Replacement Beef Heifers Research Articles

195 Effect of selection for growth and maternal influence on crossbred Angus heifer development

Abstract This multiyear experiment was designed to determine the effects of sire yearling weight (YW) and maternal influence (MILK) expected progeny differences (EPD) on production and fertility of beef replacement heifers. Sires were classified as moderate (< 50th percentile) or high for YW EPD (122 ± 29; from 79 to 172) and as low (< 50th percentile) or high for MILK EPD (27 ± 8; from 5 to 40). Fall-born (n = 214) and spring-born (n = 207) heifers were enrolled in the study. Birth weight (BW), weaning weight (WW), and YW of the heifers were measured. In addition, reproductive tract score (RTS), dry matter intake (DMI), and average daily gain (ADG) while consuming an unprocessed grass hay diet were determined in a subsample of enrolled heifers. Neogen Igenity Beef scores (NIBS) were also run on this subset. Pregnancy rate and conception rate at fixed timed artificial insemination (FTAI) were also determined. Adjusted BW, WW and YW and RTS were analyzed using the GLIMMIX procedure of SAS (9.4, SAS Institute Inc., Cary, NC), with YW and MILK EPD as fixed effects and year of birth as random effect. Effects of sire YW and MILK classification on the likelihood of pregnancy and successful FTAI were also analyzed using the GLIMMIX procedure of SAS. Pearson correlation coefficients between independent and dependent variables were obtained using the CORR procedure of SAS. Sire MILK EPD had no effect (P ≥ 0.13) on the body weight of fall- or spring-born heifers. However, fall-born heifers were 0.12 kg and 0.34 kg heavier (P = 0.06 and 0.001, respectively) per unit increase in sire YW EPD at weaning and yearling time, respectively. There was no effect of sire YW EPD on fall-born heifer DMI as percentage of body weight (DMI % BOW; P = 0.74) nor ADG (P = 0.90) while consuming the low-energy diet. Spring-born heifers had significantly greater (all, P ≤ 0.001) adjusted BW, WW, and YW (0.02, 0.23 and 0.37 kg per unit increase in sire YW EPD, respectively. Reproductive tract score was strong and negatively correlated (P ≤ 0.001) with DMI % BOW. Heifer YW NIBS were moderate and positively correlated (P < 0.001) with ADG. There was a tendency (P = 0.09) for a weak and negative correlation between residual feed intake genetic scores and DMI % BOW. Sire genetic merit for yearling growth was transmitted to replacement heifers. However, neither ADG, nor unprocessed forage DMI % BOW was influenced by genetic potential for growth during this study. Further research is needed to assess the benefits of using genomic profile of heifers for maternal, performance and carcass traits, alongside sire EPDs, when selecting and developing beef replacement heifers.

143 Short- and long-term effects of heat stress in cow-calf pairs adapted to tropical and subtropical regions

Abstract Chronic exposure to high temperatures and humidity can limit beef cattle performance in tropical/subtropical environments, regardless of breed. Despite better heat adaptability compared with Bos taurus cattle, heat-stressed Bos indicus cattle also experience an increase in body temperature above the physiological limit. As body temperature increases, cascades of behavioral and physiological events are triggered to lessen heat load but often at the expense of productive outcomes. Contrary to other species and feedlot beef cattle, the effects of heat stress on physiology and performance of grazing cow-calf pairs have not been evaluated in detail, particularly for Bos indicus cattle. Preliminary data showed opposite outcomes to heat stress in Bos indicus vs. Bos taurus cattle, limiting the implications of the existing data generated from studies using beef and dairy Bos taurus cattle. This presentation will share some nutritional and management practices to mitigate heat stress in grazing beef cattle. Practices mentioned herein include altering the timing of body weight (BW) growth pattern (stair-step, SST) and immunomodulatory feed ingredient (IFI) supplementation for replacement beef heifers, and maternal access to shade to reduce heat load. For 100 d before the breeding season, Bos indicus-influenced beef heifers grazing warm-season grasses received a constant supplementation amount or SST strategy (50 d of low then 50 d of high supplementation), with or without IFI. Under severe heat stress conditions, IFI supplementation reduced heifer vaginal temperature but did not increase their growth and reproduction, whereas the SST strategy lowered internal body temperature, enhanced growth performance and pregnancy success compared with a conventional constant supplementation practice. Our group is also focused on the critical need to determine the specific effects of heat stress mitigation during pre- and postnatal phases on physiology and performance of Bos indicus-influenced cow-calf pairs. Study 1 evaluated the impacts of maternal access to artificial shade from 83 d prepartum until 50 d postpartum on body thermoregulation, performance, and physiology of beef heifers and their first offspring. Removing maternal access to shade led to greater maternal respiration rate, vaginal and body surface temperatures and reduced maternal body condition score and calf BW at birth. Nonetheless, offspring born from cows with no access to shade were remarkably heavier during a 60-d post-weaning period and had decreased plasma indicators of inflammation and positive effects to humoral immune response. Study 2 is a multi-year, USDA/NIFA-funded study designed to capitalize on the ability of cattle to reprogram physiological/immunological systems following exposure to stress during gestation. Study 2 combined gestational and postnatal heat abatement to enhance the overall growth/immune/reproductive performance of grazing Bos indicus-influenced cow-calf pairs. Partial data on long-term growth and reproductive performance, physiology, metabolome, and microbiome of both cows and their female offspring will be shared in this presentation.

PSV-30 Effects of divergent residual feed intake on performance, feed efficiency, feeding behavior and gaseous exchange in replacement beef heifers

PSV-30 Effects of divergent residual feed intake on performance, feed efficiency, feeding behavior and gaseous exchange in replacement beef heifers

150 Effects of diet type on performance and methane yield in replacement beef heifers

Abstract The objective of this experiment was to determine the relationships among enteric gas production, body weight (BW) gain, and feed intake for growing heifers consuming two energy divergent diets. Fifty-five fall born yearling Angus and Angus cross heifers were used in a 157-d experiment. Heifers were fed two consecutive diets at the Oklahoma State University Range Cow Research Center. Heifers were sorted into one of two drylot pens based on BW. Each drylot pen was equipped with individual intake monitoring system (C-Lock Inc., Rapid City, SD) with a stocking rate of 3.3 heifers per feeder. The first intake segment (HAY) was initiated with a 21 d of adaptation followed by 70 d of data collection. Heifers were offered ad libitum access to long stem unprocessed bermudagrass hay and a salt/mineral/vitamin supplement. After the HAY period, heifers were adapted to a 50% forage, 50% concentrate diet (TMR) during a 14-d adaptation period, followed by 52-d of data collection. Means and standard deviations for phenotypic traits of DMI, ADG, RFI, and CH4 were 6.7 ± 0.7 kg, 0.44 ± 0.13kg, and 194.6 ± 17.56 g/d respectively for HAY and 14.3 ± 1.34 kg, 1.72 ± 0.20 kg, and 280 ± 24.69 g/d respectively for TMR. Pearson correlations between diets for DMI, ADG, and CH4 were 0.32, -0.16, and 0.29, respectively. Coefficient of variation for DMI was 10.8% for HAY and 9.4% for TMR. Coefficient of variation for ADG was 29.9% for HAY and 11.6% for TMR. Methane intensity was calculated as CH4, g/day divided by DMI, kg/d resulting in 29.6 ± 3.5 and 19.9 ± 2.2 g CH4/kg DMI for HAY and TMR, respectively. In summary, HAY DMI was moderately and positively correlated with TMR DMI while ADG was not correlated among the two diet types. The HAY diet generated less total daily CH4, although more CH4 per unit of feed intake.

101 Effects of moderate exercise regimen on reproductive development of replacement beef heifers reared in drylots at a high stocking density

Abstract This experiment evaluated growth and reproductive development of beef heifers reared at a high stocking density and provided with access to an exercise area. The experiment was replicated over 2 yr, with a total of 180 Angus × Brahman heifers. Each year, 90 heifers were ranked by age (264 ± 1 d) and body weight (BW; 200 ± 2 kg) on d 0, and assigned to a) 1 of 6 drylot pens (10 × 14 m pens; 10 heifers/pen) resulting in a stocking density of 14 m2/heifer (DENS), or b) 1 of 3 paddocks (2-ha paddocks; 10 heifers/paddock) resulting in a stocking density of 2,000 m2/heifer (CON). On d 15, 3 DENS pens were randomly selected and given access to an exercise area (DENS-EX) for 1 h three times weekly. Negligible forage was available for CON heifers, whereas all heifers received the same limit fed diet which averaged 13 kg/heifer daily of a corn-based diet. Heifer shrunk BW was recorded after 16 h of feed and water withdrawal on d -3 and 225 for BW gain calculation. Heifer temperament (chute score, exit velocity, and temperament score) were evaluated on d 0 and 225. Heifers were also fitted on d 0 with a pedometer behind their shoulder and an ear tag (CowManager, Select Sires, Plain City, OH) to record behavioral responses. Each week, pedometer results were recorded, and blood samples were collected for puberty evaluation via plasma progesterone. Heifers from CON had more (P < 0.05) steps per week compared with DENS and DENS-EX (23,973, 6,706, and 12,354 steps/week, respectively; SEM = 1,247), and DENS-EX heifers had more (P < 0.05) steps per week compared with DENS. Heifers from CON spent more (P < 0.05) time ruminating and eating compared with DENS and DENS-EX. No treatment effects (P ≥ 0.91) were detected for heifer BW gain (0.820, 0.815, and 0.824 kg/d for CON, DENS, and DENS-EX, respectively; SEM = 0.016). Heifers from DENS had greater (P ≤ 0.05) exit velocity and temperament score on d 225 compared with DENS-EX and CON. Heifers from DENS experienced delayed puberty attainment (treatment x day; P < 0.01) compared with DENS-EX and CON. A greater (P ≤ 0.05) proportion of CON heifers were pubertal by day 105 compared with DENS and DENS-EX (30.0, 11.6, and 15.0%, respectively; SEM = 6.5), whereas a greater (P < 0.05) proportion of CON and DENS-EX heifers were pubertal by d 154 compared with DENS (61.7, 66.7, and 43.3%, respectively; SEM = 6.5). Results from this experiment demonstrate that providing heifers with an exercise area alleviated the negative effects associated with high stocking density on their reproductive development. This work is supported by the USDA-NIFA AFRI program (#2021-67015-34083).

180 Differences in Gene Expression in Granulosa Cells Harvested from Fertile and Sub-Fertile Beef Heifers

Abstract Infertility in beef replacement heifers is one of the leading contributors to economic losses in the cow-calf sector of the beef production industry. Successful reproduction is complex, involving multiple tissues and biological systems. This complexity makes identifying the leading causes of subfertility difficult. One potential source of fertility issues is poor oocyte health. As developing oocytes are dependent on granulosa cells (GCs) and physically coupled with GCs, we hypothesized that the gene expression profile would be different between the GCs from fertile heifers and those from sub-fertile heifers. The objective of this study was to identify differences in gene expression in GCs collected from beef heifers of differing fertility status, either fertile or sub-fertile. To gather this information, Angus-Simmental crossbred heifers underwent an estrus synchronization and fixed-time artificial insemination (AI) protocol (7-Day CO-synch + CIDR). At 41 days post-AI, heifers were pregnancy checked through ultrasound and palpation. Heifers pregnant to AI were classified as fertile (n = 8). Any heifers that remained non-pregnant following AI were exposed to bulls of proven fertility for 61 days. Bull-exposed heifers were evaluated for pregnancy 34 days after the bulls were removed. The non-pregnant heifers following both AI and natural service were classified as sub-fertile (n = 5). Pregnancies were terminated in fertile heifers, and heifers from both groups were allowed to resume normal cyclicity before GCs being harvested. RNA was extracted from GCs and quality was checked for each sample. Total RNA from GCs of 13 heifers was subjected to the library preparation and sequencing on the Nova-Seq platform. Through the application of DESeq2, 79 genes were identified as significantly differentially expressed genes (DEGs) with P-value < 0.05 and absolute (log2 fold change) > 0.5 including DNER, HOXD10, CD52, CXCL12, and HOXD11. DEGs, along with co-expressed genes, were over-represented in pathways associated with the regulation of MAP kinase activity, regulation of serine/threonine kinase activity, MHC protein binding, and plasma membrane signaling receptor complex. Through the pursuit of knowledge regarding the function of top DEGs, increased sample size, and more diverse sample collection time points, we may improve our understanding of the causation of heifer fertility issues. Improving our knowledge of heifer infertility has the potential to develop therapeutic options, and in turn, increase the efficiency and sustainability of cow-calf production systems.

181 Effects of Moderate Exercise Regimen on Reproductive Development of Replacement Beef Heifers Reared in Drylots at a High Stocking Density

Abstract This experiment evaluated the physiological and reproductive responses of beef heifers reared at a high stocking density and provided with access to an exercise area. Ninety Angus × Brahman heifers were ranked by age (257 ± 2 days), body weight (BW; 216 ± 2 kg), and temperament score on day 0 and assigned to a) 1 of 6 drylot pens (10x14 m pens; 10 heifers/pen) resulting in a stocking density of 14 m2/heifer (DENS), or b) 1 of 3 paddocks (2-ha paddocks; 10 heifers/paddock) resulting in a stocking density of 2,000 m2/heifer (CON). On day 15, 3 DENS pens were randomly selected and given access to an exercise area (DENS-EX) for 1 hour three times weekly. Negligible forage was available for CON heifers, whereas all heifers received the same limit fed diet which averaged 13 kg/heifer daily of a corn-based diet. Heifer shrunk BW was recorded after 16 h of feed and water withdrawal on days -3 and 225 for average daily gain calculation. On day 0, heifers were fitted with a pedometer behind their shoulder and an ear tag (CowManager, Select Sires, Plain City, OH) to record behavioral responses. Each week, pedometer results were recorded, and blood samples were collected for puberty evaluation via plasma progesterone. Heifers from CON had more (P < 0.05) steps per week compared with DENS and DENS-EX, and DENS-EX heifers had more (P < 0.05) steps per week compared with DENS. Heifers from CON spent more (P < 0.05) time ruminating and eating compared with DENS and DENS-EX. No treatment effects (P ≥ 0.12) were detected for heifer BW gain or temperament variables. Heifers from DENS experienced delayed puberty attainment given a greater (P < 0.05) proportion of CON heifers were pubertal by day 98 compared with DENS and DENS-EX, whereas a greater (P < 0.05) proportion of DENS-EX heifers were pubertal by day 154 compared with DENS heifers (treatment × day interaction, P < 0.01). Collectively, results from this experiment demonstrate that providing heifers reared at a high stocking density access to an exercise area does not result in similar reproductive responses as those reared on pasture at a low stocking density. This work is supported by the USDA National Institute of Food and Agriculture (#2021-67015-34083).

PSVIII-A-4 Evaluation of Blood Parameters Associated to Environmental Stress in Grazing Beef Heifers with Divergent Residual Feed Intake

Abstract There is considerable interest in improved feed efficiency to enhance sustainability in beef production, but a lack of understanding exists on the interaction between residual feed intake (RFI) and environment while grazing. Increasing variation in environmental conditions has been documented in western Canada with summers becoming warmer. This study evaluated blood parameters and rumen temperature (RT) of grazing beef heifers with divergent residual feed intake (RFI) during summer (July to August) of 2022. Forty-four crossbred beef heifers (358 ± 4.78 kg body weight; approximately 14 months of age) previously tested for RFI in drylot and classified as more (n = 21; LOW-RFI = -0.9 ± 0.70) or less feed efficient (n = 23; HIGH-RFI = 1.3 ± 1.00) were grazed at 2.72 AUM/ha over 7 wk in Alberta, Canada. Rumen temperatures were automatically recorded throughout the study using the Smart Rumen Bolus by Moonsyst. Plasma was collected every 14 ± 1 d for 42 d to determine concentrations of blood urea nitrogen (BUN), non-esterified fatty acids (NEFA), insulin-like growth factor 1 (IGF-1), β-Hydroxybutyric acid (BHBA), leptin (LEP), free triiodothyronine (fT3), haptoglobin (HP), heat shock protein 70 (HSP70), and gamma-aminobutyric acid (GABA). Environmental conditions were assessed by calculating the Climate Comprehensive Index using temperature, wind speed, solar radiation, and humidity data from a weather station within 1 km of the grazed pastures. Daily weather conditions were considered to impose risk to cause mild, moderate, severe, and extreme stress for 8, 21, 8, and 1 days, respectively. Plasma and RT data were analyzed as a completely randomized design with repeated measures. An RFI × day interaction was observed for BUN (P = 0.018). LOW-RFI had greater (P = 0.02) BUN on d 42 compared with HIGH-RFI heifers (42.5 vs. 32.6 mg/dL, respectively), while GABA tended to be greater (P ≤ 0.09) for HIGH-RFI heifers on d 0 and 42. Free T3 concentrations were greater (P = 0.04; 8.54 vs. 7.78 pmol/L, respectively), whereas HP was less (P = 0.01) in LOW-RFI heifers. However, HP concentrations were below the threshold for inflammation throughout the study. There was also an effect of day (P < 0.01) for fT3, IGF-1, LEP, NEFA, HSP70, and BHBA. Leptin and HSP70 concentrations were greatest on d 14 and 28, whereas BHBA was the greatest (P < 0.01) and IGF-1 the least on d 42 (P < 0.01). An RFI × hour interaction was detected for RT (P = 0.0003), where HIGH-RFI heifers had greater RT throughout the day. In summary, weather conditions in western Canada changed blood parameters of replacement beef heifers during summer. Feed efficient heifers had decreased RT and greater plasma concentrations of fT3, which could be associated with metabolic homeostasis and regulation of thermogenesis.

Feeding strategies for rearing replacement beef heifers in a grazing system under tropical conditions

Our objective was to evaluate the effects of pre- and post-weaning protein supplement on the productive response and nutritional and metabolic status of replacement beef heifers grazed on tropical pasture. Fifty-six Nellore heifers (7.7 ± 0.1 months age) with an average initial body weight (BW) of 237 ± 3.5 kg were distributed in a completely randomized design in 2 × 2 factorial arrangement. The four strategies were: US-ME, unsupplemented heifers at pre-weaning and supplemented with 5 g/kg BW at post-weaning; US-HI, unsupplemented heifers at pre-weaning and supplemented with 7.5 g/kg BW at post-weaning; ME-ME, heifers supplemented with 5 g/kg BW at pre-weaning and post-weaning; and ME-HI, heifers supplemented with 5 g/kg BW at pre-weaning and 7.5 g/kg BW at post-weaning. On average, crude protein (CP) intake and CP: digested organic matter (DOM) ratio were influenced (P < 0.05) by protein supplement in the post-weaning period, with a higher intake of CP and CP:DOM ratio in HI heifers than in ME heifers (average CP of 0.812 vs 0.665 kg/day and average DOM of 204 vs 174 g CP/kg). Nonetheless, the post-weaning protein supplement did not affect the intake of total dry matter (DM), pasture DM, organic matter (OM), neutral detergent fiber corrected for ash and protein residue (apNDF), non-fibrous carbohydrates, and DOM. The CP digestibility was highest (P = 0.005) for HI heifers than for ME heifers (average of 0.732 vs 0.645 g/g DM). The pre-weaning and post-weaning protein supplement did not affect the concentration of insulin-like growth factor–1 (IGF-1), progesterone, albumin, globulins, glucose, and triglycerides, and liver mRNA expression of carbamoyl phosphate synthetase-1 (CPS-1) and phosphoenolpyruvate carboxykinase (PEPCK). Finally, the pre-weaning and post-weaning protein supplement did not affect growth performance, carcass traits, and body growth in the post-weaning. Supplementation during pre-weaning does not bring any carry-over effect on the productive performance and metabolic status of heifers supplemented during post-weaning. However, supplementation in post-weaning with 5 or 7.5 g/kg BW allows a compensatory growth of heifers that are unsupplemented at pre-weaning. Therefore, the supply of 7.5 g/kg BW of protein supplement for beef heifers only during the post-weaning period is recommended.

Physical traits, performance data, and reproductive tract maturity score can be used to predict fertility and likelihood of early conception in beef replacement heifers consigned to a heifer development program in the southeastern United States.

To identify growth and reproductive measurements that can be used to select heifers with the potential to be more reproductively efficient. A total of 2,843 heifers consigned to the Georgia Heifer Evaluation and Reproductive Development program between 2012 and 2021 with a mean (min, max) age of heifers at delivery of 347 days (275, 404). Reproductive tract maturity score (RTMS), weight at delivery as a percentage of target breeding weight, hip height 3 to 4 weeks after delivery, and average daily gain during the first 3 to 4 weeks after delivery were evaluated as potential predictors of the variables of interest. The model-adjusted odds of pregnancy were 1.40 to 1.67 times higher for heifers with an RTMS of 3, 4, or 5 when compared to heifers with an RTMS of 1 or 2. For every 2.5-cm increase in hip height and every 1-month increase in age at the beginning of the breeding period the model-adjusted odds of pregnancy were 1.10 and 1.16 times higher, respectively. The model-adjusted pregnancy hazard rate for heifers with an RTMS of 3, 4, or 5 was 1.19 to 1.25 times higher than that of heifers with an RTMS of 1 or 2. For every 2.5-cm increase in hip height, the model-adjusted hazard rate for pregnancy was 1.04 times greater. Physical traits related to animal maturity and attainment of early puberty can be used to select heifers that are more likely to become pregnant early in their first breeding season.

Evaluating the use of luteal color Doppler ultrasonography and pregnancy-associated glycoproteins to diagnose pregnancy and predict pregnancy loss in Bos taurus beef replacement heifers.

The objective of this study was to evaluate the use of corpus luteum (CL) color Doppler (CD) ultrasonography and pregnancy-associated glycoproteins (PAG) for early pregnancy diagnosis and examine their ability to predict late embryonic/early fetal mortality (LEM) in Bos taurus beef replacement heifers. Beef heifers (n = 178) were exposed to a 7-d CO-Synch + CIDR protocol followed by fixed-time artificial insemination (day 0). On days 20 and 22, B-mode and CD ultrasonography were performed to evaluate CL morphometries and blood perfusion, respectively. Heifers were considered nonpregnant when CL area was <2 cm2 or estimated luteal blood perfusion was ≤30% of the total luteal area. Blood samples were collected on days 25 and 29 to estimate circulating concentrations of PAG. Conventional ultrasonography on days 29 and 94 was utilized to determine pregnancy status and considered the gold standard method for pregnancy diagnosis. Pregnant heifers had greater (P < 0.01) CL diameter, area, volume, and blood perfusion when compared with nonpregnant heifers on days 20 and 22. Accuracy of CD on days 20 and 22, and PAG on days 25 and 29 were 91%, 94%, 96%, and 98%, respectively. No false-negative results were observed for CD on both days 20 and 22 (negative predicted value = 100%) and false-positive results represented 8% and 6% of the diagnoses. Heifers that experienced LEM between days 29 and 94 of gestation had decreased luteal (P = 0.02) volume on day 20 and tended (P = 0.07) to have decreased concentrations of PAG on day 29 compared with heifers that maintained pregnancy. However, both CD and PAG failed to predict embryonic mortality. In conclusion, CD successfully detected most nonpregnant replacement heifers as early as day 20 of gestation, while resulting in no false negative diagnoses. Both CD and PAG failed to predict LEM in the present study.

311 Administering a Bovine Appeasing Substance to Beef Heifers During an Estrous Synchronization Protocol and its Impacts on Temperament and Pregnancy Rate

Abstract This experiment evaluated the impacts of administering a bovine appeasing substance (BAS) to Bos taurus (angus crossed) beef replacement heifers at the initiation of an estrous synchronization (TAI) protocol on their temperament and pregnancy rates. A total of 348 heifers at four locations were stratified by body weight (BW); reproductive tract score (RTS), and temperament score [TS; average of exit velocity (EV) and chute score (CS), determined at the day of initiation of TAI) and assigned to receive BAS (IRSEA Group, Quartier Salignan, France; n = 173) or placebo (water; CON; n = 175). Treatments (5 mL) were topically applied to the nuchal skin area of each heifer at the initiation of the TAI protocol. Within location, heifers were allocated to pens (6 pens per treatment; pen being the experimental unit) and received a free-choice total mixed ration during the duration of the experiment. Temperament (EV, CS) was assessed three times (days 0, 7 and 9) during the TAI protocol by the same trained technician. Pregnancy rate was determined by ultrasonography between days 45 and 55 post TAI. Heifer BW (379.5±5 kg), RTS (3.8±0.06), CS on days 0, 7 and 9 (2.33±0.06, 2.08±0.04, and 1.91±0.04, respectively), and EV on days 0, 7 and 9 (1.35±0.03, 1.28±0.03, and 1.39±0.03 m/s, respectively), and estrus expression prior to TAI (40.2±5.9%) were similar (P&amp;gt;0.10) between treatments. Pregnancy rate to TAI differed among locations (P&amp;lt; 0.05); however, it was not affected by treatment (39.7±8.2% and 41.0±3.7% for CON and BAS, respectively), with no treatment by location interaction. In conclusion, administration of BAS to beef heifers at the initiation of a TAI protocol did not alter temperament, measured as CS and EV, and failed to increase pregnancy rates.

286 Effects of Presynchronization with Prostaglandin F2α and a Progestin, and Delayed Insemination on Pregnancy Rates with Sexed Semen in Replacement Beef Heifers

Abstract To determine effects of presynchronization and delayed fixed-time artificial insemination (TAI) on pregnancy rates (PR/AI) with sexed semen, 1,844 beef heifers were enrolled in a completely randomized design at 12 locations. Within location, heifers were randomly assigned to one of five treatments: 1 and 2), heifers administered prostaglandin F2α (PGF) on day -7, gonadotropin-releasing hormone (GnRH) and a CIDR insert on day 0, PGF at CIDR removal on day 7, and another injection of GnRH at TAI 72 hours later with conventional (CTRL72-CNV) or sexed semen (CTRL72-SEX); 3 and 4), treated the same as CTRL72 but received a CIDR insert on day -7 at PGF administration and TAI at 60 hours with conventional (CIDR60-CNV) or sexed semen (CIDR60-SEX); 5), treated the same as CIDR60 but had TAI delayed to 72 hours with sexed semen (CIDR72-SEX). Estrus expression between day 7 and TAI did not differ (P=0.92) between CIDR60 and CIDR72 heifers but was greater (P&amp;lt; 0.001) in CIDR60 and CIDR72 heifers compared with CTRL72 heifers. Among treatments, PR/AI differed (P&amp;lt; 0.001) and were greater (P≤0.003) in CTRL72-CNV and CIDR60-CNV heifers than CIDR60-SEX and CIDR72-SEX heifers. Furthermore, PR/AI were greater (P&amp;lt; 0.001) in CTRL72-SEX and CIDR60-SEX heifers when compared with CIDR72-SEX heifers but only tended (P=0.09) to differ between CTRL72-SEX and CIDR60-CNV heifers. No differences (P=0.33) were determined between CTRL72-CNV and CIDR60-CNV or between CTRL72-SEX and CIDR60-SEX heifers (P=0.22). In conclusion, no differences were determined between heifers presynchronized with only PGF and those presynchronized with PGF and a CIDR insert when inseminated with either conventional or sexed semen. Therefore, use of a CIDR insert for an additional 7 days was not beneficial to PR/AI when heifers were TAI at 60 hours with either conventional or sexed semen. Additionally, delaying TAI to 72 hours with sexed semen after presynchronization with both PGF and a CIDR insert has a negative impact on PR/AI.

PSIII-A-19 Thermotolerance and Residual Feed Intake in Bos-Indicus Influenced Beef Heifers

Abstract This study investigated the relationship between thermotolerance and residual feed intake (RFI) in Bos-indicus influenced replacement beef heifers. Multiple individual vaginal temperatures (VT) collected during the summer in Florida were used to select the most (n = 14; thermotolerant) and least (n = 13; non-thermotolerant) heat tolerant heifers to undergo a feed efficiency test in the fall. The maximum initial VT difference between groups was of 0.19 and 1.2 ± 0.065 °C (P &amp;lt; 0.01) for thermotolerant and non-thermotolerant heifers, respectively. Heifers (398 ± 11.3 kg; approximately 720 d of age) were randomly allocated to four concrete-floored pens equipped with two GrowSafe feed bunks each and received a common ad libitum total mixed ration (16.9% crude protein and 52% total digestible nutrients) for 56 d (14 d adaptation and 42 d evaluation period). Body weight (BW) was collected on d -1, 0, 14, 28, 41, and 42, while VT was recorded (10 min intervals for 4 consecutive d) from d 29 to 32, using temperature probes placed intravaginally with a hormone-free controlled internal drug release device. Final BW, average daily gain (ADG), dry matter intake (DMI), DMI as a percentage of BW, RFI, and VT were analyzed as a completely randomized design. Final BW, ADG, DMI, and VT collected during the feeding period were not affected by thermotolerance phenotype (P ≥ 0.42); however, heifers previously classified as thermotolerant had decreased RFI (P = 0.01; -1.32 vs. 1.27 ± 3.31 kg, respectively) and DMI as a percentage of BW (P = 0.01) when compared with non-thermotolerant heifers. In conclusion, Bos-indicus influenced replacement beef heifers previously classified as thermotolerant based on multiple vaginal temperature measurements collected throughout the summer had decreased residual feed intake when measured in the fall, indicating the potential of more heat tolerant heifers to be more feed efficient.

87 Awardee Talk: Frequency of Energy Supplementation Modulates Growth, Reproduction, Immune Function, and Fetal Programming in Beef Cattle

Abstract Fluctuations in nutrient intake and metabolism can be detrimental to beef cattle performance. Multiple studies evaluated the impacts of reducing the frequency of energy supplementation from daily (7X) to once (1X) or 3 times (3X) weekly during heifer development, calf preconditioning, and late gestation of beef cows on growth, reproduction, immune function, and progeny performance. Reducing the supplementation frequency from 7X to 3X weekly: (1) did not impact average daily gain (ADG; P = 0.52) but hastened (P ≤ 0.05) puberty and pregnancy attainment of beef heifers; and (2) reduced ADG (P = 0.02), increased (P ≤ 0.03) plasma indicators of physiological stress (cortisol and haptoblogin), and decreased (P ≤ 0.05) humoral immune response against pathogens associated with bovine respiratory disease (BRD) in preconditioning beef steers. Reducing the supplementation frequency from 7X to either 3X or 1X weekly during late gestation did not (P ≥ 0.21) impact cow prepartum body condition score and reproduction, but linearly decreased (P = 0.05) calf preweaning growth. The negative effects of infrequent energy supplementation may be attributed to greater fluctuations in plasma concentrations of insulin growth factor-1, glucose, insulin, and urea nitrogen compared to frequent energy supplementation. Later attempts to offset such negative effects of infrequent supplementation observed that neither increasing the supplementation amount (P ≥ 0.21) nor altering the timing of vaccination relative to weaning (P ≥ 0.12) prevented performance reductions in beef cattle supplemented infrequently. Only a gradual reduction in supplementation frequency for preconditioning calves prevented a reduction on growth and improved (P ≤ 0.05) the immune response against BRD pathogens. Combined, these results revealed that frequent energy supplementation during preconditioning of beef steers, development of replacement beef heifers, and late gestation of beef cows was required to optimize their growth, immunity, and reproduction, and the growth performance of their progeny.

Physical Traits and Reproductive Measurements Associated with Early Conception in Beef Replacement Heifers.

Simple SummaryDeveloping and raising replacement beef heifers requires a large capital investment for producers. Therefore, it is imperative to discover traits and management practices to eliminate subfertile heifers prior to breeding and pregnancy determination. In this study, four years of data was analyzed from a centralized heifer development yard in the Midwest of the United States. The objective of this study was to analyze various heifer physical characteristics and management practices in order to quantify their impact on pregnancy and date of conception. Physical measurements can be used to improve the ability to select and develop heifers for improved reproductive longevity. Veterinarians have an opportunity to work with their clients to utilize this information to select replacements that fit the ranch environment. This should result in increased reproductive efficiency and cost optimization for the replacement heifer enterprise.Developing and raising replacement heifers requires a large capital investment for producers. Therefore, it is imperative to discover traits and management practices to eliminate subfertile heifers prior to breeding and pregnancy determination. In this study, four years of data was analyzed from a centralized beef heifer development yard in the Midwest of the United States. The objective of this study was to analyze various heifer physical characteristics and management practices in order to quantify their impact on pregnancy and date of conception. Logistic regression models were built to investigate risk factors associated with conception to artificial insemination (AI), pregnancy by natural service after AI exposure, and pregnancy in the first 21-days of the breeding season. Age at entry, average daily gain from entry to breeding, pelvic width, and year were associated with AI pregnancy (p < 0.05). On the second model, average daily gain from entry to yearling weight, weight at breeding, weight at pregnancy diagnosis, and age at AI were significantly associated with pregnancy. There were no associations with reproductive tract score with any of the response variables analyzed. These results indicate there are physical measurements that can be used to improve the ability to select and develop heifers for improved reproductive performance.

Meta-analysis of the effects of monensin on performance of beef replacement heifers and beef cows.

Although performance benefits of monensin have been extensively studied in finishing cattle, growing cattle, and dairy cows, considerably less published work is available evaluating response to monensin supplementation in cow-calf production systems. This meta-analysis investigated the impacts of monensin on performance of beef cows and developing replacement heifers. The replacement heifer analysis was conducted using data from 18 different peer-reviewed publications and experiment station reports. The mature cow analysis included 21 different publications and experiment station reports. The metaphor package (version 2.4-0; Viechtbauer, 2010) for R (version 4.0.3; www.r-project.org) was used to determine the overall effect size of monensin compared to a negative control. Each study’s n, means, and SEM or P value was used to calculate the mean difference and estimate of within study variance for responses of interest. In replacement heifers, monensin treatment increased (P < 0.01); average daily gain (+0.03 ± 0.008 kg/d), feed efficiency (+0.013 ± 0.008 gain:feed), and percentage cycling before the breeding season (+15.9 ± 5.13%); while decreasing (P < 0.01): dry matter intake (0.293 ± 0.081 kg), and age at puberty (‐8.9 ± 1.48 d). Six studies reporting ad libitum forage intake for mature cows showed decreased (P = 0.008) DMI by 0.85 ± 0.32 kg/d. Six studies reported milk yield and revealed an increase (P = 0.01) of 0.39 ± 0.15 kg/d when cows were supplemented with monensin. Monensin supplementation resulted in a reduction (P = 0.02) in days to first estrus by 18 ± 8.2 d and percentage of cows exhibiting estrus prior to the breeding season was increased by 19 ± 8% (P = 0.03). There were no differences in artificial insemination pregnancy nor total pregnancy for either the heifer or mature cow data sets. This analysis indicates potential for use of monensin in heifer development and beef cow production systems. Further research is needed to elucidate the effects on reproductive efficiency, DMI, milk production, weight, and body composition change.

Effects of Pre-Synchronization With Prostaglandin F2α and a Progestin, and Delayed Insemination on Pregnancy Rates With Sexed Semen in Replacement Beef Heifers

To determine the effects of pre-synchronization and delayed fixed-time artificial insemination (TAI) on pregnancy rates (PR/AI) with sexed semen, 1,844 beef heifers were enrolled in a completely randomized design at 12 locations. Within a location, the heifers were randomly assigned to one of the five treatments: (1 and 2), heifers were administered prostaglandin F2α (PGF) on Day -7, gonadotropin-releasing hormone (GnRH), and a controlled internal drug releasing (CIDR) insert on Day 0, PGF at CIDR removal on Day 7, and a second injection of GnRH at TAI 72 h later with either conventional (CTRL72-CNV) or sexed semen (CTRL72-SEX); (3 and 4), treated the same as CTRL72 but received a CIDR insert on Day -7 at PGF administration and TAI at 60 h with either conventional (CIDR60-CNV) or sexed semen (CIDR60-SEX); (5), treated the same as CIDR60 but had TAI delayed to 72 h with sexed semen (CIDR72-SEX). Estrus detection patches were applied to all heifers on Day 7 and were evaluated for activation at TAI. Estrus expression did not differ (p = 0.92) between CIDR60 and CIDR72 heifers, but was greater (p &amp;lt; 0.001) in CIDR60 and CIDR72 heifers compared with CTRL72 heifers. Among treatments, PR/AI differed (p &amp;lt; 0.001) and were greater (p ≤ 0.003) in CTRL72-CNV and CIDR60-CNV heifers than CIDR60-SEX and CIDR72-SEX heifers (51.6 and 48.1 vs. 37.5 and 25.3%, respectively). In addition, PR/AI were greater (p &amp;lt; 0.001) in CTRL72-SEX and CIDR60-SEX heifers when compared with CIDR72-SEX (42.0 and 37.5 vs. 25.3%, respectively) heifers but only tended (p = 0.09) to differ between CTRL72-SEX and CIDR60-CNV heifers. No differences (p = 0.33) were determined between CTRL72-CNV and CIDR60-CNV or between CTRL72-SEX and CIDR60-SEX heifers (p = 0.22). In conclusion, no differences were determined between heifers pre-synchronized with only PGF and those pre-synchronized with PGF and a CIDR insert when inseminated with either conventional or sexed semen. Therefore, the use of a CIDR insert for an additional 7 days was not beneficial to PR/AI when heifers were TAI at 60 h with either conventional or sexed semen. Furthermore, delaying TAI to 72 h with sexed semen after pre-synchronization with both PGF and a CIDR insert had a negative impact on PR/AI.

5 Early Pregnancy Diagnosis inbos Taurus beef Replacement Heifers Using Color Doppler Ultrasonography

Abstract The objective of this study was to evaluate the use of corpus luteum (CL) color doppler ultrasonography (CD) for early pregnancy diagnosis in Bos taurus beef replacement heifers. Beef heifers (n = 183) from two locations were exposed to a 7-d CO-Synch + CIDR protocol followed by fixed-time artificial insemination (day 0). On days 20 and 22, B-mode and CD ultrasonography were performed to evaluate CL morphometries and blood perfusion, respectively. Heifers were considered non-pregnant when CL area was &amp;lt; 20 mm2 or estimated luteal blood perfusion was ≤ 25%. Conventional ultrasonography on day 29 was utilized to determine pregnancy status and considered the gold standard method for pregnancy diagnosis. Pregnant heifers had greater CL diameter, CL area, and CL volume when compared to non-pregnant heifers on days 20 and 22 (P &amp;lt; 0.001). Additionally, percentage of central, peripheral, and total luteal blood perfusion, as well as the respective blood perfusion scores were greater (P &amp;lt; 0.001) in pregnant compared with non-pregnant heifers on both day 20 and 22. Sensitivity, specificity, positive predicted value (PPV), negative predicted value (NPV), and accuracy for CD on day 20 were 100, 70, 86, 100, and 90, respectively. Sensitivity, specificity, PPV, NPV, and accuracy for CD on day 22 were 100, 76, 90, 100, and 92, respectively. Pairwise comparison of receiver operating characteristics curve analysis indicated no differences (P = 0.47) between CD on days 20 and 22 (area under the curve = 0.82 and 0.84, respectively). In conclusion, CD successfully detected most non-pregnant replacement heifers on day 20 and 22, while false negative results were absent (NPV = 100%).

Morphological and physiological measures as predictors of age at puberty and conception in beef heifer genotypes

This study examined the utility of postweaning morphological and physiological measures as predictors of age of puberty and conception in beef heifers. Data were used from 309 spring-born heifer progeny [initial age 231 d (SD = 16); BW 256 kg (SD = 52)] of beef and dairy dams sired by early-maturing (EM) or late-maturing (LM) breeds and bred (12 wk) to calve at 24 mo of age within a grass-based production system. Body weight, composition and linear measurements, blood metabolites, pubertal age, and pregnancy were determined. Mean ages at puberty and conception were 429 d (range = 275–496 d) and 458 d (range = 398–534 d), respectively. Pubertal age was strongly correlated with age at first AI (r = 0.68) and conception (r = 0.48). Body weight deposition from 8 to 13 mo of age was negatively associated with age at puberty (r = −0.33), first AI (r = −0.17), and conception (r = −0.12). Pubertal age was negatively associated with BW at 10 and 13 mo (r = −0.15 to −0.19), ultrasonic measures of fatness from 10 to 15 mo of age (r = −0.15 to −0.30), IGF-1 concentrations from 8 to 13 mo (r = −0.22 to −0.31), and insulin (r = −0.22 to −0.24) and leptin (r = −0.18 to −0.21) concentrations at 10 and 13 mo. Prediction equations developed using multiple regression explained 25% of the variation in pubertal age for EM heifers [IGF-1 concentrations at 8 mo (15%), leptin (4%) and glucose (3%) concentrations at 10 mo, and BW at 13 mo (3%)] and 30% for LM heifers [IGF-1 (18%) and glucose (5%) concentrations at 8 mo and insulin concentrations (4%) and lumbar fat thickness (3%) at 13 mo]. In relatively well-grown replacement beef heifers, BW was a weak predictor of pubertal status. Physiological measures, particularly IGF-1 concentrations at 8 mo of age, were superior.