The effects of calcitonin on the development of and Ca2+ levels in heat-shocked bovine preimplantation embryos in vitro

Impact of Heat Stress on Oocyte Developmental Competence and Pre-Implantation Embryo Viability in Cattle

Rectal and vaginal temperatures are utilised in both in vivo and in vitro models to study the effects of heat stress on oocyte competence and embryo viability in cattle. However, uterine temperature increases by only 0.5 °C in heat-stressed cows, significantly lower than simulated increases in in vitro models. Temperature variations within oviducts and ovarian follicles during heat stress are poorly understood or unavailable, and evidence is lacking that oocytes and pre-implantation embryos experience mild (40 °C) or severe (41 °C) heat stress inside the ovarian follicle and the oviduct and uterus, respectively. Gathering detailed temperature data from the reproductive tract and follicles is crucial to accurately assess oocyte competence and embryo viability under realistic heat stress conditions. Potential harm from heat stress on oocytes and embryos may result from reduced nutrient availability (e.g., diminished blood flow to the reproductive tract) or other unidentified mechanisms affecting tissue function rather than direct thermal effects. Refining in vivo stress models in cattle is essential to accurately identify animals truly experiencing heat stress, rather than assuming heat stress exposure as done in most studies. This will improve model reliability and aid in the selection of heat-tolerant animals.

Exploring the impact of heat stress on oocyte maturation and embryo development in dairy cattle using a culture medium supplemented with vitamins E, C, and coenzyme Q10

Heat stress is a significant factor affecting the fertility of dairy cattle due to the generation of free radicals. In assisted reproductive techniques, the inclusion of protective antioxidants becomes crucial to mitigate potential cellular damage. This study aimed to explore the impact of supplementing vitamins E, C, and coenzyme Q10 into the oocyte culture medium, with the goal of ameliorating the adverse effects of heat stress on oocyte maturation and embryo development in dairy cattle. A group of fifty Holstein dairy cows were synchronized, and their oocytes were harvested using the ovum pick-up method. High-quality oocytes were subjected to in vitro maturation (IVM) and in vitro fertilization (IVF) procedures, utilizing a culture medium containing, no supplements (Group 1), 100 μM of vitamins E (Group 2) and C (Group 3), along with 50 μM of coenzyme Q10 (Group 4). The ensuing zygotes were cultured, and the ensuing embryos were evaluated for blastocyst formation by the seventh day. An analysis of the blastocysts' inner cell mass (ICM) and trophectoderm (TE) cells was also conducted. The findings revealed that the group receiving supplementation of vitamin E and coenzyme Q10 exhibited significantly higher maturation and cleavage rates in comparison to both the control and the vitamin C groups. Furthermore, the count of ICM, TE, and blastocyst cells was notably elevated in the vitamin E supplemented group when compared to the control group. In summary, the effectiveness of vitamin E in enhancing IVM, IVF, and embryo development under conditions of heat stress surpassed that of vitamin C and coenzyme Q10.

Developmental programming of production and reproduction in dairy cows: II. Association of gestational stage of maternal exposure to heat stress with offspring's birth weight, milk yield, reproductive performance and AMH concentration during the first lactation period

Although the negative effect of maternal exposure to heat stress on production and reproduction of offspring has been reported, there are some discrepancies among various studies about which gestational stage is more critical in this regard. Therefore, the present research was conducted to identify during which stage(s) of pregnancy maternal exposure to heat stress would lead to more dramatic decrease in productive and reproductive performance of offspring. To this end, offspring were classified based on the gestational stage they were in utero exposed to heat stress into four categories, including heat stress exposure (HSE) during only the first trimester of gestation (HSE1), HSE during the first and second trimester of gestation (HSE2), HSE during the second and third trimester of gestation (HSE3) and HSE during only the third trimester of gestation (HSE4). In study I, data of birth weight, milk yield and reproductive variables of 11,788 offspring and data of the month they were conceived were retrieved. In study II, blood samples (n = 521) were collected from offspring in various categories of HSE for measurement of serum AMH. Offspring in HSE1 and HSE2 categories were heavier than offspring in HSE3 and HSE4 categories (P < 0.0001). Offspring in HSE1 and HSE3 categories had the lowest and highest milk production, respectively (P < 0.05). First service conception rate was the greatest and worst in HSE1 and HSE4 categories, respectively (P < 0.05). Service per conception and calving to conception interval were greater in HSE2 than HSE4 category (P < 0.05). Concentration of AMH was lower in HSE1 than HSE4 category (P < 0.05). In conclusion, the present study indicated that the early stage of gestation could be a more critical period for the negative impact of in utero heat stress on developmental programming of milk production and ovarian reserves. Yet an evident temporal pattern for the adverse effect of maternal heat stress on developmental programming of reproductive performance in offspring was not found.