Influence of post-insemination nutrition on embryonic development in beef heifers.

Previous studies have demonstrated that a decrease in nutrition immediately following AI reduces pregnancy success in beef heifers. The objective of this experiment was to determine if nutrient restriction following AI impacted early embryonic development among non-super ovulated heifers. Beef heifers in eight replications (Rep; Rep 1; n = 14, Rep 2; n = 15, Rep 3; n = 15, Rep 4; n = 14, Rep 5; n = 15, Rep 6; n = 15, Rep 7; n = 25, Rep 8; n = 25) across two locations (UMN, SDSU) were developed in a dry-lot and fed 125% NRC requirements from weaning to timed-AI (d 0). Heifers were timed-AI to a single sire in all replications. Immediately following AI, heifers were assigned, based on age, weight, and estrous response to one of two post-AI nutritional treatments. Half the heifers in each replication continued on the pre-insemination diet, serving as the control treatment (CON) and the remaining heifers were restricted to a sub-maintenance diet (RES). At UMN, heifers in the RES treatment were fed the same diet, but intake was limited to 80% NEm, while at SDSU, DMI remained the same, but diet composition was altered with the addition of straw to reduce NEm to 50% of requirements. On d 6, single embryos were collected nonsurgically and recovered embryos (CON; n = 46, RES; n = 42) were evaluated to determine quality (grade 1-9) and stage (1-4). Embryos were then stained and evaluated to determine the number of dead cells and total blastomeres. In Reps 1 through 6, concentrations of IGF-1 were assessed on d 0 and 6 and progesterone concentrations on d 4 and 6. Data were analyzed using the Mixed procedures of SAS. There were no treatment by Rep or treatment by location interactions for any embryo parameter evaluated, thus all data were pooled. Embryo stage and quality were improved (P < 0.01) in the CON (4.4 ± 0.16, 2.2 ± 0.19, respectively) compared to RES treatment (3.7 ± 0.16, 2.9 ± 0.19, respectively). Embryos in the CON treatment had greater total blastomeres (66.9 ± 5.05; P < 0.01) and tended to have a greater percentage of live cells (P < 0.10; 80.9 ± 4.19%) compared to RES (47.9 ± 5.41; 69.7 ± 4.39%, respectively). Progesterone and IGF-1 concentrations did not differ between treatments. In summary, nutrient restriction for 6 days immediately following AI resulted in poorer quality embryos that were delayed in stage of development, suggesting that immediate changes in nutritional status after insemination can alter early embryonic development.

Assessment of serum 25-hydroxyvitamin D concentrations of beef cows and calves across seasons and geographical locations.

Vitamin D is critical for the growth and development of calves and positively contributes to immune function of cattle. Serum 25-hydroxyvitamin D (25(OH)D) concentrations above 20 ng/mL have traditionally been considered adequate for growth and development of cattle, but recent evidence has indicated that concentrations below 30 ng/mL are insufficient for immunity. Because little information is available regarding vitamin D status of beef cattle, the objective of this study was to evaluate vitamin D status of beef cow-calf herds on pasture as affected by season and location. Serum samples were collected from 43 cow-calf pairs plus an additional 54 calves in herds located in Florida, Idaho, and Minnesota in the spring calving season. Samples were collected again over the summer months from animals in the Florida and Minnesota herds. Effects of subcutaneous injection of vitamins A, D, and E also were investigated in a subset of calves from the Idaho herd. All cows sampled had serum 25(OH)D concentrations above 30 ng/mL at the time of calving in the spring. The average serum 25(OH)D concentrations of cows rose from near 60 ng/mL in the spring to 75 ng/mL in the summer ( < 0.001). Most calves, on the other hand, had serum 25(OH)D concentrations below 20 ng/mL. The calves in the Florida and Minnesota herds similarly rose from averages of 10 to 15 ng/mL at birth to near 50 ng/mL by the end of summer. Serum 25(OH)D of severely deficient calves increased from 3 ng/mL in nonsupplemented calves to 11 ng/mL at 48 h after birth if given a bolus supplementation of 40,000 IU of vitamin D via subcutaneous injection of a vitamin A, D, and E supplement at birth ( < 0.001). Vitamin D supplementation of cows late in pregnancy has been shown to increase serum 25(OH)D of calves; however, beef cattle generally receive very little supplemental vitamin D, as was the case for the cows studied here. The lower serum 25(OH)D of cows in spring compared with summer and the prevalence of vitamin D deficiency of calves observed here indicate that increased vitamin D supplementation of cows over the winter months or vitamin D supplementation of newborn calves would be beneficial.

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.

Comparison of three CIDR-based fixed-time AI protocols in beef heifers.

Several effective fixed-time AI (FTAI) protocols have been developed to facilitate AI in beef heifers that circumvent the need for estrus detection. Among these are the 5-d CO-Synch + controlled intravaginal progesterone insert (CIDR) protocol (5dCO), PGF2α (PG) 6-d CIDR protocol (PG-6dCIDR), and 14-d CIDR-PG protocol (14dCIDR-PG). Although each of these protocols varies in duration and approach to synchronizing estrus and ovulation, each has been reported as an effective method to facilitate FTAI in beef heifers. Therefore, the objective of this study was to compare FTAI pregnancy rates in beef heifers synchronized with these 3 CIDR-based protocols. Virgin beef heifers (n = 801) at 4 locations were synchronized with 1 of 3 protocols: 1) 5dCO, an injection of GnRH (100 µg) and insertion of a CIDR on d -5, PG (25 mg) and CIDR removal on d 0 with a second injection of PG (>4 h after CIDR removal) on d 0 and FTAI at 72 h after CIDR removal, 2) PG-6dCIDR, PG (25 mg) on d -9, GnRH (100 µg) and insertion of a CIDR on d -6, PG and CIDR removal on d 0, and FTAI at 66 h after CIDR removal, or 3) 14dCIDR-PG, a 14-d CIDR insert from d -30 to -16, PG (25 mg) on d 0, and FTAI at 66 h after PG. All heifers received an injection of GnRH (100 µg) concurrent with FTAI. Timing of treatment initiation was offset to allow all heifers to receive FTAI concomitantly and at random. Pregnancy success was determined between 35 and 40 d after FTAI by transrectal ultrasonography. Blood samples were collected before the beginning of each protocol and at the initiation of each protocol to determine estrous cycling status (77%). Data were analyzed using the GLIMMIX procedures of SAS. As expected, because of the duration of protocols, fewer heifers in the 14dCIDR-PG treatment were pubertal at initiation of synchronization than in the 5dCO (P < 0.05) and PG-6dCIDR (P = 0.10) treatments. Fixed-time AI pregnancy success did not differ between treatments (P = 0.14; 62.6%, 56.9%, and 53.3% for 5dCO, PG-6dCIDR, and 14dCIDR-PG, respectively). However, heifers that had reached puberty by initiation of synchronization had greater (P < 0.01) pregnancy success compared to heifers that were prepubertal (60.7% and 47.3%, respectively). In summary, all 3 protocols had similar FTAI pregnancy success, and puberty status had the greatest impact on pregnancy success.

Effects of temporary calf removal before fixed-time artificial insemination on pregnancy rates and subsequent calf performance in suckled beef cows.

Two experiments were conducted to determine the effect of calf removal (CR) on pregnancy rate (PR) and calf performance in suckled beef cows. Cows in both experiments were synchronized with the 7-d CO-Synch + CIDR protocol [i.e., 100-µg injection of GnRH at controlled internal drug release (CIDR) device insertion (d -7) with 25-mg injection of PGF2α at CIDR removal (d 0), followed by injection of GnRH and timed AI (TAI) on d 3]. Cows were blocked by location (6 locations), stratified by days postpartum (DPP) and parity, and assigned to 1 of 2 treatments in Exp. 1: 1) control (Control; n = 156); 2) calves were separated from their dams between d 0 and 3 (CR72; n = 168); and 1 of 4 treatments in Exp. 2: 1) Control (n = 103); 2) CR72 (n = 104); 3) calves were separated from their dams between d 0 and 2 (CR48A; n = 95); and 4) similar to CR48A but CR between d 1 and 3 (CR48B; n = 53). Transrectal ultrasonography of ovarian structures was performed on d 0, 1, 2, 3, 4, and 10 (in a subset of cows) to determine pregnancy status on d 33. Blood samples were collected on d -14, -7, 0, 3, and 10 (in a subset of cows) to determine concentrations of progesterone (P4) and estradiol (E2). Calves were blocked by age as young (25 to 59 d), medium (60 to 79 d), and old (≥80 d), and were weighed on d 0, 3, 33, and 63. Overall PR did not differ among treatments and averaged 50%. Follicle growth rate from d 0 to 3 tended (P = 0.06) to be greater for CR72 (0.42 ± 0.15 mm/d) compared with Control (0.02 ± 0.15 mm/d). Young (-3.9 ± 0.3%) and old (-3.1 ± 0.4%) calves lost a greater (P < 0.001) percent of BW (PBW) during CR than medium-age (-1.6 ± 0.3%) calves exposed to CR72. In Exp. 2, PR were similar among all 3 locations (49%; P = 0.15). Young (-4.8 ± 0.6%) and medium (-3.0 ± 0.5%) calves lost greater (P < 0.01) percent body weight (PBW) during CR than old (-1.4 ± 0.6%) calves within the CR72 treatment. Calves exposed to CR48 (-2.2 ± 0.6%, -1.1 ± 0.6%, and -2.4 ± 0.6% PBW change for young, medium, and old, respectively) lost more BW than calves in the Control group (-3.7 ± 0.4%, -1.7 ± 0.5%, and -2.1 ± 0.5% PBW change for young, medium, and old, respectively). Subsequent calf weights on d 33 and 63 were greater (P < 0.05) in Controls than cows exposed to CR48 or CR72 treatments. We conclude that CR stimulated follicle growth but failed to enhance PR to TAI. However, CR had a negative impact on subsequent calf performance, which differed, depending on the duration and age of the calf when exposed to CR.

An economic evaluation of estrous synchronization and timed artificial insemination in suckled beef cows.

Partial budget analysis was used to determine the economic outcome of estrus synchronization (ES) and timed artificial insemination (TAI) in commercial cow-calf production. Suckled beef cows (n = 1,197) from 8 locations were assigned randomly within each location to 1 of 2 treatment groups: 1) cows were inseminated artificially after synchronization of ovulation using the CO-Synch + CIDR protocol, which includes a 100-µg injection of GnRH (OvaCyst; TevaAnimal Health, St. Joseph, MO) when a controlled internal drug-releasing device (CIDR; Pfizer Animal Health, New York, NY) containing 1.38 g of progesterone was inserted. The CIDR was removed 7 d later, and cows received a 25-mg injection of PGF(2α) (PGF; Lutalyse; Pfizer Animal Health), followed in 66 h with TAI and a second 100-µg injection of GnRH (TAI; n = 582), and 2) cows were exposed to natural service (NS) without estrous synchronization (Control; n = 615). Within each herd, cows from both treatments were maintained together in similar pastures and were exposed to bulls 12 h after the last cow in the TAI treatment was inseminated. Overall, the percentage of cows exposed to treatments that subsequently weaned a calf was greater (P < 0.05) for TAI (84%) than Control (78%) cows. In addition, survival analysis demonstrated that cumulative calving distribution differed (P < 0.05) between the TAI and Control treatments. Weaning weights per cow exposed to treatments were greater (P < 0.01) for cows in the TAI treatment (193.4 ± 4.3 kg) than those cows in the Control treatment (175.9 ± 4.3 kg). Overall, increased returns plus decreased costs ($82.32) minus decreased returns plus increased costs ($33.18) resulted in a $49.14 advantage per exposed cow in the TAI treatment compared with the Control treatment. Location greatly influenced weaned calf weights, which may have been a result of differing management, nutrition, genetic selection, production goals, and environments. We concluded that ES and TAI had a positive economic impact on subsequent weaning weights of exposed cows.

Administration of human chorionic gonadotropin to suckled beef cows before ovulation synchronization and fixed-time insemination: replacement of gonadotropin-releasing hormone with human chorionic gonadotropin.

Two experiments were conducted to evaluate whether hCG administered 7 d before initiating the CO-Synch + controlled internal drug release (CIDR) ovulation synchronization protocol (Exp. 1 and 2), or replacing GnRH with hCG at the time of AI (Exp. 1), would improve fertility to a fixed-time AI (TAI) in suckled beef cows. In addition, the effects of hCG on follicle dynamics, corpus luteum development, and concentrations of progesterone (P4) were evaluated. In Exp. 1, cows were stratified by days postpartum, age, and parity and assigned randomly to a 2 × 2 factorial arrangement of 4 treatments: 1) cows received 100 µg of GnRH at CIDR insertion (d -7) and 25 mg of PGF(2α) at CIDR removal (d 0), followed in 64 to 68 h by a TAI plus a second injection of GnRH at TAI (CG; n = 29); 2) same as CG but the second injection of GnRH at the time of insemination was replaced by hCG (CH; n = 28); 3) same as CG, but cows received hCG 7 d (d -14) before CIDR insertion (HG; n = 28); and 4) same as HG, but cows received hCG 7 d (d -14) before CIDR insertion (HH; n = 29). Pregnancy rates were 52, 41, 59, and 38% for GG, GH, HG, and HH, respectively. Cows receiving hCG (39%) in place of GnRH at TAI tended (P = 0.06) to have poorer pregnancy rates than those receiving GnRH (56%). Pre-CO-Synch hCG treatment increased (P < 0.05) the percentage of cows with concentrations of P4 >1 ng/mL at d -7, increased (P < 0.02) concentration of P4 on d -7, and decreased (P < 0.001) the size of the dominant follicle on d 0 and 3, compared with cows not treated with hCG on d -14. In Exp. 2, cows were stratified based on days postpartum, BCS, breed type, and calf sex and then assigned to the CG (n = 102) or HG (n = 103) treatments. Overall pregnancy rates were 51%, but no differences in pregnancy rates were detected between treatments. Pre-CO-Synch hCG treatment increased (P < 0.05) the percentage of cows cycling on d -7 and increased (P < 0.05) concentrations of P4 on d -7 compared with pre-CO-Synch controls. Therefore, pretreatment induction of ovulation after hCG injection 7 d before initiation of CO-Synch + CIDR protocol failed to enhance pregnancy rates, but replacing GnRH with hCG at the time of AI may reduce pregnancy rates.

Administration of human chorionic gonadotropin 7 days after fixed-time artificial insemination of suckled beef cows.

We determined the effects of administering hCG 7 d after a fixed-time AI (TAI) on ovarian response, concentrations of progesterone, and pregnancy rates in postpartum suckled beef cows. Cows at 6 locations received 100 microg of GnRH (Fertagyl, Intervet Animal Health, Millsboro, DE) and a controlled internal drug release (CIDR) device (CIDR EAZI-Breed, Pfizer Animal Health, New York, NY), followed in 7 d by 25 mg of PGF(2alpha) (Lutalyse, Pfizer Animal Health) and CIDR removal. At 64 h after CIDR removal, cows received an injection of GnRH and AI (d 0), and then were stratified by days postpartum and parity and assigned randomly to 2 treatments administered 7 d after TAI: 1) 1 mL of saline (saline; n = 252); or 2) 1,000 IU of hCG (Chorulon, Intervet Animal Health; n = 254). Blood samples were collected on d -21, -10, and 33 relative to TAI (d 0) at all locations, on d 7 and 68 at 5 locations, and on d 14 at 1 location to determine concentrations of progesterone. Transrectal ultrasonography was used to determine pregnancy status on d 33 and 68 at all locations, to monitor response of follicles and corpora lutea (CL) in response to treatment at 1 location (n = 106) on d 7 and 14, and to determine the number of CL present in pregnant cows on d 33 in 3 locations (n = 130). Pregnant cows had greater (P < 0.05) concentrations of progesterone at the time of treatment (d 7) compared with nonpregnant cows (3.7 +/- 0.1 vs. 2.6 +/- 0.2 ng/mL, respectively). On d 14, hCG-treated cows had a greater (P < 0.05) volume of luteal tissue (12.1 +/- 0.5 vs. 7.3 +/- 0.5 cm(3), respectively) and greater concentrations of progesterone (6.8 +/- 0.4 vs. 5.4 +/- 0.5 ng/mL, respectively) compared with saline-treated cows. A greater (P < 0.01) percentage of hCG-treated cows (90.6%) had multiple CL on d 14 compared with saline-treated cows (0%), and a greater percentage of pregnant cows treated with hCG (74.6%) had multiple CL on d 33 compared with saline-treated cows (3.0%). Pregnancy rates of hCG-treated cows (56.3%) tended (P = 0.07) to differ from those of saline-treated cows (50.0%). Concentrations of progesterone in pregnant hCG-treated cows were greater (P < 0.05; 7.7 +/- 0.3 vs. 5.8 +/- 0.3 ng/mL, respectively) on d 33 than for pregnant saline-treated cows, but were similar between treatments on d 68 (7.2 +/- 0.3 vs. 6.7 +/- 0.4 ng/mL, respectively). We conclude that treatment with hCG increased the volume of luteal tissue on d 14 and concentrations of progesterone on d 14 and 33 after TAI. Treatment with hCG tended to increase pregnancy rates at 5 of 6 locations from 1.1 to 27 percentage points (average = 10.2) compared with saline, but cumulative pregnancy rates determined on d 68 after TAI were similar between treatments.

Generating high quality impervious cover data.

Nonpoint source pollution (NPS) from urban or suburban areas is rapidly increasing as the population increases in the United States. Research in recent years has consistently shown a strong relationship between the percentage of impervious cover in a drainage basin and the health of the receiving stream. In this paper, we quantify the amount of impervious cover within 56 14-digit hydrologic unit codes (HUCs) in Frederick County, Maryland, USA. This test data set will help in the development of region-wide impervious cover estimation methodologies. The software, sampling and analysis systems were developed to yield accurate and reproducible results. Digital orthophoto quarter quadrangles (DOQQ) from the U.S. Geological Survey were chosen as the basic media for the analysis. Ground features were identified and categorized by human analysts with the help of Geographic Information System (GIS) software and a prototype "cover tool" extension.