The economic effects of an estrus synchronization protocol using prostaglandin in beef heifers

We estimated the effect of estrus synchronization on reproduction, production and economic outcomes in 272 beef heifers randomly allocated to a synchronized Test group or an unsynchronized Control group. The Test group received AI upon estrus detection for 6 days followed by PGF2 treatment of heifers that had not shown estrus by day 6 (PGF/6). In both groups AI was continued for 50 days, followed by a 42-day bull breeding period. Heifers were followed through their second breeding season and until they had weaned their first calves. Synchronization resulted in a reduction in median days to first insemination (8 vs. 11 in the Test and Control groups, respectively, P < 0.01) and median days to calving of calves born to AI (14 vs. 20, P = 0.04). There was no significant difference in pregnancy rate to the AI period (60.0% vs. 51.8%, P = 0.18), final pregnancy rate (82.2% vs. 83.2%, P = 0.87) or pregnancy rate to the subsequent breeding season (96.0% vs. 95.0%, P = 1.00). Although mean calf weaning mass was not significantly different (207.0 kg vs. 201.4 kg, P = 0.32), the total mass of calves weaned in this study was 14,843 kg vs. 13,060 kg and the benefit: cost ratio for synchronization was 2.8. It was therefore concluded that a PGF/6 protocol may affect the total mass of calves weaned by changing days to calving, weaning rate, the ratio of male: female calves born and/or the birth mass of calves.     

Effects of one versus two doses of prostaglandin F2alpha on AI pregnancy rates in a 5-day, progesterone-based, CO-Synch protocol in crossbred beef heifers

The present study determined whether a 5-d progesterone-based CO-Synch protocol with a single dose of prostaglandin F_2α (PGF) at progesterone withdrawal on Day 5, would yield a timed AI pregnancy rate similar to two doses of PGF given 6 h apart on Day 5. Angus cross beef heifers (N = 562) at six locations were used. All heifers received 100 µg of gonadorelin hydrochloride (GnRH) and a controlled internal drug release (CIDR) insert on Day 0. Within farm, heifers were randomly allocated to receive one dose of 25 mg dinoprost (PGF) at CIDR removal on Day 5 (1 PGF; N = 264), or two doses of 25 mg PGF, with the first dose given on Day 5 at CIDR removal, and the second dose 6 h later (2 PGF; N = 298). Most heifers (N = 415) received a heat detector patch at CIDR removal. After CIDR removal, heifers were observed twice daily through Day 7 for estrus and heat detector aid status was recorded. On Day 8, heifers were given 100 µg of GnRH, heat detector aid status was recorded, and heifers were inseminated approximately 72 h after CIDR removal. Accounting for significant variables such as location (P < 0.01), heifers in estrus at or prior to AI (P < 0.001), and a treatment by location interaction (P < 0.01), two doses of PGF on Day 5 tended to have higher pregnancy rates to timed AI compared to those that received one dose of PGF (P = 0.06). In conclusion, heifers given two doses of PGF at CIDR removal on Day 5, in a 5-d CIDR-CO-Synch protocol, tended to have a higher pregnancy rate than those that received only one dose of PGF.     

Response to biostimulation in peri-puberal beef heifers: influence of male-female proximity and heifer's initial body weight

The objectives were to determine if exposure of 12 mo old peri-puberal beef heifers to androgenized steers for 35 d hastened puberty, and if the response was related to the physical proximity between males and females and to heifer's initial body weight. Hereford x Aberdeen Angus heifers (n = 131), 12 mo old, were assigned to two treatments: 1) Exposed group, exposed to androgenized steers from Day 0 to Day 35 (E, n = 66); or 2) Control group, isolated from the steers and other males (C, n = 65). Cyclic activity was determined through estrous behavior detection (twice daily) and weekly ultrasound imaging to detect a CL. For each Exposed heifer, an association index (with males) was determined thrice weekly, based on the distance to androgenized steers every 10 min for 4 h (until cyclic activity began). Data were analyzed according to heifer's initial body weight, which was categorized into three ranges (low, medium, and high, designated LW, MW, and HW, respectively). The cumulative proportion of cyclic heifers was greater for Exposed than Control heifers as of Day 21. By the end of the exposure period, more Exposed than Control heifers had attained puberty (16/66 vs. 2/65; P < 0.001). Within the HW classification, more Exposed than Control heifers became puberal (11/20 vs. 2/21; P = 0.002). However, there were no differences between MW and LW in the proportions of heifers that reached puberty. Association index in Exposed heifers was greater in HW than in MW and LW (0.10 ± 0.09 vs. 0.06 ± 0.03 and 0.06 ± 0.04; P < 0.05), and in heifers that began cyclic activity compared to those that did not in the MW heifers (0.09 ± 0.05 vs. 0.05 ± 0.02; P = 0.01) and tended to be different in the HW treatment (0.12 ± 0.10 vs. 0.06 ± 0.02; P = 0.09). In conclusion, exposure of peri-puberal beef heifers to androgenized steers for 35 d advanced puberty in heavier heifers; an earlier response occurred in heifers with greater proximity to androgenized steers.     

Artificial insemination at 56 h after intravaginal progesterone device removal improved AI pregnancy rate in beef heifers synchronized with five-day CO-Synch + controlled internal drug release (CIDR) protocol

The objective was to determine whether timed artificial insemination (TAI) 56 h after removal of a Controlled Internal Drug Release (CIDR, 1.38 g of progesterone) insert would improve AI pregnancy rate in beef heifers compared to TAI 72 h after CIDR insert removal in a 5-days CO-Synch + CIDR protocol. Angus cross beef heifers (n = 1098) at nine locations [WA (5 locations; n = 634), ID (2 locations; n = 211), VA (one location; n = 193) and WY (one location; n = 60)] were included in this study. All heifers were given a body condition score (BCS; 1-emaciated; 9-obese), and received a CIDR insert and 100 μg of gonadorelin hydrochloride (GnRH) on Day 0. The CIDR insert was removed and two doses of 25 mg of dinoprost (PGF_2α) were given, first dose at CIDR insert removal and second dose 6 h later, on Day 5. A subset of heifers (n = 629) received an estrus detector aid at CIDR removal. After CIDR removal, heifers were observed thrice daily for estrus and estrus detector aid status until they were inseminated. Within farm, heifers were randomly allocated to two groups and were inseminated either at 56 h (n = 554) or at 72 h (n = 544) after CIDR removal. All heifers were given 100 μg of GnRH at AI. Insemination 56 h after CIDR insert removal improved AI pregnancy rate compared to insemination 72 h (66.2 vs. 55.9%; P < 0.001; 1 - β = 0.94). Locations, BCS categories (≤ 6 vs. > 6) and location by treatment and BCS by treatment interactions did not influence AI pregnancy rate (P > 0.1). The AI pregnancy rates for heifers with BCS ≤ 6 and > 6 were 61.8 and 60.1%, respectively (P > 0.1). The AI pregnancy rates among locations varied from 54.9 to 69.2% (P > 0.1). The AI pregnancy rate for heifers observed in estrus at or before AI was not different compared to heifers not observed in estrus [(65.4% (302/462) vs. 52.7% (88/167); P > 0.05)]. In conclusion, heifers inseminated 56 h after CIDR insert removal in a 5-days CO-Synch + CIDR protocol had, on average, 10.3% higher AI pregnancy rate compared to heifers inseminated 72 h after CIDR insert removal.     

Body composition of beef heifers at puberty

Three trials were conducted to study age, weight, percent body fat and protein content of 131 crossbred and purebred beef heifers at puberty, to investigate relationships among various pubertal measurements and to determine if body fat and protein values could be used in combination with age, weight and shoulder height to predict the onset of puberty. Trials 1 and 2 compared heifers on treatments of high (H), medium (M) and low (L) levels of energy. The rations were formulated at 120, 100 and 80 percent of the National Research Council (NRC) recommendation for energy. The protein level was 100 percent of the NRC recommendation for all three treatments. Each animal was examined every two weeks per rectum for the presence of follicles and corpora lutea. The presence of a mature corpus luteum indicated the attainment of puberty. Trial 3 heifers were fed the same level of nutrition but ovulation data were based on weekly rectal palpations and on the presence of greater than 2.0 ng/ml blood plasma progesterone. Percentage of fat and protein were quantified in all trials using a whole body counter. In Trial 1 there was a significant difference (P<0.01) among energy levels for mean weight and percent fat values at puberty, but no differences in age at puberty. Even though heifers in Trial 2 were also fed different energy levels, there were no differences among treatments for the variables measured. The onset of puberty in Trial 2 appeared to be delayed due to cooler than normal weather during that experimental period. Heifers in Trial 2 tended to be older and reached puberty approximately one month later in the year than heifers in Trials 1 and 3, despite similarities in weight gain among the trials. In all trials, high R(2) values for multiple stepwise regression analyses indicated that body composition estimates were useful in predicting weight at puberty in beef heifers. The results of this study do not support a critical body weight or body composition hypothesis in the beef heifer. It was concluded that these data indicate environmental factors may have more effect than nutrition on the onset of puberty.     

Two doses of prostaglandin improve pregnancy rates to timed-AI in a 5-day progesterone-based synchronization protocol in beef cows

The objective was to compare reproductive performance of Angus-cross beef cows synchronized with GnRH, a progesterone-based intravaginal insert (Controlled Internal Drug Release, CIDR) for 5-d, and one dose of either dinoprost (PGF) or cloprostenol (CLP, a PGF analogue) or two doses of PGF on the day of CIDR withdrawal. All cows (N = 830) at six locations received 100 μg of GnRH and a CIDR on Day 0. Within farm, cows were randomly allocated to receive 25 mg of PGF at the time of CIDR insert removal on Day 5 (1 × PGF; N = 277), two 25 mg doses of PGF, the first given on Day 5 at the time of CIDR removal and the second 7 h later (2 × PGF; N = 282), or 500 μg of CLP at the time of CIDR removal on Day 5 (1 × CLP; N = 271). All cows were given 100 μg of GnRH on Day 8 (72 h after CIDR removal) and concurrently inseminated (5-d CO-Synch + CIDR). Cows were fitted with a pressure-sensitive estrus detection device at the time of CIDR withdrawal. Timed-AI pregnancy rates were greater (P < 0.0001) in the 2 × PGF (69.0%) than the 1 × PGF (52.0%) and 1 × CLP (54.3%) treatments. However, breeding-season pregnancy rates were not different among treatments (87.0% for 1 × PGF, 92.9% for 2 × PGF and 87.5% for 1 × CLP; P > 0.1). In conclusion, cows that received two doses of PGF on the day of CIDR removal in a 5-d CO-Synch + CIDR synchronization protocol had excellent timed-AI pregnancy rates that were greater than in cows receiving a single treatment with either PGF or CLP.     

Insemination timing affects pregnancy rates in beef cows treated with CO-Synch protocol including an intravaginal progesterone insert

Our objective was to determine the optimal time to artificially inseminate lactating beef cows (Bos taurus typicus) after using the standard CO-Synch protocol that also included a progesterone-releasing, intravaginal controlled internal drug release (CIDR) insert. Cows (N = 605) at three locations were inseminated at four different times after CIDR insert removal and the prostaglandin F_2α administration of the CO-Synch + CIDR protocol: 48, 56, 64, or 72 h. Blood samples were collected 9 to 10 d before and on the day of CIDR insertion. Based on elevated (>1 ng/mL) serum progesterone concentrations, 60% of 605 cows had previously ovulated (were cycling) at the initiation of the study, with a range of 39.6% to 67.9% among locations (P < 0.05). Age of cow, body condition score, and days postpartum affected (P ≤ 0.05) cycling status before ovulation was synchronized. Averaged across treatments, pregnancy rate to artificial insemination (AI) at Day 32 was affected (P ≤ 0.05) by pretreatment cycling status and body condition. Younger cows (≤3 yr) tended to have greater AI pregnancy rates when inseminated at 56 h, whereas older cows had similar pregnancy rates when inseminated at 56 h or later (timing of AI by age interaction; P = 0.085). Pregnancy loss between Days 32 and 63 was greatest (quadratic effect; P < 0.05) when cows were inseminated at 48 and 72 h. In summary, insemination times at or after 56 h improved AI pregnancy rates when using the CO-Synch + CIDR program. Further work is warranted to examine age effects on timing of AI in the CO-Synch + CIDR program.     

Effect of organic or inorganic trace mineral supplementation on follicular response, ovulation, and embryo production in superovulated Angus heifers

We determined whether source of trace mineral supplementation prior to embryo collection affected embryo production and quality. Angus half-sibling heifers (n = 20) originating from a common herd were assigned to three treatment groups using a 3 × 3 latin square design replicated in time (3×) and space (6× complete and 1× incomplete): (1) heifers received no added mineral to their diet (control; n = 53); (2) heifers received a commercially available organic mineral supplement (organic; n = 52); or (3) heifers received an all inorganic mineral supplement (inorganic; n = 55). All heifers had ad libitum access to hay and were fed a supplement containing corn and soybean meal. Treatments were initiated 23 days prior to embryo recovery. Heifers were given a 45-day adaptation period of no mineral supplementation before initiating a new treatment. Ovarian structures were evaluated using transrectal ultrasonography to determine the presence and number of follicles and CL on each ovary. The mean number of recovered ova/embryos was similar among treatments (4.1 ± 0.7, 3.8 ± 0.7, and 3.3 ± 0.7 for control, inorganic, and organic treatments, respectively), the number of unfertilized oocytes was greater (P < 0.05) for inorganic (2.3 ± 0.5) and control (1.6 ± 0.5) treated heifers than organic (0.4 ± 0.4) treated heifers. No differences among treatments existed for the number of degenerate or transferable embryos, but individual heifer influenced the total number of embryos/ova, unfertilized ova, and transferable embryos recovered. We conclude that heifer accounted for the greatest differences in embryo production and quality. Source of trace mineral supplementation did not significantly alter embryo number or quality in superovulated purebred Angus heifers fed a well-balanced diet, meeting all trace mineral requirements.     

Synchronization of estrus in cyclic beef heifers with the prostaglandin analog alfaprostol

Seventy-eight Hereford-Angus crossbred heifers were injected intramuscularly twice with 6 mg of alfaprostol^b in 6 ml of propylene glycol. On each representative day of a 20-day estrous cycle (estrus = Day 0), either three or four heifers received their first injection. The second injection was given 12 days after the first, regardless of the response to the first injection. Thirty-nine heifers were not treated. The first alfaprostol injection reduced serum progesterone to less than 1 ng/ml in all heifers injected after Day 4. A total of 79.5% ($\text{62}\text{78}$) of the heifers exhibited estrus by five days after the first injection. Average interval from injection to estrus was 63 hours. The second injection occurred on Days 6 through 16 for all but one heifer, with 75.6% ($\text{59}\text{78}$) falling on Days 8 through 11 of the estrous cycle. Estrus was detected in 93.6% ($\text{73}\text{78}$) of the heifers within five days after the second injection, with an average interval to estrus of 66 hours.Day of cycle at second injection did not affect the interval to estrus. Conception occurred in 79.4% ($\text{58}\text{73}$) of the heifers inseminated in the five days after the second injection. Occurrence of estrus and conception was no different in treated heifers after five days of the insemination period than in nontreated heifers after 21 days of the insemination period, where 94.9% ($\text{37}\text{39}$) were observed in estrus and 83.8% ($\text{31}\text{37}$) conceived. Overall percent conception for a 55-day insemination period was 89.7 ($\text{70}\text{78}$) for treated and 87.2 ($\text{34}\text{39}$) for nontreated heifers. Day of cycle at first or second injection did not affect conception after the second injection. Some signs of estrus were observed in 11 of the 16 heifers injected before Day 5.A second trial to determine if alfaprostol induced luteolysis early in the cycle was conducted. Twenty purebred Angus, Hereford, or Simmental heifers received either one or two injections of alfaprostol on either Day 1, 2, 3, or 4. Only five heifers showed any signs of estrus, and the three that were inseminated did not conceive. Subsequent cycle length indicated that luteolysis occurred in only one heifer.Data suggest that alfaprostol is an effective luteolytic agent in cyclic beef heifers after Day 4 and that two injections 12 days apart will effectively synchronize estrus in heifers when distributed throughout the cycle at the first injection without affecting conception rate.     

Comparison of long-term CIDR-based protocols to synchronize estrus in beef heifers

Two experiments evaluated long-term controlled internal drug release (CIDR) insert-based protocols to synchronize estrus and compare differences in their potential ability to facilitate fixed-time artificial insemination (FTAI) in beef heifers. In Experiment 1 estrous cycling heifers (n = 85) were assigned to one of two treatments by age and body weight (BW). Heifers with T1 received a CIDR from days 0 to 14, gonadotropin releasing hormone (GnRH) on day 23, and prostaglandin F_2α (PG) on day 30. Heifers with T2 received a CIDR from days 2 to 16, GnRH on day 23, and PG on day 30. Ovaries were evaluated by ultrasonography on days 23 and 25 to determine ovulatory response to GnRH. In Experiment 2 heifers (n = 353) were assigned within reproductive tract scores by age and BW to one of four treatments. Heifers in T1 and T2 received the same treatments described in Experiment 1. Heifers in T3 and T4 received the same treatments as T1 and T2, respectively, minus the addition of GnRH. In Experiments 1 and 2, heifers were fitted with HeatWatch transmitters for estrous detection and AI was performed 12 h after estrus. In Experiment 1 heifers assigned to T1 had larger dominant follicles at GnRH compared to T2 (P < 0.01) but response to GnRH, estrous response after PG, mean interval to estrus, and variance for interval to estrus after PG did not differ (P > 0.10). AI conception and final pregnancy rate were similar (P > 0.50). In Experiment 2 estrous response after PG did not differ (P > 0.70). Differences in mean interval to estrus and variance for interval to estrus (P < 0.05) differed based on the three-way interaction of treatment length, GnRH, and estrous cyclicity status. AI conception and final pregnancy rates were similar (P > 0.10). In summary, the greater estrous response following PG and resulting AI conception and final pregnancy rates reported for heifers assigned to the two treatments in Experiment 1 and among the four treatments in Experiment 2 suggest that each of these long-term CIDR-based protocols was effective in synchronizing estrus in prepubertal and estrous cycling beef heifers. However, the three-way interaction involving treatment length, GnRH, and estrous cyclicity status in Experiment 2 clearly suggests that further evaluation of long-term CIDR-based protocols is required with and without the addition of GnRH and on the basis of estrous cyclicity status to determine the efficacy of these protocols for use in facilitating FTAI.     

Effects of progesterone presynchronization and eCG on pregnancy rates to GnRH-based, timed-AI in beef cattle

Three experiments were conducted to determine the effects of low-dose progesterone presynchronization and eCG on pregnancy rates to GnRH-based, timed-AI (TAI) in beef cattle (GnRH on Day 0, PGF_2α on Day 7, with GnRH and TAI on Day 9, 54-56 h after PGF_2α). Experiments 1 and 2 were 2 × 2 factorials with presynchronization (with or without a once-used CIDR; Days −15 to 0 in Experiment 1 and Days −7 to 0, with PGF_2α at insertion, in Experiment 2), and with or without 400 IU eCG on Day 7 in suckled cows. In Experiment 3, suckled cows and nulliparous heifers were either presynchronized with a twice-used CIDR (Days −5 to 0) and PGF_2α at insertion, or no treatment prior to insertion of a new CIDR (Days 0-7). Presynchronization increased (P < 0.05) ovulation rate to GnRH on Day 0 (75.0% vs 48.7%, 76.7% vs 55.0%, and 60.0% vs 36.1% for Experiments 1, 2, and 3, respectively), increased the diameter of the preovulatory follicle in Experiments 1 and 2, and increased the response to PGF_2α (regardless of parity) in Experiment 1 (P < 0.01), and in primiparous cows in Experiment 2 (P < 0.01). Effects of presynchronization on pregnancy rates (53.4% vs 54.1%, 57.7% vs 45.3%, and 54.3% vs 44.4% for Experiments 1, 2, and 3, respectively) were influenced by parity and eCG (P < 0.05). Treatment with eCG had no effect (P > 0.05) on the diameter of the preovulatory follicle (Experiment 1), or the response to PGF_2α (Experiments 1 and 2), but tended (P = 0.08) to improve pregnancy rates, especially in primiparous cows that were not presynchronized (P < 0.01). However, the effects of eCG and presynchronization were not additive.     

Impacts of stocking density on development and puberty attainment of replacement beef heifers

In all, 60 Angus×Hereford heifers were ranked by age and BW (210±2 days and 220±2 kg) on day 0, and assigned to: (a) one of three drylot pens (10×14 m pens; 10 heifers/pen) resulting in a stocking density of 14 m²/heifer (HIDENS; n=3), or (b) one of three pastures (25 ha pastures; 10 heifers/pasture), resulting in a stocking density of 25 000 m²/heifer (LOWDENS; n=3). Pastures were harvested for hay before the beginning of this experiment, and negligible forage was available for grazing to LOWDENS heifers during the experiment (days 0 to 182). All heifers received the same limited-fed diet, which averaged (dry matter basis) 4.0 kg/heifer daily of hay and 3.0 kg/heifer daily of a corn-based concentrate. Heifer shrunk BW was recorded after 16 h of feed and water withdrawal on days −3 and 183 for BW gain calculation. On day 0, heifers were fitted with a pedometer behind their right shoulder. Each week, pedometer results were recorded and blood samples were collected for puberty evaluation via plasma progesterone. Plasma samples collected on days 0, 28, 56, 84, 112, 140, 161 and 182 were also analyzed for cortisol concentrations. On days 0, 49, 98, 147 and 182, hair samples were collected from the tail switch for analysis of hair cortisol concentrations. On days 28, 102 and 175, blood samples were collected for whole blood RNA isolation and analysis of heat shock protein (HSP) 70 and HSP72 mRNA expression. Heifers from LOWDENS had more (P<0.01) steps/week compared with HIDENS. No treatment effects were detected (P=0.82) for heifer BW gain. Plasma cortisol concentrations were greater (P⩽0.05) in LOWDENS compared with HIDENS heifers on days 84, 140, 161 and 182 (treatment×day interaction; P<0.01). Hair cortisol concentrations were greater (P<0.01) in HIDENS compared with LOWDENS heifers beginning on day 98 (treatment×day interaction; P<0.01). Heifers from LOWDENS had greater (P=0.04) mean mRNA expression of HSP72, and tended (P=0.09) to have greater mean mRNA expression of HSP70 compared with HIDENS. Heifers from HIDENS experienced delayed puberty attainment and had less (P<0.01) proportion of pubertal heifers on day 182 compared with LOWDENS (treatment×day interaction; P<0.01). In summary, HIDENS altered heifer stress-related and physiological responses, and delayed puberty attainment compared with LOWDENS.     

Effects of Fermenten supplementation to beef cattle

Two experiments were conducted to evaluate a commercially available supplemental N source for beef cattle (Fermenten^®; Church & Dwight Co., Inc., Princeton, NJ, USA). The first experiment evaluated kinetics of in vitro NH₃-N release using batch cultures of rumen fluid incubated with: control (no N added), soybean meal, urea, and Fermenten^®. Ammonia-N was measured at 0, 0.5, 2, 4, 6, 8, 12 and 24 h after incubation began. A treatment by time interaction (P<0.01) occurred in which, during the initial 2 h, Fermenten^® cultures had the highest (P<0.01) NH₃-N but, from 4 to 24 h, the highest (P<0.01) NH₃-N concentrations were with urea-incubated cultures. The total increase in NH₃-N concentrations from 0 to 24 h of incubation was less for Fermenten^® (P<0.01) than for the soybean meal and urea. The second experiment assessed effects of Fermenten^® supplementation on growth, blood parameters, voluntary forage intake and reproductive performance of beef heifers. Sixty heifers, stratified by initial body weight (BW), were randomly allocated to one of two treatments that consisted of iso-nitrogenous grain-based supplements containing either Fermenten^® (72 g/kg, as-fed) or urea (9.7 g/kg, as-fed). Supplements were offered three times weekly at a rate of 2.4 kg of dry matter per heifer daily. Shrunk BW was measured on days 0 and 112 for calculation of daily body weight gain. Body volume measurements were completed on days 0, 28, 56, 84 and 112, whereas pelvic area was assessed on days 0, 56 and 112. Blood samples were collected on days 28, 56, 84 and 112 for analysis of metabolites and hormones. On day 56, 2 heifers, which were randomly selected from each pasture, were placed in individual feeding stations for 26 days to determine treatment effects on voluntary forage intake. On day 112, all heifers were grouped by treatment and exposed to bulls for 60 days. Fewer heifers offered the Fermenten^® supplement attained puberty (P<0.05) and became pregnant during the study compared to heifers fed urea (0.60 and 0.93, respectively; P<0.01). Addition of Fermenten^® to batch cultures of rumen fluid rapidly increased NH₃-N concentrations, whereas further increases occurred in a slower and steady rate. Beef heifers fed a supplement containing Fermenten^® had similar growth and development, but inferior reproductive performance, than heifers fed a supplement containing urea.     

Pregnancy diagnosis based on the fecal progesterone concentration in beef and dairy heifers and beef cows

The present study was undertaken to examine whether pregnancy diagnosis was possible by measuring fecal progesterone concentrations in beef and dairy heifers and beef cows. Rectal fecal samples collected on days 18–24 after insemination or days 11–17 after embryo transfer were mixed with methanol and shaken for preparation of a fecal solution. After centrifugation, the supernatant was extracted with petroleum ether followed by an enzyme immunoassay for progesterone. All pregnant animals showed fecal progesterone concentrations greater than 50 ng/g of fecal material on days 18–24 after AI or estrus. In non-pregnant animals, however, the fecal progesterone concentrations ranged widely from 5 to 180 ng/g of fecal material. In non-pregnant cattle, the percentage of cattle with <50 ng progesterone/g of fecal material compared with the total number was 37–60% on days 18–20, whereas the percentages increased more than 70% to a maximum of 78.1% on day 23. When 50 ng/g was considered as the cut-off value, the sensitivity and specificity of positive pregnancy tests were less than 70% on days 21–24, and 100% for negative pregnancy tests on days 18–24. There were significant differences in the mean fecal progesterone concentrations between pregnant and non-pregnant cattle on days 19–24. These results suggest that feces can be utilized to substitute for plasma and milk to measure progesterone for the purpose of pregnancy diagnosis in heifers and cows.     

Ultrasonography for detection of pregnancy and study of embryonic development in heifers

Real-time B-mode ultrasonography was used to evaluate uterine changes associated with the estrous cycle in 22 ovulatory periods in 12 nulliparous heifers. Irregular, nonechogenic (black) areas were seen on the images of uterine horns during the periovulatory period. These nonechogenic areas were presumably due to intraluminal fluids since they coincided with the discharge of clear, viscous mucus preceding ovulation and blood-tinged mucus after ovulation. Eight heifers were bred until five pregnant heifers were obtained for study of the ultrasonic morphology of the conceptus. Ultrasound examinations were done daily to day 50 of pregnancy. Discrete, nonechogenic areas were first visible within the uterus between days 12 and 14, when they were approximately 2 mm in diameter. These discrete nonechogenic structures were identified as the embryonic vesicle, since they were observed only in heifers later confirmed to be pregnant and were always in the uterine horn ipsilateral to the corpus luteum. The presence of an embryo within the embryonic vesicle was confirmed by observing an echogenic (white) area with rhythmic pulsations (heartbeat). The embryonic vesicle gradually increased in length from the day of first observation until day 26 when it extended past the curvature of the horn and began to encroach into the contralateral horn. In all heifers, by day 32 the vesicle extended to the tip of the contralateral horn. The embryo was first visible between days 26 and 29 when the mean length was 10 mm. The embryo increased in length an average of 1.1 mm per day. A heartbeat was detectable in the embryo on the first day observed. In one superovulated heifer, five vesicles were visible in the uterine horns by day 14 and by day 33 seven embryos were observed; two of the seven embryos apparently resorbed by day 43.     

Anemia associated with anestrus in beef heifers inoculated with Anaplasmamarginale: Endocrinology and ovarian changes

Eleven cyclic Hereford heifers were synchronized to estrus with a commercial luteolytic agent. Eight heifers had been inoculated with $\text{Anaplasma}$$\text{marginale}$. Six of the eight inoculated heifers became anemic, i.e. packed cell volume, red blood cell counts and hemoglobin decreased. White blood cell counts were elevated during severe anemia. Anemic heifers did not show behavioral estrus or ovulate, and during this stage, serum concentrations of progesterone and estradiol-17β were significantly depressed. Mature beef heifers that have acute anaplasmosis suffer from inhibited ovarian function and anestrus.     

Factors influencing estrus and conception in dairy heifers after prostaglandin F2-alpha

The influence of interval between insemination (AI) and estrus on subsequent fertility of PGF(2alpha)-treated (two injections of 25 mg, 11 days apart) heifers was assessed in two experiments. In Experiment I, 240 heifers were allotted to Control (AI 8 to 16 hr after estrus detection), PGF(2alpha)-E (AI 8 to 16 hr after estrus within five days of second PGF(2alpha)) or PGF(2alpha)-T (AI 80 hr after second PGF(2alpha)). In Experiment II, 130 heifers were assigned to control (AI as before) or PGF(2alpha) (AI 72 or 80 hr after second PGF(2alpha)) with half the PGF(2alpha) heifers receiving 100 mug GnRH 72 hr after first PGF(2alpha). Heifers of both experiments that were bred at a predetermined time were arrayed by interval from AI to estrus. Conception rates of heifers detected in estrus from 32 hr before AI to 24 hr after AI did not differ (x(2)=3.35, df=5, P>0.5). The percentage of GnRH-treated heifers in estrus within five days (81.8%) was not (P>0.75) greater than those not receiving GnRH (77.3%) but they had higher (P<0.05) serum progesterone (P(4)) concentration at second PGF(2alpha) (3.17 vs 2.41 ng/ml). When P(4) values were arrayed for both groups at 1 ng intervals, the percentage of heifers exhibiting estrus increased with increasing P(4) level (P<0.05).     

Timed artificial insemination should be performed early when used norgestomet ear implants are applied for synchronizing ovulation in beef heifers

The present study evaluated the effect of the type of norgestomet ear implant (new vs. used) on the ovarian follicular response (experiment 1) and pregnancy per artificial insemination (AI) (P/AI; experiment 2) of beef heifers subjected to an estradiol plus progestin timed artificial insemination (TAI) program. In experiment 1, 57 cyclic beef heifers were randomly assigned to one of two groups according to the type (new or previously used for 9 days) of norgestomet ear (NORG) implant. At the time of NORG implant insertion, the heifers were treated with 2 mg of intramuscular estradiol benzoate. Eight days later, the NORG implants were removed, and the heifers received an intramuscular administration of 150 μg of d-cloprostenol, 300 IU of equine chorionic gonadotropin, and 0.5 mg of estradiol cypionate. The heifers had their ovaries scanned every 12 hours from the time of NORG implant removal to 96 hours after verifying the occurrence and timing of ovulation. No difference (P = 0.89) was observed in the ovulation rates between the two treatments (new = 80.0%; 24/30 vs. used = 81.5%; 22/27). However, the heifers treated with a used NORG implant had (P = 0.04) higher proportion (36.4%; 8/22) of early ovulation (between 36 and 48 hours after NORG implant removal) compared with the heifers treated with a new NORG implant (8.3%; 2/24). In experiment 2, at the beginning of the synchronization protocol, 416 beef heifers were randomly assigned into two groups, as described in the experiment 1. Two days after the NORG implant removal, the heifers were reassigned to be inseminated at 48 or 54 hours after NORG implant removal. There was an interaction (P = 0.03) between the type of NORG implant and the timing of TAI on P/AI. The timing of insemination only had an effect (P = 0.02) on the P/AI when the heifers were treated with a used NORG implant [(TAI 54 hours = 41.9% (44/105) vs. TAI 48 hours = 58.6% (58/99)]. In conclusion, beef heifers synchronized with a used NORG implant plus estradiol exhibited a higher proportion of earlier ovulations, and TAI in these heifers should be performed 48 hours after removal of used NORG implants.     

Estrus synchronization and pregnancy rates in cyclic and noncyclic beef cows and heifers treated with syncro-mate B or Norgestomet and Alfaprostol

Postpartum lactating cows (N=118) and virgin heifers (N=60) were treated with subcutaneous Norgestomet implants for nine days and received either an intramuscular injection (im) of 5 mg estradiol valerate and 3 mg Norgestomet at the time of implant insertion or an im injection of 5 mg Alfaprostol 24 hr before implant removal. Animals were artificially inseminated 12 hr after detection of estrus. Of the cows and heifers, 78% and 88%, respectively, were in estrus within five days after implant removal (P<0.09). There was no difference between treatments in the proportion of animals in estrus or in the timing of estrus (P<0.85). Estrus was detected in a greater (P<0.05) proportion of animals that were cyclic prior to treatment (88%) than among those that were anestrous prior to treatment (77%). Pregnancy rates after five days were similar between heifers that were cyclic (42%) or anestrous (47%) prior to treatment; however, the five-day pregnancy rate in cows that were anestrous prior to treatment was 38% lower than that in cows that were cyclic prior to treatment (17 vs 55%, P<0.01). Although the treatments synchronized or induced estrus in both cyclic and anestrous animals, marked variability in estrous response and fertility among previously cyclic or anestrous postpartum cows limited the effectiveness of the treatments.     

Neither duration of progesterone insert nor initial GnRH treatment affected pregnancy per timed-insemination in dairy heifers subjected to a Co-synch protocol

Our objectives were to: 1) compare response to cloprostenol, synchrony of ovulation, and pregnancy per timed-AI (P/TAI) in a 5 d versus a 7 d Co-synch + PRID protocol (Experiment 1); and 2) investigate whether the initial GnRH is necessary to achieve acceptable P/TAI in a 5 d Co-synch + PRID protocol (Experiment 2) in dairy heifers. In Experiment 1, 64 Holstein heifers, 15 to 17 mo, were assigned by age to receive 100 μg of GnRH and a PRID for 5 or 7 d (PRID5 and PRID7, respectively). At PRID removal 500 μg of cloprostenol (PGF) was given i.m. Heifers received the second GnRH treatment concurrently with TAI at 72 (PRID5) or 56 (PRID7) h after PRID removal. Transrectal ultrasonography monitored ovarian dynamics, ovulation synchrony, and pregnancy status (28 and 45 d after TAI). Plasma progesterone concentrations were determined at PRID removal and TAI. Five of seven heifers that ovulated before TAI became pregnant, and only two heifers did not respond to PGF treatment in the PRID5 group. Five PRID5 and 2 PRID7 heifers failed to ovulate after the second GnRH. However, P/TAI did not differ between PRID5 (59.4%) and PRID7 (58.1%). Overall ovulation response to first GnRH treatment was only 31.7%, and a larger proportion of heifers that did not ovulate became pregnant (65.1 versus 45.0%). In Experiment 2, 56 Holstein heifers, assigned as in Experiment 1, were subjected to a PRID5 protocol with (PRID5G) or without (PRID5NoG) GnRH at PRID insertion; all heifers were TAI 72 h after PRID removal. Transrectal ultrasonography and progesterone determinations were performed as in Experiment 1. Pregnancy per TAI did not differ whether or not heifers received GnRH at PRID insertion (67.9 versus 71.4%). Consistent with our previous findings, seven of nine heifers that ovulated before TAI became pregnant, and only two heifers did not respond to PGF treatment. Combining both experiments, length of proestrus but not ovulatory follicle diameter was identified as a significant predictor of probability of pregnancy 28 d after TAI, with a maximum predicted probability of 80.1% when the length of proestrus was 3 d. In summary, a PRID5 protocol resulted in comparable P/TAI to a PRID7 protocol. Most of the heifers that ovulated before TAI in the PRID5, PRID5G, and PRID5NoG protocols became pregnant. More than one PGF or a GnRH treatment at PRID insertion in a 5 d Co-synch + PRID protocol was not required to achieve acceptable P/TAI in dairy heifers.