The effect of age at weaning on the health status of bull calves in a feedlot

Incidence of morbidity and mortality in a feedlot were compared among 381 bull calves weaned one month apart (October 3 and November 1). The calves were 156 and 192 days old at weaning in the earlier and later weaned groups, respectively. Following an adjustment period, the calves were fed a mixed finishing diet containing 90% concentrate ad lib for 140 days in a feedlot. The rate of morbidity did not differ significantly between the two weaning groups. Sick calves in the earlier weaned group had a longer treatment period than those in the later weaned group (3.2 vs 1.4 days, p<0.05). Infections of the respiratory tract were the major cause of sickness and most of the respiratory infections occurred in the early stages of the feedlot period. The frequency of respiratory infections was higher among the earlier weaned calves compared with that in the later weaned group (p<0.01) indicating a higher susceptibility to these infections when calves were weaned at younger ages. Bloat was the second most common health problem among the bulls; however, its incidence did not differ between the two groups (p>0.05). The rate of mortality did not differ significantly between the two groups.     

Evaluations of genotypexenvironment interactions of beef bulls performance-tested in feedlot or pasture

Purebred Angus (n = 96) and Polled Hereford (n = 96) bull calves sired by bulls of either low or high yearling weight performance lines were assigned to either creep-fed or non-creep-fed treatment before weaning for four calf crops. For each breed, after weaning in the fall, half of the calves within each of the four groups were fed a high concentrate diet for 189 d after weaning in a feedlot and the remainder were put on winter temporary pastures (rye or ryegrass) followed by summer grazing on pearl millet and bermudagrass pastures for 329 d after weaning. Dependent variables were ADG for various intervals and the complete test period, weight, height and scrotal circumference at periodic intervals, and weight per day of age at regular intervals during the test. The model included breed, performance line, sire nested within breed and line, year, age of dam, preweaning treatment, postweaning treatment, and two- and three-factor interactions. Age of calf was included as a covariate for weight, height, and scrotal circumference measurements. Line and breed differences generally were significant for weight but not for height. The interaction of primary interest (line by preweaning treatment by postweaning treatment) was not significant. The high growth performance line gained faster than low growth performance line for all intervals and were 45 kg heavier by 189 d after weaning. Preweaning treatment did not affect postweaning ADG but did affect weight per day of age. Creep-fed calves were heavier than non-creep-fed calves and maintained this advantage during the postweaning treatment periods in both the feedlot and pasture. Both preweaning treatment groups had similar ADG after weaning. Angus were 23 kg heavier at weaning than Polled Herefords; however, breed weight means were similar by 16 mo of age. In summary, bulls from different selection lines for growth were identified in feedlot and pasture when adjustments were made for prior management effects. The lack of significant interactions in these data indicates that central test station data, appropriately adjusted, are useful for ranking bulls on genetic merit for growth in feedlot and on pasture.     

Use of trainer animals to improve performance and health of newly arrived feedlot calves

Four trials were conducted to determine the efficacy of using trainer animals to improve the health and performance of newly arrived feedlot calves. For all trials, trainer animals were given 3 wk to adapt to the feedlot before arrival of the feeder calves and initiation of the trials. Trainer animals were present with newly received feedlot calves for 14 d after arrival and then were removed from the pens for the remaining 14 d of the experiments. In Trial 1, trainer animals were six crossbred beef steers and six mature cull beef cows. Newly received calves were allotted to 18 pens with 10 calves/pen. Six pens contained a trainer steer and six pens contained a trainer cow. Similar procedures were used for the subsequent three trials, except 12 trainer cows and 24 pens were used, and in Trial 4 half of the calves were allotted to pasture paddocks for 14 d before placement in their feedlot pens. During wk 1 of Trial 1, calves with trainer cows and steers gained weight more rapidly (P < .10) than those without a trainer animal (1.12 vs .67 kg/d, respectively). During wk 2, this trend was reversed and overall gains did not differ (P > .20) among treatment groups. Morbidity was 16.7 for control calves, 28.3% for calves with trainer steers, and 8.3% for calves with trainer cows. Four of six trainer steers required antibiotic treatment for respiratory disease. On d 1, a greater (P < .05) percentage of calves in the trainer cow group (81.7%) were observed eating during the first 30 min after feeding compared with either the steer trainer group (60%) or the control group containing no trainer animal (48.3%). This trend continued on d 2 but was not evident on d 3 or 7. In Trial 2, overall gains were 10% greater (P < .06) and final BW was higher (P < .01) for calves with trainer cows than for those without trainers. Trainer cows resulted in a substantial reduction (P < .01) in calf morbidity compared with calves housed alone. In Trial 3, trainer cows did not improve performance or health of newly received calves. More (P < .07) calves with trainers than without were eating 5 min after feeding on d 1, 2, 4, and 8. In Trial 4, the presence of trainer cows the first 2 wk did not affect (P > .27) gains. However, calves placed on pasture after arrival had lower (P < .03) gains during wk 1 than those housed in the feedlot. Calves placed in pasture paddocks upon arrival had more than twice (P < .01) the incidence of morbidity of those placed directly in the feedlot. In these trials, trainer cows had a significant effect on eating behavior of newly received calves, but health and performance benefits were variable.     

Effect of competition on gain in feedlot bulls from Hereford selection lines

This study examined competition effects on ADG in the feedlot of 1,882 Hereford bulls representing 8 birth years from a selection experiment. Each year, 8 feedlot pens were used to feed bulls in groups, with 2 pens nested within each of the 4 selection lines. Gains were recorded for up to 8 periods of 28 d. Models for analyses included pen effects (fixed or random), fixed effects such as year and line, and random direct genetic, competition genetic (and in some analyses competition environmental), and environmental effects. Each pen mate as a competitor affected the records of all others in the pen. All lines traced to common foundation animals, so the numerator relationships among and within pens were the bases for separating direct and competition genetic effects and pen effects. For this population and pen conditions (average of 30 bulls per pen), the major results were 1) competition genetic effects seemed present for the first 28-d period but not for the following 7 periods; 2) models with pens considered as fixed effects could not separate variances and covariance due to direct and competition genetic effects; 3) models without competition effects had large estimates of the variance component due to pen effects for gain through 8 periods; and 4) models with genetic and environmental competition effects accounted for nearly all of the variance traditionally attributed to pen effects (even though estimates of the competition variance component were small, the estimates of pen variance were near zero).     

Grazing and feedlot performance of yearling stocker cattle integrated with spring- and fall-calving beef cows in a year-round grazing system

Effects of calving season and finishing system on forage and concentrate consumption and carcass characteristics of calves were compared. In each of 3 yr, two replicates of three growing and finishing systems were compared including 1) spring calves finished on a high-grain diet in a feedlot immediately post-weaning (WF); 2) spring calves backgrounded on a hay-corn gluten diet over winter for 179 +/- 18 d after weaning, grazed for 98 +/- 9 d in cool-season grass-legume pastures, and finished on a high-grain diet in a feedlot (SGF); and 3) fall calves backgrounded on a hay-corn gluten feed diet over winter for 69 +/- 31 d after weaning, grazed for 98 +/- 9 d in cool-season grass-legume pastures, and finished on a high-grain diet in a feedlot (FGF). During the grazing phase, calves on the SGF and FGF treatments were equally stocked with spring-calving cow-calf pairs before grazing by pregnant fall-calving cows in a first-last rotational stocking system at a rate of 1.9 standard livestock units/ha. As designed, retained calves in the FGF system spent 110 fewer days in the drylot during backgrounding than retained calves in the SGF system (P = 0.01), resulting in less feed provided during winter. A greater (P < 0.01) quantity of hay was fed to SGF calves after weaning over winter (1,305 kg of DM per calf) than the quantity fed to FGF calves (305 kg of DM per calf). Quantity of grain (including commercial starter) fed to SGF calves after weaning did not differ (P = 0.28) from that fed to FGF calves (126 vs. 55 kg of DM per calf); however, calves in the FGF system required 80 and 71 kg of DM per calf more concentrate to finish to an equivalent external fat thickness compared with SGF and WF calves, respectively (P = 0.02). Average daily gains in the feedlot were greater (P < 0.01) for SGF and FGF calves than for WF calves during all 3 yr. There were no differences (P = 0.69) in carcass quality grades among calves in all groups, but SGF calves had greater (P < 0.01) hot carcass weight and LM area measurements at slaughter than FGF or WF calves. Although calves in the FGF system were 25 kg lighter than calves in the WF system at slaughter (P = 0.03), and had a lower dressing percent (P = 0.03), other carcass characteristics did not differ between these two groups. Lower stored-feed requirements and similar carcass quality characteristics made retention of a fall calf crop advantageous over retention of a spring calf crop for use as stocker animals before finishing.     

Effect of oral meloxicam on health and performance of beef steers relative to bulls castrated on arrival at the feedlot

Castration in weaned calves is stressful and affects profitability by reducing ADG and increasing susceptibility to disease. This study evaluated the effect of meloxicam, a nonsteroidal anti-inflammatory drug (NSAID), on performance and health of calves received as steers compared with bull calves surgically castrated on arrival at the feedlot. British × Continental bulls (n = 145) and steers (n = 113; BW = 193 to 285 kg) were transported for 12 h in 3 truckloads (d 0), weighed, and randomly assigned to receive either lactose placebo (CONT; 1 mg/kg) or meloxicam (MEL; 1 mg/kg) suspended in water and administered per os, 24 h before castration. On d 1, bulls were surgically castrated (CAST) and steers were processed without castration (STR). Combinations of CONT/MEL and CAST/STR were allocated to 24 pens (6 pens per treatment) of 8 to 14 calves each. Pen was the experimental unit. Plasma meloxicam concentrations at the time of castration (d 1) were determined by HPLC-mass spectroscopy. Pen-level ADG, DMI, and G:F were estimated using BW obtained on d 0, 14, and 28 and weigh-back of feed. Individual animals were classified as sick based on a depression score of ≥2 on a 5-point scale and a rectal temperature of ≥39.8°C. On d 0, 1, and 14, calf chute temperament was evaluated using a 4-point scale. Data were analyzed using generalized linear mixed models and survival curve analyses. Castration reduced pen ADG (P < 0.001) and G:F (P < 0.001) from d 1 to 14, yet no effects (P > 0.45) were apparent by d 28. For all treatment groups, DMI increased with days on feed (P < 0.0001) but was less in CAST compared with STR calves (P < 0.016) throughout the study. From d 15 to 28, ADG increased (P = 0.0011) in CAST but not STR calves, and G:F decreased (P = 0.0004) in STR but not CAST calves. In CAST calves only, MEL treatment reduced the pen-level first pull rate (P = 0.04) and reduced bovine respiratory disease morbidity rate (P = 0.03). The frequency of chute escape behavior was greater on arrival and at castration in CAST vs. STR calves (P < 0.01) but not significantly different at d 14 (P = 0.22). Mean MEL concentrations at castration were no different between treated STR and CAST calves (P = 0.70). Meloxicam administration before castration in postweaning calves reduced the incidence of respiratory disease at the feedlot. These findings have implications for developing NSAID protocols for use in calves at castration with respect to addressing animal health and welfare concerns.     

Conglutinin and immunoconglutinin titers in stressed calves in a feedlot

OBJECTIVE: To determine whether increased conglutinin titers are evident in stressed calves that do not develop respiratory tract disease in feedlots, compared with respiratory tract disease, and to determine the increase in immunoconglutinin titers. ANIMALS: 101 mixed-breed beef calves. PROCEDURE: Calves were processed at 4 farms of origin and allowed to remain with their dams for another 100 days. Calves from each farm were brought to a centrally located order-buyer barn. In a feedlot, 101 calves were assigned to pens and observed daily for clinical signs of acute respiratory tract disease. When sick calves were detected, they were treated with antibiotics and isolated in a pen for 4 days. Conglutinin and immunoconglutinin titers were determined for all calves. RESULTS: During the 28-day study, 73 calves developed respiratory tract disease, whereas 28 calves remained healthy. Mean conglutinin titers differed significantly among calves from the 4 farms. Significant differences were not detected in conglutinin titers among calves on the basis of sex, morbidity, or vaccination status against Mannheimia haemolytica at each farm, the order-buyer barn, or the feedlot on days 8, 15, and 28 after arrival. Immunoconglutinin titers in calves differed significantly among farms and morbidity status. CONCLUSIONS AND CLINICAL RELEVANCE: Mean conglutinin titers in calves do not appear to be associated with the incidence of acute respiratory tract disease; however, increased immunoconglutinin titers appear to be associated with recovery of stressed calves from respiratory tract disease during the first 15 days after arrival in a feedlot.     

Effect of organic matter addition to the pen surface and pen cleaning frequency on nitrogen mass balance in open feedlots

Three finishing trials were conducted to determine the effects of dietary manipulation and management on N losses from open feedlots. In each experiment, 96 steers were assigned randomly to 12 nutrient balance pens. In Trial 1, calves were fed for 180 d during the winter/spring months; in Trial 2, yearlings were fed for 132 d in the summer. In Trials 1 and 2, N losses from pens were compared directly by adding OM to the pen surface or indirectly by feeding digestible ingredients designed to increase OM excretion. The dietary treatment (BRAN) included 30% corn bran (DM basis) replacing dry-rolled corn. Pens where OM was directly added received sawdust applications (SAWDUST) at a rate to match OM excretion from the BRAN diet. These two treatments were compared with a conventional, 75% dry-rolled corn diet (CON). Because CON and SAWDUST diets were identical, performance for both treatments was similar during Trials 1 and 2. The BRAN diet decreased (P < 0.10) gain efficiency during Trials 1 and 2 by 9.5% relative to CON. Fecal N excretion was greater (P < 0.01) for calves and yearlings when BRAN was fed compared with CON. Adding OM to the pen surface increased (P < 0.01) the amount of N in manure removed from pens and reduced (P < 0.10) N losses in Trial 1. Nitrogen losses were not significantly different among treatments in Trial 2. In Trial 3, calves were fed for 166 d during the winter/spring months. A 2 x 2 factorial design was used to evaluate pen cleaning frequency and diets similar to CON and BRAN. Pens were either cleaned monthly or once at the end of the feeding period. Daily DMI was greater (P = 0.01) and ADG was lower (P < 0.01) when cattle were fed BRAN compared with CON. Responses from all three trials indicate a negative effect of BRAN on gain efficiency. Dietary treatment and cleaning frequency interacted for N balance in the feedlot. Nitrogen losses decreased and manure N increased (P < 0.10) for cattle fed BRAN compared with CON when pens were cleaned monthly. Feeding BRAN did not affect total manure N, but resulted in higher N losses when pens were cleaned only once. For all trials, BRAN increased the amount of N remaining in composted manure. Adding OM to pen surfaces and/or cleaning pens more frequently may decrease N losses from open feedlot pens and from compost, although responses seem influenced by ambient temperature or season.     

Association between the existence of calves persistently infected with bovine viral diarrhea virus and commingling on pen morbidity in feedlot cattle

OBJECTIVE: To determine the association between the existence of a calf persistently infected (PI) with bovine viral diarrhea virus (BVDV) and pen morbidity. ANIMALS: 5,041 calves in 50 pens at a feedlot in Iowa. PROCEDURE: In a longitudinal study, ear notches were collected from cattle and tested for BVDV antigen. Characteristics of each pen (owner, sex, disease rate, number of groups, and source) were recorded. The association between the existence of a BVDV-PI calf and morbidity in each pen was examined. RESULTS: Commingling was associated with an increase in respiratory tract disease (odds ratio [OR], 3; 95% confidence interval [CI], 2.5 to 3.6). Ten BVDV-PI calves (10/5,041 [0.2%]) were identified in 8 of 50 pens. A BVDV-PI calf was associated with reduced pen-level respiratory tract disease (OR, 0.7; 95% CI, 0.5 to 0.9). Disease prevalence (mean +/- SD morbidity, 7.9 +/- 3.1%) was lowest in pens containing single-source cattle and a BVDV-PI calf (4 pens containing 302 cattle), compared with single-source cattle with no BVDV-PI calf (mean morbidity, 11.89 +/- 9.7%; 31 pens containing 3,093 cattle), commingled cattle with no BVDV-PI calf (mean morbidity, 29.3 +/- 16.22%; 11 pens containing 1,127 cattle), and commingled cattle with a BVDV-PI calf (mean morbidity, 28.6 +/- 10.1%; 4 pens containing 519 cattle). CONCLUSIONS AND CLINICAL RELEVANCE: Commingling was the greatest risk factor associated with morbidity in each pen. A BVDV-PI calf in a pen was not associated with increased disease prevalence in commingled groups.     

Effects of Prenatal Androgenization and Implantation on the Performance and Carcass Composition of Lactating Heifers in the Single-Calf Heifer System

Two experiments were conducted to evaluate feedlot performance of heifers and calves and the lactational characteristics and carcass composition and quality of heifers while in the single-calf heifer (SCH) system. In Exp. 1, 24 lactating Angus × Holstein heifers were slowly adapted to an 85% concentrate diet, and one-half of the heifers were implanted with Finaplix-H®, both at 11 wk postpartum. Heifer-calf pairs were then placed in feedlot pens, equipped with pinpointer feeding devices, and fed an 85% concentrate diet for 102 d. The control (C) and implanted (I) heifers had similar (P=0.27) daily gains and similar (P=0.30) DMI; however, I heifers consumed 8.9% less (P<0.05) DM as a percentage of BW. Pair efficiency of feed conversion tended to be higher (P<0.09) for I heifers than for C heifers. Hot carcass weight tended to be higher (P<0.10) for the I heifers. Ribeye area was 13% greater (P<0.05) and marbling score was 8.7% lower (P<0.01) for the I heifers than for the C heifers. In Exp. 2, 26 lactating Angus × Simmental heifers were used in the SCH system. Heifer adaptation to a high concentrate diet began 3 to 4 wk prepartum. Two to 3 d postpartum, 16 control (C) and 10 prenatally androgenized (PA) heifer-calf pairs were weighed, and eight C and five PA heifers were implanted with Synovex-H®. They were then placed in feedlot pens equipped with pinpointer feeding devices. By 1 wk postpartum, all heifers were adapted to an 85% concentrate diet and fed until they possessed approximately 1.1 cm s.c. fat cover over the 12th and 13th ribs. Heifers were slaughtered 12 h postweaning. The PA heifers tended to consume more (P<0.11) DM than C heifers. Gain:feed (G:F) was similar (P=0.35) for the C and PA heifers; however, the C heifers tended to have an improved (P<0.08) pair G:F. Heifer G:F and pair G:F were both similar (P=0.53) for the I and nonimplanted heifers. Most carcass measurements were unaffected by treatment; however, the I heifers tended to have higher marbling scores (P<0.07).     

Efficacy of parenteral antibiotics for disease prophylaxis in feedlot calves

Trimethoprim-sulfadoxine (TMPSDX) and two formulations of oxytetracycline (OTC) were examined for their prophylactic efficacy in feedlot calves when given by intramuscular injection on arrival at a large commercial feedlot. The study included 2,112 high-risk feeder calves that developed disease early in the feeding period. Both formulations of OTC reduced bovine respiratory disease morbidity during the first two weeks on feed and for the entire feeding period by 15-19% (p<0.05), and they also reduced all fatal fibrinous pneumonia by 67% and 84% (p<0.05). All three drugs significantly reduced all fatal disease in animals first treated during the second week on feed, but not for the overall feeding period. Oxytetracycline with 2-pyrrolidone reduced the incidence of all fatal disease by 44% (p<0.05) during the entire feeding period. The case fatality risk for calves first treated during the second week on feed was lower (p<0.05) in the TMPSDX group and in the OTC with polyvinyl-pyrrolidone group.     

Effect of intranasal vaccination against bovine enteric coronavirus on the occurrence of respiratory tract disease in a commercial backgrounding feedlot

OBJECTIVE: To measure antibody titers against bovine coronavirus (BCV), determine frequency of BCV in nasal swab specimens, and compare calves treated for bovine respiratory tract disease (BRD) between those given an intranasally administered vaccine and control calves. DESIGN: Randomized clinical trial. ANIMALS: 414 heifer calves. PROCEDURE: Intranasal BCV antigen concentration and antibody titer against BCV were measured on entry to a feedlot. Calves were randomly assigned to receive 3.0 mL of a modified-live virus vaccine against bovine enteric coronavirus and rotavirus or 3.0 mL of saline (0.9% NaCl) solution. Calves were confined to 1 of 2 pens, depending on vaccination status, for a minimum of 17 days of observation (range, 17 to 99). Selection of calves for treatment of BRD and scoring for severity of disease were done by veterinarians unaware of treatment status. RESULTS: Intranasal BCV (125/407 [31%]) and serum antibody titers > or = 20 against BCV (246/396 [62%]) were identified in calves entering the feedlot. Vaccination was associated with significant decrease in risk of treatment for BRD; intranasal BCV on entry to the feedlot was associated with increased risk of treatment. Univariate analysis revealed that control calves with intranasal BRD on entry to the feedlot and those with antibody titer < 20 were significantly more likely to be treated for BRD. CONCLUSIONS AND CLINICAL RELEVANCE: These data provide further evidence of an association between BCV and respiratory tract disease in feedlot calves. An intranasally administered vaccine appeared to reduce risk of treatment for BRD.     

Effect of zeranol on sexual development of crossbred bulls

Three groups of 1/2 Simmental X 1/4 Brahman X 1/4 Hereford bull calves were used during two different years to study effects of zeranol on sexual development. At 154 d of age, half the calves were implanted with 36 mg zeranol and half, not implanted, served as controls. Implanted calves were reimplanted at 90-d intervals throughout the trial (9 mo) each year. Trial 1 was conducted with 24 calves and Trial 2 was conducted the following year with 10 bulls. Twenty-four days after weaning (200 d of age) and at 28-d intervals thereafter, bulls in drylot in Trial 1 were weighted, scrotal circumference (SC) was measured and an ejaculate of semen was collected by electroejaculation to determine puberty. At these times, bulls were given 200 micrograms of GnRH i.m. and blood was collected at 0, 1, 2, 3, 4 and 5 h after GnRH. Serum concentrations of LH and testosterone (TEST) were determined. At slaughter, testis weight, length and circumference and pubertal status were recorded. Bulls implanted with zeranol had smaller SC than control bulls during the entire 9-mo period (P less than .0001). More control bulls reached puberty than did implanted bulls (82.4 vs 23.5%, respectively; P less than .001). Control bulls had larger testis measurements at slaughter (P less than .0001). Implants did not alter total weight gain or ADG (P greater than .10).(ABSTRACT TRUNCATED AT 250 WORDS)     

Testicular development, daily sperm production and epididymal sperm reserves in 15-mo-old Angus and Hereford bulls: effects of bull strain plus dietary energy

Bull calves (n = 143) were obtained from two strains of Angus and two strains of Hereford cattle for which replacements were selected on the basis of superior feedlot growth performance on either high- or medium-energy diets. From weaning to slaughter at 15 mo of age, bulls were fed either the high-energy (80% grain + 20% forage) or medium-energy diet (100% forage) corresponding to their strain. Bulls in high-energy diet groups had a greater (P less than .05) scrotal circumference at 12 mo, but not 15 mo of age, than bulls in medium-energy diet groups. Compared with Hereford bulls, Angus had greater (P less than .01) scrotal circumference (36.1 vs 33.9 cm) and greater (P less than .05) paired testes weight (570 vs 464 g) at 15 mo of age. Daily sperm production per gram testicular parenchyma (DSP/g) was affected by strain-diet (P less than .01) but not by breed. Bulls in medium-energy diet groups had 12% greater DSP/g than did high-energy diet bulls (17.4 X 10(6) vs 15.5 X 10(6)). Daily sperm production (DSP) was 9% and 30% greater (P less than .01) for medium-energy diet bulls in 1980 (8.2 X 10(9) vs 7.5 X 10(9)) and 1981 (8.0 X 10(9) vs 6.2 X 10(9)), respectively, compared with high-energy diet bulls. The effect (P less than .01) of breed on DSP was attributed to breed differences in paired testes weight.(ABSTRACT TRUNCATED AT 250 WORDS)     

Prophylactic medication of feedlot calves with tilmicosin

The parenteral administration to calves of the antibiotic tilmicosin either on arrival at a feedlot or 72 hours later was evaluated in a group of 308 steer calves. The calves were allotted to 24 pens so that there were eight replicates of the two medicated groups and eight replicates of the control group. The need for veterinary treatment was reduced significantly (P less than 0.05) during the first month of the feeding period in the two medicated groups. The medicated groups had an improved average daily weight gain (P less than 0.01) over the trial period compared with the non-medicated animals. This improved average daily gain by the medicated groups was not reduced when animals with respiratory disease were excluded from the calculations. The medicated groups also had an improved feed conversion efficiency (P less than 0.01) over the first 60 days of the feeding period compared with the non-medicated animals.     

Genotype x environment interactions for postweaning performance in crossbred calves grazing winter wheat pasture or dormant native prairie.

Data from 403 calves from Angus, Brahman, and reciprocal-cross cows sired by Polled Hereford bulls were used to evaluate the impact of postweaning backgrounding forages on postweaning BW, gains, and carcass traits. Calves were born (spring of 1991 through 1994) and reared on either endophyte-infected tall fescue or common bermudagrass pastures. After weaning, calves were transported 360 km to the Grazinglands Research Laboratory, west of El Reno, OK, and, within breed and preweaning forage, were assigned to one of the following winter stocker treatments: 1) winter wheat pasture or 2) dormant native prairie plus supplemental CP. In March, winter stocker treatments were ended and calves were grazed as a single group on cool-season grasses until early July (1992, 1993, and 1994) or late May (1995), when the feedlot phase began. In the feedlot, calves were fed a high concentrate diet for an average of 120 d until a backfat thickness of > 10 mm was reached. Calves were shipped in truck load lots to Amarillo, TX (350 km), for processing and collection of carcass data. Averaged over calf breed group, calves wintered on wheat pasture gained faster (P < 0.01) during the stocker phase (0.71 vs 0.43 kg); had heavier (P < 0.01) final feedlot weights (535 vs 512 kg); lower feedlot (P < 0.01) ADG (1.37 vs 1.53 kg); heavier (P < 0.01) carcass weights (337 vs 315 kg); larger (P < 0.01) longissimus muscle (84.9 vs 81.8 cm2); higher percentage (P < 0.01) of kidney, heart, and pelvic fat (2.32 vs 2.26); and higher (P < 0.01) dressing percentage (62.2 vs 61.3) than calves backgrounded on native prairie. Maternal heterosis for stocker ADG was evident in calves backgrounded on native prairie but not on winter wheat (P < 0.10), but the two environments were similar in maternal heterosis for feedlot ADG and carcass traits. Calves wintered on native prairie were restricted in growth and expressed compensatory gain during the feedlot phase but not during the spring stocker phase. Dormant native grasses can be used to winter stocker calves excess to the winter wheat pasture needs, but ownership of these calves would have to be retained through the feedlot phase to realize any advantage of built-in compensatory gain. Finally, these data suggest that expression of maternal heterosis for weight gain is more likely in calves backgrounded on native prairie than in calves grazed on winter wheat.     

Influence of grazing dormant native range or winter wheat pasture on subsequent finishing cattle performance, carcass characteristics, and ruminal metabolism

A winter grazing/feedlot performance experiment repeated over 2 yr (Exp. 1) and a metabolism experiment (Exp. 2) were conducted to evaluate effects of grazing dormant native range or irrigated winter wheat pasture on subsequent intake, feedlot performance, carcass characteristics, total-tract digestion of nutrients, and ruminal digesta kinetics in beef cattle. In Exp. 1, 30 (yr 1) or 67 (yr 2) English crossbred steers that had previously grazed native range (n = 38) or winter wheat (n = 59) for approximately 180 d were allotted randomly within previous treatment to feedlot pens (yr 1 native range = three pens [seven steers/pen], winter wheat = two pens [eight steers/pen]; yr 2 native range = three pens [eight steers/pen], winter wheat = four pens [10 or 11 steers/pen]). As expected, winter wheat steers had greater (P < 0.01) ADG while grazing than did native range steers. In contrast, feedlot ADG and gain efficiency were greater (P < 0.02) for native range steers than for winter wheat steers. Hot carcass weight, longissimus muscle area, and marbling score were greater (P < 0.01) for winter wheat steers than for native range steers. In contrast, 12th-rib fat depth (P < 0.64) and yield grade (P < 0.77) did not differ among treatments. In Exp. 2, eight ruminally cannulated steers that had previously grazed winter wheat (n = 4; initial BW = 407 +/- 12 kg) or native range (n = 4; initial BW = 293 +/- 23 kg) were used to determine intake, digesta kinetics, and total-tract digestion while being adapted to a 90% concentrate diet. The adaptation and diets used in Exp. 2 were consistent with those used in Exp. 1 and consisted of 70, 75, 80, and 85% concentrate diets, each fed for 5 d. As was similar for intact steers, restricted growth of cannulated native range steers during the winter grazing phase resulted in greater (P < 0.001) DMI (% of BW) and ADG (P < 0.04) compared with winter wheat steers. In addition, ruminal fill (P < 0.01) and total-tract OM digestibility (P < 0.02) were greater for native range than for winter wheat steers across the adaptation period. Greater digestibility by native range steers early in the finishing period might account for some of the compensatory gain response. Although greater performance was achieved by native range steers in the feedlot, grazing winter wheat before finishing resulted in fewer days on feed, increased hot carcass weight, and improved carcass merit.     

Efficacy of plastic pot scrubbers as a replacement for roughage in high-concentrate cattle diets.

Effects of plastic pot scrubbers on feedlot performance and ruminal metabolism of steers fed all-concentrate diets were determined. In Trial 1, 31 crossbred steers (means initial BW, 290 kg) were penned and fed individually. Treatments were 1) 85% concentrate-15% corn silage diet, 2) 100% concentrate diet, and 3) 100% concentrate diet + ruminal insertion of eight plastic pot scrubbers per steer. During the first 112 d of the trial, steer ADG did not differ (P greater than .10) due to treatment. From d 113 to 152, steers provided with pot scrubbers had 16% greater ADG than those fed the 100% concentrate diet without pot scrubbers (P = .18). In Trial 2, 78 crossbred steers (means initial BW, 315 kg) were penned individually and fed the diets used in Trial 1. Steers fed the 100% concentrate diet received zero, four or eight pot scrubbers. From d 113 to 167, steers provided with four or eight pot scrubbers or fed the 85% concentrate diet had greater (P less than .10) gains than steers fed the 100% concentrate diet without pot scrubbers. In Trial 3, 120 steers (means initial BW, 286 kg) were grouped in 12 pens and limit-fed an all-concentrate diet for 84 d. Sixty steers were provided with six pot scrubbers each. Performance was not affected (P greater than .10) by the use of pot scrubbers during the 84-d growing phase. During the subsequent 84-d finishing phase, half the steers receiving each treatment were switched to either an 85% concentrate-15% corn silage or an 100% concentrate diet offered for ad libitum consumption.(ABSTRACT TRUNCATED AT 250 WORDS)     

Behavior of feedlot cattle affects voluntary oral and physical interactions with manila ropes

Providing cattle with access to manila ropes has shown promise as a means of monitoring zoonotic bacteria in pens of feedlot cattle. Studies were conducted to determine the impacts of climate, animal age and BW, number of ropes, duration of placement, and previous rope access on efficacy of ropes as a sampling technique for feedlot cattle. Eight pens of commercial finishing cattle (average 196 +/- 19 animals per pen, 536.7 +/- 22.9 kg) were monitored for a total of 7 d in October of 2003 (commercial study). One rope was tied on the pen railing adjacent to the feed bunk in each pen, and the proportion of animals within the pen contacting the rope was recorded. In a second study, 80 cattle housed in 8 pens (each 270 m(2); 10 animals/pen) were monitored for 1 d/wk using video cameras (video study). Video images were collected for 8 consecutive weeks immediately after weaning (average BW = 252.7 +/- 30.6 kg) and for 6 wk at the end of the finishing period (average BW 541.2 +/- 42.8 kg). In the commercial study, the proportion of cattle contacting the rope per pen increased over the first 6 h to 70% (P < 0.05), although approximately 50% of the cattle contacted the rope within 2 h after placement. A 40 degrees C reduction in ambient temperature on d 6 caused cattle to cease contact with the ropes, although after 6 d of acclimation to reduced ambient temperature, interactions with ropes recovered to 47% of previous values. In the video study, weaned calves required 2 wk of acclimation to the feedlot environment before contact with the rope was maximized. Contact with the rope was most frequent 3 to 8 wk after entry into the feedlot and decreased (P < 0.05) as cattle approached slaughter weight. It is likely that ropes will be most effective at monitoring zoonotic bacteria in pens of cattle during the mid-feeding period where the pen environment is stable and cattle are inquisitive but not highly reactive.     

The effect of bovine viral diarrhea virus infections on health and performance of feedlot cattle

The aim of this study was to investigate the effect of bovine viral diarrhea virus (BVDV) infections (unapparent acute infections and persistent infections) on the overall health and performance of feedlot cattle. Calves from 25 pens (7132 calves) were enrolled in the study. Overall and infectious disease mortality rates were significantly higher (P < 0.05) in pens categorized at arrival as positive for type I BVDV and lower in pens that were positive for type II BVDV than in negative pens. Mortality attributed to BVDV infection or enteritis was significantly more common (P < 0.05) in the pens containing persistently infected (PI) calves than in pens not containing PI calves (non-PI pens). There were no statistically detectable (P > or = 0.05) differences in morbidity, overall mortality, average daily gain, or the dry matter intake to gain ratio between PI and non-PI pens. Although type-I BVDV infections in feedlots appear to contribute to higher mortality rates, the presence of PI calves alone does not appear to have a strong impact on pen-level animal health and feedlot performance.