The concurrent and carry over effects of long term changes in energy intake before insemination on pregnancy per artificial insemination in heifers

Effects of pasture management and supplementation on the productive performance of recently lambed ewes

The hypothesis was tested that the performance of lactating ewes is affected by the supplementation level and pasture management. Two supplementation levels (0.5 and 1.0% of body weight, BW) and two pasture managements (mowed and non-mowed) were tested. Forty adult ewes (2 years old) with an average weight at lambing of 62.97 ± 7.0 kg (day 0) and an average the body condition score of 2.5 points (day 0) were evaluated. Verminosis was monitored with periodic deworming. The number of eggs per gram of feces (EPG) of ewes at lambing was used as a covariate for performance assessments. Ewes lost an average of 7.5 kg over the 90 days post-partum (12% BW). The weaning rate was 53%. The body condition of the ewes was influenced by the post-partum period. The ewes mobilized their body reserves in the first 30 days of lactation. Mowing management negatively affected the nutritive value of the forage. Supplementation with 0.5% BW was sufficient for nutritional management post-partum. Pasture management (mowed vs. not mowed) cannot prevent post-partum weight loss. Supplementation levels and pasture management altered the morphological and chemical components of the pasture.

Maternal metabolic health and fertility: we should not only care about but also for the oocyte!

Metabolic disorders due to obesity and unhealthy lifestyle directly alter the oocyte's microenvironment and impact oocyte quality. Oxidative stress and mitochondrial dysfunction play key roles in the pathogenesis. Acute effects on the fully grown oocytes are evident, but early follicular stages are also sensitive to metabolic stress leading to a long-term impact on follicular cells and oocytes. Improving the preconception health is therefore of capital importance but research in animal models has demonstrated that oocyte quality is not fully recovered. In the in vitro fertilisation clinic, maternal metabolic disorders are linked with disappointing assisted reproductive technology results. Embryos derived from metabolically compromised oocytes exhibit persistently high intracellular stress levels due to weak cellular homeostatic mechanisms. The assisted reproductive technology procedures themselves form an extra burden for these defective embryos. Minimising cellular stress during culture using mitochondrial-targeted therapy could rescue compromised embryos in a bovine model. However, translating such applications to human in vitro fertilisation clinics is not simple. It is crucial to consider the sensitive epigenetic programming during early development. Research in humans and relevant animal models should result in preconception care interventions and in vitro strategies not only aiming at improving fertility but also safeguarding offspring health.

Uterine infusion of bacteria alters the transcriptome of bovine oocytes

Postpartum uterine infection reduces fertility in dairy cattle; however, the mechanisms of uterine infection-mediated infertility are unknown. Paradoxically, infection-induced infertility persists after the resolution of disease. Oocytes are a finite resource, which are present at various stages of development during uterine infection. It is likely that oocyte development is influenced by uterine infection-induced changes to the follicular microenvironment. To better understand the impact of infection on oocyte quality we employed global transcriptomics of oocytes collected from heifers after receiving intrauterine infusion of pathogenic Escherichia coli and Trueperella pyogenes. We hypothesized that the oocyte transcriptome would be altered in response to intrauterine infection. A total of 452 differentially expressed genes were identified in oocytes collected from heifers 4 days after bacteria infusion compared to vehicle infusion, while 539 differentially expressed genes were identified in oocytes collected from heifers 60 days after bacteria infusion. Only 42 genes were differentially expressed in bacteria-infused heifers at both Day 4 and Day 60. Interferon, HMGB1, ILK, IL-6, and TGF-beta signaling pathways were downregulated in oocytes collected at Day 4 from bacteria-infused heifers, while interferon, ILK, and IL-6 signaling were upregulated in oocytes collected at Day 60 from bacteria-infused heifers. These data suggest that bacterial infusion alters the oocyte transcriptome differently at Day 4 and Day 60, suggesting different follicle stages are susceptible to damage. Characterizing the long-term impacts of uterine infection on the oocyte transcriptome aids in our understanding of how infection causes infertility in dairy cattle.

An overview on how cumulus cells interact with the oocyte in a condition with elevated NEFA levels in dairy cows

Metabolic stress in humans and animals is associated with impaired fertility. A major characteristic of metabolic stress is elevated levels of free fatty acids (NEFAs) in blood due to mobilization of body fat reserves. Dairy cows undergo a period of metabolic stress during the peri-calving period, the so-called negative energy balance (NEB) in the early weeks postpartum. At the time of NEB, both saturated and unsaturated NEFAs are mobilized to serve as an alternative energy supply for cells, however in particular saturated NEFAs can have a detrimental effect on somatic cells. Circulating NEFAs are also reflected in the follicular fluid of ovarian follicles and hence reach the cumulus-oocyte-complex (COC), which implies a potential risk for the developing oocyte. To this end, the current review focusses on the impact of NEFAs on the quality of the oocyte.

Conception rates and calving intervals of different beef breeds at a farm in the semi-arid region of Namibia

A retrospective study from 2004 to 2017 investigated the effect of bull age, cow age and breed on conception rates, and calving intervals of beef cattle at Neudamm farm, Khomas region, Namibia. Bulls ranging from 4 to 14 years of age were used to breed cows up to 17 years of age. A total of 1804 pregnancies were diagnosed in Afrikaner (81.8%), Nguni (14.1%), and Simmental (4.1%) cows. The overall conception rate of beef cattle during the study period was 71.7 ± 9.5%. The overall conception rate of the Nguni cows (78.3%) was significantly higher than that of the Afrikaner (70.9%) and the Simmental cows (64.9%) (p < 0.05). The age of sires had no effect on overall conception rate in all three breeds (p > 0.05). Afrikaner dams more than 10 years old had the least rate of conception (60.4%, p < 0.05) within that breed category. Nguni dams between four to 10 years had the greatest conception rate (86.5%, p < 0.05). Age of dams had no effect on conception rates in Simmental cattle (p > 0.05). The overall mean length of all calving intervals in the Nguni cows (366 ± 35 days) was significantly shorter than those of the Afrikaner cows (487 ± 62 days) and the Simmental cows (484 ± 110 days) (p < 0.05). The 2013 breeding season produced the highest overall conception rates (~ 85%), and the 2007 breeding season produced the lowest overall conception rate (~ 51%). From a fertility point of view, the Nguni breed seemed best suited for the semi-arid conditions which are prevalent in most of Namibia.

The influence of in vitro fertilization and embryo culture on the embryo epigenetic constituents and the possible consequences in the bovine model

Medically assisted reproductive technologies, such as in vitro embryo production, are increasingly being used to palliate infertility. Eggs are produced following a hormonal regimen that stimulates the ovaries to produce a large number of oocytes. Collected oocytes are then fertilized in vitro and allowed to develop in vitro until they are either frozen or transferred to mothers. There are controversial reports on the adverse impacts of these technologies on early embryos and their potential long-term effects. Using newly developed technological platforms that enable global gene expression and global DNA methylation profiling, we evaluated gene perturbations caused by such artificial procedures. We know that cells in the early embryo produce all cells in the body and are able to respond to their in vitro environment. However, it is not known whether gene perturbations are part of a normal response to the environment or are due to distress and will have long-term impacts. While the mouse is an established genetic model used for quality control of culture media in clinics, the bovine is a large mono-ovulating mammal with similar embryonic kinetics as humans during the studied developmental window. These model systems are critical to understand the effects of assisted reproduction without the confounding impact of infertility and without the limitations imposed by the scarcity of donated human samples and ethical issues. The data presented in this review come mostly from our own experimentation, publications, and collaborations. Together they demonstrate that the in vitro environment has a significant impact on embryos at the transcriptomic level and at the DNA methylation level.

Pregnancy losses in cattle: potential for improvement

For heifers, beef and moderate-yielding dairy cows, it appears that the fertilisation rate generally lies between 90% and 100%. For high-producing dairy cows, there is a less substantive body of literature, but it would appear that the fertilisation rate is somewhat lower and possibly more variable. In cattle, the major component of embryo loss occurs in the first 16 days following breeding (Day 0), with emerging evidence of greater losses before Day 8 in high-producing dairy cows. In cattle, late embryo mortality causes serious economic losses because it is often recognised too late to rebreed females. Systemic concentrations of progesterone during both the cycle preceding and following insemination affect embryo survival, with evidence of either excessive or insufficient concentrations being negatively associated with survival rate. The application of direct progesterone supplementation or treatments to increase endogenous output of progesterone to increase embryo survival cannot be recommended at this time. Energy balance and dry matter intake during the first 4 weeks after calving are critically important in determining pregnancies per AI when cows are inseminated at 70-100 days after calving. Level of concentrate supplementation of cows at pasture during the breeding period has minimal effects on conception rates, although sudden reductions in dietary intake should be avoided. For all systems of milk production, more balanced breeding strategies with greater emphasis on fertility and feed intake and/or energy must be developed. There is genetic variability within the Holstein breed for fertility traits, which can be exploited. Genomic technology will not only provide scientists with an improved understanding of the underlying biological processes involved in fertilisation and the establishment of pregnancy, but also, in the future, could identify genes responsible for improved embryo survival. Such information could be incorporated into breeding objectives in order to increase the rate of genetic progress for embryo survival. In addition, there is a range of easily adoptable management factors, under producer control, that can either directly increase embryo survival or ameliorate the consequences of low embryo survival rates. The correction of minor deficits in several areas can have a substantial cumulative positive effect on herd reproductive performance.

Effects of dry matter and energy intake on quality of oocytes and embryos in ruminants

The success of herd fertility involves the development of healthy follicles, viable oocytes and embryos capable of establishing and maintaining a pregnancy. Herein we discuss how nutrition interacts with reproduction throughout follicle development and pregnancy establishment, focusing on dry matter and energy intake. High feed intake, especially associated with moderate to high body condition, before and through superstimulation protocols, natural or induced single-ovulations or before ovum pick-up has detrimental effects on the quality of oocytes or embryos. Feed restriction or high energy supply can be used strategically to obtain either more or better quality oocytes or embryos. Altering diets that provide different concentrations of circulating insulin may improve ovarian status, oocyte quality, embryo development and pregnancy establishment and maintenance. Some sources of fat can positively affect reproductive performance, such as polyunsaturated fatty acids, improving embryo quality and pregnancy. In contrast, fat supplementation in the diet may compromise embryo cryotolerance. Finally, nutrition can alter concentrations of circulating or intrafollicular hormones and metabolites and the expression of genes in cattle oocytes and embryos. For an adequate feeding program to benefit reproductive performance, factors such as genetic group, source of energy, metabolic status, physiological status and level of feed intake must be taken into account.