Strategies that enhance embryonic development and reduce pregnancy loss in dairy cows submitted to environmental stress or endometrial inflammation

Abstract

The decrease in fertility of modern dairy cows is probably multi-factorial and associated with high milk production. Lactating dairy cows are subjected to a variety of challenges including metabolic and environmental stressors, particularly during the early postpartum period. Epidemiological studies have shown that between 40 to 60% of cows will suffer from one or more clinical episodes of disease within the first 60 days postpartum. The extensive embryonic losses observed in dairy cows can greatly improve the knowledge of how the conceptus and the endometrium are modified to adapt to these adverse scenarios. The main objective of this research is to unveil the mechanisms in the endometrium and conceptus related to sub-fertility in dairy cows and to propose strategies that enhance embryonic development and reduce pregnancy loss. The experiments will be conducted at the University of British Columbia (UBC) Dairy Centre and at commercial dairies in the Fraser Valley and elsewhere when appropriate. There wil be conduct 5 experiments, but the studant will participate of Experiments 1 and 3. The first experiment will be a case control study in which health disorders (mastitis, lameness and ketosis) will be monitored weekly from parturition to 30 days postpartum. Two-hundred cows will have their weight, body condition score and gait score recorded soon after calving and 30 days later. Cows will have their ovaries scanned by ultrasound twice a week. Blood samples will be collected twice a week throughout the experimental period and analyzed for progesterone, estradiol, non-esterified fatty acids (NEFA), beta-hydroxybutyrate (BHBA), glucose, acute phase proteins (ceruloplasmin and haptoglobin), pro-inflammatory cytokines (IL1, IL6, IL8, TNF-±). Hair from the tail and fecal samples will be collected at calving, and at 3 and 6 weeks postpartum for the measurement of cortisol. At around 30 days postpartum, the same cows will have their estrous cycle synchronized. A sub-population of 40 cows (20 per group; healthy vs. clinically ill with mastitis, lameness and ketosis) will have the pre-ovulatory follicle aspirated for hormone analyses of the follicular fluid. On day 17 of the estrous cycle following the induced ovulation, a uterine biopsy will be collected from the endometrium of another 40 cows. The endometrium biopsy sample will then be tested for functional target genes. In the tird experiment, 80 healthy early-lactating dairy cows will be blocked by parity, milk production and body condition score and randomly assigned into a crossover experimental design. Treatments will be Control (no chronic stress/inflammation is induced) and Stress (chronic stress/inflammation is induced for two to three weeks). After these treatments have been applied cows will have their estrous cycle synchronized Blood, hair and fecal samples, as well as ovarian ultrasonography data will be collected and analyzed. On experimental day zero (end of ovarian synchronization) cows will then be assigned to receive (pregnant) or not (non-pregnant) artificial insemination. The collection of endometrium biopsies and elongated conceptus will occur at two different time points of the estrous cycle and early gestation. One half of the cows will have endometrium biopsies and conceptus collected on day 12 estrous cycle or pregnancy and the other half on day 17 of the estrous cycle or pregnancy. Tissues will be processed for extraction of mRNA and later processed for microarray analysis (Affymetrix) and protein measurements (western blotting). (AU)