Comparison of fertility of liquid or frozen semen when varying the interval from CIDR removal to insemination.

Cryopreservation allows for long-term storage of semen; however, it leads to damage of sperm that may result in complete loss of viability or changes that possibly decrease sperm functionality. Liquid semen is not exposed to these stressors and may result in a longer lifespan in the female reproductive tract, thus increasing the range in timing of insemination without affecting fertility. The objective of this study was to compare fertility of liquid and frozen semen when varying the interval from CIDR removal to AI using the 7-day CO-Synch+CIDR protocol for synchronization of time of estrus. Within age group, crossbred cows (n=389) were randomly assigned to insemination at 36 or 60h after CIDR removal with either liquid or frozen semen (36L, 60L, 36F, and 60F) from one of two Angus bulls. Cows were monitored for estrous activity from CIDR removal until 60h thereafter. Cows that failed to exhibit estrus received GnRH (100µg, i.m.), and a blood sample was collected for analysis of estradiol concentration. There was no difference in pregnancy rates when liquid or frozen semen (53% and 52%) was used, but cows inseminated at 60h had a greater (P<0.01) pregnancy rate than those inseminated at 36h (72% and 31%). There was no time of AI by semen type interaction (P=0.57). Estrus was detected in 63%, 61%, 56%, and 62% of 36F, 36L, 60F, and 60L, respectively (only 5% and 1% of 36F and 36L were detected in estrus before insemination). Overall cows that exhibited estrus had a greater pregnancy rate compared with cows that did not (P<0.01; 79% compared with 24%). Among cows that did not exhibit estrus, those inseminated with liquid semen tended to have greater pregnancy rates than those inseminated with frozen semen (P=0.06). Cows that became pregnant had greater (P<0.01) concentrations of estradiol at 60h than those that did not (10.7±0.55 compared with 7.9±0.26pg/mL). In summary, there was no difference in pregnancy success between liquid and frozen semen. However, cows that exhibited estrus and were inseminated at 60h after CIDR removal had greater pregnancy success compared to cows that did not exhibit estrus.

Expression of estrus before fixed-time AI affects conception rates and factors that impact expression of estrus and the repeatability of expression of estrus in sequential breeding seasons.

Expression of estrus after PG and before fixed-time AI has been reported to change the uterine environment, increase accessory sperm numbers, fertilization rates, and overall embryo survival. Thus, expression of estrus can strongly impact overall pregnancy success. Because of variation in percentage of beef females detected in estrus and number of animals per study, it can be difficult to detect a significant effect of estrus on pregnancy success. Thus, a meta-analysis was conducted using data from 10,116 beef females in 22 studies that utilized variations of the 5 most common fixed-time AI protocols (CO-Synch, 7-day CO-Synch+CIDR, 5-day CIDR, PG 6-day CIDR, and the 14-day CIDR protocols) to examine the effect of detection in standing estrus on subsequent fixed-time AI pregnancy success. A random-effects model was used to combine the studies/herds. The overall model indicated a positive effect of estrus on conception rates with cows detected in estrus before fixed-time AI having a 27% greater (P<0.05; 95% CI=22-32%) conception rate compared with those not detected in estrus. Next we determined factors that influenced expression of estrus. Data were available on 547 cows synchronized with a CIDR based fixed-time AI protocols and observed for estrus before AI during 2-4 breeding seasons. Analysis of these cows indicated that days postpartum (P=0.22) did not impact estrous expression. In contrast, BCS influenced estrous expression (P=0.04) with cows in a BCS of ≤4 (51±5%) having decreased expression of estrus compared to cows with a BCS>4 (≥70±4%). Initiation of estrous cycles before the breeding season also influenced estrous expression (P=0.03), with anestrous cows having greater expression of estrus compared with estrus-cycling cows (78±5% vs. 70±5%, respectively). In conclusion, among all currently recommended fixed-time AI protocols, cows detected in estrus before fixed-time AI had improved conception rates, with BCS and estrus-cycling status having the greatest influence on expression of estrus.

Effects of BPA and BPS exposure limited to early embryogenesis persist to impair non-associative learning in adults.

BACKGROUND: Bisphenol-A (BPA) is a polymerizing agent used in plastic bottles and several routinely used consumer items. It is classified among endocrine disrupting chemicals suspected to cause adverse health effects in mammals ranging from infertility and cancer to behavioral disorders. Work with the invertebrate lab model Caenorhabditis elegans has shown that BPA affects germ cells by disrupting double-stranded DNA break repair mechanisms. The current study utilizes this model organism to provide insight into low-dose and long-term behavioral effects of BPA and bisphenol-S (BPS), a supposed safer replacement for BPA. FINDINGS: Experiments presented in our report demonstrate that the effects of embryonic exposure to considerably low levels of BPA persist into adulthood, affecting neural functionality as assayed by measuring habituation to mechano-sensory stimuli in C. elegans. These results are noteworthy in that they are based on low-dose exposures, following the rationale that subtler effects that may not be morphologically apparent are likely to be discernible through behavioral changes. In addition, we report that embryonic exposure to BPS follows a pattern similar to BPA. CONCLUSIONS: Building upon previous observations using the C. elegans model, we have shown that exposure of embryos to BPA and BPS affects their behavior as adults. These long-term effects are in line with recommended alternate low-dose chemical safety testing approaches. Our observation that the effects of BPS are similar to BPA is not unexpected, considering their structural similarity. This, to our knowledge, is the first reported behavioral study on low-dose toxicity of any endocrine disrupting chemical in C. elegans.