Effect of a nutritional reconditioning program for thin dairy cattle on body weight, carcass quality, and fecal pathogen shedding

Gabriele U. Maier Departments of Medicine and Epidemiology, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.

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Bruce R. Hoar Departments of Medicine and Epidemiology, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.

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Carolyn L. Stull Population Health and Reproduction, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.

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Philip H. Kass Population Health and Reproduction, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.

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Veronica Villanueva Departments of Medicine and Epidemiology, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.

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John Maas Population Health and Reproduction, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.

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Abstract

Objective—To assess changes in body weight, carcass quality, and fecal pathogen shedding in cull dairy cows fed a high-energy ration for 28 or 56 days prior to slaughter.

Design—Randomized clinical trial.

Animals—31 adult Holstein dairy cows.

Procedures—Cows were randomly assigned to a control (immediate slaughter) group or a 28-day or 56-day feeding group. Cows in the feeding groups received a high-energy feed and were weighed every 7 days. Carcasses were evaluated by USDA employees. Fecal and blood samples were collected at the start and end of the feeding periods.

Results—Body condition score and adjusted preliminary yield grade were significantly increased in both feeding groups, compared with values for the control group; body weight, hot carcass weight, dressing percentage, and ribeye area were significantly increased after 56 days, but not after 28 days, compared with values for the control group. Average daily gain and marbling score were significantly lower after feeding for 28 days versus after 56 days. Prevalence of Escherichia coli O157:H7 shedding in feces decreased from 14% to 5.6%, but this difference was not significant. Cows seropositive for antibodies against bovine leukemia virus that had signs of lymphoma and lame cows had a low average daily gain. Net loss was $71.32/cow and $112.80/cow for the 28-day and 56-day feeding groups, respectively.

Conclusions and Clinical Relevance—Feeding market dairy cows improved body condition and carcass quality. Cows seropositive for antibodies against bovine leukemia virus that have signs of lymphoma and lame cows might be poor candidates for reconditioning.

Abstract

Objective—To assess changes in body weight, carcass quality, and fecal pathogen shedding in cull dairy cows fed a high-energy ration for 28 or 56 days prior to slaughter.

Design—Randomized clinical trial.

Animals—31 adult Holstein dairy cows.

Procedures—Cows were randomly assigned to a control (immediate slaughter) group or a 28-day or 56-day feeding group. Cows in the feeding groups received a high-energy feed and were weighed every 7 days. Carcasses were evaluated by USDA employees. Fecal and blood samples were collected at the start and end of the feeding periods.

Results—Body condition score and adjusted preliminary yield grade were significantly increased in both feeding groups, compared with values for the control group; body weight, hot carcass weight, dressing percentage, and ribeye area were significantly increased after 56 days, but not after 28 days, compared with values for the control group. Average daily gain and marbling score were significantly lower after feeding for 28 days versus after 56 days. Prevalence of Escherichia coli O157:H7 shedding in feces decreased from 14% to 5.6%, but this difference was not significant. Cows seropositive for antibodies against bovine leukemia virus that had signs of lymphoma and lame cows had a low average daily gain. Net loss was $71.32/cow and $112.80/cow for the 28-day and 56-day feeding groups, respectively.

Conclusions and Clinical Relevance—Feeding market dairy cows improved body condition and carcass quality. Cows seropositive for antibodies against bovine leukemia virus that have signs of lymphoma and lame cows might be poor candidates for reconditioning.

Sending thin dairy cattle to market or directly to slaughter raises animal welfare and public health concerns, along with concerns related to supplying meat of inferior quality. Current cull rates for milk cows in the dairy industry vary between 22% and 27% annually.1 Approximately 95% of culled dairy cows are sent to slaughter, with the remainder going to other operations.1 The meat from dairy cows contributes substantially to domestic meat production, with dairy cows representing 8.6% of all slaughtered cattle in 2009.2 The main reasons dairy cattle are culled include reproductive problems (26.3%), udder and mastitis problems (23%), and poor production (16.1%). Lameness or injury (16%), other diseases (3.7%), aggression (0.7%), sales to other dairies (5.8%), and non-specified reasons (8.4%) account for the remainder.1 A large number of dairy cows arrive at the slaughterhouse in thin condition. When BCS was scored on a scale from 1 to 5, with 1 indicating severe undercondition and 5 indicating severe overcondition, 41% of cows at slaughter had a BCS of 2.0 or lower and 22% had a BCS of 1.5 or lower in 2007.3,4 Cows that leave the farm in thin condition are more likely to fall down in trucks and become nonambulatory.5

Following the first case of bovine spongiform encephalopathy in the United States in 2003, the Secretary of Agriculture announced an immediate ban on the slaughter of all nonambulatory cattle to decrease the risk of cattle infected with bovine spongiform encephalopathy entering the food supply.6,7 The inhumane handling of so-called downer animals depicted in videotapes recorded by the Humane Society of the United States in 2008 led to public demand for more humane handling of animals at slaughterhouses and the recall of 143 million lb of beef because meat from nonambulatory animals had illegally entered the food chain.8,9 Dairy cows make up the highest proportion of nonambulatory cows, as illustrated by a 2001 study10 of 7,382 nonambulatory cattle arriving at 19 slaughterhouses in Canada, of which approximately 90% were dairy breeds. Thin cows are also more likely to become bruised because of a lack of fat cover, leading to carcass defects and economic loss.11

Salmonella spp and Escherichia coli O157:H7 are important food-borne human pathogens that can be shed in the feces of animals. Cull dairy cows have a higher prevalence of Salmonella shedding than do other milking cows on farms. In a study12 involving 91 dairies and 97 cull dairy markets in 19 states in the United States, 18.1% of milk cows expected to be culled within 7 days and 14.9% of culled dairy cows at market were found to be shedding Salmonella spp, compared with 5.45% of milk cows on farm.12 A decrease in feed intake was given as a possible explanation for the increased predisposition to fecal Salmonella shedding.

As early as 1994,11 feeding cull cows a high-energy ration for a period after the culling decision has been made but prior to shipping has been suggested as a method of improving BW, body condition, carcass quality, and producer profits. Cull cow feeding trials13,14 in the past have evaluated differences in carcass quality between cows fed a high-energy diet versus control cows. In 1 study,13 improved carcass quality traits (eg, increased dressing percentage, lower shearing force, and improved organoleptic meat qualities) were found for cows fed high-energy diets for 98 days prior to slaughter, compared with results of feeding control diet. Similarly, a different study14 found that feeding market dairy cows a high-concentrate diet for 90 days with or without the addition of a β-adrenoceptor agonist can improve several key economically relevant carcass traits.14

These feeding regimens could also help reduce the risk of antimicrobial residues in meat. One study15 assessing antimicrobial residues in cull cows found that 31% of cows treated with procaine penicillin G, at doses corresponding to animal BWs that had been estimated by the farm manager, had residue concentrations that exceeded the 10-day label withdrawal recommendation by a mean of 3.1 ± 1.9 days.15 Additional feeding time before slaughter was suggested as a way to decrease the risk of antimicrobial residue violations.

In addition to the benefits of improved meat quality and reduced risk of antimicrobial residues in meat, feeding cull cows prior to slaughter could improve their overall health and resilience and thereby decrease the incidence of accidents during transport that result in nonambulatory animals, which are required by federal regulations at USDA plants to be condemned and not enter the human food supply. Furthermore, shedding of Salmonella spp and E coli O157:H7 may be decreased, and the feeding practice could result in a safer meat product. Despite these potential advantages, this management tool is largely ignored by producers as evidenced by the large percentage of cows arriving in thin body condition at slaughter. Furthermore, a study15 investigating management strategies of market dairy cattle through questionnaires sent to 142 dairies in New Mexico found that none of the dairies had a specific feeding protocol for market cows prior to selling.

The purpose of the study reported here was to assess changes in BW, carcass quality, and fecal pathogen shedding in cull dairy cows fed a high-energy ration for 28 or 56 days prior to slaughter. In addition, the study was meant to serve as a first step in determining characteristics that could be used to identify animals for which the feeding protocol would not be warranted because of a likely poor response as a result of underlying health conditions.

Materials and Methods

Cattle and dietary treatments—All animal use and handling techniques were approved by the University of California-Davis Animal Care and Use Committee. Holstein dairy cows (n = 31) with a BCS of 2.5 or less were purchased at a local livestock market by a contracted buyer and shipped to the University of California-Davis feedlot. No histories were available on any of the animals (ie, origin, reason for culling, age, and previous drug treatments were unknown). On arrival, cows were evaluated for health status by a veterinarian. Initial BCS and initial lameness score (1 to 5 scale; 1 = no lameness and 5 = extremely lame) were assigned independently by 2 trained scorers.16 Age was estimated on the basis of erupted incisors and a brucellosis ear tattoo when legible, and initial BW was recorded. As the cows exited the livestock trailer, they were randomly assigned by use of a random numbers table to either immediate slaughter (control), feeding of a high-concentrate diet for 28 days, or feeding of a high-concentrate diet for 56 days. Control cows had access to feed and water while at the feedlot and were transported the next day to a federally inspected commercial abattoir for slaughter. Cows in the 28-day and 56-day feeding groups were placed in separate pens. For the first 21 days, they were fed a feedlot starter ration consisting of 40% corn, 35% alfalfa hay, 20% oat hay, 1.5% molasses, 1.5% fat, 1.0% beef trace salt, 0.5% monosodium phosphate, 0.5% urea, 0.1% monensin premix, and 0.1% insect growth regulator (approx 2.80 Mcal/kg). For the remainder of the study period, a feedlot intermediate ration consisting of 23.4% alfalfa hay, 65.1% rolled corn, 4.0% distiller's dried grains, and 7.5% mineral mix was fed (approx 3.31 Mcal/kg).a The starter ration was analyzed and found to contain 13.5% crude protein (dry-matter basis), while the intermediate ration was 13.0% crude protein (dry-matter basis). Feed bunks were visually inspected daily, and the amount of feed offered the following day was adjusted according to the present day's consumption. Body weight was measured every 7 days, and ADG was determined for each cow. Cows were visually inspected for health problems daily. Any health problems that occurred during the feeding period were addressed by a veterinarian with a level of care comparable to treatment available on a typical dairy farm.

Diagnostic testing—On arrival, fecal samples were tested for the presence of Salmonella spp and E coli O157:H7. Feces were obtained from the rectum with a rectal sleeve, placed in sterile specimen bags, and submitted for bacteriologic culture the same day. Additional fecal samples were obtained immediately prior to slaughter from cows in the 28-day and 56-day feeding groups and tested for E coli O157:H7 and Salmonella spp.

Escherichia coli isolation and identification were performed as described17; a PCR assay was used to determine whether isolates were the O157:H7 strain. Briefly, fecal samples were enriched in tryptic soy broth and incubated with magnetic beads.b After being washed with a microorganism-purification system,c beads were spread onto sorbitol McConkey agar and rainbow agar and incubated overnight. Suspect colonies were patched onto lysogeny broth agar and incubated overnight. Patched colonies were immunoblotted onto a nitrocellulose membrane.d Colonies positive for O157 were detected by use of a mouse anti-O157 monoclonal antibody as the primary antibody and a goat anti-mouse IgG conjugated to alkaline phosphatase as the secondary antibody. Deoxyribonucleic acid of immunoblotpositive colonies was extracted by boiling. A real-time PCR assay with primers for rfbE confirmed colonies were E coli O157. Addtional PCR assays were used to analyze for the presence of virulence genes (stx1, stx2, eae, and hly) and fliC, the structural gene of the H7 serogroup.

For detection of Salmonella spp, fecal samples were plated directly onto Hektoen enteric and xylose-lysinetergitol 4 agar culture plates, inoculated into selenite enrichment broth, and incubated at 35°C (95°F) in air for 24 hours. If no suspected Salmonella spp colonies were observed on culture plates after 24 hours, the selenite broth culture was subcultured onto Hektoen enteric and xylose-lysine-tergitol 4 plates and incubated for an additional 24 hours at 35°C in air. Suspected colonies on either culture medium were serogrouped by means of slide agglutination that first used polyvalent antiserum for serogroups A to I and then used individual monovalent antisera. In addition, colonies with the biochemical properties of Salmonella spp were sent to the USDA National Veterinary Services Laboratories in Ames, Iowa, for serotyping.

On arrival, cows were also tested for antibodies against MAP and BLV and for bovine viral diarrhea virus antigen. In addition, blood samples were obtained for CBCs and trace element screening (Fe, Mg, Zn, Cu, Ca, P, Na, and K). Blood samples were collected by jugular venipuncture into 2 plain evacuated tubes, 2 tubes containing EDTA, and 1 tube containing sodium heparin and were submitted to the California Animal Health and Food Safety Laboratory for testing, except that 1 tube containing EDTA was submitted to the diagnostic laboratory at the University of California-Davis Veterinary Medical Teaching Hospital for a CBC. An additional blood sample (EDTA-containing tube) was collected immediately prior to slaughter for cows in the 28-day and 56-day feeding groups and submitted for a CBC. Blood samples were allowed to clot at room temperature for 1 hour before separation of serum by centrifugation and transfer into cryovials. Serum samples were kept refrigerated at 4°C (39.2°F) until submission to the California Animal Health and Food Safety Laboratory for serologic testing the same day. Serum was tested for antibodies against MAP by use of an ELISA.e The manufacturer's recommended interpretation was modified to account for the variability of results obtained with this kit. In brief, sample-to-positive ratios < 0.20 were reported as negative results, ratios between 0.20 and 0.35 were reported as suspicious results, and ratios > 0.35 were reported as positive results.18 Testing for anti-BLV antibody was performed with an anti-BLV antibody ELISAf followed by a confirmatory anti-BLV antibody agar gel immunodiffusion test kitg for ELISA-positive samples. Another test kith was used for detection of bovine viral diarrhea virus antigen. All serologic tests were performed according to manufacturers' guidelines unless otherwise specified.

Carcass data—Cows were slaughtered at a USDA-inspected slaughter facility either following purchase (control group) or after 28 or 56 days of feeding, and carcasses were graded by a USDA Meat Grading and Certification employee. Meat graders were unaware of the nature of the study and were therefore blinded to the treatments. The following carcass characteristics were evaluated: HCW, maturity, marbling, quality grade, adjusted PYG, ribeye area, percentage of KPH, and final yield grade.19 Dressing percentage was calculated by dividing HCW by the last recorded BW.

Maturity scores were recorded by USDA graders as letter grades with either a plus or minus or a number between 0 and 100 as a qualifier. These scores were converted into a number according to the following scheme: A− = 100, A = 150, A+ = 200, B− = 200, B = 250, B+ = 300, and so forth. When the letter was followed by a number, the score was determined by use of the following scheme: A0 = 100, A100 = 200, B0 = 200, B50 = 250, and so forth.20 Marbling scores were recorded by USDA graders as descriptive terms from slight to practically devoid (PD) plus a number between 0 and 100. These scores were converted to a numeric value by use of the following scheme: PD = 100, PD80 = 180, traces = 200, and slight = 300. The quality grade was recorded by USDA graders as a term with a plus or minus qualifier from cutter to select. This grade was translated into a score according to the following scheme: select + = 12, select = 11, select − = 10, standard + = 9, standard = 8, and so forth.21 Percentage of KPH was recorded by USDA graders as a percentage and a score. The score was based on the following formula: typical KPH percentage was considered to be 3.5%; for each percentage point of KPH less than this, 0.2 of a grade was subtracted from the PYG.19 When the USDA grader had only recorded the score, the KPH percentage was determined on the basis of the same formula. For example, if −0.6 was recorded, the KPH percentage was calculated to be 0.5%. Other values (ie, HCW, ribeye area, and adjusted PYG) were analyzed on the basis of the actual numbers recorded by USDA graders.

Economic analysis—Feed costs were recorded for the entire study population. For the 28-day and 56-day feeding groups, feed cost per cow per day was calculated. A price equivalent to the price per kilogram of live weight was determined by dividing the meat price paid at slaughter for the entire group by the sum of the last weights recorded for the group. The increase in value associated with feeding was determined by multiplying the difference in BW between the beginning and end of the feeding periods by the price per kilogram of live weight. This increase in value was compared with the cost incurred by feeding.

Statistical analysis—Statistical analysis was conducted with a commercial software package.i Each animal was the experimental unit for all variables measured in the trial. One animal in the control group was euthanized before transport to slaughter because of an inability to rise, 1 animal in the 28-day feeding group was euthanized during the trial period because of severe respiratory disease, and 1 animal in the 56-day feeding group died of severe pneumonia early in the trial. Euthanasia was performed by IV injection of an overdose of sodium pentobarbital. These animals were excluded from the analyses. Descriptive statistics included group means and SDs. Dressing percentage and percentage of KPH were analyzed after an arcsine square root transformation. Variables were evaluated for normality by use of the Kolmogorov-Smirnov test. Differences between group means were compared by use of a 1-way ANOVA and Tukey post hoc test for normally distributed variables or the Kruskal-Wallis procedure and Mann-Whitney U post hoc test for nonnormally distributed variables or variables with unequal variances between groups. A Fisher exact test was used to analyze differences between groups for count data (eg, the number of individuals seropositive for antibodies against MAP and BLV). An ANCOVA was used to evaluate the covariates age, initial BW, and initial BCS for confounding and effect modification of the outcome variable ending BW. The Wilcoxon signed rank test was used to compare initial versus final neutrophil count and neutrophil-to-lymphocyte ratio, and the McNemar test was used to evaluate shedding of E coli O157:H7 and Salmonella spp before and after feeding. Values of P < 0.05 were considered significant.

Results

Feedlot performance—Mean ± SD initial BW of all cows was 484 ± 52.7 kg (1,066 ± 116.2 lb). There were no significant differences in age, initial BCS, or initial BW among groups (Table 1). Final BCS was significantly (P = 0.001) greater in fed versus control cows but did not differ significantly between the 28-day and 56-day feeding groups. Final BW was significantly (P = 0.001) greater for cows in the 56-day feeding group versus cows in the 28-day feeding group and cows in the control group, but no significant difference was seen between the control group and the 28-day feeding group. Group differences for final BW remained significant after adjusting for initial BCS (P = 0.003), age (P = 0.003), and initial BW (P < 0.001). Covariate-by-group interactions were not significant. Cows in the 56-day feeding group gained a mean of 36 ± 22.8 kg (80 ± 50.2 lb) during the first 28-day period and another 43 ± 17.7 kg (94 ± 38.9 lb) during the second 28-day period, for a total gain of 79 ± 34.1 kg (174 ± 75.2 lb). Average daily gain was significantly (P = 0.029) greater in the 56-day feeding group (1.4 ± 0.61 kg [3.1 ± 1.34 lb]) than in the 28-day feeding group (0.3 ± 1.24 kg [0.7 ± 2.72 lb]; Figure 1).

Table 1—

Age and body condition for 3 groups of adult Holstein cows (n = 31) in a trial designed to assess the effects of a nutritional reconditioning program.

 GroupP value*
TraitControl28-day56-dayOverall56-day vs 28-day
Number1099  
Estimated age (y)2.8(1.10)2.6 (0.68)3.2(1.37)0.680.55
BCS
   Initial2.1 (0.35)2.1 (0.22)2.3(0.32)0.220.33
   Final2.1 (0.35)a2.5 (0.37)b2.7 (0.24)b0.0010.43
BW(kg)
   Initial485 (60.5)474(50.0)493(51.5)0.820.81
   Final485 (60.5)a485 (35.4)a572 (52.0)b0.0010.004
ADG (kg)0.3(1.24)a1.4 (0.61)b0.029

Values are mean (SD). Holstein cows with a BCS ≤ 2.5 were purchased at a local livestock market and randomly assigned to 1 of 3 groups. Control cows had access to feed and water while at the feedlot and were transported the next day to a federally inspected commercial abattoir for slaughter. Cows in the 28-day and 56-day feeding groups were placed in separate pens. For the first 21 days, they were fed a feedlot starter ration consisting of 40% corn, 35% alfalfa hay, 20% oat hay, 1.5% molasses, 1.5% fat, 1.0% beef trace salt, 0.5% monosodium phosphate, 0.5% urea, 0.1% monensin premix, and 0.1% insect growth regulator (approx 2.80 Mcal/kg). For the remainder of the study period, a feedlot intermediate ration consisting of 23.4% alfalfa hay, 65.1% rolled corn, 4.0% distiller's dried grains, and 7.5% mineral mix was fed (approx 3.31 Mcal/kg).

P values were based on a 1-way ANOVA and Tukey post hoc test or Kruskal-Wallis test and Mann-Whitney U post hoc test.

One cow from each group was lost during the trial period; data from these cows were not included in the analyses. One cow in group 1 was unable to rise and was euthanized, 1 cow in group 2 had chronic pneumonia and was euthanized, and 1 cow in group 3 died of chronic pneumonia. — = Not applicable.

Mean values without a superscript in common were significantly (P < 0.05) different.

Health variables and fecal pathogen shedding—There were no significant differences in percentages of cows seropositive for antibodies against BLV or MAP among groups (Table 2). Initial neutrophil count was also not significantly different among groups. Pairwise comparisons of neutrophil counts between prefeeding and postfeeding time points revealed significantly lower final neutrophil counts (P = 0.016) and lower neutrophil-to-lymphocyte ratios (P = 0.005). No feces were retrievable from 1 cow in the 28-day feeding group. Initially, 4 cows were shedding E coli O157:H7 (3 in the 28-day feeding group and 1 in the 56-day feeding group) while none were shedding in the control group. After the feeding periods, 1 cow, which was not one of the initial shedders, was shedding in the 28-day feeding group and none of the cows in the 56-day feeding group were shedding; there was no significant difference between initial and final shedding percentages. Only 2 animals initially shed Salmonella spp: 1 in the control group (Salmonella montevideo) and 1 in the 28-day feeding group (Salmonella mbandaka). Culture of feces obtained after the feeding periods resulted in no positive culture results for either the 28-day or 56-day feeding group. There was no significant difference between initial and final shedding percentages in the 2 groups.

Figure 1—
Figure 1—

Average daily gain (kg) in cull dairy cows fed a high-energy ration for 28 or 56 days prior to slaughter. aCow with an initial lameness score of 2 (on a scale from 1 to 5) in which lameness resolved without treatment. bBovine leukemia virus–seropositive cow with enlarged mandibular lymph nodes. cBovine leukemia virus–seropositive cow with a mildly proptosed eye that was treated for lameness (sole abscess). dCow treated for lameness (sole abscess).

Citation: Journal of the American Veterinary Medical Association 239, 12; 10.2460/javma.239.12.1594

Table 2—

Health variables and fecal pathogen shedding for cows in Table 1.

 GroupP value*
TraitControl28-day56-dayOverall56-day vs 28-dayInitial vs final
Number (n)1099   
BLV seropositive (n)3240.690.62 
MAP seropositive (n)1210.821.0 
Neutrophil count (× 103/μL)     0.016
   Initial5.5 (4.82)3.3 (1.61)7.2 (7.52)   
   Final5.5 (4.82)2.4 (1.69)2.4 (0.97)   
Neutrophil-to-lymphocyte ratio     0.005
   Initial1.2 (1.22)0.8 (0.46)1.4 (1.53)   
   Final1.2 (1.22)0.4 (0.14)0.6 (0.31)   
E coli 0157:H7 shedding     0.38
   Initial031   
   Final010   
Salmonella shedding     1.0
   Initial110   
   Final100   

Data are given as number of cows or as mean (SD).

P values are based on a 1-way ANOVA and Tukey post hoc test, Fisher exact test (categorical variables), Wilcoxon rank test (neutrophil count and neutrophil-to-lymphocyte ratio), or McNemartest (Escherichia coli and Salmonella shedding).

Titer considered suspicious.

No feces were retrievable from 1 cow in the 28-day feeding group during initial fecal sampling.

Lameness—Three animals (1 in each group) had a lameness score of 2 (mildly lame), and 2 animals (1 in the control group and 1 in the 56-day feeding group) had a lameness score of 3 (moderately lame). One animal in the control group was mistakenly not assigned a lameness score.

Carcass quality—Hot carcass weight, dressing percentage, and ribeye area were significantly (P = 0.001) greater in the 56-day feeding group than in the 28-day feeding group or the control group (Table 3). There were no significant differences in these variables between the control group and the 28-day feeding group. There were no significant differences in percentage of KPH, yield grade, maturity score, or quality grade between groups. The 28-day feeding group had a significantly (P < 0.001) lower marbling score than did the 56-day feeding group and the control group. The control group had a significantly (P < 0.001) lower adjusted PYG than did the 28-day and 56-day feeding groups, but adjusted PYG was not significantly different between the 28-day and 56-day feeding groups.

Table 3—

Carcass characteristics for cows in Table 1.

 GroupP value*
TraitControl28-day56-dayOverall56-day vs 28-day
HCW (kg)221 (27.6)a224 (28.2)a285 (33.2)b< 0.0010.001
Dressing percentage45.5 (2.52)a46.0 (3.08)a49.9 (3.26)b0.0080.03
Ribeye area (in2)7.3 (2.34)a6.66 (1.72)a9.78 (1.20)b0.003< 0.001
KPH (%)0.7 (0.47)1.0 (0.35)0.7 (0.36)0.150.14
Yield grade2.3 (0.59)2.8 (0.40)2.4 (0.43)0.0660.19
Maturity290 (144.9)273 (34.6)351 (134.7)0.430.34
Marbling§257 (95.9)a135 (14.2)b303 (52.2)a< 0.001< 0.001
Adjusted PYG2.2 (0.14)a2.5 (0.04)b2.5 (0.19)b0.0010.73
Quality grade7.0 (2.91)6.6 (2.13)6.6 (2.85)0.591.00

Analysis based on arcsine square root transformation.

A = 100, B = 200, C = 300, D = 400, E = 500.

Practically devoid = 100, traces = 200, slight = 300.

Quality grade score: 1 = low cutter, 2 = average cutter, 3 = high cutter, 4 = low utility, 5 = average utility, 6 = high utility, 7 = low standard, 8 = average standard, 9 = high standard, 10 = low select, 11 = average select, and 12 = high select.

In each row, means without a superscript letter in common were significantly (P, 0.05) different.

See Table 1 for remainder of key.

Economics—Cost for feed per cow per day was determined to be $2.74 for the 28-day feeding group and $2.98 for the 56-day feeding group or $76.77/cow for the 28-day feeding period and $166.76/cow for the 56-day feeding period. The price of meat paid at the slaughterhouse was $2,956.62 for all animals in the control group, $2,690.10 for all animals in the 28-day feeding group, and $3,503.00 for all animals in the 56-day feeding group. The live weight equivalents were $0.61/kg ($0.28/lb) for the control group, $0.62/kg ($0.28/lb) for the 28-day feeding group, and $0.68/kg ($0.31/lb) for the 56-day feeding group. These numbers resulted in a net loss of $71.32/cow for the 28-day feeding group and a net loss of $112.80/cow for the 56-day feeding group.

Discussion

To our knowledge, this is the first study evaluating fecal shedding of pathogens or CBCs in reconditioned market cows as an assessment of animal health and food safety. Results of the present study indicated that feeding market dairy cows improved body condition and carcass quality. Body condition score and adjusted PYG increased significantly in both the 28-day and 56-day feeding groups, whereas BW, ADG, HCW, dressing percentage, and ribeye area increased after 56 days but not after 28 days. The study provided some evidence that fecal shedding of E coli O157:H7 may decrease over either a 28-day or 56-day feeding period; however, significant decreases in shedding percentages were not identified, possibly because of the small study size. Our data also suggested that leukocyte counts may normalize during either a 28-day or 56-day feeding period. However, leukocyte counts did not appear to be a good prognostic indicator for performance during reconditioning. As has been shown in previous studies,14,22–24 feeding cows a high-concentrate diet improved several carcass traits, such as HCW, dressing percentage, and ribeye area. The present study suggested that 56 days may be a sufficient feeding duration to result in improved carcass traits. The present study represented a first step in developing an algorithm for discerning the most appropriate management of culled dairy cattle in terms of economics, food safety, and humane treatment.

In the present study, 2 separate durations of feeding periods were compared with regard to changes in BCS, BW, and ADG. Overall, cows in the 56-day feeding group performed better than did cows in the 28-day feeding group, with higher absolute weight gains and ADG throughout the study period. Comparing the groups at the end of the 28-day period, cows in the 56-day feeding group had a significantly greater BW gain than did cows in the 28-day feeding group. There was a further increase in ADG in the 56-day feeding group from 1.30 ± 0.81 kg (2.86 ± 1.78 lb) during the first 28 days to 1.42 ± 0.61 kg (3.12 ± 1.34 lb) at the end of the 56-day feeding period. In 1 study,25 the ADG reported for cull cows fed a high-energy diet for 70 days with (1.23 kg [2.71 lb]) or without (1.36 kg [3.00 lb]) the addition of zilpaterol hydrochloride was similar to the ADG observed in the 56-day feeding group in the present study. However, a different study15 found a higher ADG of 1.4 kg (3.1 lb) in cows fed for 30 days, compared with 0.9 kg (2.0 lb) in cows fed for 60 days. Final BCS in the present study was not different between feeding groups; however, scorers were not blinded to the treatment, which was a shortcoming of this study. The change in BCS seen in the present study has been observed in other studies,15,24 in which BCS improved during the initial feeding period of 28 or 30 days, but did not significantly increase with prolonged feeding. Body condition score in dairy cattle varies during the lactation cycle, but should ideally range from 2.25 during peak lactation up to 3.75 during the nonlactating period.3 The 3 groups of cows in the present study, with an initial BCS between 2.1 and 2.3, therefore represented animals at the lower end of the spectrum, and the increase in BCS observed showed a return to a weight within the expected physiologic range. The overall difference in performance between the feeding groups might have been dependent on the initial health status of the cows. These animals represented a typical group of market dairy cows that were preselected only on the basis of their initial BCS. With a relatively small sample size, variability in resilience between groups owing to chance alone cannot be excluded, even though individuals were randomly assigned to the treatment groups. Variability in weight gain observed during cull cow feeding trials is often high, likely for this reason. Because cows often are leaving the herd because of health problems, it is important to discern which animals are good candidates for a reconditioning program to achieve desirable feedlot performance.

Three of 28 animals in the present study were seropositive for antibodies against MAP, and 1 had a titer (determined with an ELISA) classified as suspicious.e In a study26 assessing seroprevalence of antibodies against MAP in adult dairy cattle in California, 4.6% were found to be seropositive, compared with 14.3% in the present study. That study26 used the same test kit and accepted the manufacturer's cutoff for a positive result as a standard-to-positive ratio > 0.25. Johne's disease is certainly a risk factor for culling; however, the seropositive animals in our study did not have clinical signs of Johne's disease, and those in the feeding groups had good feedlot performance, except for 1 animal that was also seropositive for antibodies against BLV.

Nine of 28 (32.1%) animals in the present study were seropositive for antibodies against BLV. This compares with 40.8% of seropositive animals found in the USDA National Animal Health Monitoring System's 1996 dairy study.27 One study28 found no association between serologic status for BLV and cull rate in 1 dairy herd in Maryland. A different study29 found greater cull rates among seropositive cows than among seronegative cows more than 36 months old. Because many infected animals do not manifest clinical signs, infection status alone may not be a good indicator of feedlot performance. Persistently high lymphocyte counts are associated with BLV infection in dairy cattle.30 Only 10% of carriers, however, develop lymphoid tumors, which are often apparent on physical examination either as enlarged lymph nodes or tumors of the uterus. In the present study, 2 animals that were seropositive for antibodies against BLV and also had signs of lymphoma performed poorly, while other seropositive animals, even those with high lymphocyte counts, performed well. One animal in the 28-day feeding group had enlarged mandibular lymph nodes and an ADG of −2.2 kg (−4.8 lb; Figure 1). A different BLV-seropositive animal in the 56-day feeding group had a mildly proptosing eye and an ADG of 0.5 kg (1.0 lb). Even though no statistically robust conclusion can be drawn from these examples, they could serve as indicators that animals with clinical signs of lymphoma are poor candidates for reconditioning.

We observed a decrease in neutrophilia prevalence over course of the study period. Neutrophilia, defined as a neutrophil count greater than the upper limit of the reference range (6.8 × 103/μL), was observed in 7 of 28 cows at purchase: 4 in the control group and 3 in the 56-day feeding group. No neutrophilia was observed at the end of the feeding periods in either of the feeding groups, and overall neutrophil count decreased significantly during the feeding period. One cow with initial neutrophilia was treated with dinoprost tromethaminej (25 mg, IM) for metritis, which subsequently resolved, and had a normal neutrophil count at the end of 56 days. Actual neutrophil count did not seem to be associated with outcome, as some cows with very high initial neutrophil counts performed well and developed no clinical signs that required any treatment. Physiologic neutrophilia due to epinephrine release might have been responsible for some of the high initial neutrophil counts.31 Neutrophil count alone does not appear to be a good indicator of performance during reconditioning, and individual clinical signs are more important in the evaluation of cattle for this purpose. However, the absence of neutrophilia at the end of the feeding periods suggested an improvement in overall health of cows in the feeding groups versus the control group and could be regarded as a positive effect of reconditioning. In addition, mean ± SD neutrophil-to-lymphocyte ratios changed from 0.8 ± 0.46 (prefeeding timepoint) to 0.4 ± 0.14 (postfeeding timepoint) in the 28-day feeding group and from 1.4 ± 1.53 (prefeeding timepoint) to 0.6 ± 0.31 (postfeeding timepoint) in the 56-day feeding group. Because the normal neutrophil-to-lymphocyte ratio in cattle is approximately 0.5, this change was further evidence for improved well-being in the study cows over the feeding periods.32

The present study did not identify significant differences in fecal shedding of Salmonella spp between groups; however, the statistical analysis had low power. A study12 evaluating shedding of Salmonella organisms by culled dairy cattle found a significantly higher percentage of fecal Salmonella shedding in culled cows, compared with cows in production. The physiologic conditions under which cattle are more likely to harbor E coli O157:H7 are still not entirely understood, but a higher prevalence of shedding in nonambulatory cows than in healthy cows has previously been shown.33 In the present study, 4 of 28 cows were shedding E coli O157:H7 in their feces at the time of purchase (ie, immediately after culling from the herd). At the end of the feeding periods, those 4 had stopped shedding, but 1 of the 18 other cows shed E coli O157:H7. Although we did not identify a significant decrease in the prevalence of shedding, the study's observations support the hypothesis that thin cows allowed time to improve their condition prior to slaughter are at reduced risk of shedding E coli O157:H7. Conversely, shedding is often intermittent; hence, these results could also be attributable to the sampling protocol. The fact that a large proportion of slaughtered dairy cows are processed into ground beef, a product that is at higher risk of E coli O157:H7 contamination than are other meat products because of the type of processing, makes this hypothesis worth exploring with studies that incorporate a larger number of animals.34,35

Of the 3 animals in the present study that were initially assessed as lame, 2 performed below average in terms of ADG. The cow in the 28-day feeding group did not require further treatment, and lameness resolved. Its ADG was 0.4 kg (0.9 lb) after 28 days of feeding (Figure 1). The 2 cows in the 56-day feeding group both required treatment for sole abscesses involving multiple limbs and performed poorly with ADGs of 0.5 and 0.9 kg after 56 days of feeding. Lameness is one of the factors leading to nonambulatory cattle because lame cows spend less time eating and more time lying down and thus become more susceptible to injury during transport.11 It appears, however, that once a cow is chronically lame, reconditioning is difficult, as the cows in this study that were initially lame gained less weight. Prevention and early treatment are key in dealing with this problem. One study14 found a significant improvement in lameness scores after 90 days of feeding, which was attributed to the removal of the physiologic stress of lactation and the physical stress of walking to the milking parlor several times daily. In the present study, this effect could not be observed.

In the present study, HCW, dressing percentage, and ribeye area were significantly greater in the 56-day feeding group than in the control group or 28-day feeding group. There was no difference in maturity scores between groups. Marbling was lower in the 28-day feeding group versus the control group or 56-day feeding group. Quality grade and adjusted PYG were greater in the feeding groups versus the control group. Results for carcass characteristics after reconditioning differ in the literature. One study15 did not find any differences in carcass characteristics with additional feeding for 30 or 60 days, except for a significant increase in the percentage of KPH in the 60-day feeding group.15 In a study23 with young and mature cows fed for a mean of 89 days, both groups had significantly greater HCW and marbling scores than did their respective controls. In a study14 involving feeding cull cows for 90 days with or without the addition of ractopamine hydrochloride, feeding led to significantly greater HCW, dressing percentage, and marbling score, but no significant change in ribeye area, percentage of KPH, or quality grade; ractopamine supplementation did not lead to any additional improvements in HCW, dressing percentage, ribeye area, percentage of KPH, or yield grade in that study. Results of a study23 involving feeding cull cows for periods between 14 and 56 days found increased HCW, dressing percentage, and adjusted PYG after 28 days of feeding, but no additional increase after 56 days of feeding. Percentage of KPH did not differ with feeding time in that study. Finally, a study22 comparing carcasses of dairy and beef cattle perceived as fed or nonfed found that fed dairy cattle carcasses had a significantly higher HCW, ribeye area, and marbling score than did nonfed cattle carcasses, but found no difference in PYG or maturity score. Although not a goal of the present study, additional studies that include either ractopamine hydrochloride or zilpaterol hydrochloride with the addition of an anabolic implant such as trenbolone acetate are warranted. The β-adrenocepter agonists ractopamine and zilpaterol theoretically should improve carcass value by increasing muscle synthesis and carcass weight by repartitioning dietary energy toward lean tissue, while growth implants can further improve ADG, feed efficiency, and meat yields.14,25,36

It is interesting that feeding trials do not seem to produce consistent results such as changes in carcass characteristics. Reasons for this might be differences in feed composition between studies or confounding because of disparities in experimental groups despite randomization. This is more likely to happen when sample sizes are small, as was the case in the present study as well as in several of the previously mentioned studies. A further reason might be that some of the characteristics are assessed subjectively, such as marbling or percentage of KPH, which may introduce variability between graders. The increase in dressing percentage observed in the present study was probably partly due to a decrease in udder size as has previously been observed and documented.14 When cull cows enter into reconditioning trials, they are no longer milked during the feeding period, which leads to cessation of milk production, resorption of fluids, and a decrease in tissue mass.

In the present study, no profit was achieved with the amount of weight gained, given the cost of feed incurred. One study15 found that cows gaining 1.4 kg/d for 30 days, with a sale price of $0.88/kg ($0.4/lb) of live BW and feed cost of $2.34/d, led to a loss of $1.11/d.15 Time of year, quantity of feed purchased, and market fluctuations contribute to the profitability of feeding cull cows. Clearly, more favorable conditions than those during the present study are necessary to achieve economic feasibility and thus make this practice attractive to producers. In addition, cost of labor and veterinary care needs to be taken into consideration, as these decrease profit margins further. However, these calculations do not take into account that reconditioned cows are less likely to become debilitated during transport and thus are less likely to become non-ambulatory, which results in condemnation and loss of all meat products. Future studies that examine the possibility of using less expensive feed sources, such as feed refusals, and early identification and elimination of the few cattle that fail to perform have the potential to result in positive economic returns.

ABBREVIATIONS

ADG

Average daily gain

BCS

Body condition score

BLV

Bovine leukemia virus

BW

Body weight

HCW

Hot carcass weight

KPH

Kidney, pelvic, and heart fat

MAP

Mycobacterium avium subsp paratuberculosis

PYG

Preliminary yield grade

a.

UC Davis Premix, Suspension Supplement No. 714-2428, West-way, New Orleans, La.

b.

O157 Dynal magnetic beads, Invitrogen/Dynal, Carlsbad, Calif.

c.

Dynal Beadretriever, Invitrogen/Dynal, Carlsbad, Calif.

d.

Protran BA85, Whatman/Schleicher & Schuell, Sanford, Me.

e.

HerdChek ELISA Mycobacterium paratuberculosis antibody test kit, Idexx Corp, Westbrook, Me.

f.

Bovine leukemia virus antibody ELISA test kit, VMRD, Pullman, Wash.

g.

BLV antibody agar gel immunodiffusion test kit, Veterinary Diagnostic Technology Inc, Wheat Ridge, Colo.

h.

HerdChek bovine viral diarrhea virus antigen/serum plus test kit, Idexx Corp, Westbrook, Me.

i.

SPSS, version 17.9, SPSS Inc, Chicago, Ill.

j.

Lutalyse, Pfizer, New York, NY.

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  • Figure 1—

    Average daily gain (kg) in cull dairy cows fed a high-energy ration for 28 or 56 days prior to slaughter. aCow with an initial lameness score of 2 (on a scale from 1 to 5) in which lameness resolved without treatment. bBovine leukemia virus–seropositive cow with enlarged mandibular lymph nodes. cBovine leukemia virus–seropositive cow with a mildly proptosed eye that was treated for lameness (sole abscess). dCow treated for lameness (sole abscess).

  • 1.

    US National Animal Health Monitoring System. Dairy 2007. Fort Collins, Colo: USDA APHIS Veterinary Services, National Animal Health Monitoring System, 2007.

    • Search Google Scholar
    • Export Citation
  • 2.

    USDA Agricultural Marketing Service. 2009 annual meat trade review: meat, livestock, grain & slaughter data. Des Moines, Iowa: The Livestock and Grain Market News Service Staff, 2009;2.

    • Search Google Scholar
    • Export Citation
  • 3.

    Wildman EE, Jones GM, Wagner PE, et al. A dairy cow body condition scoring system and its relationship to selected production characteristics. J Dairy Sci 1982; 65:495501.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 4.

    National Cattlemen's Beef Association Beef Quality Assurance Program. Executive summary of the 2007 national market cow and bull beef quality audit. Centennial, Colo: National Cattlemen's Beef Association, 2007.

    • Search Google Scholar
    • Export Citation
  • 5.

    Grandin T. Welfare of cattle during slaughter and the prevention of nonambulatory (downer) cattle. J Am Vet Med Assoc 2001; 219:13771382.

    • Search Google Scholar
    • Export Citation
  • 6.

    Antemortem inspection. 9 CFR 309.

  • 7.

    Stull CL, Payne MA, Berry SL, et al. A review of the causes, prevention, and welfare of nonambulatory cattle. J Am Vet Med Assoc 2007; 231:227234.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 8.

    JAVMA News. Cruelty investigation prompts massive recall of beef. Available at: www.avma.org/onlnews/javma/mar08/080315e.asp. Accessed Sep 9, 2011.

    • Search Google Scholar
    • Export Citation
  • 9.

    JAVMA News. USDA ending downer cow slaughter exception. J Am Vet Med Assoc 2008; 233:19.

  • 10.

    Doonan G, Appelt M, Corbin A. Nonambulatory livestock transport: the need for consensus. Can Vet J 2003; 44:667672.

  • 11.

    Smith GCMJ, Tatum JD, Kukay CC, et al. Improving the consistency and competitiveness of non-fed beef and the salvage value of cull cows and bulls. In: Executive summary of the national non-fed beef quality audit. Engelwood, Colo: National Cattlemen's Beef Association, 1994.

    • Search Google Scholar
    • Export Citation
  • 12.

    Wells SJ, Fedorka-Cray PJ, Dargatz DA, et al. Fecal shedding of Salmonella spp. by dairy cows on farm and at cull cow markets. J Food Prot 2001; 64:311.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 13.

    Habermann W, Luger K, Frickh J, et al. Is the fattening of cull cows worthwhile? Analysis of feeding regimen, meat quality and profitability [in German]. Bodenkultur 2000; 51:5969.

    • Search Google Scholar
    • Export Citation
  • 14.

    Allen JD, Ahola JK, Chahine M, et al. Effect of preslaughter feeding and ractopamine hydrochloride supplementation on growth performance, carcass characteristics, and end product quality in market dairy cows. J Anim Sci 2009; 87:24002408.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 15.

    Rogers CA, Fitzgerald AC, Carr MA, et al. On-farm management decisions to improve beef quality of market dairy cows. J Dairy Sci 2004; 87:15581564.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 16.

    Sprecher DJ, Hostetler DE, Kaneene JB. A lameness scoring system that uses posture and gait to predict dairy cattle reproductive performance. Theriogenology 1997; 47:11791187.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 17.

    Cooley M, Carychao D, Crawford-Miksza L, et al. Incidence and tracking of Escherichia coli O157:H7 in a major produce production region in California. [serial online] PLoS ONE 2007; 2:e1159. Available at: www.plosone.org/article/info:doi/10.1371/journal.pone.0001159. Accessed Sep 1, 2010.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 18.

    Adaska JM, Munoz-Zanzi CA, Hietala SK. Evaluation of result variability with a commercial Johne's disease enzyme-linked immunosorbent assay kit and repeat testing of samples. J Vet Diagn Invest 2002; 14:423426.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 19.

    Jensen W. Understanding beef carcass evaluation. Santa Barbara, Calif: University of California Cooperative Extension, 2005;16.

  • 20.

    Barkmann S, Berg EP, Forrest J, et al. Indiana 4-H/FFA meat evaluation and identification contest: coach's guide. REV 12/95 ed. West Lafayette, Ind: Purdue University Cooperative Extension Service, 1995.

    • Search Google Scholar
    • Export Citation
  • 21.

    Hale DS, Goodson K, Savell JW. Beef quality and yield grades. College Station, Tex: Texas AgriLife Extension Service, 2010.

  • 22.

    Stelzleni AM, Patten LE, Johnson DD, et al. Benchmarking carcass characteristics and muscles from commercially identified beef and dairy cull cow carcasses for Warner-Bratzler shear force and sensory attributes. J Anim Sci 2007; 85:26312638.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 23.

    Jones SDM. Tissue growth in young and mature cull Holstein cows fed a high energy diet. J Anim Sci 1983; 56:6470.

  • 24.

    Schnell TD, Belk KE, Tatum JD, et al. Performance, carcass, and palatability traits for cull cows fed high-energy concentrate diets for 0, 14, 28, 42, or 56 days. J Anim Sci 1997; 75:11951202.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 25.

    Ewing AE, Ahola JK, Doumit ME, et al. Pre-harvest feeding, feeding duration, and inclusion of a β-agonist on market dairy cow feedlot performance and carcass characteristics, in Proceedings. 42nd Annu Meet Am Assoc Bovine Pract 2009;6672.

    • Search Google Scholar
    • Export Citation
  • 26.

    Adaska JM, Anderson RJ. Seroprevalence of Johne's-disease infection in dairy cattle in California, USA. Prev Vet Med 2003; 60:255261.

  • 27.

    Ott SL, Johnson R, Wells SJ. Association between bovine-leukosis virus seroprevalence and herd-level productivity on US dairy farms. Prev Vet Med 2003; 61:249262.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 28.

    Rhodes JK, Pelzer KD, Johnson YJ, et al. Comparison of culling rates among dairy cows grouped on the basis of serologic status for bovine leukemia virus. J Am Vet Med Assoc 2003; 223:229231.

    • Crossref
    • Search Google Scholar
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