E. L. Larimore

Influence of estrus at fixed-time artificial insemination on early embryonic development in beef cattle

It has been repeatedly demonstrated that estrous expression before fixed-time AI (TAI) results in increased pregnancy success. Therefore, the objective of this experiment was to determine if preblastocyst embryonic developmental characteristics differed from heifers that did or did not exhibit estrus before TAI. Beef heifers (n = 113) were synchronized using the 5-d CO-Synch + controlled internal drug release device with TAI on d 0. Before TAI, estrous expression was assessed twice daily. On d 6, single embryos were collected and visually evaluated to determine quality (International Embryo Transfer Society standards; 1-4, in which 1 = excellent/good and 4 = degenerate) and stage (1-9, in which 1 = unfertilized and 9 = expanded hatched blastocyst). Embryos were stained and evaluated to determine number of dead blastomeres, number of total blastomeres, and number of accessory sperm. Estrous expression before TAI did not affect the percent of embryos recovered (P = 0.59), number of dead cells (P = 0.99), or number of total cells (P = 0.25). However, heifers that exhibited estrus had increased mean (P = 0.03) and median accessory sperm numbers and (P = 0.01) percent live cells when compared with nonestrus heifers. Heifers that exhibited estrus also produced embryos that had a more advanced stage (P = 0.03) and improved quality (P = 0.04) when compared with those heifers not exhibiting estrus. When all heifers were evaluated, there was no correlation between circulating concentration of estradiol at TAI and embryo quality or embryo stage. There was a significant correlation between accessory sperm numbers and embryo quality (P = 0.01) and embryo stage (P < 0.01), such that as accessory sperm numbers increased, embryo quality and stage increased. In conclusion, exhibiting estrus before TAI resulted in improved embryo quality and advanced embryo stage on d 6 and increased the number of accessory sperm associated with the embryo.

Using estrus detection patches to optimally time insemination improved pregnancy risk in suckled beef cows enrolled in a fixed-time artificial insemination program

A multilocation study examined pregnancy risk (PR) after delaying AI in suckled beef cows from 60 to 75 h when estrus had not been detected by 60 h in response to a 7-d CO-Synch + progesterone insert (CIDR) timed AI (TAI) program (d -7: CIDR insert concurrent with an injection of GnRH; d 0: PGF injection and removal of CIDR insert; and GnRH injection at TAI [60 or 75 h after CIDR removal]). A total of 1,611 suckled beef cows at 15 locations in 9 states (CO, IL, KS, MN, MS, MT, ND, SD, and VA) were enrolled. Before applying the fixed-time AI program, BCS was assessed, and blood samples were collected. Estrus was defined to have occurred when an estrus detection patch was >50% colored (activated). Pregnancy was determined 35 d after AI via transrectal ultrasound. Cows ( = 746) detected in estrus by 60 h (46.3%) after CIDR removal were inseminated and treated with GnRH at AI (Control). Remaining nonestrous cows were allocated within location to 3 treatments on the basis of parity and days postpartum: 1) GnRH injection and AI at 60 h (early-early = EE; = 292), 2) GnRH injection at 60 h and AI at 75 h (early-delayed = ED; = 282), or 3) GnRH injection and AI at 75 h (delayed-delayed = DD; = 291). Control cows had a greater ( < 0.01) PR (64.2%) than other treatments (EE = 41.7%, ED = 52.8%, DD = 50.0%). Use of estrus detection patches to delay AI in cows not in estrus by 60 h after CIDR insert removal (ED and DD treatments) increased ( < 0.05) PR to TAI when compared with cows in the EE treatment. More ( < 0.001) cows that showed estrus by 60 h conceived to AI at 60 h than those not showing estrus (64.2% vs. 48.1%). Approximately half (49.2%) of the cows not in estrus by 60 h had activated patches by 75 h, resulting in a greater ( < 0.05) PR than their nonestrous herd mates in the EE (46.1% vs. 34.5%), ED (64.2% vs. 39.2%), and DD (64.8% vs. 31.5%) treatments, respectively. Overall, cows showing estrus by 75 h (72.7%) had greater ( < 0.001) PR to AI (61.3% vs. 37.9%) than cows not showing estrus. Use of estrus detection patches to allow for a delayed AI in cows not in estrus by 60 h after removal of the CIDR insert improved PR to TAI by optimizing the timing of the AI in those cows.

Beef heifers with diminished numbers of antral follicles have decreased uterine protein concentrations

Previous research demonstrated a favorable relationship between the number of follicles detectable in the bovine ovary by ultrasonography and fertility, and bovine females with diminished numbers of antral follicles had smaller reproductive tracts. Therefore, we hypothesized that uterine function would be compromised in beef heifers with diminished numbers of antral follilcles. Angus heifers (n=480) were submitted for ultrasonographic evaluation of antral follicle number at 325 and 355d of age. After the second ultrasonographic examination, 40 pubertal heifers with the greatest average number of antral follicles (30.9±0.7) and 40 pubertal heifers with the lowest average number of antral follicles (14.2±0.7) were synchronized with two i.m. injections of prostaglandin F2α (25mg) administered 11d apart, and heifers were slaughtered on d6 (n=26 heifers/group) or d16 (n=14 heifers/group) of the resultant estrous cycle. The uterus was weighed, flushed for determination of protein content, and representative samples were fixed for determination of endometrial gland morphometry. Heifers in the Low group had fewer surface antral follicles and smaller reproductive tracts than heifers in the High group (P<0.01). Protein content of the uterine flushes was decreased in heifers in the Low group (P<0.01); however, there was no difference in the percent area of the endometrium occupied by endometrial glands. From these results, we conclude that the uterine environment of beef heifers with diminished numbers of antral follicles is less conducive to supporting early embryonic survival.

Postweaning nutritional programming of ovarian development in beef heifers

Peripubertal caloric restriction increases primordial follicle numbers at breeding, which may improve reproductive potential. Our hypothesis was that feed restriction was changing primordial follicle number through stimulation of follicle formation via leptin, roundabout axon guidance receptor, homolog 4 (), or or through inhibition of follicle activation via anti-Müllerian hormone (). Heifers ( = 30) were fed a ration consisting of 30% alfalfa hay, 69.8% corn silage, and 0.2% salt as DM. Heifers received the control diet for 42 d before an initial 6 heifers were ovariectomized at 8 mo of age. The remaining 24 heifers were divided into 2 treatment groups. Controls were offered 97.9 g DM/kg BW over the entire feeding period. Stair-step heifers received 67.4 g DM/kg BW for 84 d. Following the 84-d restriction, heifers were stepped up to receive 118.9 g DM/kg BW over a 15-d period and were held at this feeding level 68 d. At the end of the feed restriction (11 mo of age), ovaries were collected from 6 heifers per treatment, and at the end of the refeeding period (13 mo of age), ovaries were collected from 6 heifers per treatment. Plasma leptin concentrations were greater in control heifers than in stair-step heifers at 11 mo of age ( < 0.0001). In histological sections, stair-step heifers had more primordial follicles ( = 0.03) than control heifers at 13 mo of age. There was no difference in secondary or antral follicle numbers between dietary treatment groups or ages. Relative abundance of mRNA in ovarian cortex of control heifers was greater at 13 mo than at 11 mo or before feed restriction (8 mo; = 0.01). Relative abundance of mRNA in stair-step heifers at 13 mo was greater than before feed restriction ( = 0.02) and at 11 mo did not differ from 8 or 13 mo ( = 0.70). Relative abundance of mRNA in the ovarian cortex followed a similar pattern, being greater in stair-step heifers at 11 mo compared with control heifers ( = 0.001). At 13 mo, mRNA did not differ between treatments ( = 0.30). Abundance of mRNA in the ovarian cortex did not change due to dietary treatment or age ( > 0.10). In conclusion, developing heifers on a stair-step compensatory growth scheme resulted in larger ovarian reserve before the onset of breeding, which may have beneficial effects on increasing reproductive lifespan.

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.

Uterine environment and pregnancy rate of heifers with elevated plasma urea nitrogen

Diets high in protein are associated with lower reproductive performance and changes in the uterine environment. The objective of this study was to determine the effect of elevated systemic concentrations of urea nitrogen on the uterine environment and pregnancy success in beef heifers. Heifers (n=150) were matched by breed, age, and body weight then randomly assigned to one of two dietary treatments: 1) Control (10% CP) or 2) High protein (14% CP) over three replicates (n=40/replicate). Estrus was synchronized with an injection of PGF2α. Uterine pH, plasma urea nitrogen (PUN), ammonia, and glucose concentrations were determined on d 7 of the estrous cycle. Pregnancy status was determined by ultrasonography 30 d following the breeding season. In vitro fertilization was performed on heifers precluded from uterine analysis (n=15/diet) to determine the effect of a High Protein diet on oocyte quality. Plasma urea concentrations were greater in the High Protein diet compared to Control (P<0.001). There was no effect of diet on plasma ammonia (P=0.12), plasma glucose (P=0.40), uterine pH (P=0.67), interval to estrus (P=0.54), duration of estrus (P=0.38), or pregnancy rate (P=0.83). There was no effect of diet (P>0.40) on the number of oocytes collected, number of oocytes cleaved, amount of blastocysts, percentage of oocytes cleaved and percentage of blastocysts present. In summary, high nitrogen diets increased PUN concentrations in heifers; however, there were no deleterious effects on reproduction.