Angus-cross Beef Research Articles

Rumination and Activity Patterns in Angus and Angus-Cross Beef Calves: Influences of Sex, Breed, and Backgrounding Diet.

Simple SummaryRumination and activity behavior are important indices for monitoring the welfare and health status of beef cattle. Stress, excitement, and diseases can alter the rumination and activity patterns of beef cattle. Backgrounding allows producers to feed a variety of forages to improve growth performance before the beef calves enter the feedlot. This study was designed to evaluate the influences of sex, breed, and backgrounding diet on rumination, and the activity patterns in Angus and Angus-cross beef calves. Moreover, the daily variations in rumination and activity in Angus and Angus-cross beef calves under different backgrounding systems were studied. Our results demonstrated that the time of the day and backgrounding diet influenced rumination and activity patterns of Angus and Angus-cross beef calves.The objectives of this study were to evaluate the influences of sex, breed, and backgrounding diet on rumination and activity patterns in Angus and Angus-cross beef calves; and the daily variations in rumination and activity in Angus and Angus-cross beef calves under different backgrounding systems. A total of 62 freshly weaned calves were vaccinated and randomly stratified by sex (heifers and steers), breed (Angus and Angus × Simmental cross), and assigned randomly to 3 backgrounding treatments for 55 days. The peak values for rumination and activity in heifers, steers, Angus, and Angus × Simmental cross occurred during the dark and light phases of the dark/light cycle, respectively. Beef calves backgrounded on cover crops had higher (p < 0.05) rumination (45.33 ± 1.57 min) compared with calves backgrounded on a perennial pasture (43.96 ± 1.47 min) diet. Similarly, drylot calves (24.16 ± 0.68 min) had higher (p < 0.05) activity compared to perennial pasture (23.49 ± 0.72 min). The results showed that sex and breed did not influence rumination and activity of Angus and Angus-cross beef calves during the study period. We concluded that the time of the day and backgrounding diet influenced rumination and activity patterns of Angus and Angus-cross beef calves.

Association of gastrointestinal parasite burden, serum cytokines and hormones concentrations, and pregnancy in Angus-cross beef cows

The objective was to elucidate the relationships among gastrointestinal (GI) parasite load, serum cytokines (Th 1 – Interleukin (IL) 2, Interferon (IFN) γ and Tumor necrosis factor (TNF) α; Th 2- IL4, IL6, and IL10) levels, hormones (progesterone, cortisol, 8-epi-prostaglandin F2 alpha (isoprostane), prolactin, substance-p, and prostaglandin F metabolites) concentrations, and pregnancy in beef cattle. Angus-cross beef cows (n = 700; age, 3–8 y) were blocked by age and body condition score (BCS, 1–9), and were randomly assigned to treatment (n = 350, TRT, 50 mg of eprinomectin/50 kg BW, im) or control (n = 350, CON, no treatment) on Day -30. Cows were synchronized using Controlled Internal Drug Release insert (CIDR) + CO-Synch protocol and artificially inseminated at a fixed time on Day 0 (66 h after CIDR removal). Fecal samples were collected to determine fecal egg count per gram (FEG, McMaster method) on Days -30, -23, -16, -7, 7, 0, 16 and 23, and blood samples were collected on Days -7, 0, 7, 16 and 23. Serum cytokines were determined on Days -7, 0, 7, 16 and 23, and circulating hormones were measured on Day 16. BCS were recorded on Day 16 following artificial insemination (AI), and pregnancy status was diagnosed on Day 30 and 60. Pregnancy/AI varied among treatment groups on Day 30 [TRT, 62.0% (217/350); CON, 54.9% (192/350) (P = 0.05)] and Day 60 [TRT, 60.9% (213/350); CON, 51.7% (181/350) (P < 0.05)]. Pregnancy loss between 30 and 60 days for TRT and CON groups were 1.8% (4/217) and 5.7% (11/192), respectively (P < 0.05). The BCS on Day 16 did not differ among treatment groups (P> 0.1). Four groups of 40 cows were selected based on their pregnancy status and treatment: pregnant, TRT; non-pregnant, TRT; pregnant, CON; and non-pregnant, CON to compare the mean FEG, cytokines, and hormones levels. The FEG and cytokine concentrations were significantly (P < 0.05) influenced by treatment, pregnancy status, day, treatment by pregnancy status, and treatment by day. Day 16 hormone concentrations were considerably influenced by treatment, pregnancy status, and treatment by pregnancy. Although FEG on Day -30 did not differ among the groups (P> 0.1), it was lower in treated, pregnant cows compared with cows in other three groups from Day -23 onwards (P < 0.05). Overall and pairwise comparisons showed that serum concentrations of Type 1 cytokines, IL2, IFNγ, and TNFα were lower (P < 0.05) from gestational Day 7 onwards in treated, pregnant cows compared with cows in other three groups. In contrast, serum concentrations of Type 2 cytokines, IL4, IL6 and IL10 were greater (P < 0.05) from gestational Day 7 onwards in treated, pregnant cows compared with cows in other groups. Serum concentrations of progesterone was greater and other hormones were lower for pregnant cows in TRT group compared to cows in other groups on gestational Day 16. In conclusion, GI parasite load was reduced; Th 1 cytokines levels were decreased; Th 2 cytokines concentrations were increased; progesterone level was increased; and cortisol, substance-P, prolactin, isoprostane, and PGFM were decreased in pregnant, TRT cows. These changes also resulted in an increase in P/AI. It is plausible that direct and bidirectional host-parasite interactions mediated by cytokines and hormones may have promoted maternal tolerance of an immunologically diverse conceptus and the establishment of pregnancy.

Evaluation of KemTRACE® Chromium on Animal Performance and Immune System of Weaned Beef Calves

Abstract Weaned beef calves are stressed and have a compromised immune system making them highly susceptible to various infections. The study evaluated the effect of feeding chromium supplements on beef calves’ performance and immune function. Angus cross beef calves (n = 120) were randomly assigned to pens (n = 12 pens; 6 pens/treatment; 10 calves/pen) in a completely randomized design with subsampling. Calves were fed free-choice Bermuda grass hay, water, and minerals and 2 % of BW of 50 % soyhulls and 50 % corn-gluten mix; dietary treatments used were control (no chromium; n = 60) and chromium-supplemented (0.4 % KemTRACE® chromium; n = 60) during preconditioning trial for 60 days. Calves were weighed on d 0, 30, and 60. Blood samples were collected to perform complete blood counts, serum biochemistry analysis, and pro-inflammatory cytokines (IL-2, TNF-alpha) and anti-inflammatory cytokines (IL-4) measurements using ELISA kits. PHA and COVA challenges respectively assessed cell-mediated and humoral immune responses. Data were analyzed using GLIMMIX procedures of SAS 9.4 (SAS Inst. Inc., Cary, NC) without considering random effect. Results showed that chromium supplementation did not affect the total body weight gain, average daily gain, and feed efficiency of beef calves (P &amp;gt; 0.05). Eosinophil concentration was significantly higher (P &amp;lt; 0.01), and BUN was significantly lower (P &amp;lt; 0.05) in chromium-treated calves. IL-2 was significantly higher (P &amp;lt; 0.05) in chromium-treated than in control calves. TNF-alpha and IL-4 were significantly reduced (P &amp;lt; 0.05) in chromium-supplemented than in control calves. IL-6 was not significantly different (P &amp;gt; 0.05) in chromium-treated than in control calves. Although not significant (P = 0.1), skinfold thickness after the PHA challenge tended to be higher for chromium-treated calves than control groups, which align with a high IL-2 response. Results suggest that chromium supplementation may alter the animals’ inflammatory immune response, so it might be considered a suitable feed additive to improve the immune response in the preconditioning calves.

Timed artificial insemination strategies with or without short-term natural service and pregnancy success in beef heifers

Objective was to compare estrous response, and first service and breeding season pregnancy rates in Angus cross beef heifers that received four progesterone (CIDR, vaginal insert) -based estrous-synchronization treatment regimens for timed artificial insemination (TAI) with or without short-term natural service (NS). Heifers (n = 1744; 4 locations) were assigned a reproductive tract score (RTS: 1 = immature, acyclic to 5 = mature, cyclic), body condition score (BCS: 1 = emaciated to 9 = obese) and temperament score (0 = calm to 1 = excitable). Within location, heifers were assigned to either of four treatment regimens. Heifers in Select-Synch + CIDR (C) + short-term NS (SSC + NS) treatment (n = 438) received 100 μg GnRH im + CIDR on Day −7 and CIDR removal + 25 mg PGF2α (im) + estrus-detection patches in the morning of Day 0 and were subjected to NS (bull to heifer ratio, 1:25) from the morning of Day 2 (48 h from CIDR removal) to evening of Day 8. Heifers in CO-Synch + C (COSC) +TAI + NS treatment (n = 433) received 100 μg GnRH + CIDR on Day −7 and CIDR removal + 25 mg PGF2α im + estrus-detection patches in the morning of Day 0 + 100 μg GnRH im + TAI on Day 2, 60 h from CIDR removal, and were subjected to natural service (bull: heifer, 1:25) from the evening of Day 2 immediately after AI through Day 8. Heifers in COSC + TAI treatment (n = 443) received 100 μg GnRH + CIDR on Day −7 and CIDR removal + 25 mg PGF2α im + estrus-detection patches in the morning of Day 0 + 100 μg GnRH im + TAI on Day 2, 60 h from CIDR removal. Heifers in SSC + split time AI (STAI) treatment (n = 430) received 100 μg GnRH + CIDR on Day −7 and CIDR removal + 25 mg PGF2α im + estrus-detection patches in the morning of Day 0. Heifers determined to be in estrus were inseminated at 64 h after PGF2α (25 mg, im) administration and non-estrous heifers determined to be in estrus 20 h later (at 84 h) were inseminated at that time, whereas remaining non-estrous heifers at 84 h received GnRH (100 μg) and were inseminated concomitantly. In SSC + NS and COSC + TAI + NS treatments, natural service bulls were removed and reintroduced (@ bull: heifer, 1:40) on Day 22 and kept until Day 63. In COSC + TAI and SSC + STAI bulls (bull: heifer, 1:40) were introduced on Day 14 and retained until Day 63. All heifers, irrespective of treatment regimens, were observed for estrus three times a day from Day 2 through Day 8. Pregnancy diagnosis was performed on Day 93, 30 days from end of breeding season. Accounting for temperament (P < 0.0001), BCS (P < 0.0001) and RTS (P < 0.0001), the breeding program influenced the estrous response (P < 0.0001). Heifers in COSC + TAI + NS (86.8%), SSC + STAI (84.9%), and SSC + NS (86.5%) treatments had greater estrous response compared with heifers in COSC + TAI (75.8%) treatment. Accounting for temperament (P < 0.01), BCS (P < 0.05) and RTS (P < 0.01), the treatment regimens influenced first service pregnancy rate (P < 0.05). Heifers in COSC + TAI + NS treatment had greater first service pregnancy rate (60.3%) compared with COSC + TAI (54.2%) (P < 0.05). First service pregnancy rate for heifers in SSC + STAI (59.3%) and SSC + NS (57.3%) treatments did not differ from COSC + TAI + NS and COSC + TAI treatments. Accounting for temperament (P < 0.001), BCS (P < 0.0001) and RTS (P < 0.0001), the treatment regimens influenced breeding season pregnancy rate (P < 0.05). Breeding season pregnancy rate for heifers in COSC + TAI + NS (95.4%) and COSC + STAI (94.5%) treatments were greater than that of heifers in COSC + TAI (90.8%) treatment (P < 0.05), and heifers in SSC + NS (94.1%%) treatment did not differ from heifers in other treatments. In conclusion, progesterone-based CO-Synch timed artificial insemination with short-term natural service treatment regimen resulted in proportionately more pregnancies than without short-term natural service treatment regimen. In addition, 64/84 h split-time AI or natural service following Select-Synch treatment regimen could be implemented as an alternative as these treatment regimens resulted in similar pregnancy rate as progesterone based CO-Synch timed artificial insemination with short-term natural service treatment regimen.

Feeding selenium-biofortified alfalfa hay during the preconditioning period improves growth, carcass weight, and nasal microbial diversity of beef calves.

We previously reported that feeding Se-biofortified alfalfa hay to weaned beef calves in a preconditioning program decreases morbidity and mortality during the feedlot period. To understand the mode of action by which supranutritional Se supplementation supports calf health, we examined the effect of agronomic Se-biofortification on nasal microbiome and fecal parasites. Recently weaned Angus-cross beef calves (n = 30) were randomly assigned to two groups and fed an alfalfa hay-based diet for 9 weeks in a preconditioning program. Alfalfa hay was harvested from fields fertilized with sodium selenate at a rate of 0 or 90 g Se/ha. Calculated Se intake from dietary sources was 1.09 and 27.45 mg Se/calf per day for calves consuming alfalfa hay with Se concentrations of 0.06 and 3.47 mg Se/kg dry matter, respectively. Feeding Se-biofortified alfalfa hay for 9 weeks was effective at increasing whole-blood Se concentrations (556 ± 11 vs 140 ± 11 ng/mL; P < 0.001) and increasing body weight (PTreatment, = 0.03) in weaned beef calves. Slaughter yield grades were higher for calves that had been fed Se-enriched alfalfa hay during the preconditioning period (PTreatment = 0.008). No significant differences were observed in fecal parasite load, which remained low. The nasal microbiome and microbiota diversity within calves and across calves expanded from weaning (week 0) to the feedlot period (week 12), which was promoted by feeding Se-biofortified alfalfa hay. Especially concerning was the expansion of nasal Mycoplasmataceae in the feedlot, which reached over 50% of the total microbiota in some calves. In conclusion, we identified dietary Se-biofortified alfalfa hay as a potential promoter of nasal microbiome genome and microbiota diversity, which may explain in part high-Se benefits for prevention of bovine respiratory disease complex in beef calves.

262 Heat stress alleviation and dynamic temperature measurement for growing beef cattle

Abstract Heat stress continues to be a challenge for feedlot producers, forcing physiological adaptations in beef cattle that can have a negative impact on gain and carcass quality. Feedlots may want to incorporate systems that aid in mitigating heat stress, including sprinkler systems, which are commonly found on dairies. The objective of this study was to determine the impact of sprinkler systems on the body temperature of growing feedlot steers applied at three different temperature thresholds. Thirty-two Angus-cross beef steers (298 ± 15 SD days of age) were randomly assigned to 8 pens. Treatments were assigned to pens according to location to avoid drainage issues, with one replicate located on the eastern side of the feedlot and the other replicate located on the western side. Treatments including no sprinklers (C), high temperature threshold sprinklers (HT), moderate temperature threshold sprinklers (MT) or low temperature threshold sprinklers (LT). Sprinklers (flow rate: 5.11 L/min) were activated at 33°C (HT), 28°C (MT), and 23°C (LT) for five minutes at corresponding temperatures every thirty minutes for 57 days. Rectal temperature of steers in their pens was measured in the morning (0800 h), afternoon (1500 h), and evening (1900 h) three days each week (Monday, Wednesday, Friday) for a total of 19 experimental days. Weather measurements, including ambient temperature, windspeed, humidity and solar radiation were recorded at each measurement time along with the maximum values for each day. The change in body temperature (ΔBT) between the morning and afternoon was affected by ambient temperature (P &amp;lt; 0.01); MT (P = 0.02) and LT (P = 0.02) – different than C. There was no significant difference between sprinkler treatments and the control group (P &amp;gt; 0.05). Day affected (ΔBT) between the morning and afternoon (P &amp;lt; 0.05) and the afternoon and evening (P &amp;lt; 0.05). When averaged by day, the control group was significantly higher than MT (P = 0.04) between the morning and afternoon. The control group was also significantly higher than LT between the morning and afternoon (P = 0.03) and the afternoon and evening (P &amp;lt; 0.01). The change in steer body temperature between afternoon and morning was affected by ambient temperature, and averaged across days, lowering the temperature threshold for sprinkling decreased in the afternoon and evening body temperature increase in steers.

Influence of stocking rate and advancing season on forage intake, digestibility, and ruminal fermentation in steers supplemented with dried distillers grains with solubles while grazing northern Great Plains rangelands.

The objectives of this study were to evaluate the effects of stocking rate and advancing season on diet chemical composition, intake, digestibility, and ruminal fermentation in steers supplemented with distillers grains with solubles [0.3% of body weight (BW)] while grazing northern Great Plains rangelands. Angus cross beef steers (n = 188; 320 ± 30.3 kg initial BW) were used to establish targeted stocking rates, and 12 ruminal cannulated steers (272 ± 20.0 kg initial BW) were used for diet sampling while cograzing with the noncannulated animals on 12 pastures (n = 3 per treatment). Stocking rates were set to target 65%, 50%, 35%, and 20% of an average annual above-ground biomass remaining at the end of the grazing season (May–September). Five 10-d collection periods were conducted for May 13–22, June 10–19, July 8–17, August 5–14, and September 2–11. There was no difference in steer BWs or average daily gain during any of the collection periods or between stocking rate (P ≥ 0.10). Organic matter (OM), neutral detergent fiber, and acid detergent fiber of forage masticate samples were not affected (P ≥ 0.25) by stocking rate. Crude protein, and all N fractions of forage masticates also did not differ between stocking rate treatments (P ≥ 0.18). Forage OM intake (grams per kilogram of BW) increased cubically across the entire grazing season (P = 0.05). Organic matter digestibility decreased quadratically (P < 0.01) from May to September. Neutral detergent fiber digestibility showed a cubic effect (P < 0.01) across the grazing season, increasing from May to June, then decreasing till September. Crude protein digestibility decreased linearly (P < 0.01) as the season advanced. Ruminal ammonia and volatile fatty acid (VFA) concentrations were affected by stocking rate × period interactions (P ≤ 0.02). Ruminal pH, ammonia, and VFA concentrations were not affected by the stocking rate (P > 0.13) but were impacted by the advancing season (P < 0.01). Ruminal pH increased quadratically (P ≤ 0.01) with advancing season (6.3 to 6.6 ± 0.05 from May to September, respectively). The results of this study demonstrate that intake, fermentation, and digestibility of northern Great Plains forages were influenced more by seasonal factors associated with forage maturity than stocking rate under the conditions of this study.

Form of Supplemental Selenium in Vitamin-Mineral Premixes Differentially Affects Early Luteal and Gestational Concentrations of Progesterone, and Postpartum Concentrations of Prolactin in Beef Cows.

Simple SummarySoils with inadequate levels of selenium are widespread in the northwest, northeast, and southeast USA. Therefore, dietary supplementation of forage-grazing beef cattle with additional selenium is recommended in these regions for optimal growth, immune function, and fertility. We have reported that the form of selenium provided to Angus-cross cows can affect circulating concentrations of progesterone on day 6 of the estrous cycle, a time when increased progesterone is known to promote fertility. Hence, we sought to confirm this initial finding, determine the effect of the form of selenium on peripheral concentrations of progesterone during gestation, and determine the effect of the form of selenium on circulating concentrations of prolactin during lactation. Cows were supplemented with equimolar amounts of either an inorganic form, or a 1:1 mixture of inorganic and organic forms of selenium throughout this study. We confirmed our original finding that the mixed (1:1 inorganic to organic selenium) supplement increased systemic progesterone in the early luteal phase of the estrous cycle, and determined that cows maintained on this same supplement had elevated concentrations of progesterone throughout gestation. Interestingly, these same cows revealed a treatment-induced decrease in systemic prolactin during late lactation. The form of selenium provided to cows can be manipulated to affect reproductive responses and offers a viable management tool to improve fertility in cows in regions with selenium-deficient soils.Soils with marginal to deficient levels of selenium (Se) are widespread in the northwest, northeast, and southeast US. Supplementation to the diet of forage-grazing beef cattle with a vitamin-mineral mix containing additional Se is recommended in these geographic regions. We have reported that the form of supplemental Se provided to Angus-cross beef cows can affect circulating levels of progesterone (P4) on day 6 of the estrous cycle, a time when increased P4 is known to promote fertility. The objectives of this study were to (1) confirm and expand upon our initial report that the form of Se provided to cows affects early luteal-phase concentrations of systemic P4, (2) determine the effects of the form of Se on concentrations of P4 during gestation, and (3) determine the effects of the form of Se on concentrations of prolactin (PRL) during lactation. Throughout this study, Angus-cross beef cows had ad libitum access to a vitamin-mineral mix containing 35 ppm of Se in either an inorganic form (ISe) or a 1:1 mix of inorganic and organic forms (MIX). We observed a MIX-induced increase (p = 0.006) in systemic concentrations of P4 on day 7 but not on days 4 or 10 of the estrous cycle, consistent with our earlier report. We observed a MIX-induced increase (p = 0.02) in the systemic concentration of P4 at months 1, 3, 5, and 7 of gestation, and a MIX-induced decrease (p < 0.05) in systemic concentrations of PRL at months 5 and 6 of lactation. In summary, the form of Se provided to cows can be manipulated to affect the early luteal phase and gestational concentrations of P4, and postpartum concentrations of PRL.

Presynchronization with CIDR, with or without GnRH, prior to CO-Synch in beef heifers

Objectives were to compare ovarian responses and pregnancy per AI (P/AI) in Angus-cross beef heifers (n = 521; 4 locations) synchronized with CIDR–CO–Synch (CCOS) versus CIDR-GnRH–CO–Synch (CGCOS) protocols. Heifers were assigned a reproductive tract score (RTS: 1, immature, acyclic; 5, mature, cyclic), body condition score (BCS: 1, emaciated; 9, obese) and temperament score (0, calm, 1, excitable). Heifers in the CCOS (n = 261) group received a CIDR on Day −20 (removed on Day −13), 100 μg GnRH on Day −10, 25 mg PGF2α on Day −3 and were timed inseminated 60 h later, with concomitant GnRH (Day 0). Heifers in the CGCOS (n = 260) group received a CIDR on Day −26 (removed on Day −19), 100 μg of GnRH on days −16 and −10, 25 mg of PGF2α on Day −3 and were timed inseminated 60 h later, with concomitant GnRH (Day 0). Ovarian ultrasonography was done in a subset of heifers (n = 60; 30 in each group) to determine number and size of ovarian follicles and presence of corpus luteum (CL). There was increased (P < 0.05) percentage of heifers with CL in CGCOS group compared to heifers in CCOS group on Day −10 (82.3 vs 68.2%) and on Day −3 (88.3 vs 75.1%). Average size of the largest ovarian follicle on Day 0 was greater for heifers in CGCOS group compared to CCOS group (P < 0.05). However, P/AI did not differ between CCOS and CGCOS groups, 55.0% (143/260) and 59.8% (156/261), respectively (P > 0.1). In conclusion, CIDR presynchronization with or without GnRH (CCOS and CGCOS protocols) in beef heifers resulted in similar P/AI. Adding GnRH to presynchronization with CIDR resulted in more heifers with a CL at PGF2α and increased preovulatory follicle diameter at AI. Future studies are needed with bigger sample size and CIDR + CO-Synch treatment as control to determine economic benefit.

Comparison of parasite load and average daily weight gain in suckling beef calves treated with macrocyclic lactones in either an extended-release injectable or a pouron formulation

The objective of the study was to compare the effect of macrocyclic lactones anthelmintic in either an extended-release injectable (ERI) or a pour-on (PO) formulation on parasite load and average daily weight gain in suckling beef calves. Spring born Angus cross beef calves (n=1228) grazing on 17 pastures from 4 cow-calf operations in Washington State during 2017 were included. Calves in each pasture were randomly assigned to ERI (n=611; Long Range®, 50 mg of eprinomectin/ml, Merial Inc., Duluth, GA, USA; @ 50 mg or 1ml/50 kg BW) or PO (n=671; Ivomec®, 5 mg ivermectin/ml; Merial Inc., Duluth, GA; @ 500 mcg or 1 ml/10 kg BW) treatment 105 days prior to weaning (approximately at 8 months of age) at the time of pasture turn-out in mid-May. Calves were weighed initially, at mid-trail (approximately 55 days after start) and at weaning. Faecal samples were taken from a subset of calves (n=30/pasture; 15 in each treatment group, a total of 510 calves) for faecal egg counts (FEC) at the start of the study and again at 15, 30, 60 and 90 d later. The data were analyzed using a mixed model. The FEC did not vary between calves in treatment and control groups on day 0 (P>0.1). However, accounting for temperament by treatment interaction, ERI treated calves had lower FEC compared with PO treated calves on day 90 (P<0.01). Accounting for gender (P<0.05), temperament (P<0.05) and treatment by age (P<0.01), ERI treated calves gained more weight compared with PO treated calves (P<0.01). In conclusion, treatment of nursing calves at late-spring with ERI experienced a reduction in GI (gastrointestinal) parasite load and a measurable but modest increase in weight gain compared with calves treated with PO.

Injectable or transdermal flunixin meglumine improves pregnancy rates in embryo transfer recipient beef cows without altering returns to estrus

Objectiveswere to determine effects of 1) injectable or transdermal flunixin meglumine (FM) at embryo transfer (ET) compared to an untreated control group on pregnancy per ET (P/ET; ∼35 d after ET); 2) embryo and recipient factors on P/ET; 3) FM on hormone concentrations; and 4) FM on returns to estrus. Angus-cross beef cows (n = 1145) at five locations were scored for body condition (BCS; 1–9) and temperament (0 or 1) and given Select-Synch + CIDR. Recipient cows with a corpus luteum (CL) ≥1.5 cm received a frozen-thawed embryo 7 d after estrus and were concurrently given 1.1 mg/kg injectable FM im (INJFM; n = 384), 3.3 mg/kg transdermal FM pour on (TDFM; n = 388), or nothing (CON group; n = 373). Blood samples were collected at ET and 7 d later (60 cows). Accounting for temperament (P < 0.05), ET difficulty score (1–3, easy to difficult; P < 0.01), treatment by temperament (P < 0.001) and treatment by embryo quality (P < 0.05), FM treatments affected P/ET (P < 0.05). The P/ET for cows given INJFM [62.8% (241/384)] or TDFM [58.7% (228/388)] were not different (P = 0.26), but they were greater (P = 0.01 and P = 0.04, respectively) than P/ET for controls [51.2% (191/373)]. The P/ET was greater for calm versus excitable cows, 60.2 (463/769) and 52.4% (197/376), respectively (P < 0.01) and was lower for difficulty score 3 [49.2% (156/317)] compared to score 1 [62.7% (254/405; P < 0.001) or score 2 [59.1% (250/423; P < 0.01)]. There was no effect (P > 0.1) of cow age, BCS, or stage of embryo development on P/ET. Pregnancy rates for embryo quality grade 1 (excellent/good) and grade 2 (fair) were 60.4% (314/520) and 55.4% (346/625), respectively (P > 0.05). Percentages of non-pregnant recipient cows in estrus from Days 18–26 did not differ among treatment groups (P > 0.1). Control cows had lower progesterone concentrations and greater substance-P, PGFM and 8-isoprostane PGF2α concentrations at 7 d after ET compared to FM-treated cows (P < 0.05). In conclusion, injectable or transdermal FM improved pregnancy rates in ET recipients, without affecting nonpregnant cows return to estrus.

9 Performance of color Doppler ultrasonography of the corpus luteum for pregnancy diagnosis in beef heifers with or without a controlled internal drug release at different days after fixed-time artificial insemination

Colour Doppler ultrasonography (CDU) of the corpus luteum (CL) has the potential to be used for early pregnancy diagnosis in order to improve reproductive efficiency and increase the use of fixed-time AI (FTAI) in beef cattle. The objective of the present study was to determine the sensitivity and specificity of CDU of the CL for pregnancy diagnosis in beef heifers with or without a CIDR at different days after FTAI. Angus-cross beef heifers (n=84) were synchronized using a 5-day Co-Synch with AI at 60h after CIDR removal. On Day 15 post-AI, heifers were randomly assigned to receive a CIDR (Eazi-Breed CIDR, Zoetis, Parsippany-Troy Hills, NJ) for 9 days or remain as untreated controls. Heifers were evaluated by transrectal CDU (MyLab Delta, Esoate, Genoa, Italy; 7.5-MHz linear array probe, pulse repetition frequency=960Hz) at 15, 17, 20, and 22 days post-AI. Heifers were determined to be pregnant by CDU if colour pixels covered &amp;gt;10% of the periphery of the CL and contained at least 2 colour internal tracts penetrating toward the centre of the CL. Heifers were evaluated by B-mode ultrasonography on Day 28 to determine true pregnancy status. Differences between days and treatments were evaluated using generalized estimating equations. Pregnancies per AI at Day 28 after FTAI were 53.6% (45/84) and were not different between CIDR (52.4%; 22/42) and control (54.8%; 23/42) heifers (P=0.83). Sensitivity and specificity for CIDR and control heifers at different days are shown in Table 1. There was no effect of treatment (P=0.49), day (P=0.99), or treatment by day interaction (P=0.99) on test sensitivity. Specificity was different (P&amp;lt;0.01) between days; however, no treatment (P=0.91) or treatment by day interaction (P=0.82) was identified. Specificity was lowest on Days 15 and 17 and increased to reach its maximum at Day 22. Although no differences between treatments were observed, specificity on Day 22 was numerically greater in CIDR-treated heifers. Positive and negative predictive values for CDU at Day 22 were 84 and 94.1%, respectively, for CIDR-treated heifers and 79.3 and 100%, respectively, for control heifers. Cohen’s Kappa indicated slight (0.19), fair (0.27), moderate (0.50), and substantial (0.73) agreement between conventional ultrasound at Day 28 and CDU at Days 15, 17, 20, and 22, respectively. In summary, CDU showed excellent sensitivity between Days 15 and 22, indicating a very low rate of false-negative results. However, high specificity (low false-positive rate) was achieved only at Day 22. Thus, pregnancy diagnosis by CDU at Day 22 after FTAI coupled with the use of a CIDR may be an effective strategy to identify nonpregnant heifers and attempt their prompt resynchronization. Table 1.Sensitivity and specificity (%) for pregnancy diagnosis by CDU in beef heifers with or without a CIDR at different days after FTAI

Flunixin meglumine improves pregnancy rate in embryo recipient beef cows with an excitable temperament

Objectives were to determine effects of: 1) handling temperament and administration of flunixin meglumine, an inhibitor of prostaglandin F2a (PGF2a) synthesis, given at the time of embryo transfer, on pregnancy rates in beef cattle embryo transfer recipients; 2) handling temperament and flunixin meglumine on peripheral concentrations of progesterone, cortisol, substance-P, prostaglandin F metabolites (PGFM, (13,14-dihydro-15-keto-PGF2a) and isoprostane 8-epi PGF2a; and 3) flunixin meglumine treatment on proportion of non-pregnant recipient cows returning to estrus within an expected interval. Angus cross beef cows (n = 710) at 7 locations were assigned a body condition score (BCS: 1, emaciated; 9, obese) and a temperament score [0, calm, slow chute exit; walk (n = 352), 1, excited, fast chute exit; jump, trot or run (n = 358)] and were synchronized with Select-Synch with a controlled internal drug release (CIDR) protocol. Estrus detection aids were applied at CIDR removal and cows were observed thrice daily for estrus until 72 h. Recipient cows that expressed estrus and had a corpus luteum received a frozen-thawed embryo on Day 7 after estrus. At the time of transfer, recipient cows were randomly allocated to receive 10 mL of flunixin meglumine im, immediately after transfer (n = 365) or served as an untreated control (n = 345). In a subset of cows (n = 80), ovarian ultrasonography was performed on the day of embryo transfer to determine corpus luteum volume and blood samples were collected twice, at the time of embryo transfer and 7 d later. All cows received estrus detection aids again on Day 14 (7 d after embryo transfer) and were observed for estrus twice daily until Day 24. Accounting for treatment (P > 0.1), embryo transfer difficulty score (P < 0.1), temperament by treatment interaction (P < 0.05), recipient cows with calm temperament had a higher pregnancy rate compared to those with an excited temperament [59.4 (209/352) vs 51.7% (185/358)]. The pregnancy rate for excitable cows without flunixin meglumine was lower (46.3% 81/175) compared to excitable cows that did received flunixin meglumine [56.8% (104/183)], and calm cows that did [59.3% (108/182)] or did not [59.4% (104/170)] receive flunixin meglumine. Proportions of non-pregnant recipient cows returning to estrus on Days 18–24 were not different between flunixin meglumine and control groups, 87.6% (134/153) and 84.0% (137/163), respectively (P > 0.1). At the time of embryo transfer and 7 d later, there were moderate to strong correlations among circulating concentrations of progesterone, cortisol, substance-P, PGFM and isoprostane 8-epi PGF2a. Among excitable cows, progesterone concentrations were lower and cortisol, substance-P, PGFM and isoprostane 8-epi PGF2a concentrations were greater for cows in the control group compared to cows that received flunixin meglumine. In conclusion, administration of flunixin meglumine improved pregnancy rates in excitable recipient cows following embryo transfer without affecting the proportion of non-pregnant cows returning to estrus.

Fertility of Angus cross beef heifers after GnRH treatment on day 23 and timing of insemination in 14-day CIDR protocol.

This study compared artificial insemination pregnancy rate (AI-PR) between 14-day CIDR-GnRH-PGF2α-GnRH and CIDR-PGF2α-GnRH synchronization protocol with two fixed AI times (56 or 72hr after PGF2α). On day 0, heifers (n=1311) from nine locations assigned body condition score (BCS: 1, emaciated; 9, obese), reproductive tract score (RTS: 1, immature, acyclic; 5, mature, cyclic) and temperament score (0, calm; and 1, excited) and fitted with a controlled internal drug release (CIDR, 1.38g of progesterone) insert for 14days. Within herd, heifers were randomly assigned either to no-GnRH group (n=635) or to GnRH group (n=676), and heifers in GnRH group received 100μg of GnRH (gonadorelin hydrochloride, IM) on day 23. All heifers received 25mg of PGF2α (dinoprost, IM) on day 30 and oestrous detection aids at the same time. Heifers were observed for oestrus thrice daily until AI. Within GnRH groups, heifers were randomly assigned to either AI-56 or AI-72 groups. Heifers in AI-56 group (n=667) were inseminated at 56hr (day 32 PM), and heifers in AI-72 group (n=644) were inseminated at 72hr (day 33 AM) after PGF2α administration. All heifers were given 100μg of GnRH concurrently at the time AI. Controlling for BCS (p<.05), RTS (p<.05), oestrous expression (p<.001), temperament (p<.001) and GnRH treatment by time of insemination (p<.001), the AI-PR differed between GnRH treatment [GnRH (Yes - 60.9% (412/676) vs. No - 55.1% (350/635); p<.05)] and insemination time [AI-56 - 54.6% (364/667) vs. AI-72 - 61.8% (398/644); (p<.01)] groups. The GnRH treatment by AI time interaction influenced AI-PR (GnRH56 - 61.0% (208/341); GnRH72 - 60.9% (204/335); No-GnRH56 - 47.9% (156/326); No-GnRH72 - 62.8% (194/309); p<.001). In conclusion, 14-day CIDR synchronization protocol for FTAI required inclusion of GnRH on day 23 if inseminations were to be performed at 56hr after PGF2α in order to achieve greater AI-PR.

Expression of Na+/H+ exchanger isoforms 1, 2, 3, and 4 in bovine endometrium and the influence of uterine pH at time of fixed-time AI of pregnancy success

Cows that exhibit estrus prior to fixed-time AI had increased sperm transport to the site of fertilization, and improved embryo quality on d 6 after insemination. Sperm transport is influenced by uterine pH, and research has reported that uterine pH decreased at onset of estrus, but must return to normal prior to ovulation. Therefore, the objectives of these studies were to investigate a possible mechanism for the regulation of uterine pH around the onset of estrus, and to determine if uterine pH at time of fixed-time AI influenced pregnancy success. In experiment 1, Angus-cross beef cows (n=40 and 28 in rep. 1 and 2, respectively) were synchronized with the PG 6-day CIDR protocol (PGF2α on d -9, GnRH and insertion of a CIDR on d -6, and PGF2α and CIDR removal on d 0). Cows were blocked by follicle size at time of CIDR removal, and uterine biopsies were collected at 0, 12, 24, 36, 48, 60 (Rep. 1), 72, 84, or 96h (Rep2) after CIDR removal, and total cellular RNA was extracted from all biopsies. Estrus was monitored by the HeatWatch Estrous Detection System. In experiment 2, 223 postpartum beef cows in 2 herds were synchronized with a fixed-time AI protocol (herd 1: n=97; CO-Synch plus CIDR protocol; herd 2: n=126; Co-synch protocol). Uterine pH was determined at time of AI (n=80 and 63 for herd 1 and 2, respectively), and estrus was monitored by visual estrus detection with the aid of an ESTROTECT estrous detection patches, and pregnancy was determined by transrectal ultrasonography. In experiment 1, there was a significant (P<0.01), quadratic relationship in expression of Na+/H+ exchanger isoforms 1, 2, and 3 among animals that exhibited estrus, with expression greatest at time of CIDR removal, decreasing to the onset of estrus, and then increasing again following the onset of estrus. Among cows that did not exhibit estrus, the preceding relationship did not exist (P>0.46). In experiment 2, cows that had initiated estrus prior to fixed-time AI had decreased (P=0.01) uterine pH compared to cows that did not initiate estrus (6.78±0.03 and 6.89±0.03, respectively), and uterine pH at AI had an approximately linear effect on pregnancy success within the observed pH range. Furthermore, cows that initiated estrus prior to AI had increased (P=0.05) pregnancy success (52% vs. 38%) compared to cows that had not initiated estrus. In summary, expression of Na+/H+ exchanger isoforms 1, 2, and 3 decreased after CIDR removal among cows that exhibited estrus, but did not change among cows that did not exhibit estrus. Additionally, as uterine pH decreased pregnancy success tended to increase (P=0.076, logistics regression). Thus, Na+/H+ exchanger isoforms 1, 2, and 3 appear to be key regulators of uterine pH around the onset of estrus, and this change in uterine pH is critical for pregnancy success. Summary sentenceExpression of Na+/H+ exchanger isoforms 1, 2, and 3 decreased after CIDR removal among cows that exhibited estrus, but did not change among cows that did not exhibit estrus, and as uterine pH decreased, pregnancy success tended to increase.

Estrous synchronization strategies to optimize beef heifer reproductive performance after reproductive tract scoring

Three experiments comparing four estrous synchronization protocols were conducted to determine estrous expression rate and artificial insemination pregnancy rate (AI-PR) in heifers with a range (1–5) of reproductive tract scores (RTSs). At enrollment (Day 0), 1783 Angus cross beef heifers from six locations were given body condition score and RTS. The four protocols were: (1) HRTS-DPGF group—heifers with RTS 5 received prostaglandin F2α (PGF; Dinoprost 25 mg; im) on Days 0 and 14; (2) HRTS-CIDR-PGF group—heifers with RTS 5 received a CIDR (1.3-g progesterone) insert on Day 7, followed by CIDR removal and PGF on Day 14; (3) LRTS-CIDR-PGF group—heifers with RTS 4 or less received a CIDR insert on Day 7, followed by CIDR removal and PGF on Day 14; and (4) HRTS-Select-Synch group—heifers with RTS 5 received 100 μg of gonadorelin diacetate tetrahydrate (gonadotropin releasing homone; im) on Day 7 and PGF on Day 14. In all groups, heifers observed in estrus were artificially inseminated (within 120 hours after PGF) using the AM-PM rule. In Experiment 1, estrus expression rates were 82.2% (282/343) and 88.5% (184/208) for HRTS-DPGF and LRTS-CIDR-PGF, respectively (P < 0.05), whereas AI-PR were 51.3% (176/343) and 59.1% (123/208; P < 0.1). In Experiment 2, estrus expression rates were 79.6 (168/211), 86.9 (186/214) and 84.2% (176/209) for HRTS-DPGF, HRTS-CIDR-PGF, and LRTS-CIDR-PGF groups (P > 0.1) and AI-PR were 52.1 (110/211), 60.3 (129/214), and 58.4% (122/209; P > 0.05). In Experiment 3, estrus expression rates were 77.5 (131/169), 85.5 (142/166), and 83.3% (219/263) for HRTS-DPGF, HRTS-Select-Synch and LRTS-CIDR-PGF (P > 0.05) and AI-PR were 53.3 (90/169), 60.2 (100/166), and 58.6% (154/263; P > 0.1). Overall, estrus expression rates for HRTS-DPGF, HRTS-Select-Synch, LRTS-CIDR-PGF, and HRTS-CIDR-PGF groups were 80.4 (581/723), 85.5 (142/166), 85.1 (579/680), and 86.9% (186/214), respectively; higher for heifers in LRTS-CIDR-PGF and HRTS-CIDR-PGF groups compared to heifers in HRTS-DPGF group (P < 0.05). The AI-PR for heifers in HRTS-DPGF was lower (52.0 [376/723]) compared with HRTS-Select-Synch (60.2 [100/166]), LRTS-CIDR-PGF (58.7 [399/680]), and HRTS-CIDR-PGF (60.3 [129/214]); P < 0.05). In conclusion, heifers achieved greater AI-PR after CIDR-PGF or HRTS-Select-Synch estrous synchronization protocols. Even though acceptable AI-PRs achieved in heifers with RTS 5 that were subjected to a double PGF protocol, the reproductive performance was reduced compared with other protocols used in this study.

Evaluating the effects of late-gestation supplementation on timed–artificial insemination pregnancy rates and body composition in beef cattle

ABSTRACT Nonlactating Angus cross beef cows were used to evaluate pregnancy rates and postpartum performance following late-gestation liquid protein or dried distillers grains (DDG) supplementation. In Exp. 1, 166 multiparous cows were stratified by BW, BCS, age, and pregnancy status to receive a free-choice liquid-protein or DDG supplement fed to be isonitrogenous for 77 d during late gestation. In Exp. 2, 53 nulliparous and 36 primiparous cows were stratified similar to Exp. 1 and fed DDG at maintenance (DDG-1) or 1.2 times maintenance (DDG-1.2) energy requirements for 44 d during late gestation. Body weight and BCS were measured at initial supplementation, calving (except BW), timed AI, and weaning to determine BW and BCS change. Cows were sorted into 3 age groups (Exp. 1) and evaluated for BW and BCS change at weaning. All females were synchronized with a 7-d CO-Synch plus controlled intravaginal drug-release protocol with 72 h of timed AI. In Exp. 1, cows fed DDG had greater (P 0.10) on BW or BCS change. Timed-AI pregnancy rates were similar (P > 0.10) across treatments for both experiments. Late-gestation supplementation with DDG had positive effects on animal performance, with the greatest effect in the younger females.

Fertility after implementation of long- and short-term progesterone-based ovulation synchronization protocols for fixed-time artificial insemination in beef heifers

Two experiments were conducted to evaluate the effect of long-term (LT; a 14-day controlled internal drug release insert [CIDR]–PGF2α [PGF]–GnRH) and short-term (ST; 5-day CO-Synch + CIDR) progesterone-based protocols on pregnancy rate to fixed-time artificial insemination (FTAI) in beef heifers. In experiment 1, Angus cross beef heifers (N = 1887) at nine locations received a body condition score and a reproductive tract score (RTS). Within the herd, heifers were randomly assigned to LT-72 and ST-56 protocol groups. Heifers in the LT-72 group received a CIDR from Days 0 to 14, followed by 25 mg of PGF 16 days later (Day 30). Heifers in the ST-56 group received a CIDR and 100 μg of gonadorelin hydrochloride (GnRH) on Day 25 followed by 25 mg of PGF at CIDR removal on Day 30 and a second dose of PGF 6 hours later (Day 30). Artificial insemination was performed at 56 hours (Day 32) after CIDR removal for the ST-56 group and at 72 hours (Day 33) after CIDR removal for the LT-72 group, and all heifers were given GnRH (100 μg, intramuscular) at the time of AI. In experiment 2, Angus cross beef heifers (N = 718) at four locations received a body condition score and an RTS. Within the herd, heifers were randomly assigned to LT-72 and ST-72 protocol groups. The protocol was similar to experiment 1 except that AI was performed at 72 hours after CIDR removal for both LT-72 and ST-72 groups. In experiment 1, no difference in AI pregnancy rates between the LT-72 and ST-56 groups was observed (54.5% [489 of 897] and 55.5% [549 of 990], respectively; P = 0.92) after accounting for the RTS. The AI pregnancy rates for heifers with RTS 3 or less, 4, and 5 were 52.6%, 53.6%, and 59.9%, respectively (P < 0.05). In experiment 2, controlling for the RTS, no difference in AI pregnancy rates was observed between the LT-72 and ST-72 groups, 56.9% (198 of 347) and 57.8% (214 of 371), respectively (P = 0.87). The AI pregnancy rates for heifers with RTS 3 or less, 4, and 5 were 49.3%, 58.4%, and 62.1%, respectively (P < 0.05). In conclusion, heifers synchronized for fixed-time AI with LT and ST protocols resulted in a similar AI pregnancy rate. Approximately, 55% of the herd was pregnant to one insemination in 33 days with the LT protocol compared with just 8 days with the ST protocol.

Effect of reproductive tract scoring on reproductive efficiency in beef heifers bred by timed insemination and natural service versus only natural service

The objective was to determine the effects of reproductive tract score (RTS) on reproductive performance in beef heifers bred by timed artificial insemination followed by natural service (AI-NS) or by natural service only (NSO). Angus cross beef heifers (n = 2660) in the AI-NS group were artificially inseminated at a fixed time (5- or 7-day CO-Synch + controlled internal drug release protocol) once, then exposed to bulls 2 weeks later (bull-to-heifer ratio = 1:40–1:50) for the reminder of the 85-day breeding season. Angus cross beef heifers (n = 1381) in NSO group were submitted to bulls (bull-to-heifer ratio = 1:20–1:25) for the entire 85-day breeding season. Heifers were reproductive tract scored from 1 (prepubertal) to 5 (cyclic) 4 weeks before, and were body condition scored (BCS) from 1 (emaciated) to 9 (obese) at the beginning of breeding season. Pregnancy diagnosis was performed 70 days after AI for AI-NS group and 2 months after the end of breeding season for both groups. Heifers in both groups were well managed and of similar age (14.9 ± 0.4 [AI-NS] and 14.7 ± 0.8 [NSO] months). Pregnancy rates (PRs) and number of days to become pregnant were calculated using PROC GLIMMIX and PROC LIFETEST procedures of SAS. Adjusting for BCS (P = 0.07), expressed estrus (P < 0.05), year (P < 0.05), and BCS by year interaction (P < 0.05), the AI-PR was greater for heifers in AI-NS group with higher RTS (P < 0.0001; 40.7%, 48.3%, 57.6%, and 64.6% for RTS of 2 or less, 3, 4, and 5, respectively). Controlling for BCS (P < 0.05), year (P < 0.05) and the breeding season pregnancy rates (BS-PRs) were greater for heifers in the AI-NS group with higher RTS (P < 0.01; 81.2%, 86.5%, 90.4%, and 95.2% for RTS of 2 or less, 3, 4, and 5, respectively). Similarly, adjusting for BCS, year (P < 0.05), the BS-PR was greater for heifers in NSO group with higher RTS (P < 0.01; 79.7%, 84.3%, 88.4%, and 90.2% for RTS of 2 or less, 3, 4, and 5, respectively). Heifers with higher RTS in both groups became pregnant earlier in the breeding season compared with heifers with lower RTS (log-rank statistics: P < 0.0001). Heifers in the AI-NS group become pregnant at a faster rate compared with those in the NSO group (P < 0.01). The BS-PR for heifers with RTS 5 was different between AI-NS and NSO groups (P < 0.0001). In conclusion, the RTS influenced both the number of beef heifers that became pregnant during the breeding season and the time at which they become pregnant. Furthermore, irrespective of RTS, heifers bred by NSO required more time to become pregnant than their counterparts in herds that used timed AI. The application of RTS system is reliant on the use of synchronization protocol. The application of RTS for selection may plausibly remove precocious females with lower RTS. On the contrary, application of RTS would help select heifers that will become pregnant earlier in breeding season.

Effect of the first GnRH and two doses of PGF2α in a 5-day progesterone-based CO-Synch protocol on heifer pregnancy

The objectives were (1) to determine the effects of gonadorelin hydrochloride (GnRH) injection at controlled internal drug release (CIDR) insertion on Day 0 and the number of PGF2α doses at CIDR removal on Day 5 in a 5-day CO-Synch + CIDR program on pregnancy rate (PR) to artificial insemination (AI) in heifers; (2) to examine how the effect of systemic concentration of progesterone and size of follicles influenced treatment outcome. Angus cross beef heifers (n = 1018) at eight locations and Holstein dairy heifers (n = 1137) at 15 locations were included in this study. On Day 0, heifers were body condition scored (BCS), and received a CIDR. Within farms, heifers were randomly divided into two groups: at the time of CIDR insertion, the GnRH group received 100 μg of GnRH and No-GnRH group received none. On Day 5, all heifers received 25 mg of PGF2α at the time of CIDR insert removal. The GnRH and No-GnRH groups were further divided into 1PGF and 2PGF groups. The heifers in 2PGF group received a second dose of PGF2α 6 hours after the administration of the first dose. Beef heifers underwent AI at 56 hours and dairy heifers at 72 hours after CIDR removal and received 100 μg of GnRH at the time of AI. Pregnancy was determined approximately at 35 and/or 70 days after AI. Controlling for herd effect (P < 0.06), the treatments had significant effect on AI pregnancy in beef heifers (P = 0.03). The AI-PRs were 50.3%, 50.2%, 59.7%, and 58.3% for No-GnRH + PGF + GnRH, No-GnRH + 2PGF + GnRH, GnRH + PGF + GnRH, and GnRH + 2PGF + GnRH groups, respectively. The AI-PRs were ranged from 50% to 62.4% between herds. Controlling for herd effects (P < 0.01) and for BCS (P < 0.05), the AI pregnancy was not different among the treatment groups in dairy heifers (P > 0.05). The AI-PRs were 51.2%, 51.9%, 53.9%, and 54.5% for No-GnRH + PGF + GnRH, No-GnRH + 2PGF + GnRH, GnRH + PGF + GnRH, and GnRH + 2PGF + GnRH groups, respectively. The AI-PR varied among locations from 48.3% to 75.0%. The AI-PR was 43.5%, 50.4%, and 64.2% for 2.5 or less, 2.75 to 3.5, and greater than 3.5 BCS categories. Numerically higher AI-PRs were observed in beef and dairy heifers that exhibited high progesterone concentrations at the time of CIDR insertion (>1 ng/mL, with a CL). In addition, numerically higher AI-PRs were also observed in heifers receiving CIDR + GnRH with both high and low progesterone concentration (<1 ng/mL) initially compared with heifers receiving a CIDR only with low progesterone. In dairy heifers, there were no differences in the pregnancy loss between 35 and 70 days post-AI among the treatment groups (P > 0.1). In conclusion, GnRH administration at the time of CIDR insertion is advantageous in beef heifers, but not in dairy heifers, to improve AI-PR in the 5-day CIDR + CO-Synch protocol. In addition, in this study, both dairy heifers that received either one or two PGF2α doses at CIDR removal resulted in similar AI-PR in this study regardless of whether they received GnRH at CIDR insertion.