Newly arrived feedlot cattle are subjected to multiple stressors and exposed to pathogens as they travel through marketing channels between the ranch of origin and feedlot.1 The incidence of BRD, the most important and costly disease of feedlot cattle, is associated with these stressors. A reported morbidity rate of 75% and mortality rate of 50% for feedlot cattle can be attributed to BRD,2 and results of surveys3,4 indicate that despite improvements in vaccines and antimicrobial drugs, BRD mortality rates are increasing. In addition to costs associated with treatments and death of affected cattle, BRD may have a greater economic impact as a result of losses in animal performance and carcass quality.5–8 Therefore, identifying better methods to classify the BRD risk of cattle and predict and diagnose BRD events is important to the cattle industry.
Acute-phase proteins are synthesized by the liver as a portion of the immune system's acute response to infection.9 The APP haptoglobin has been investigated as a biomarker that can be used to discriminate between acute and chronic infection in cattle10 and to monitor the response to antimicrobial treatment.11 Haptoglobin concentrations of beef calves determined at the time of arrival at a feedlot have been correlated with the number of eventual treatments because of signs of BRD.12,13 The purpose of the study reported here was to evaluate the effect of serum haptoglobin concentration at the time of arrival at a feedlot on subsequent animal performance and BRD morbidity and mortality rates.
Materials and Methods
Sample—Beef calves arriving at feedlots were used in 2 experiments. All procedures were approved by the Oklahoma State University Institutional Animal Care and Use Committee.
Experiment 1
Animals—Heifer calves (n = 360; mean ± SD initial BW, 241 ± 16.6 kg) that were British and British-Continental crossbreeds were assembled by an order buyera in Kentucky. Calves were purchased at the West Kentucky Livestock Market and at other regional auction markets. As each truckload lot of 90 calves was assembled, each calf received an individually numbered tag in the left ear. In addition, a blood sample was collected in evacuated tubesb via jugular venipuncture for serum harvest. After blood collection, tubes were held on ice prior to and during transport to the laboratory for processing. Prior to transport, calves were maintained (approx 4 to 48 hours) in covered holding pens (loads 1, 2, and 4) or an open grass paddock (load 3) and given ad libitum access to long-stemmed grass hay and water. In separate lots of 180 (ie, 2 truckloads/lot), calves were transported 957 km to a research feedlot.c Calves were transported on September 11 and 13, 2007, respectively, for a 63-day preconditioning study.
Preconditioning phase—After arrival at the feedlot (day of arrival = day −1), calves were allowed to rest for 5 to 6 hours without access to feed or water prior to initial processing, which consisted of measurement of BW, collection of a skin sample (ear notch) for the detection of animals persistently infected with BVDV by use of immunohistochemical analysis, d and collection of a blood sample via jugular venipuncture for serum harvest.b Blood samples were transported to our laboratory, where serum was harvested and haptoglobin concentration was measured by use of a bovine ELISA.e Blood samples were allowed to clot at approximately 21°C for approximately 3 hours. Blood samples were then centrifuged at 3,000 × g and 4°C for 20 minutes. Samples were diluted 1:10,000 in tris-buffered saline (0.9% NaCl) solution with Tween 20f at a pH of 4.0 prior to analysis. The intra-assay and interassay coefficients of variation were < 5%.
Calves in lot 1 were stratified on the basis of the range and magnitude of values for serum haptoglobin concentration at the time of arrival at the feedlot. Consideration also was given to the pens available for the experiment (6 pens/arrival lot). Calves were classified as having a low (< 1.0 μg/mL), medium (1.0 to 3.0 μg/mL), or high (> 3.0 μg/mL) serum haptoglobin concentration. Within haptoglobin groups, calves were stratified on the basis of BW at the time of arrival and were assigned to 1 of 2 pens/group (6 pens for lot 1) by use of a computer-generated randomization table.g Thirty-three, 31, and 25 calves were classified as having low, medium, and high serum haptoglobin concentrations, respectively, and were assigned to the 6 pens. The same cutoff serum haptoglobin concentrations were used in both lots 1 and 2. However, more calves were classified as having a high concentration than a medium or low concentration; therefore, 3 pens were used for calves with a high concentration (34 or 35 calves/pen), 2 for calves with a medium concentration (18 calves/pen), and 1 for calves with a low concentration (20 calves/pen). Of the original 360 calves, 337 were used in the experiment. One calf was excluded from the experiment because it was persistently infected with BVDV, whereas the remaining calves were excluded because serum samples obtained at the time of arrival at the feedlot were misidentified or additional (repeated) haptoglobin analysis was required but could not be completed prior to routine processing after arrival at the feedlot.
Adjacent pens shared an automatic water basin, and care was taken to segregate haptoglobin groups. Calves were assigned to pens such that no calves with low and high serum haptoglobin concentrations were in adjacent pens or shared automatic water basins. Blood samples were collectedb for serum haptoglobin concentration determination, and calves were weighed on days 7, 14, 21, and 63 and at any time that antimicrobial treatment was administered for clinical signs of BRD. On day 62, only 50% of the previous day's allotment of feed was delivered and automatic water basins were turned off at 5 pm; BW was measured on day 63.
Processing—The morning after arrival (day 0), all calves were processed and sorted into assigned pens. Processing consisted of recording BW of each calf; vaccination against bovine herpesvirus-1, BVDV (types 1 and 2), bovine parainfluenza-3, bovine respiratory syncytial virus,h and clostridial pathogensi; and deworming with moxidectin.j Calves in experiment 1 each received a growth-promoting implant that contained estradiol and trenbolone acetate.k Calves received a booster vaccinationh against respiratory viral pathogens on day 7.
Feeding management—The open dirt pens measured 12.2 × 30.5 m and had a 12.2-m concrete feed bunk. Calves were fed twice daily (approx 7 am and 1:30 pm) a 65%-concentrate receiving-growing ration formulated to meet or exceed nutrient requirements.14 During the interval between arrival at the feedlot and processing and for 7 days after processing, long-stemmed prairie hay was offered in the feed bunk in addition to the mixed ration. The amount of feed delivered was such that < 0.22 kg of feed/calf remained each morning.
Assessment and treatment of sick calves—Each morning, trained personnel evaluated the calves for clinical signs of BRD. The evaluation procedures used were standard for the facility and adapted from an assessment system.15,1 Specific subjective signs of BRD included signs of depression (hanging head, sunken or glazed eyes, slow movement, arched back, difficulty in standing, knuckling or dragging toes when walking, and stumbling), abnormal appetite (completely inappetent, eating less than or with less aggression than penmates, gaunt, or obvious BW loss), and signs of respiratory problems (labored breathing, extended head and neck, and noise when breathing). On the basis of detection of and the degree of one or more of these clinical signs, the trained personnel assigned a severity score from 1 to 4, where 1 = mild, 2 = moderate, 3 = severe, and 4 = moribund (calves would not stand without assistance or stood and walked only a short distance before again becoming recumbent). After a severity score was assigned, calves were moved from the pen to the processing chute for measurement of rectal temperature.m When rectal temperature was < 40°C and severity score was < 3, no antimicrobial treatment was administered. Calves with a rectal temperature ≥ 40°C were administered antimicrobial treatment. In addition, calves with a severity score of 3 or 4 were administered antimicrobial treatment regardless of the rectal temperature. Following evaluation or treatment, all calves were returned to their pens. Throughout the experiment, the investigators were not aware of the serum haptoglobin concentration group of each calf and whether antimicrobial treatments were administered.
Each calf could receive a maximum of 3 antimicrobial treatments. All doses were calculated by rounding the calf's current BW up to the nearest 11.3 kg. All pharmaceuticals were administered in accordance with the manufacturer's label directions. The first treatment was administered in the left side of the neck in accordance with beef quality-assurance guidelines, and subsequent injections were administered in alternating sides of the neck. The first treatment consisted of 10 mg of tilmicosinn/kg. After tilmicosin treatment, calves were allotted a 120-hour posttreatment interval, except for calves with a severity score of 3 or 4, for which the posttreatment interval was only 72 hours. After the described posttreatment interval, calves that required a second treatment received 10 mg of enrofloxacino/kg. After a 48-hour posttreatment interval, calves that required a third treatment received ceftiofur hydrochloride,p which consisted of 2 doses (2.2 mg/kg) administered 48 hours apart.
Calves defined as chronically ill were removed from the pens; calves were not eligible for removal on the basis of being chronically ill before day 21. To be defined as chronically ill, a calf must have been administered all 3 antimicrobial treatments in accordance with the protocol, with a 48-hour posttreatment interval following the last dose of ceftiofur. In addition, the calf must have been assigned a severity score of 3 or 4 on the day of removal and had a net loss of BW over at least a 21-day period. Any calf that died or was euthanized was submitted to the Oklahoma Animal Disease Diagnostic Laboratory for postmortem examination.
Performance during the finishing phase and carcass characteristics—At the beginning of the finishing phase, calves received a second growth-promoting implant that contained trenbolone acetate and estradiolq and were gradually transitioned to a 94%-concentrate finishing diet. The diet was formulated to meet or exceed nutrient requirements14 and contained 2.09 and 1.36 Mcal of net energy for maintenance and gain, respectively, and 156 g of crude protein/kg of dry matter. Initial and final BWs were obtained prior to the start of the finishing period and 1 day prior to slaughter. The number of days calves were in the feedlot during the finishing phase was 139, 152, 174, and 189, respectively, for the 4 lots. Calves were transported 478 km to a commercial slaughter plant, where trained personnel from Oklahoma State University collected carcass data, including HCW, longissimus muscle area, marbling score, and estimated kidney, pelvic, heart, and 12th-rib fat thickness. Yield grade was calculated from HCW longissimus muscle area, 12th-rib fat thickness, and kidney, pelvic, and heart fat thickness. Quality grade was determined from marbling score and maturity data.
Determination of lung lesions—Lungs from 189 calves were evaluated in the slaughter plant for the presence and severity of pulmonary lesions as evidence of bronchopneumonia. The scoring procedure used was adapted from a published system.16 Lungs were visually observed and briefly palpated. For each side (right and left), the presence and severity (0, 1, 2, or 3) of lesions were recorded, along with the absence or presence of interlobular adhesions or missing lobes indicative of thoracic adhesions. Overall evidence of bronchopneumonia (present vs absent) was based on the presence of a lesion, adhesion, or missing lobe for each side and for both lungs.
Experiment 2
Animals—Steer and bull calves (mean ± SD BW, 241 ± 24.4 kg), primarily British and British-Continental crossbreeds, were purchased at an Oklahoma auction marketr in 2 lots (n = 128 and 288 calves, respectively) on September 17 and October 1, 2007, and then transported 107 km to the research feedlotc for a 42-day preconditioning study. At arrival at the feedlot (day −1), calves were allowed to rest for approximately 1 hour without access to feed or water. Then, each calf was identified by insertion of a sequentially numbered tag in the left ear. The BW was measured, and sex (steer or bull) was determined. In addition, a skin sample (ear notch) was collected for the determination of cattle persistently infected with BVDV by use of immuno-histochemical analysis.d In addition, a blood sampleb was collected from each calf via jugular venipuncture for determination of the serum haptoglobin concentration.
Similar to experiment 1, calves were stratified on the basis of serum haptoglobin concentration at the time of arrival at the feedlot. However, because of the author's experience with similar calves (purchased at the same auction by the same buyer) in previous years, we expected the clinical BRD morbidity rate to range from < 10% to 50%. Combining this experience, difference in sex, distance of transport, and the measured haptoglobin concentrations (which were lower than those measured in experiment 1), we decided to use different haptoglobin values for segregation of calves in experiment 2 than had been used for the calves in experiment 1. Calves in experiment 2 were assigned to groups on the basis that they had or did not have detectable serum haptoglobin concentrations at the time of arrival. Bulls (n = 27) were not included in the experiment because of the potential for dramatic increases in serum haptoglobin concentration as a part of the inflammatory response associated with surgical castration during processing after arrival at the feedlot. In addition, 120 calves in each group in lot 2 were randomly selected for inclusion in the experiment because of constraints in pen space. Therefore, 345 calves (initial mean ± SD BW, 240 ± 22.8 kg) were enrolled in the experiment. Six pens of calves that had no detectable serum concentration of haptoglobin (23, 24, or 30 calves/pen; n = 167 calves) and 6 pens of calves in which serum haptoglobin was detected (29 or 30 calves/pen; 178 calves) were used. Similar to experiment 1, calves that had no detectable serum haptoglobin concentration and calves with a detectable serum haptoglobin concentration did not share automatic water basins. Calves were weighed prior to feeding on days 7, 14, and 21. On day 41, only 50% of the previous day's allotment of feed was provided and water basins were turned off at 5 pm; BW was measured on day 42.
Performance during the preconditioning phase, feeding management, and assessment and treatment of sick calves were conducted in the same manner in experiment 2 as in experiment 1, except calves in experiment 2 did not receive a growth-promoting implant. Data on the performance during the finishing phase, carcass characteristics, and lung lesions were not obtained for the calves in experiment 2.
Statistical analysis—Data from each experiment were analyzed separately as randomized complete block designs by use of a commercially available software program.s For all preconditioning phase performance variables and subjective and objective signs of morbidity, pen was the experimental unit. For performance data, the model contained the serum haptoglobin concentration group at the time of arrival to the feedlot as a fixed effect and arrival lot as a random effect. Similarly, mean serum haptoglobin concentrations measured at the time of treatment because of signs of BRD were calculated and analyzed. Haptoglobin concentrations from the samples obtained prior to transport to the feedlot (day −2) and on days 0, 7, 14, 21, 42, and 63 were analyzed as a randomized complete block design with repeated measures.s Animal nested within pen was considered the experimental unit. The model statement contained the fixed effects of haptoglobin concentration, day, and the haptoglobin group-by-day interaction, and the random statement included arrival lot, pen, and animal nested within pen. The model was subjected to multiple covariance structures, and the best-fit model was selected to contain the covariance structure that yielded the smaller Akaike and Schwarz-Bayesian criteria on the basis of their −2 residual log-likelihood. A first-order antedependence covariance structure was used for the analysis. Because the haptoglobin group-by-day interaction was significant (P < 0.001), interaction least squares means were separated for each day.s
Nonparametric data (morbidity and mortality rates) were analyzed as binomially distributed variables by use of the model. Frequencies were estimated,s and odds ratios were used to compare calves that had medium or high serum haptoglobin concentrations with those that had a low serum haptoglobin concentration (experiment 1) or calves that had a detectable serum haptoglobin with those that did not have a detectable serum haptoglobin concentration (experiment 2). For experiment 1, orthogonal polynomial contrasts were used to test the linear and quadratic effects of serum haptoglobin concentration at the time of arrival to the feedlot.
The BW, ADG, carcass characteristics, and lung lesions for the finishing phase in experiment 1 were analyzed as a randomized complete block design. Calf was considered the experimental unit, and serum haptoglobin concentration group at the time of arrival was the fixed effect. Least squares means were separated with a Fisher protected least significant difference test. For all analyses, denominator df was corrected by use of the Kenward-Rogers test.s Least squares means were considered significantly different at values of P ≤ 0.05.
Results
Data were analyzed and results reported for both experiments.
Experiment 1
Serum haptoglobin concentration—Mean ± SD serum haptoglobin concentration for all calves at time of arrival to the feedlot was 4.22 ± 3.78 μg/mL. After allocation to the respective serum haptoglobin concentration group at the time of arrival, serum haptoglobin concentration was highest for the high group, intermediate for the medium group, and lowest for the low group (Table 1). When considered for the entire experiment, serum haptoglobin concentration was significantly (P < 0.001) affected by serum haptoglobin concentration group, time, and the serum haptoglobin concentration group-by-time interaction. Least squares means were determined for the serum haptoglobin concentration group-by-time interaction. Serum haptoglobin concentrations were significantly (P < 0.001) lower in samples obtained from calves prior to transport from the order-buyer facility than in samples obtained at the time of arrival at the feedlot. Peak serum haptoglobin concentration was detected in samples obtained at arrival for calves in the medium and high groups and on day 7 for calves in the low group. By day 7, serum haptoglobin concentrations did not differ significantly (P = 0.299) among the 3 groups. Mean serum haptoglobin concentrations decreased from days 14 to 63; however, they remained higher (but not significantly [P = 0.095] different) for the high group than for the low and medium groups on day 14 and higher (but not significantly [P ≤ 0.055] different) for the high and medium groups than for the low group on days 21 and 63.
Mean serum haptoglobin concentration (mg/mL) of calves in experiment 1 grouped on the basis of the serum haptoglobin concentration (low, ≤ 1.0 μg/mL; medium, 1.0 to 3.0 μg/mL; or high, > 3.0 μg/mL) at the time of arrival to a feedlot.
| Day | Low (n = 3 pens) | Medium (n = 4 pens) | High (n = 5 pens) | SEM |
|---|---|---|---|---|
| −2* | 0.18a,b | 0.08a | 0.34b | 0.073 |
| 0 | 0.60a | 1.90a | 7.80b | 0.203 |
| 7 | 1.87 | 1.95 | 2.32 | 0.234 |
| 14 | 1.72 | 1.66 | 2.30 | 0.274 |
| 21 | 0.89 | 1.37 | 1.55 | 0.220 |
| 42 | 0.41 | 0.73 | 0.69 | 0.161 |
| 63 | 0.02 | 0.06 | 0.21 | 0.089 |
Calves arrived at the feedlot on day −1 and were allowed a rest period before processing. Significant (P < 0.001) effects were detected for haptoglobin group, day, and the haptoglobin group-by-day interaction.
Samples on day −2 were obtained at the order-buyer facility prior to transport of calves to the feedlot.
Within a row, means with different superscript letters differ significantly (P ≤ 0.05).
Performance during the preconditioning phase—At arrival to the feedlot, calves in the medium group had a significantly (P = 0.002) lower BW, compared with BW of calves in the low and high groups (Table 2). However, by day 7, BW did not differ significantly (P = 0.499) among the 3 groups, and no significant (P ≥ 0.266) differences in BW were detected among the 3 groups throughout the remainder of the experiment. The ADG was significantly (P = 0.011) higher for the low and medium groups, compared with ADG for the high group, from days 0 to 7. For days 8 to 14, 1 to 21, 22 to 42, and 43 to 63 and the entire experiment, ADG did not differ significantly (P ≥ 0.183) among the 3 groups. The DMI decreased significantly (P = 0.028) from days 1 to 7 and 1 to 21 as serum haptoglobin concentration of calves at the time of arrival to the feedlot increased from < 1.0 μg/mL to > 3.0 μg/mL. The ratio of ADG to DMI did not differ significantly (P = 0.965) during the 63-day period. During the first week of the experiment, calves in the medium group were significantly (P = 0.003) more efficient at utilization of DMI for weight gain, compared with the efficiency of calves in the high group. However, during the third week after arrival (days 15 to 21), calves in the high group were significantly (P = 0.039) more efficient than were calves in the medium and low groups.
Mean values for BW, ADG, DMI, and the ratio of ADG to DMI in calves allotted to 3 groups on the basis of the serum haptoglobin concentration at the time of arrival to a feedlot in experiment 1.
| Variable | Day | Low (n = 3 pens) | Medium (n = 4 pens) | High (n = 5 pens) | SEM | P value* |
|---|---|---|---|---|---|---|
| BW (kg) | 0 | 242a | 239b | 242a | 0.59 | 0.002 |
| 7 | 246 | 244 | 244 | 1.24 | 0.499 | |
| 14 | 250 | 247 | 245 | 5.46 | 0.266 | |
| 21 | 259 | 255 | 256 | 4.87 | 0.609 | |
| 42 | 286 | 287 | 286 | 4.21 | 0.983 | |
| 63 | 322 | 316 | 314 | 5.14 | 0.344 | |
| ADG (kg/d) | 1–7 | 0.58a | 0.77a | 0.17b | 0.134 | 0.011 |
| 8–14 | 0.70 | 0.46 | 0.22 | 0.784 | 0.194 | |
| 15–21 | 1.21 | 1.15 | 1.47 | 0.185 | 0.291 | |
| 1–21 | 0.81 | 0.80 | 0.63 | 0.224 | 0.287 | |
| 22–42 | 1.33 | 1.47 | 1.42 | 0.143 | 0.699 | |
| 43–63 | 1.69 | 1.42 | 1.33 | 0.181 | 0.339 | |
| 1–63 | 1.27 | 1.23 | 1.13 | 0.078 | 0.183 | |
| DMI (kg/d) | 1–7 | 3.37a | 3.30a | 2.74b | 0.303 | 0.005 |
| 8–14 | 4.18 | 3.80 | 3.41 | 0.471 | 0.066 | |
| 15–21 | 5.48 | 4.98 | 4.70 | 0.519 | 0.086 | |
| 1–21 | 4.33a | 4.02a,b | 3.61b | 0.420 | 0.028 | |
| 22–42 | 7.32 | 7.19 | 6.69 | 0.687 | 0.195 | |
| 43–63 | 8.24 | 8.30 | 7.73 | 0.418 | 0.363 | |
| 1–63 | 6.58 | 6.39 | 5.89 | 0.496 | 0.111 | |
| DMI (percentage of BW) | 1–7 | 1.38a | 1.36a | 1.13b | 0.124 | 0.003 |
| 8–14 | 1.69a | 1.54a,b | 1.39b | 0.174 | 0.054 | |
| 15–21 | 2.15 | 1.97 | 1.87 | 0.159 | 0.067 | |
| 1–21 | 1.73a | 1.62a | 1.45b | 0.153 | 0.015 | |
| 22–42 | 2.69 | 2.65 | 2.47 | 0.216 | 0.131 | |
| 43–63 | 2.71 | 2.75 | 2.58 | 0.107 | 0.323 | |
| 1–63 | 2.34 | 2.30 | 2.12 | 0.159 | 0.079 | |
| Ratio of ADG to DMI | 1–7 | 0.169a,b | 0.235a | 0.061b | 0.049 | 0.032 |
| 8–14 | 0.151 | 0.092 | 0.047 | 0.195 | 0.134 | |
| 15–21 | 0.217a | 0.238a | 0.316b | 0.050 | 0.039 | |
| 1–21 | 0.181 | 0.193 | 0.173 | 0.038 | 0.672 | |
| 22–42 | 0.182 | 0.212 | 0.214 | 0.035 | 0.448 | |
| 43–63 | 0.206 | 0.170 | 0.174 | 0.038 | 0.523 | |
| 1–63 | 0.194 | 0.193 | 0.192 | 0.008 | 0.965 |
Values were considered significant at P ≤ 0.05.
See Table 1 for remainder of key.
Assessment and treatment of sick calves—Overall, BRD morbidity rate was 57.6% (194/337 calves) and mortality rate was 8.6% (29/337 calves). Total morbidity rate typically increased (but not significantly [P = 0.077]) as the serum haptoglobin concentration at the time of arrival to the feedlot increased (Table 3). Compared with the results for the low group, the odds ratio that a calf in the medium and high group was likely to require treatment was 1.48 and 2.05, respectively. However, there were no significant (P ≥ 0.533) differences among the 3 groups with regard to the distribution of calves that required only 1 or 2 treatments because of BRD. Significantly (P = 0.021) more calves in the medium and high groups required 3 treatments, compared with the number of calves in the low group that required 3 treatments. The odds that a calf in the medium and high groups would require 3 treatments were 188% and 336%, respectively, as great as the odds that a calf in the low group would require 3 treatments. However, there was not a significant (P = 0.517) difference in the number of calves that were classified as chronically ill among the 3 groups. Although numerically higher for the medium and high groups than for the low group, there were no significant (P = 0.659) differences in total mortality or case fatality rates among the 3 groups.
Mean values for morbidity and mortality rates and treatments for calves allotted to pens on the basis of serum haptoglobin concentration at the time of arrival at a feedlot in experiment 1.
| Odds ratio* | ||||||||
|---|---|---|---|---|---|---|---|---|
| Variable | Low | Medium | High | SEM | P value† | Medium | High | |
| Total morbidity rate (%)‡ | 48.26 | 57.99 | 65.65 | 11.75 | 0.077 | 1.48 | 2.05 | |
| Calves requiring ≥ 2 treatments (%)§ | 47.07 | 57.04 | 62.34 | 8.70 | 0.291 | 1.49 | 1.86 | |
| Calves requiring 3 treatments (%) | 10.43a | 25.09b | 28.12b | 8.82 | 0.021 | 2.88 | 3.36 | |
| Calves treated 1 time (%) | 29.40 | 25.66 | 32.45 | 5.74 | 0.533 | 0.83 | 1.15 | |
| Calves treated 2 times (%) | 10.47 | 11.22 | 11.11 | 3.19 | 0.984 | 1.08 | 1.07 | |
| Calves treated 3 times (%) ∥ | 5.13a | 10.15a,b | 16.27b | 7.79 | 0.054 | 2.09 | 3.60 | |
| Chronically ill (%) | 1.84 | 4.42 | 3.49 | 2.95 | 0.517 | 2.46 | 1.93 | |
| Calves chronically ill/calves treated 3 times (%) | 18.18 | 18.52 | 12.50 | 7.48 | 0.811 | 1.02 | 0.64 | |
| Total mortality rate (%) ¶ | 5.81 | 9.18 | 9.80 | 2.92 | 0.682 | 1.64 | 1.76 | |
| Case fatality rate (%) | 8.69 | 13.56 | 15.79 | 4.45 | 0.659 | 1.65 | 1.96 | |
The low serum haptoglobin concentration group is the referent group for comparison.
Values were considered significant at P ≤ 0.05.
Percentage of calves treated at least 1 time because of BRD.
Percentage of calves that required 2 or more treatments because of BRD.
Excluded calves defined as chronically ill.
Percentage of deaths attributed to BRD.
See Table 1 for remainder of key.
The number of days that calves were in the feedlot prior to first treatment not differ significantly (P = 0.360) among the 3 serum haptoglobin concentration groups (Table 4). However, the number of days that calves were in the feedlot prior to the second treatment was significantly (P = 0.048) lower for the high group (10.5 days) than for the low (13.0 days) and medium (13.6 days) groups. The number of days that calves were in the feedlot prior to the third treatment did not differ significantly (P = 0.112) as serum haptoglobin concentration at the time of arrival increased.
Mean values for number of days until treatment and subjective severity score, rectal temperature, and serum haptoglobin concentration of calves at the time of treatment because of BRD in experiment 1.
| Variable | Low (n = 3 pens) | Medium (n = 4 pens) | High (n = 5 pens) | SEM | P value* |
|---|---|---|---|---|---|
| First treatment | |||||
| Day of treatment | 5.8 | 6.7 | 5.1 | 0.93 | 0.360 |
| Severity score | 1.4 | 1.4 | 1.4 | 0.15 | 0.819 |
| Rectal temperature (°C) | 40.97 | 41.15 | 41.20 | 0.072 | 0.082 |
| Serum haptoglobin concentration (mg/mL) | 3.17 | 3.18 | 3.50 | 0.365 | 0.685 |
| Second treatment | |||||
| Day of treatment | 13.0a | 13.6a | 10.5b | 0.96 | 0.048 |
| Severity score | 1.6 | 1.9 | 2.0 | 0.32 | 0.236 |
| Rectal temperature (°C) | 40.98 | 40.95 | 40.97 | 0.107 | 0.979 |
| Serum haptoglobin concentration (mg/mL) | 3.37 | 3.13 | 3.24 | 0.510 | 0.942 |
| Third treatment | |||||
| Day of treatment | 24.1 | 17.5 | 17.2 | 2.49 | 0.112 |
| Severity score | 2.0 | 1.8 | 1.7 | 0.14 | 0.160 |
| Rectal temperature (°C) | 40.70 | 40.84 | 40.72 | 0.149 | 0.675 |
| Serum haptoglobin concentration (mg/mL) | 3.10 | 2.42 | 3.57 | 0.994 | 0.288 |
| Day chronically ill calves removed | 39.3 | 25.7 | 29.9 | 5.84 | 0.255 |
| Day of death | 26.3 | 27.7 | 35.8 | 8.33 | 0.607 |
Severity of illness was scored as follows: 1 = mild, 2 = moderate, 3 = severe, and 4 = moribund.
Values were considered significant at P ≤ 0.05.
See Table 1 for remainder of key.
When considering measured variables for calves that required treatment because of BRD, there was not a significant (P ≥ 0.288) difference in serum haptoglobin concentration among the low, medium, and high groups at the time of the first, second, or third treatment. Rectal temperature at the time of the first treatment did not differ significantly (P = 0.082) among the low (40.97°C), medium (41.15°C), and high (41.20°C) groups. Rectal temperature also did not differ significantly (P ≥ 0.675) among haptoglobin groups at the time of the second and third treatments. The subjective severity score assigned at the time of the treatments did not differ significantly (P ≥ 0.160) among the 3 groups.
Performance during the finishing phase and carcass characteristics—Variables that measured performance during the finishing phase and carcass characteristics did not differ significantly (P ≥ 0.110) among the 3 serum haptoglobin concentration groups (Table 5).
Mean values for BW at the end of the finishing period, ADG, carcass characteristics, and prevalence of pulmonary lesions for calves allotted to pens on the basis of the serum haptoglobin concentration at the time of arrival at a feedlot in experiment 1.
| Variable | Low (n = 3 pens) | Medium (n = 4 pens) | High (n = 5 pens) | SEM | P value* |
|---|---|---|---|---|---|
| No. of days in the feedlot | 224 | 222 | 222 | 3.24 | 0.110 |
| Initial BW (kg) | 289 | 294 | 291 | 11.48 | 0.416 |
| Final BW (kg) | 517 | 527 | 522 | 6.85 | 0.476 |
| ADG (kg/d) | 1.41 | 1.45 | 1.44 | 0.040 | 0.671 |
| HCW (kg) | 330 | 334 | 333 | 4.37 | 0.766 |
| HCW/final BW (%) | 63.79 | 63.26 | 63.70 | 0.301 | 0.272 |
| Longissimus muscle area (cm2) | 77.6 | 79.0 | 78.7 | 1.274 | 0.637 |
| Fat thickness at 12th rib (cm) | 1.27 | 1.37 | 1.33 | 0.057 | 0.469 |
| Kidney, pelvis, and heart fat (%) | 1.88 | 1.89 | 1.95 | 0.059 | 0.494 |
| USDA yield grade | 3.06 | 3.10 | 3.09 | 0.097 | 0.942 |
| Marbling score† | 446 | 444 | 438 | 12.46 | 0.828 |
| Lung lesions (%)‡ | |||||
| Overall§ | 63.80 | 61.31 | 60.83 | 8.02 | 0.951 |
| Severe ∥ | 17.26a,b | 27.74a | 11.23b | 6.98 | 0.050 |
| Adhesion¶ | 18.83 | 20.95 | 27.57 | 6.30 | 0.492 |
| Missing# | 10.31 | 12.62 | 12.71 | 6.19 | 0.953 |
Values were considered significant at P ≤ 0.05.
Marbling was scored as follows: 300 = slight, 400 = small, and 500 = modest.
Lung lesions were observed in 189 calves at slaughter.
Percentage of calves that had lungs with at least one of the following: lesions (score 1, 2, or 3), interlobular adhesions, or a missing lobe.
Percentage of calves that had lungs with lesions scored as 2 or 3.
Percentage of calves that had at least 1 interlobular adhesion.
Percentage of calves that had substantial tissue missing.
See Table 1 for remainder of key.
Lung lesions—No significant (P ≥ 0.492) differences were detected in the proportion of calves that had evidence of pulmonary damage, interlobular adhesions, or missing lobes among the 3 serum haptoglobin concentration groups (Table 5). However, the medium group had the significantly (P = 0.050) highest proportion of calves with lesions classified as severe, followed by the proportion of calves in the low group, and then the proportion of calves in the high group.
Experiment 2
Serum haptoglobin concentration—Mean ± SD serum haptoglobin concentration measured in samples obtained at the time of arrival to the feedlot was 0.238 ± 0.504 μg/mL. Mean serum haptoglobin concentration was significantly (P < 0.001) higher in calves that had a detectable serum haptoglobin concentration at the time of arrival (0.451 ± 0.057 μg/mL) than in calves without a detectable serum haptoglobin concentration (Table 6).
Mean values for performance variables of calves allotted to pens on the basis of whether they had or did not have a detectable serum haptoglobin concentration at the time of arrival at a feedlot in experiment 2.
| Variable | Days | No detectable concentration (n = 6 pens) | Detectable concentration (n = 6 pens) | SEM | P value* |
|---|---|---|---|---|---|
| Serum haptoglobin concentration at time of arrival (mg/mL) | −1 | −0.008 | 0.451 | 0.057 | < 0.001 |
| BW (kg) | 0 | 244 | 235 | 1.22 | < 0.001 |
| 7 | 242 | 230 | 1.28 | < 0.001 | |
| 14 | 249 | 237 | 2.32 | 0.003 | |
| 21 | 256 | 245 | 3.42 | 0.009 | |
| 42 | 278 | 266 | 2.05 | 0.003 | |
| ADG (kg/d) | 1–7 | −0.27 | −0.78 | 0.249 | 0.043 |
| 8–14 | 1.00 | 0.95 | 0.289 | 0.885 | |
| 15–21 | 0.97 | 1.24 | 0.331 | 0.358 | |
| 1–21 | 0.57 | 0.47 | 0.120 | 0.436 | |
| 22–42 | 1.04 | 1.02 | 0.111 | 0.779 | |
| 1–42 | 0.80 | 0.74 | 0.037 | 0.283 | |
| DMI (kg/d) | 1–7 | 3.49 | 2.99 | 0.186 | 0.043 |
| 8–14 | 4.79 | 4.17 | 0.232 | 0.011 | |
| 15–21 | 5.38 | 4.98 | 0.421 | 0.149 | |
| 1–21 | 4.55 | 4.04 | 0.274 | 0.035 | |
| 22–42 | 7.02 | 6.38 | 0.130 | 0.006 | |
| 1–42 | 5.78 | 5.19 | 0.189 | 0.012 | |
| DMI (percentage of mean BW for the period) | 1–7 | 1.43 | 1.29 | 0.076 | 0.126 |
| 8–14 | 1.95 | 1.79 | 0.091 | 0.054 | |
| 15–21 | 2.13 | 2.07 | 0.152 | 0.554 | |
| 1–21 | 1.82 | 1.68 | 0.097 | 0.117 | |
| 22–42 | 2.63 | 2.49 | 0.045 | 0.060 | |
| 1–42 | 2.22 | 2.07 | 0.065 | 0.062 | |
| Ratio of ADG to DMI | 1–7 | −0.080 | −0.275 | 0.081 | 0.039 |
| 8–14 | 0.204 | 0.233 | 0.055 | 0.689 | |
| 15–21 | 0.183 | 0.241 | 0.052 | 0.286 | |
| 1–21 | 0.124 | 0.114 | 0.021 | 0.720 | |
| 22–42 | 0.149 | 0.160 | 0.018 | 0.362 | |
| 1–42 | 0.138 | 0.141 | 0.007 | 0.700 |
Calves arrived at the feedlot on day −1 and were allowed a rest period before processing.
Values were considered significant at P ≤ 0.05.
Performance during the preconditioning period—Calves with a detectable serum haptoglobin concentration at the time of arrival had a significantly (P = 0.009) lower BW on days 0, 7, 14, 21, and 42 than did calves without a detectable serum haptoglobin concentration at the time of arrival (Table 6). For the first 7 days of the study, BW decreased in both groups; calves with a detectable serum haptoglobin concentration had a significantly (P = 0.043) lower ADG (−0.78 kg/d) than did calves without a serum haptoglobin concentration (−0.27 kg/d). The ADG for days 8 to 14, 15 to 21, 21 to 42, and 1 to 21 and for the entire experiment did not differ significantly (P ≥ 0.283) between the 2 groups. The DMI was significantly (P ≤ 0.043) lower for calves with a detectable serum haptoglobin concentration than for calves without a detectable serum haptoglobin concentration on days 1 to 7, 8 to 14, 22 to 42, 1 to 21, and 1 to 42. When expressed as a percentage of mean BW, DMI was significantly (P = 0.054) lower for calves with a detectable serum haptoglobin concentration at the time of arrival than for calves without a detectable serum haptoglobin concentration at the time of arrival for days 8 to 14, and it was lower (but not significantly [P ≤ 0.062] different) for calves with a detectable serum haptoglobin concentration at the time of arrival for days 22 to 42 and days 1 to 42 (0.14% and 0.15% lower, respectively).
The ratio of ADG to DMI during the first week of the experiment (which was a period when the calves in both groups had a decrease in BW) differed significantly (P = 0.039) between the calves without a detectable serum haptoglobin concentration at the time of arrival to the feedlot and calves with a detectable serum haptoglobin concentration at the time of arrival to the feedlot (−0.080 and −0.275, respectively). The ratio of ADG to DMI did not differ significantly (P ≥ 0.286) between the 2 groups of calves for the remainder of the experiment.
Assessment and treatment of sick calves—Overall morbidity rate did not differ significantly (P = 0.172) between calves without a detectable serum haptoglobin concentration at the time of arrival (63/167 [37.7%]) and calves with a detectable serum haptoglobin concentration at the time of arrival (102/178 [57.3%]; Table 7). Similarly, the number of calves that required only 1 or 2 treatments because of BRD did not differ significantly (P ≥ 0.442) between the 2 groups; however, the number of calves that required 3 treatments was significantly (P = 0.032) higher in the group with a detectable serum haptoglobin concentration at the time of arrival (22/178 [12.4%]) than in the group without a detectable serum haptoglobin concentration at the time of arrival (9/167 [5.4%]). Because of the low incidence, the number of calves that died or were classified as chronically ill were not analyzed statistically.
Mean values for morbidity and mortality rates and treatments for calves with or without a detectable serum haptoglobin concentration at the time of arrival at a feedlot in experiment 2.
| Variable | No detectable concentration (n = 6 pens) | Detectable concentration (n = 6 pens) | SEM | P value* | Odds ratio† |
|---|---|---|---|---|---|
| Total morbidity rate (%)‡ | 37.72 | 57.30 | 3.75 | 0.172 | 2.21 |
| Calves requiring ≥ 2 treatments (%)§ | 36.51 | 49.02 | 6.07 | 0.362 | 1.67 |
| Calves requiring 3 treatments (%) | 5.43 | 13.56 | 3.07 | 0.034 | 2.73 |
| Calves treated 1 time (%) | 23.95 | 29.21 | 3.41 | 0.469 | 1.31 |
| Calves treated 2 times (%) | 8.38 | 12.36 | 2.47 | 0.442 | 1.54 |
| Calves treated 3 times (%) ∥ | 5.78 | 11.81 | 3.71 | 0.091 | 2.19 |
| Chronically ill (%) | 0.00 | 2.25 | — | — | — |
| Total mortality rate (%) | 0.60 | 2.81 | — | — | — |
| BRD mortality rate (%)¶ | 0 | 2.25 | — | — | — |
Values were considered significant at P ≤ 0.05.
Calves with no detectable serum haptoglobin concentration is the referent group.
— = Data were not analyzed statistically.
See Table 3 for remainder of key.
Calves with a detectable serum haptoglobin concentration at the time of arrival required the first treatment significantly (P = 0.008) sooner (approx 3 days earlier) than did calves without a detectable serum haptoglobin concentration at the time of arrival (5.4 and 8.5 days that calves received feed prior to first treatment after arrival at the feedlot, respectively; Table 8). The number of days that calves were in the feedlot prior to third treatment also was less (but not significantly [P = 0.082] different) for calves with a detectable serum haptoglobin concentration at the time of arrival than for calves without a detectable serum haptoglobin concentration at the time of arrival (19.2 vs 25.9 days, respectively). Rectal temperature did not differ significantly (P = 0.923) between the 2 groups at the time of the first treatment. Rectal temperature was significantly (P = 0.054) higher for calves with a detectable serum haptoglobin concentration than for calves without a detectable serum haptoglobin concentration at the time of the second treatment; however, rectal temperature was significantly (P = 0.042) lower for calves with a detectable serum haptoglobin concentration than for calves without a detectable serum haptoglobin concentration at the time of the third treatment. Subjective severity score was significantly (P = 0.032) higher for calves with a detectable serum haptoglobin concentration than for calves without a detectable serum haptoglobin concentration at the time of the first (1.3 vs 1.5, respectively) and third (1.3 vs 2.1, respectively) treatments; the subjective severity score did not differ significantly (P = 0.308) between the 2 groups at the time of the second treatment.
Mean values for number of days until treatment because of BRD, subjective severity score, and rectal temperature for calves with and without detectable serum haptoglobin concentrations at the time of arrival in a feedlot in experiment 2.
| Variable | No detectable concentration (n = 6 pens) | Detectable concentration (n = 6 pens) | SEM | P value* |
|---|---|---|---|---|
| First treatment | ||||
| Day of treatment | 8.5 | 5.4 | 1.09 | 0.008 |
| Severity score | 1.3 | 1.5 | 0.16 | 0.032 |
| Rectal temperature (°C) | 40.95 | 40.96 | 0.101 | 0.923 |
| Second treatment | ||||
| Day of treatment | 16.4 | 13.5 | 1.25 | 0.126 |
| Severity score | 1.6 | 1.8 | 0.17 | 0.308 |
| Rectal temperature (°C) | 40.70 | 41.02 | 0.103 | 0.054 |
| Third treatment | ||||
| Day of treatment | 25.9 | 19.2 | 2.54 | 0.082 |
| Severity score | 1.3 | 2.1 | 0.23 | 0.026 |
| Rectal temperature (°C) | 41.19 | 40.61 | 0.185 | 0.042 |
Severity of illness was scored as follows: 1 = mild, 2 = moderate, 3 = severe, and 4 = moribund.
Values were considered significant at P ≤ 0.05.
Discussion
In cattle, haptoglobin has been the most widely studied APP10 and has been found to increase rapidly in response to multiple pathogens during natural10,11 and experimental17,18 exposure. Haptoglobin functions to bind hemoglobin, which is released into the blood as a result of RBC hemolysis, to prevent use by bacteria.19 Haptoglobin is produced by hepatocytes after stimulation with proinflammatory cytokines, such as interleukin-1 and tumor necrosis factor-α, as a part of the acute-phase response.9 Exposure to the viral BRD pathogen BVDV alone does not result in increased serum haptoglobin concentrations.18 However, intratracheal administration of the bacterial pathogen Mannheimia haemolytica results in elevated serum haptoglobin concentrations 18 hours after M haemolytica challenge exposure, which remains greater than the haptoglobin concentration in control animals 96 hours after challenge exposure. Viral and bacterial pathogens increase concentrations of proinflammatory cytokines, but challenge exposure with pathogens results in the greatest concentrations of interleukin-1 and tumor necrosis factor-α.18 This finding suggests that viral and bacterial pathogens may have an additive effect, with an increased immune response and possibly severity of clinical disease resulting from a combination of both types of pathogens.
The BRD complex has a multifactorial etiology and multiple predisposing factors.1 Risk factors that affect BRD incidence include prenatal and preweaning nutrition and health management and postweaning factors, which include duration of the weaning period prior to transport, transportation and marketing stress, commingling, and nutrition and health management.1,15 The heifer calves in experiment 1 were classified at the time of arrival to the feedlot as having a high risk of developing BRD because they had several of these risk factors, including high marketing stress with at least 60% of the calves routed through separate auction markets and order-buyer facilities, commingling, and longdistance transport. The combination of these stressors and likely pathogen exposure during marketing resulted in increased serum haptoglobin concentrations after arrival at the feedlot, compared with the concentration before transport. This is similar to results of other studies15,20–23 in which transportation of calves and transport at the time of weaning versus after a preconditioning period increased haptoglobin concentrations. Serum haptoglobin concentration was measured in the present study through day 63, which is longer than in most published reports. Although decreased in magnitude, serum haptoglobin concentrations remained higher in calves with high and medium concentrations at the time of arrival, compared with concentrations in calves with low concentrations at arrival, on days 14, 21, and 63 and remained higher, compared with pretransport concentrations, through day 42. This period of an elevated haptoglobin concentration was longer than in another study21 in which haptoglobin concentration was higher on days 5 and 17 or day 7 (experiments 1 and 2, respectively), compared with the concentration before transport. The greatest mean haptoglobin concentration was detected on day 7 after arrival in 1 experiment in another study,13 although by days 14 and 28 in that study, concentrations had decreased below values for day 0. An elevated haptoglobin concentration has been detected for 96 hours in steers challenge exposed with BVDV and M haemolytica but with no transport stress.18 The acute-phase response is transient, and APP concentrations typically decrease to baseline values within days after reaching a peak.24 In experiment 1 of the present study, the higher mean haptoglobin concentrations maintained in calves with medium and high concentrations at the time of arrival to the feedlot as well as an increase in serum haptoglobin concentration in calves with low concentrations at arrival, compared with the concentration at arrival, could have reflected transport stress, clinical or subclinical BRD, or an acute-phase response associated with adaptation to a higher-concentrate diet.25 Different animals within a pen could be in various phases of an acute-phase response induced by different factors; thus, APP production may be decreasing in some animals but may be peaking or just beginning to increase in others, which could explain the prolonged increase in mean haptoglobin concentrations in the present study.
Serum haptoglobin concentrations in calves at a feedlot has also been negatively correlated with ADG in calves that were weaned at the time of transport, but not in calves that were weaned prior to transport.22 In contrast to results of the present study, morbidity attributable to BRD was not observed in that study,22 which suggests that those cattle had subacute infection and a related acute-phase response or an acute-phase response induced by stress associated with typical management of healthy calves with sufficient effects on nutrient metabolism and animal growth to be similar to the response associated with clinical disease.18,26
In the present study, ADG decreased as haptoglobin concentration increased only during the early phase of the feeding period. Morbidity attributable to BRD was prevalent in these cattle during the first days after arrival at the feedlot, with a mean interval from first feeding to first treatment of 9 days in all groups. Therefore, any decrease in animal performance attributable to serum haptoglobin concentration at the time of arrival to the feedlot cannot be separated from an acute-phase response caused by the stress of typical management versus an immune response in clinically ill animals. The lower initial BW in calves of experiment 2 with a detectable haptoglobin concentration at time of arrival may have been the result of greater susceptibility to stress and multiple acute-phase responses throughout the lives of those calves prior to arrival at the feedlot.
The DMI associated with the serum concentration of haptoglobin at arrival typically decreased as haptoglobin concentration at arrival increased. Although a correlation between haptoglobin concentration and DMI has not been reported, it is established that newly arrived calves have a decrease in DMI after arrival.27 In a summary of 18 experiments, only 83.4% and 94.6% of sick and healthy calves, respectively, had consumed any feed by day 7 after arrival, and measured DMI of sick calves was 58%, 68%, and 88% that of healthy calves during the first week, week 4, and week 8, respectively.27 Sick calves also made fewer visits to the feed bunk and spent less total time at the feed bunk daily.28,29 Therefore, lower DMI in the present study was likely associated with subclinical or clinical infections in calves with higher haptoglobin concentrations.
In feedlot cattle, haptoglobin concentration at the time of arrival has been positively correlated with the number of times an animal receives antimicrobial treatment because of BRD during the arrival period.12,13 When haptoglobin concentration was measured on days 0, 40, and 65 after calves were placed in a feed-lot, an association was detected between haptoglobin concentration on day 40 or 65 and subsequent development of BRD.30 However, haptoglobin concentration could not be accurately used to predict BRD episodes within 10 days after measurement. In experiment 1 of the study reported here, total morbidity rate was positively correlated with serum haptoglobin concentration at time of arrival to the feedlot. Calves with medium and high concentrations at the time of arrival had odds that were 48% and 105% as great, respectively, of being treated at least once, compared with the likelihood of treatment for calves with a low serum haptoglobin concentration at the time of arrival. This difference was attributable to the fact that more calves with medium and high concentrations required 3 treatments or were ultimately classified as chronically ill, compared with the number of calves in the low serum haptoglobin concentration group. This difference was also evident in experiment 2, in which the odds that calves with a detectable serum haptoglobin concentration at the time of arrival would be treated 3 times were 304% as high as the odds for calves with no detectable serum haptoglobin concentration. Calves in experiment 2 were considered at lower risk than were the calves in experiment 1 because the calves in experiment 2 were transported directly from the auction market to the feedlot without further commingling at an order-buyer facility and the distance they were transported was much less. In another studyt that involved the use of steers purchased at the same markets and by the same buyer as for experiment 2 in the present study, no difference was detected in serum haptoglobin concentration at the time of arrival between calves treated 0, 1, or > 1 time because of clinical signs of BRD.
At the time of BRD treatment, no difference in serum haptoglobin concentration existed between haptoglobin groups in both experiments, and interestingly, the haptoglobin concentrations at the time of treatment were within the medium range defined in experiment 1. The lower number of days in the feedlot until first treatment of calves with a detectable serum haptoglobin concentration, compared with that for calves without a detectable serum haptoglobin concentration, in experiment 2 indicated that an active disease may have been involved in calves in which serum haptoglobin concentrations were detectable at the time of arrival. In both experiments, increases in haptoglobin concentrations resulted in a lower number of days in the feedlot until the second and third treatments. Possibly, earlier intervention targeted only at cattle with higher haptoglobin concentrations at arrival could reduce the impacts of BRD on morbidity and mortality rates and performance in those cattle and decrease the administration of antimicrobials to animals that are not ill.1 The inconsistencies observed between haptoglobin concentration group at the time of arrival and rectal temperature in both experiments indicated that separate mechanisms exist for inducing fever and the APP response after pathogen challenge exposure.18 Similarly, in experiment 2, calves with a detectable haptoglobin concentration at the time of arrival were subjectively judged to have a worse clinical condition (ie, higher clinical scores) at the first and third treatment. In contrast, in experiment 1, calves with a low haptoglobin concentration at the time of arrival typically had higher clinical scores than did those with a high haptoglobin concentration at the time of arrival, and calves with a medium concentration at the time of arrival had intermediate scores. This observation could have been attributable to the greater number of days in the feedlot at the third treatment for calves with a low haptoglobin concentration at arrival, compared with the number of days for calves with a medium or high concentration at arrival, when sick calves could appear worse than they would have if the entire group had spent less time in the feed-lot. Although not significantly different, the odds ratios for total mortality and case fatality rates for calves with medium and high serum haptoglobin concentrations at the time of arrival, compared with those for calves with a low serum haptoglobin concentration at the time of arrival, and the fact that no deaths were attributed to BRD also support the possibility that cattle with higher haptoglobin concentrations at the time of arrival may have a more chronic disease state and that antimicrobial treatment may be less effective when clinical signs become evident.
A positive association between haptoglobin concentration and detection of lung lesions at slaughter has also been reported.30 However, the lack of association between higher haptoglobin concentration and lung lesions at slaughter in the present study may indicate that the disease was more severe in the study reported here. The more severely ill cattle in that other study24 may have survived, albeit with greater lung damage, whereas the more severely ill cattle in the present study died. Moreover, although the percentage of chronically ill cattle was numerically higher for calves with high and medium haptoglobin concentrations at the time of arrival than for calves with a low haptoglobin concentration at the time of arrival, the lower proportion of chronically ill cattle (as a percentage of calves treated 3 times) may suggest that more calves died prior to the third treatment or were designated as chronically ill. The high number of calves treated multiple times, chronically ill calves, and calves that died of BRD in all 3 haptoglobin concentration groups in experiment 1 suggested that although serum haptoglobin concentration at the time of arrival may be valuable for use in predicting subsequent BRD and severity of disease in affected calves, the response is variable. However, an increased serum haptoglobin concentration measured at the time of arrival was associated with increased risk of multiple treatments because of signs of BRD, and the use of haptoglobin concentration to predict or evaluate risk of BRD remains possible. More appropriate cutoff values for serum haptoglobin concentration at the time of arrival at a feedlot should be determined, and management strategies (which should be targeted as prophylactic treatment) to reduce the effect of BRD in calves with differing haptoglobin concentrations at the time of arrival should be evaluated.
ABBREVIATIONS
| ADG | Average daily gain |
| APP | Acute-phase protein |
| BRD | Bovine respiratory disease |
| BVDV | Bovine viral diarrhea virus |
| BW | Body weight |
| DMI | Dry-matter intake |
| HCW | Hot carcass weight |
Eastern Livestock of West Kentucky Livestock Market, Marion, Ky.
Clott activator, Becton Dickinson Vacutainer Systems, Franklin Lakes, NJ.
Oklahoma State University Willard Sparks Beef Research Center, Stillwater, Okla.
Oklahoma Animal Disease and Diagnostic Laboratory, Stillwater, Okla.
Immunology Consultants Lab, Portland, Ore.
Sigma-Aldrich, St Louis, Mo.
Excel, Microsoft Corp, Redmond, Wash.
Pyramid 5, Fort Dodge Animal Health, Overland Park, Kan.
Vision 7 with Spur, Intervet/Schering-Plough Animal Health, DeSoto, Kan.
Cydectin, Fort Dodge Animal Health, Fort Dodge, Iowa.
Component TE-G, Vetlife, Overland Park, Kan.
DART, Upjohn Pharmacia Upjohn Animal Health, Kalamazoo, Mich.
GLA M-500, GLA Agricultural Electronics, San Luis Obispo, Calif.
Micotil 300, Elanco Animal Health, Greenfield, Ind.
Baytril 100, Bayer Corp, Shawnee, Mission, Kan.
Excenel RTU, Pfizer Animal Health, New York, NY.
Revalor-IH, Intervet/Schering-Plough, Boxmeer, The Netherlands.
Oklahoma National Stockyards, Oklahoma City, Okla.
PROC MIXED, SAS, version 9.1, SAS Institute Inc, Cary, NC.
Holland BP. Measurement of exhaled nitric oxide and exhaled carbon dioxide in the breath of beef calves. MS thesis, Department of Animal Science, College of Agricultural Sciences and Natural Resources, Oklahoma State University, Stillwater, Okla, 2006.
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