Resumo
Background: Lactating dairy cow of the 21st century is considered to be sub-fertile after intensive selection for milk yield. Production of the dairy cows exemplifies the progress that can be made in the application of technology and holistic dairy cow management to optimize production. The hormonal and metabolic responses, associated with homeorrhetic and homeostatic regulatory responses to partition nutrients for lactation, coupled with intensive management contribute to the reduction in fertility. The numerous postpartum reproductive and metabolic disorders are associated with sub-optimal fertility in the breeding period. Continual advancements have been made in reproductive/lactation physiology, endocrinology, nutrition, herd health and management to improve reproductive herd fertility on commercial dairies. Objective of this presentation is to focus on current technologies and experimental approaches relative to their application in unraveling certain biological windows, which will further impact our ability to enhance reproductive efficiency coupled with increased food production and well-being of both animals and humans. Review: Feeding of omega 6- and omega 3- polyunsaturated fatty acids exert pro- and anti- inflammatory effects on the innate immune system that increases subsequent reproductive performance. Chronic exposure to a GnRH-agonist induced a marked atrophy of the postpartum uterus. Colostrum contains a pleothera of growth factors (lactocrine secretions) that influence uterine developmental programming in the pig, and neonatal exposure to estrogens/progesterone in pigs or cattle alters early programming of the uterus leading to dysfunctional reproductive tract consequences in the adult. Physiological systems to optimize ovarian and uterine function have led to timed insemination fertility programs that have enhanced herd pregnancy rates. Sequencing of the bovine genome has provided an array of new technological approaches to unravel the multi-factorial control systems to support conceptus-placental development throughout gestation and avoid pregnancy failure. A bovine microarray identified genes that were differentially expressed in conceptus and endometrial tissues at day 17 post-LH surge in cyclic and pregnant cows that were lactating or nonlactating. Expression of PAG genes within the conceptus and endometrium of pregnant cows and their association with other genes determined by standard partial correlation analyses infer a possible role of PAG in pregnancy maintenance and implantation by regulation of embryo development, trophoblast cell invasion, immune regulation, and prostaglandin metabolism. The associations detected are suggestive of potential pathways for investigation in early pregnancy at day 17 involving potential direct and indirect effects of PAG 11 produced by the conceptus. Development of microarrays of single nucleotide polymorphisms (SNP) across the bovine genome has led to Genomic Predicted Transmitting Abilities (GPTA) for various production traits including daughter pregnancy rates. More specific physiological reproductive traits have sufficient heritabilities that warrant consideration for selection. Furthermore, current technological advances are identifying candidate "fertility" genes for potential genetic selection, selection for production, health and reproductive traits will be the wave of the future as genomic and bioinformatic tools continue to be expanded and refined. Conclusion: This manuscript targets biological windows and technological advancements to improve reproductive performance of lactating dairy cows. Epidemiological analyses reveal that healthy postpartum lactating dairy cows are indeed fertile. Chronic exposure to a GnRH agonist induced postpartum uterine atrophy warranting additional research as to potential strategies to improve uterine health. Feeding of nutraceuticals such as polyunsaturated omega-6 and omega-3 fatty acids improves postpartum innate immune function and subsequent reproductive performance. Lactocrine secretions in colostrum and neonatal exposure to estrogens and progesterone influence uterine developmental programming related to subsequent reproductive competence. Reproductive management programs that optimize ovarian and uterine function permit a fertile single timed insemination to first and second inseminations. The sequencing of the bovine genome has led to thorough characterizations of the endometrium and conceptus transcriptones in response to key physiological periods such as pregnancy and lactation. Early expression of Pregnancy Associated Glycoprotein (PAG) genes within the conceptus and endometrium of pregnant cows and their association with other genes infer a possible role of PAG in pregnancy maintenance and implantation. The array of SNPs across the bovine genome and specific SNPs within candidate genes related to reproductive processes and fertility will enhance genetic selection for fertility along with production and health associated traits.