Suckled Beef Cows Research Articles

PSV-25 Investigating the effects of Chromium Propionate supplementation on productive and reproductive performance of beef cows

Abstract We investigated the effects of Chromium Propionate supplementation on reproductive performance of beef cows from pre-partum to weaning. Suckled beef cows at nine locations were enrolled in the study. Within location, cows were stratified by parity, dam age, and day postpartum (DPP) and randomly assigned to one of two treatments: 1) Control, supplementation of a mineral product at 113 gּ animal-1ּ d-1 (n = 464 cows; 13 experimental units); or 2) CrP, supplementation of mineral product at 113 gּ animal-1ּ d-1 containing 1.4 g of Chromium Propionate (0.4%KemTRACE Chromium 0.4%, Kemin Industries, Inc., Des Moines, IA; n = 489 cows; 13 experimental units). Treatments were initiated at approximately 37 d pre-calving until weaning for a total of 250 ± 12 d. Cows were enrolled in the 7-d CO-Synch+CIDR fixed-time artificial insemination (TAI) protocol followed by natural service for a 70-d breeding season. Pregnancy diagnosis was performed by ultrasonography at 55 d after TAI protocol and 40 d after the end of the breeding season. Cow body weight (BW) and body condition score (BCS) were recorded at initiation of the TAI protocol (d -10), at pregnancy diagnosis (d 55 and 110), and at weaning (d 285). Within group, mineral disappearance was determined by the difference in weight between offered mineral and refusals. Data were analyzed using the GLIMMIX and MIXED procedures of SAS with pasture/group as the experimental unit with the effect of treatment and included group (treatment × location), cow (group), and location as random variables. Age, DPP, d -10 BCS, and BW were similar (P > 0.05) between treatments (5.4 and 5.3 ± 0.61 yr, 79.2 and 79.9 ± 4.61 d, 5.1 and 5.2 ± 0.05, 515.7 and 515.6 ± 15.11 kg for Control and CrP, respectively). Mineral disappearance was similar (P = 0.999) between treatments (165.5 and 152.9 gּ animal-1ּ d-1, for Control and CrP, respectively). Cow BW was similar (P > 0.05) between treatments on d 55, 110 and 285 (558.5 and 551.4 ± 14.50 kg, 580.8 and 594.6 ± 13.51 kg, and 574.2 and 570.9 ± 14.32 kg for Control and CrP, respectively). Similarly, cow BCS did not differ (P > 0.05) between treatments on d 55, 110 and 285 (5.4 and 5.4 ± 0.09, 5.3 and 5.3 ± 0.10, and 5.1 and 5.2 ± 0.10 for Control and CrP, respectively). Calf birth and weaning BW were similar (P > 0.05) between treatments. However, CrP-supplemented cows tended (P = 0.081) to have greater estrus expression (60.2 and 68.3 ± 3.1 %, for Control and CrP, respectively) and CrP-supplemented cows had greater (P = 0.045) TAI pregnancy rate when compared with Control cows (49.9 and 55.2 ± 2.1 %). Supplementation of Chromium Propionate to beef cows from pre-partum through weaning did not affect cow BW and BCS, tended to increase estrus expression and increased TAI pregnancy rate.

The use of a recombinant equine chorionic gonadotropin (reCG) in fixed-time AI programs in beef cattle

The aim of the current study was to evaluate the effect of a novel recombinant eCG (reCG) on pregnancy rates to AI (P/AI) in suckled beef cows of different breeds that were synchronized with an estradiol/progesterone (P4)-based protocol for fixed-time AI (TAI). In experiment 1, 1244 Bos taurus suckled cows were used. On Day 0 all cows received an intravaginal P4 device (600 mg P4) and 2 mg of estradiol benzoate. On Day 7, devices were removed, and all cows received 0.150 mg of D-cloprostenol plus 1 mg of estradiol cypionate and were randomly divided to receive 140 IU or 105 IU of reCG or no reCG treatment (controls) at that time. Cows were tail painted for estrus detection and those in estrus by 48 h after P4 device removal were inseminated; whereas those not showing estrus were also inseminated and received GnRH at the same time. In experiment 2, 818 Bos taurus x Bos indicus crossbred suckled cows received the same FTAI protocol used in Experiment 1. Cows were randomly divided at the time of P4 device removal into 4 groups to receive 140 IU, 105 IU or 84 IU of reCG or no reCG treatment. In experiment 3, 345 Bos indicus suckled cows were submitted to the same FTAI protocol as those in previous experiments and were randomly divided into three groups to receive 140 IU or 105 IU of reCG, or 300 IU of serum derived eCG (PMSG). In Experiment 1, estrus rate and P/AI was greater (P < 0.05) in cows treated with reCG (79.9 and 53.5 %, 76.9 and 52.3 % for the 105 UI and 140 UI reCG groups, respectively) than those in the control group (69.9 and 44.4 %, respectively). In Experiment 2, cows treated with reCG tended (P < 0.1) to achieve a greater P/AI than control cows (38.6 %, 37.1 %, 36.2 % and 28.2 % for those receiving 84 IU, 105 IU,140 IU of reCG, and those in the control group); but when P/AI of all cows treated with reCG was contrasted to that of control cows, the difference was significant (P < 0.01). In Experiment 3, P/AI in cows treated with 84 IU of reCG (54 %) did not differ from that of cows treated with serum derived eCG (59 %) but both were greater (P < 0.05) than cows treated with 105 UI of reCG (41 %). In conclusion, treatment with reCG improved fertility in suckled Bos taurus and Bos taurus x Bos indicus beef cows. In suckled Bos indicus cows, although treatment with reCG and serum derived eCG were comparable, the higher dosage of reCG was detrimental to their P/AI.

28 Investigating the effects of Chromium Propionate supplementation on reproductive performance of beef cows

Abstract The objective of this study was to explore the effects on reproductive performance of beef cows supplemented with Chromium Propionate during the post-partum and breeding periods. A total of 955 multiparous suckled beef cows located at eight locations were enrolled in the study. Within location cows were stratified based on parity, body condition score (BCS), and days postpartum (DPP) and randomly assigned to one of two treatments: 1) Control- supplementation of a mineral product at 113 g animal/d (n = 484 cows; 16 experimental units); or 2) CrP - supplementation of mineral product at 113 g animal/d containing Chromium Propionate (0.4% animal/d, KemTRACE, Kemin Industries; n = 471 cows; 16 experimental units). Mineral supplementation was offered starting at 45 d pre-breeding, during the breeding season, and until weaning for a total of approximately 150 d. Cows were enrolled in a fixed-time artificial insemination (TAI) using the 7-d CO-Synch+CIDR protocol followed by natural service with clean-up bulls 7 d after TAI, for a 70-d total breeding season. Pregnancy diagnosis was performed by ultrasonography 55 d after TAI and again approximately 40 d after the end of the breeding season. Cow body weight (BW) and BCS were recorded at the beginning of the experiment (d -45), at the initiation of the TAI protocol (d -10), at each pregnancy diagnosis (d 55 and 110), and at weaning (d 150). Mineral intake was estimated based on the difference in weight between offered mineral and refusals. Data were analyzed using the GLIMMIX, for binomial data, and MIXED, for continuous data, procedures of SAS. Cow initial BW and DPP were similar (P &amp;gt; 0.10) between treatments (584 ± 198 kg and 78 ± 3 d, respectively). Estimated mineral intake was similar (P = 0.52) between treatments (119.6 ± 10.3 g and 124.5 ± 10.4 g animal/d, for Control and CrP, respectively). Supplementation of CrP did not influence estrus expression (58.3% vs 61.0% ± 2.5 %; P = 0.45), TAI pregnancy rates (63.1% vs 60.1 % ± 2.9 %; P = 0.56), or final breeding season pregnancy rates (94.2% vs 94.7% ± 2.9 %; P = 0.86), for CrP and Control, respectively. Chromium Propionate supplementation did not affect (P &amp;gt; 0.10) final cow BCS and BW (5.2 ± 0.03; 562.9 ± 169.93 kg). In conclusion, Chromium Propionate supplementation delivered via an oral mineral supplement during the pre-breeding and breeding periods did not influence reproductive performance and changes in BW and BCS of beef cows.

Magnitude and persistence of higher estrus-associated temperatures in beef heifers and suckled cows.

Higher estrus-associated temperatures (HEAT) are a hallmark feature in sexually active females. The overarching aim of this study was to characterize the variability, magnitude, and persistence of HEAT in heifers and suckled beef cows as well as identify associated factors when occurring during thermoneutral conditions at the onset of the spring breeding season. In both heifers and cows, estrus was induced using a 7-d controlled internal drug release (CIDR)-PGF2α protocol. Vaginal temperature after prostaglandin F2α administration was recorded every 5min using a Thermochron iButton affixed to a blank CIDR (containing no progesterone). Estrus was defined as when a heifer first stood to be mounted or when a cow had an Estrotect patch score of 3 or 4. Level of HEAT varied among individual animals. When comparing common HEAT variables using a mixed model with date nested within a year, maximum HEAT (39.9 ± 0.1 and 40.0 ± 0.1 °C) and duration (15.5 ± 0.8 and 15.4 ± 0.7) were similar in heifers and cows, respectively. However, the magnitude and persistence of HEAT differed. Total area under the HEAT curve was 117.1 ± 13.5 and 158.7 ± 12.3 for heifers vs cows, respectively (P = 0.0571). Further, 42.9% of heifers and 49% of cows had maximum HEAT ≥ 40 °C which persisted up to 6.5 and 10h, respectively. When ambient conditions were predominantly thermoneutral, temperature humidity index had minimal impact on HEAT (mixed model, repeated measures over time). Toward identifying associated factors with different aspects of HEAT using best fit hierarchical linear regression models, baseline vaginal temperature and baseline duration were the most highly associated independent variables. Follicle size, estradiol and progesterone levels, and other available animal-related variables (e.g., age, weight, hair coat score) explained only a small amount of variation in HEAT. In summary, level of HEAT varies in estrus females even under thermoneutral conditions. Because HEAT can persist for an extended time, direct effects on fertility important components are unavoidable. Whether HEAT is a good or bad component of the periovulatory microenvironment is the basis of ongoing and future studies.

Pregnancy risk in beef and dairy cows after supplementing semen with transforming growth factor beta-1 at the time of artificial insemination.

Our objective was to determine if the addition of a concentrated human recombinant transforming growth factor beta-1 (TGF) to bovine semen at the time of AI would result in increased risk of pregnancy in beef and dairy cows. Suckled beef cows (n = 1,132) in 11 herds across 2 states and lactating dairy cows (n = 2,208) in one organic-certified herd were enrolled. Beef cows received fixed-time AI (FTAI) following a 7 d CO-Synch + controlled internal drug release estrous synchronization protocol. Dairy cows were inseminated following observation of natural estrus expression. Cows received either no treatment as a control (CON) or 10ng of TGF in 10 μL added through the cut-end of a thawed straw of semen immediately prior to AI. At the time of FTAI of beef cows, the mean ± SD age was 5.0 ± 2.4 yr, BCS was 5.3 ± 0.7, and days postpartum was 78.2 ± 15.5 d. The overall pregnancy risk (PR) in beef cows was 55.2% to AI and 90.5% season-long. PR in beef cows was not affected (P = 0.27) by the addition of TGF (53.1% vs. 58.1%). Furthermore, there was no difference (P = 0.88) for season-long PR in beef cows that received TGF (91.2% vs. 91.5%). At the time of insemination of dairy cows, the mean ± SD lactation was 3.0 ± 1.3 lactations, BCS was 2.9 ± 0.3, days in milk was 115.6 ± 56.6 d, and cows had received 2.4 ± 1.5 inseminations/cow. The overall pregnancy risk to AI in dairy cows was 23.1%. PR to AI for dairy cows was not affected (P = 0.32) by addition of TGF (22.0% vs. 23.8%). In conclusion, PR to AI was not affected by addition of TGF to thawed semen immediately prior to AI in beef or dairy cows.

181 Expression of estrus and fertility of different presynchronization strategies for fixed-time artificial insemination in suckled beef cows

181 Expression of estrus and fertility of different presynchronization strategies for fixed-time artificial insemination in suckled beef cows

293 Impact of Late Embryonic and Early Fetal Mortality on Overall Productivity of Suckled Beef Cows

Abstract The objective of this study was to evaluate the effect of late embryonic and early fetal mortality (LEEFM) on the performance of beef cows exposed to fixed-timed artificial insemination (TAI). Postpartum cows (n = 207) from three locations were exposed to a 7-d CO-Synch+CIDR protocol followed by TAI (day 0) and natural service breeding starting 14 days after TAI. Two pregnancy diagnoses were performed on days 29 and 100 and cows were classified as: 1) Maintained (MAINT): cows were pregnant on day 29 and the same pregnancy was confirmed on day 100; 2) LEEFM: cows were diagnosed as pregnant on day 29 but non-pregnant or pregnant by natural service on day 100; and 3) Non-pregnant (NP): cows were diagnosed as non-pregnant to TAI on both days 29 and 100. Cows were evaluated until calves that were a product of the breeding season described herein were weaned. Final pregnancy rates were decreased (P &amp;lt; 0.01) for LEEFM compared with MAINT and NP. Calving (P &amp;lt; 0.01) and weaning rates (P &amp;lt; 0.01) were also decreased for LEEFM compared with MAINT and NP. Average calving day was decreased (P &amp;lt; 0.01) in MAINT cows compared with both NP and LEEFM; however, no differences were observed between NP and LEEFM (P = 0.46). Weaning weight was increased (P ≤ 0.05) for MAINT compared with both NP and LEEFM; however, there were no differences between NP and LEEFM ( P = 0.52). Cows that experienced LEEFM had decreased (P &amp;lt; 0.01) weaning weights per cow exposed compared with both MAINT and NP. In summary, that conceive to TAI and experience LEEFM have decreased performance compared not only to MAINT cows, but also cows that failed to conceive to TAI (NP).

Comparison of Gonadotropin-Releasing Hormone versus Estrogen-Based Fixed-Time Artificial Insemination Protocols in Grazing Bos taurus Suckled Beef Cows.

Fixed-timed artificial insemination (FTAI) protocols for beef cattle in South America are primarily based on estradiol esters and intravaginal progesterone-releasing devices (IVPD). The objective of this study was to determine the optimal gonadotropin-releasing hormone (GnRH)-based protocol as an alternative to the use of estrogen-based protocols in grazing Bos taurus suckling beef cows. All cows received an IVPD on the day of protocol initiation and prostaglandin F2α (PG) plus equine chorionic gonadotropin (eCG) treatments at the time of IVPD removal. In Experiment 1, cows (n = 235) were randomly assigned to one of four treatments: (i) 7-day estradiol = 2 mg of estradiol benzoate (EB) at IVPD insertion on Day 9 and 1 mg of estradiol cypionate (ECP) at IVPD removal on Day 2; (ii) 7-day GnRH = 10 µg of GnRH at IVPD insertion on Day 10, IVPD removal on Day 3 and GnRH at FTAI; (iii) 7 & 7 estradiol = PG at IVPD insertion on Day 16, EB on Day 9 and ECP at IVPD removal on Day 2; (iv) 7 & 7 GnRH = PG at IVPD insertion on Day 17, GnRH on Day 10, IVPD removal on Day 3 and GnRH at FTAI. In Experiment 2, cows (n = 462) were randomly assigned to one of four treatments: (i) 6-day estradiol = EB at IVPD insertion on Day 9, IVPD removal on Day 3 and GnRH at FTAI; (ii) 7-day estradiol; (iii) 7-day GnRH; (iv) 7 & 7 GnRH. In Experiment 1, plasma progesterone concentrations and percentage of cows with a corpus luteum (CL) at IVPD removal, and pregnancy per AI (P/AI) were greater for cows subjected to GnRH-based protocols compared with cows subjected to estrogen-based protocols (p < 0.01). In Experiment 2, cows subjected to the 7 & 7 GnRH protocol had the greatest P/AI (p < 0.01). In summary, GnRH-based FTAI protocols resulted in similar or greater P/AI compared to estrogen-based FTAI protocols in grazing postpartum Bos taurus suckled beef cows. The greatest P/AI was attained with the 7 & 7 GnRH protocol.

Time of insemination in relation to pregnancy rates in beef cattle after oestrus detection with automated activity monitoring system

BackgroundThe timing of artificial insemination is critical to achieve acceptable results in cattle production systems. Over the past 60 years the length and expression of oestrus in dairy cattle has altered. Recent studies have indicated the optimal timing for insemination after the commencement of oestrus may now be earlier than traditional recommendations in beef cattle, as is the case in dairy cattle. The aim of the current study was to evaluate the effect of time from onset of oestrus [as determined by an automated activity monitoring system (AAMS)] to artificial insemination (AI) on pregnancy outcome in Norwegian beef cattle. Five commercial beef suckler herds participated in a cohort study by providing data on the time of AAMS alarm and time of AI. Blood sampling on the day of AI was performed and serum progesterone concentration measured. Pregnancy detection was performed by transrectal ultrasonography and aging of the fetus performed when necessary. A mixed logistic regression model was fitted to study the effect of time from AAMS alarm to AI on pregnancy outcome. Time categories used in the model were < 12 h, 12–24 h, and > 24 h.ResultsAI periods (n = 229) with serum progesterone concentration < 1 ng/mL were available for analysis. Overall pregnancy risk per AI for the whole study period was 65.5%, with an inter-herd variation from 10 to 91%. Median time elapsed from AAMS alarm to AI was 17.75 h. Herd affected pregnancy outcome (P = 0.001), while breed and parity status (heifer/cow) did not. The time category closer to AAMS alarm 0–12 h showed a numerically lower pregnancy risk as compared to the baseline group which had AI 12–24 h after onset of oestrus.ConclusionThis study found no evidence to support a change in the recommended timing of AI in beef suckler cows.

GnRH dose at initiation of a 5-day CO-Synch + P4 for fixed time artificial insemination in suckled beef cows

The objective of the present study was to evaluate the effect of GnRH dose administered at initiation (GnRH-1) of a 5-day CO-Synch + P4 protocol on ovulatory response, expression of estrus, and fertility in suckled beef cows. Suckled beef cows (n = 1101) at four locations were randomized to receive either 100 or 200 µg of gonadorelin acetate at initiation (D-8) of a 5-day CO-Synch + P4 protocol concurrently with insertion of an intravaginal progesterone (P4) device. On D-3 the P4 device was removed, two doses of prostaglandin F2α were administered concurrently and a patch was applied to evaluate expression of estrus. Artificial insemination was performed 72 h after P4 device removal (D0) simultaneously with the administration of 100 µg of gonadorelin acetate (GnRH-2). Increasing GnRH dose at initiation of a 5-day CO-Synch + P4 did not enhance ovulatory response (P = 0.57) to GnRH-1, expression of estrus (P = 0.79), nor pregnancies per AI (P/AI; P = 0.91). Both follicle size (quadratic) and circulating P4 (linear) affected (P < 0.01) ovulatory response to GnRH-1 independent of dose. Cows that had ovulation to GnRH-1 had smaller (P < 0.001) follicle size on D-3 and reduced (P = 0.05) expression of estrus compared to cows that did not have ovulation to GnRH-1, however, P/AI did not differ (P = 0.75). In conclusion, increasing the dose of GnRH-1 in the 5-day CO-Synch + P4 protocol did not enhance ovulatory response, expression of estrus, or P/AI in suckled beef cows.

Comparison of the 7-day CO-Synch and 8-day estradiol-based protocols for estrus synchronization and timed artificial insemination in suckled Bos taurus cows

Two experiments were conducted to compare, follicle diameter (FD) on Day −1, corpus luteum (CL) area on Day 7, progesterone (P4) concentration on Day 7 and 18, pregnancy per timed artificial insemination (TAI) on Day 30, and pregnancy loss (PL) between Days 30 and 60 after TAI (TAI, Day 0) using two different synchronization protocols. In Experiment 1, Angus cows (n = 1148) were randomly assigned to either 7-d progesterone CO-Synch (7-d CO-Synch) or 8-d progesterone + estradiol (8-d P + ES) synchronization protocols for TAI. On Day −10, cows in the 7-d CO-Synch treatment group (n = 574) received a progesterone-releasing intravaginal device (PIVD; 0.5 g P4) and GnRH (0.105 mg), on Day −3 the PIVD was removed and cows received cloprostenol (0.150 mg), then, on Day 0 (64 h after PIVD removal), cows received GnRH (0.105 mg) and were TAI. On Day −10, cows in the 8-d P + ES treatment group (n = 574) received a PIVD (0.5 g P4) and estradiol benzoate (2.0 mg), on Day −2 the PIVD was removed, and cows received cloprostenol (0.150 mg) and estradiol cypionate (0.5 mg), then, on Day 0 (48 h after PIVD removal), cows were TAI. Pregnancy per TAI was determined on Days 30 and 60. In a subset of cows (7-d CO-Synch, n = 41; 8-d P + ES, n = 40), serum P4 concentration was evaluated on Day 18. In Experiment 2, anestrus (n = 34) and cyclic (n = 34) suckled beef cows were selected and submitted at random on Day −10, to either 7-d CO-Synch or 8-d P + ES treatment groups. Follicle diameter on Day −1, CL area, and serum P4 concentration on Day 7 were determined. In Experiment 1, pregnancy per TAI on Day 30 did not differ (7-d CO-Synch = 48.9%; 8-d P + ES = 45.6%) between treatments but it was greater for cows with BCS ≥5 (P < 0.01). Pregnancy loss between Days 30 and 60 did not differ between treatment groups but tended to be greater in cows with BCS <5.0 (P < 0.1). In a subset of cows, serum P4 concentration on Day 18 did not differ between treatment groups but tended to be lower (P < 0.1) in cows that had PL between Days 30 and 60 compared to cows that had no PL. In Experiment 2, FD tended to be greater (P < 0.1) and CL area was greater (P = 0.05) in anestrus cows from 7-d CO-Synch treatment. In cyclic cows, the treatment did not affect the FD or CL area. In conclusion, there was no difference in pregnancy per TAI on Day 30 and PL between Days 30 and 60 between cows using 7-d CO-Synch + PIVD or 8-d estradiol-based + PIVD protocols for estrus synchronization and TAI.

Assessing pregnancy outcomes in cow-calf operations after administration of modified-live or killed virus vaccinations at the initiation of synchronization for fixed-time AI

The objective of this study was to compare the reproductive outcomes (artificial insemination [AI] pregnancy rates, season pregnancy rates, AI pregnancy losses) and calf traits (birth and weaning weights) after vaccination of suckled beef cows against bovine herpesvirus 1 and bovine viral diarrhea virus using commercially-available modified-live virus (MLV) or killed virus (KV) vaccine at the initiation of a fixed-time AI program. Previously-vaccinated cows (n = 2138) on 14 farms throughout Virginia were enrolled in the study during the Fall 2017 and Spring 2018 breeding seasons. Animals received a single vaccination injection at 10 d pre-breeding, corresponding with time of CIDR insertion at initiation of the 7-d CO-Synch + CIDR synchronization protocol. Cows were inseminated at a fixed time (60–66 h after removal of the CIDR insert) and subsequently turned out with bulls approximately 1 wk after insemination for a natural service. Cows treated with the MLV vaccine had greater AI pregnancy rates than cows treated with the KV vaccine during the fall (P = 0.008; 54% vs. 46%, respectively), but not during the spring breeding season (P = 0.62; 48 vs. 49%). Season pregnancy rates were greater (P = 0.01) in the fall (95–96%) than in the spring breeding season (89–90%), but were not affected by vaccine treatment (P = 0.49) or treatment by season (P = 0.30) interactions. Percentage of AI pregnancy losses was not affected by season (P = 0.85), vaccine treatment (P = 0.83), or treatment by season interactions (P = 0.68). The number of cycles it took for cows to become pregnant by natural service differed by season (P = 0.006) but not treatment (P = 0.87) or treatment by season interaction (P = 0.997). Cows treated with the MLV vaccine gave birth earlier in the calving season (8.36 ± 0.6 d) than those treated with the KV vaccine (10.31 ± 0.6 d; P = 0.02). There was a main effect of season on birth weights (P = 0.008), weaning weights (P < 0.001), and ADG at weaning (P < 0.001), but no effects of treatment (P ≥ 0.26) or treatment by season interaction (P ≥ 0.10) on any of these parameters. Overall, this study demonstrated that the administration of an MLV vaccine at 10 d before fixed-time AI did not have any adverse effects on pregnancy or calf outcomes compared with KV vaccine administration.

179 Injectable progesterone priming prior to fixed-time artificial insemination in primiparous and multiparous suckled beef cows

Reproduction, Fertility and Development is an international journal publishing original research , review and comment in the fields of reproduction and developmental biology in humans, domestic animals and wildlife

Equine chorionic gonadotropin administered on day 5 of a 7-days fixed-time artificial insemination program improves ovulation synchrony and corpus luteum function in anestrous beef cows

In order to assess the effect of equine chorionic gonadotropin (eCG) administered on Day 5 or 7 of a fixed-time artificial insemination protocol (FTAI) in anestrous suckled beef cows, two experiments were performed to determine the following endpoints: Experiment 1 (n = 22), preovulatory follicle (POF) diameter, ovulation time, corpus luteum (CL) area, estradiol (E2) and progesterone (P4) concentrations; and Experiment 2 (n = 676), a field trial to evaluate conception rate using the same experimental design. In both experiments, a synchronization protocol using estradiol benzoate (EB) (Day 0), intravaginal progestin device (IVD) (Days 0 through 7), prostaglandin (PGF) (Day 7), eCG (Day 5 or 7), and GnRH (Day 9). Treatment consisted of administering 400 IU of eCG on Day 5 (T5) or Day 7 (T7 or control) concomitant with treatment with PGF2α. In experiment 1, all cows of T5 ovulated by 16 h after GnRH administration. The POF tended (P = 0.06; P = 0.07) to be larger at 1 and 2 d before ovulation in T5. The day before ovulation, E2 tended to be lower (P = 0.06) in T5 compared with T7. The CL area and the P4 concentrations were greater (P = 0.04) on day 9 in T5 compared with T7. In experiment 2, the conception rate was greater (P = 0.04) in T5 (72.2%) compared with T7 (61.0%) group. Therefore, administration of eCG on Day 5 of the designed protocol hastened ovulation of a greater follicle, which produced a larger CL and greater concentrations of progesterone by Day 9 after ovulation, resulting in 11.2% increase in cows pregnant.

PSV-B-15 Comparison of the 7-day Cosynch and 8-day Estradiol-Based Protocols for Synchronization of Ovulation and Timed Artificial Insemination in Suckled Bos Taurus Cows

Abstract The objective was to compare pregnancy rates (PR) on day 30 and pregnancy loss between days 30 and 60 (PL) after timed artificial insemination (TAI; day 0) using 2 synchronization protocols, and plasma progesterone on day 18 in suckled beef cows. Angus cows were randomly assigned to either 7-d progesterone CoSynch (7-d P + GnRH) or 8-d progesterone + estradiol (8-d P + ES) synchronization protocols for TAI. On day -10, cows in the 7-d P + GnRH treatment group (n=574) received a progesterone-releasing intravaginal device (PIVD) and GnRH, on day -3 the PIVD was removed and cows received cloprostenol. On day 0 (64 h after PIVD removal), cows received GnRH and were subjected to TAI. On Day -10, cows in the 8-d P + ES treatment group (n=574) received a PIVD and estradiol benzoate, on Day -2 the PIVD was removed, and cows received cloprostenol and estradiol cypionate. On day 0 (48 h after PIVD removal), cows were subjected to TAI. The TAI pregnancy rates for each treatment were determined on day 30 and day 60. In a subset of cows [n=81, (7-d P + GnRH, n=41; 8-d P + ES, n=40)], serum progesterone concentration was evaluated on day 18. The PR (7-d P + GnRH=48.9%; 8-d P + ES=45.6%) and PL (7-d P + GnRH=3.6%; 8-d P + ES=4.6%) did not differ (P≥0.28) between treatment groups. In a subset of cows, serum progesterone concentration on day 18 did not differ (P=0.67) between treatment groups but tended to be less (P=0.07) in cows that had PL compared with cows that had no PL. In conclusion, there was no difference in PR and PL between suckled beef cows using 7-d CoSynch or 8-d estradiol-based protocols for synchronization of ovulation and TAI.

PSV-A-1 Estrus Response and Pregnancy Rates of Beef Cows Enrolled in two Fixed-Time Artificial Insemination Protocols, with or without pre-Synchronization

Abstract Pre-synchronization strategies with prolonged exposure to exogenous progesterone have the potential to alter estrus expression and improve fertility in beef cows. The objective of this study was to evaluate the estrus response and pregnancy rate of suckled beef cows enrolled in two fixed-time artificial insemination (TAI) protocols. A total of 1,216 cows (angus-crossed) at 10 locations across VA were enrolled in the study. Within location, cows were ranked by body weight, and days postpartum and randomly assigned to one of two treatments: 1) 7&amp;7 (n = 610), cows were administered prostaglandin F2α (PGF; 25 mg) and a controlled internal drug releasing (CIDR) insert [Day -14], an injection of GnRH (100 μg [Day -7]), PGF injection and CIDR removal [Day 0], and a second injection of GnRH concurrently with TAI 64 ± 2 h later [Day 2]; 2) 7-day CO-Synch+CIDR (7-day; n = 606), cows were administered GnRH (100 μg) and a CIDR insert [Day -7], PGF (25 mg) injection and CIDR removal [Day 0], and a second injection of GnRH concurrently with TAI 64 ± 2 h later [Day 2]. All cows received an estrus alert patch (ESTROTECT) on Day 0 and were evaluated for patch activation at TAI on Day 2. Pregnancy was diagnosed by transrectal ultrasonography between 45 and 65 days after TAI. The percentage of cows exhibiting estrus between Day 0 and 2 was greater (P &amp;lt; 0.001) for 7&amp;7 compared with 7-day cows (72.8% and 55.9%, respectively). However, pregnancy rate to TAI was similar (P = 0.328) between treatments (63.8% and 61.1%, for 7&amp;7 and 7-day, respectively). We conclude that suckled beef cows enrolled in the 7&amp;7 TAI protocol had increased estrus expression, but similar pregnancy rate when compared with cows enrolled in the 7-day CO-Synch+CIDR TAI protocol.

290 Effects of Exogenous Follicle Stimulating Hormone Prior to Embryo Transfer on Beef cow Recipients

Abstract Objectives were to evaluate characteristics of corpora lutea (CL) and concentrations of progesterone (P4) in beef recipient cows stimulated with follicle stimulating hormone (FSH) prior to embryo transfer. Forty suckled beef cows received the CO-Synch+CIDR protocol and were randomly assigned to one of two treatments: 1) exogenous FSH (FSH; 1.0 mL im 2x/d on d -4 and -3, 0.5 mL 2x/d on d -2 and -1) or 2) no treatment (CON). Estrous behavior was observed for 48 hr; d 0 = expected estrus. Frozen-thawed embryos were transferred (d 7) into the 36 females observed in estrus. Transrectal ultrasonography was used to measure number of CL and size of the largest CL, blood perfusion of luteal tissue, and pregnancy (d 35). Ultrasonography and blood samples were collected on d 7, 14, 21, and 28. Data were analyzed using repeated measures of ANOVA with significance declared at P ≤ 0.05. LSMeans and SEM are presented. On d 21 and 28, cows in the FSH group had decreased (P &amp;lt; 0.05) size of the largest CL compared with CON (d 21 = 1.81±0.309 vs 3.20±0.293 cm2 and d 28 = 1.88±0.332 vs 2.84±0.322 cm2). Area of blood perfusion was similar between FSH and CON groups (P &amp;gt; 0.05), but on d 21 and 28 it was greater in pregnant cows compared with non-pregnant cows (9.78±2.109 vs 22.43±1.995 and 4.42±2.607 vs 26.38±2.533, P &amp;lt; 0.0001). On d 7, 14, and 21, FSH group had greater concentrations of P4 and number of CL (P ≤ 0.05). Additionally, on d 28, concentrations of P4 and number of CL were greater in FSH-pregnant cows compared to all others (P ≤ 0.05). In conclusion, FSH decreased size of the largest CL but increased number of CL and P4 on most days; it did not affect blood perfusion.

O27 Digestibility in suckling beef cows is improved by short-term feed restriction but did not contribute to between-animal variation in feed efficiency

O27 Digestibility in suckling beef cows is improved by short-term feed restriction but did not contribute to between-animal variation in feed efficiency

O198 Profiling suckling beef and dairy cows’ responses to feed restriction

O198 Profiling suckling beef and dairy cows’ responses to feed restriction

FISIOLOGÍA RELACIONADA AL USO DE LA ECG EN GANADO DE CARNE Y LECHE

Equine chorionic gonatrophin (eCG) is a high molecular weight glycoprotein produced by endometrial cups in the mare. ECG has primarily LH activity in the mare, but has FSH or LH activity in the cow, depending on the recipient populations in the ovary. Although eCG has been used to induce superovulation in a variety of species, several studies have demonstrated the beneficial effects of eCG on fixed-time AI (IATF) programs in beef and dairy cattle, and embryo recipients. Under these circumstances, eCG has stimulated the development of the ovulatory dominant follicle and produced ovulation of a larger follicle, resulting in a larger and more functional LC and longer embryo survival. In suckling beef cows, 400 IU of eCG at the time of removal of a progesterone device resulted in increased conception rates after IATF,and in dairy cattle managed in pastoral systems, the eCG administration resulted in a significant increase in pregnancy rates, especially in cows in anestrus. In embryo recipients, treatment with eCG has resulted in increased pregnancy rates after embryo transfer. This presentation will review some of this data and explore strategies to use the potential benefits of eCG to improve bovine reproduction.