptive response in animals kept in FS systems. Furthermore, oocyte quality assessment revealed an effect of the system for oocyte diameter (P<0.001) and levels of IGFBP2 (P<0.001), and caspase 3 levels showed a decrease in ILF compared to FS for both Holstein (P<0.001) and Girolando (P<0.001) breeds. Collectively, these parameters indicate that oocyte quality during the summer months was superior in animals maintained in the ILF system. In conclusion, the ILF system demonstrated promising results in attenuating maternal hyperthermia and mitigating its effects on oocyte quality. Additionally, our observations suggest that animals in the FS system may exhibit an adaptive response to heat stress.

Oocyte developmental potential and embryo production before puberty in cattle

With the development of in vitro technologies, embryos can be produced using oocytes retrieved directly from the ovaries, i.e., regardless of ovulation. This has allowed the use of different animal categories as oocyte donors, including prepubertal cattle. The advantages of using this strategy to shorten the generation interval and accelerate genetic gain over time were soon recognized, and the first offspring generated using oocytes collected from calves were born in the early 1990s. Nevertheless, embryo production from calves and prepubertal heifers remains a challenge. The oocytes collected before puberty present low in vitro developmental potential, and the subsequent blastocyst rates are consistently lower than those from pubertal females. The acquisition of developmental competence by the oocytes occurs progressively throughout the prepubertal period, which can be subdivided into an early, intermediate, and late prepubertal (or peripubertal) phases, each characterized by different physiological and endocrine features. Therefore, embryo yield increases with age but will only achieve its maximum after puberty. The most common strategy to improve oocyte developmental potential before puberty is the use of gonadotrophic stimulation prior to oocyte retrieval. The results with superstimulation, however, vary among studies, depending on the source, dose, and length of FSH treatment, as well as the age and breed of the donors. The use of calves and prepubertal heifers as oocyte donors should also consider the possible impacts of the oocyte retrieval technique (LOPU or OPU) and the use of exogenous hormones on their subsequent fertility and productive life.

Effects of donor age and reproductive history on developmental potential of ovum pickup oocytes in Japanese Black cattle (Wagyu)

The objectives of this study were to analyze the (1) effects of donor age and multiparity on development of in vitro fertilization (IVF) embryos after ovum pickup (OPU), (2) effects of repeated and consecutive OPU-IVF procedures on embryo development, and (3) embryo production from OPU-IVF in donors with differing embryo yields after multiple ovulation and embryo transfer technology (MOET) in Japanese Black cattle (Wagyu). Donors were pre-treated with low-dosage follicle-stimulating hormone (FSH; 200 IU total), and oocytes were collected via OPU and fertilized by IVF to generate blastocysts. The number of oocytes collected per OPU session per donor was lower in heifers (2-4 years old, 5.3 oocytes) than in primiparous and pluriparous cows (2-10 years old, 13.6-19.1 oocytes; P < 0.05). Rates of blastocyst development for oocytes from heifers (33.1%) were lower than for those from cows (2-10 years old, 44.1-54.3%; P < 0.05), and average blastocyst yield/OPU/animal was lower in heifers (3.7) than in 5-6 years old cows (10.1; P < 0.05). Donors undergoing five consecutive OPU-IVF sessions after low-dosage FSH showed similar oocyte retrieval (12.2-15.1 oocytes per OPU/animal), blastocyst development rates (35.6-45.0%), and embryo yield/OPU/animal (4.8-5.8; P > 0.05) across sessions. Additionally, embryo yield from OPU-IVF was significantly improved in animals with previous low embryo yield from MOET (5.9 vs. 2.6, respectively, P < 0.05). These results indicate that Wagyu cows with previous births can be more productive as OPU-IVF donors than heifers, and oocytes from donors undergoing to five consecutive OPU-IVF cycles are competent for embryo development without loss of embryo yield/OPU/animal. Moreover, OPU-IVF can be used for embryo production and breeding from all elite Japanese Black cattle, regardless of previous low embryo yield in routine MOET.

Effect of food supplementation on in vitro embryo production and growth performance in prepubertal Nelore heifers

In vitro embryos production from prepubertal heifers can help contribute to breeding programs; however, strategies are necessary to increase their embryo production. The aim of this study was to investigate the effects of two nutritional plans on oocyte recovery, embryo production and growth performance of prepubertal Nelore heifers. Thirty-four Nelore heifers with age of 6.5 months were divided into two feeding treatments (NP1 and NP2). The NP1 diets served as the control and NP2 diets were formulated to contain an average of 1.22-fold more energy than NP1. After 3 months of supplementation, the animals underwent follicular aspiration (ovum pick-up, OPU) every 21 d for 3 months and embryos were produced in vitro. Wither height, chest depth, body weight and subcutaneous fat of animals were measured. The number of retrieved and viable oocytes per OPU were 1.49-fold and 1.42-fold greater in NP2 heifers (p = 0.018 and p = 0.049, respectively) than those in NP1 heifers. Heifers administered NP2 produced 29.7% blastocysts, a percentage higher than NP1 animals that produced 24.40% embryos (p < 0.05). Consequently, females in the NP2 treatment showed improved body development. These results indicate a positive effect of a higher energy diet on assisted reproduction and body development in prepubertal heifers.

Perspectives of gene editing for cattle farming in tropical and subtropical regions

Cattle productivity in tropical and subtropical regions can be severely affected by the environment. Reproductive performance, milk and meat production are compromised by the heat stress imposed by the elevated temperature and humidity. The resulting low productivity contributes to reduce the farmer's income and to increase the methane emissions per unit of animal protein produced and the pressure on land usage. The introduction of highly productive European cattle breeds as well as crossbreeding with local breeds have been adopted as strategies to increase productivity but the positive effects have been limited by the low adaptation of European animals to hot climates and by the reduction of the heterosis effect in the following generations. Gene editing tools allow precise modifications in the animal genome and can be an ally to the cattle industry in tropical and subtropical regions. Alleles associated with production or heat tolerance can be shifted between breeds without the need of crossbreeding. Alongside assisted reproductive biotechnologies and genome selection, gene editing can accelerate the genetic gain of indigenous breeds such as zebu cattle. This review focuses on some of the potential applications of gene editing for cattle farming in tropical and subtropical regions, bringing aspects related to heat stress, milk yield, bull reproduction and methane emissions.