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J. Anim Sci. 2008. 86:756-762. doi:10.2527/jas.2007-0526
© 2008 American Society of Animal Science
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ANIMAL PRODUCTION

Effects of increasing dose of live cultures of Lactobacillus acidophilus (Strain NP 51) combined with a single dose of Propionibacterium freudenreichii (Strain NP 24) on performance and carcass characteristics of finishing beef steers1

J. T. Vasconcelos*,2, N. A. Elam{dagger}, M. M. Brashears* and M. L. Galyean*

* Department of Animal and Food Sciences, Texas Tech University, Lubbock 79409; and {dagger} New Mexico State University, Clayton Livestock Research Center, Clayton 88415


   Abstract
Top
 Abstract
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 LITERATURE CITED
 
Two experiments, each with a randomized complete block design, were conducted to evaluate the effects of feeding live cultures of Lactobacillus acidophilus plus Propionibacterium freudenreichii on performance and carcass characteristics of feedlot cattle. British and British x Continental steers (240 steers in each experiment; 12 pens/treatment in each study; average initial BW = 370 ± 6 kg) were fed a 92% concentrate diet based primarily on steam-flaked corn. Four treatments were evaluated, which included a control diet (lactose carrier only) or diets containing 1 x 109 cfu/(steer · d) of P. freudenreichii (strain NP 24) with 1 x 107 (L), 1 x 108 (M), or 1 x 109 (H) cfu of L. acidophilus strain NP 51/(steer · d). Data were pooled for the 2 experiments. No differences (P > 0.10) were detected among treatments for final BW, final BW based on HCW, or DMI during various stages of the feeding period or overall. Likewise, no differences among treatments were observed for either ADG or carcass-adjusted ADG (P > 0.10), except for the tendency for a quadratic effect of NP 51 dose for the overall feeding period (P = 0.10), in which cattle fed M had a lower ADG than those fed L and H. Gain efficiency on a live BW basis was improved (P = 0.02) by NP 51 treatments compared with the control, with G:F responding quadratically to NP 51 dose for the overall feeding period (P = 0.05). In contrast to G:F based on live BW, carcass-adjusted G:F tended (P = 0.14) to decrease linearly with increasing NP 51 dose because the dressing percent tended (P = 0.12) to be less for steers fed direct-fed microbial compared with control cattle. Within the direct-fed microbial treatments, there also was a tendency (P = 0.13) for a linear decrease in the dressing percent as the NP 51 dose increased. No differences were observed in other carcass characteristics (P > 0.10), except tendencies for a quadratic increase in marbling score (P = 0.11) and percentage of USDA Choice cattle (P = 0.10). These data indicate that live cultures of L. acidophilus strain NP 51 plus P. freudenreichii strain NP 24 increased G:F of feedlot cattle fed steam-flaked corn-based diets by approximately 2%, but the effects depended on the dose of Lactobacillus.

Key Words: beef cattle • feedlot • Lactobacillus acidophilus • Propionibacterium freudenreichii


   INTRODUCTION
Top
 Abstract
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 LITERATURE CITED
 
As a result of growing public concern over the use of antibiotics and other growth-promoters in the animal feed industry, interest in the effects of direct-fed microbial (DFM) feed additives on animal performance and preharvest food safety issues has increased in recent years. Microorganisms used as DFM in ruminant nutrition include viable cultures of bacteria and fungi (Krehbiel et al., 2003Go).

Several DFM products are available for use by the feedlot industry (Brown et al., 2006Go), and these microbial cultures have sometimes improved G:F and ADG in beef cattle (Krehbiel et al., 2003Go). A review of research led Krehbiel et al. (2003)Go to conclude that DFM potentially increase ADG by 2.5 to 5% and G:F by 2% when fed to finishing cattle; however, effects on performance have not been consistent. These mixed results are presumably related to the different microbial species used in the DFM, strain composition within species, and dose of these products. Selected strains of Lactobacillus acidophilus have shown efficacy for decreasing fecal shedding and hide carriage of Escherichia coli O157 (Brashears et al., 2003Go; Peterson et al., 2007Go). Therefore, continued evaluation of DFM with defined conditions of microbial strains and varying doses is needed to characterize optimal conditions for both preharvest food safety issues and feedlot cattle performance. The objective of the current study was to evaluate the effects of DFM based on 3 doses of a specific strain of L. acidophilus fed in combination with 1 dose of a specific strain of Propionibacterium freudenreichii on performance and carcass characteristics of finishing beef steers.


   MATERIALS AND METHODS
Top
 Abstract
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 LITERATURE CITED
 
Cattle

All procedures involving live animals were conducted within the guidelines and approval of the Texas Tech University Animal Care and Use Committee.

For Exp. 1, three hundred eight steers (average arrival BW = 280 kg), primarily of British and Continental breeding, were purchased in 2 separate loads through an order buyer in Joplin, Missouri, and transported 950 km to the Texas Tech University Burnett Center in New Deal, Texas. For Exp. 2, two hundred sixty-nine steers of predominantly British breeding (average BW = 370 kg) were purchased and delivered 608 km from Apache, Oklahoma, to the Burnett Center. In both experiments, cattle were unloaded, housed in soil-surfaced pens, and allowed access to a 65% concentrate diet, Sudangrass hay, and water. Cattle were processed shortly after arrival, which included the following: 1) placement of a uniquely numbered ear tag in the left ear; 2) an individual BW measurement; 3) vaccination with infectious bovine rhinotracheitis, parainfluenza-3, bovine viral diarrhea virus, bovine respiratory syncytial virus modified live virus vaccine [Prism 9, Fort Dodge Animal Health, Overland Park, KS (Exp. 1) and Titanium 5, Agri-Labs, Des Moines, IA (Exp. 2)], and Clostridium chauvoeisepticum-novyi-sordelliperfringens types C and D bacterin toxoid (either Ultra Bac 7, Pfizer Animal Health, Exton, PA or Vision 7 with Spur, Intervet Inc., Millsboro, DE in Exp. 1 or Vision 7 with Spur in Exp. 2); and 4) deworming with moxidectin down the midline of the back (Cydectin, Fort Dodge Animal Health). After processing, the cattle were returned to the soil-surfaced pens. In Exp. 1, the cattle were fed for a growing period of 38 to 49 d (depending on arrival date), in which the intake of the 65% concentrate diet was gradually increased and ultimately switched to an 82% concentrate diet before the beginning of the experiment. The experiment began with cattle being fed the 82% concentrate diet, and the diet was switched to 92% concentrate (Table 1Go) 1 wk later. In Exp. 2, the intake of the 65% concentrate diet was gradually increased, with the diet being switched to 75% concentrate approximately1 wk after arrival. The 75% concentrate diet was fed when the experiment began and then switched to an 83.5% concentrate diet and the final 92% concentrate diet (Table 1Go) at 1-wk intervals thereafter.


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  		Table 1. Composition and analyzed nutrient content (DM basis) of diets containing different direct-fed microbial treatments
 
Treatment and Pen Assignments

Based on uniformity of body frame and BW, 240 steers were selected for use in each experiment. Cattle were sorted by BW and blocked from the lightest through the heaviest BW. Within each block, steers and treatments were assigned randomly to pens. Blocks were assigned to 4 contiguous pens in the Burnett Center (5 steers/pen; 48 pens total in each study; 12 pens/ treatment). For Exp. 1, steers in the heaviest 6 blocks were implanted with Revalor S (120 mg of trenbolone acetate + 24 mg of estradiol, Intervet Inc.), and steers in the lightest 6 blocks received a Revalor IS implant (80 mg of trenbolone acetate + 16 mg of estradiol, Intervet Inc.) at the beginning of the experiment. On d 56, steers in the lightest 6 blocks were reimplanted with Revalor S. For Exp. 2, all steers were implanted with Revalor S at the beginning of the experiment and were not reimplanted.

Experimental Diets and Treatments

The treatments consisted of a control diet containing a lactose carrier only (C) or the same diet with 1 of 3 DFM treatments. Each DFM treatment diet supplied 1 x 109 cfu/(steer · d) of P. freudenreichii (strain NP 24) plus increasing doses of L. acidophilus strain NP 51: low (L) = 1 x 107, medium (M) = 1 x 108, or high (H) = 1 x 109 cfu/(steer · d). In Exp. 1, the DFM treatments were added to the final diet by mixing in water. Each day, the contents of 1 packet of freeze-dried DFM culture were reconstituted with 2.5 L of distilled water in an individual sprinkler can that was labeled with the corresponding color code for the treatment. Each packet supplied the desired dose of DFM for all the cattle in a given treatment. The order of mixing and delivery throughout the experiment was C, L, M, and H, and in an effort to minimize cross-contamination, at least 1 batch of non-DFM feed was mixed and delivered after the H diet was delivered. Once the quantity of feed that would be used to feed all the cattle on a treatment was transferred to a mixer/delivery unit (Rotomix 84-8, Dodge City, KS; set on 4 load cells; scale readability = ± 0.45 kg), the contents of the appropriate sprinkler can were added to the diet and allowed to mix for approximately 3 min. For Exp. 2, the same treatment color-coding scheme and mixing order was followed; however, the culture packet was mixed with 1 kg of air-dried ground corn rather than distilled water before it was added to the mixer.

Management, Feeding, and Weighing Procedures

In both experiments, individual initial and final BW measurements (unshrunk BW data measured on a single day are reported) were collected in the morning before feeding (typically from 0600 to 0800) using a C & S Single-Animal Squeeze Chute (Garden City, KS) set on 4 Rice Lake Weighing Systems (Rice Lake, WI) load cells, which was calibrated with 453.5 kg ( ± 0.45 kg) of certified weights on the day before or day of use. In Exp. 1, steers were weighed individually every 28 d through d 84. Interim BW measurements for steers in Exp. 2 were obtained on a pen basis using a platform scale ( ± 2.27 kg) that was calibrated with 453.5 kg of certified weights before use (collected in the morning before feeding as with individual BW data). Cattle were fed for a weighted average of 141 and 138 d in Exp. 1 and 2, respectively.

Estimates of the approximate quantity of unconsumed feed were made in each of the 48 pens at 0700 to 0730 daily, from which the daily feed allotment per pen was determined. Bunk management was designed to leave little if any feed unconsumed (0 to 0.45 kg/pen) each day. Cattle were fed to appetite, with the delivery to each pen adjusted daily by the quantity of feed, if any, remaining in the bunk before the first feeding of the day. Feed was not allowed to substantially accumulate from one day to the next. At each 28-d weigh period, feed bunks were cleaned, and orts were weighed using an Ohaus electronic balance (Ohaus Corp., Pine Brook, NJ; readability = ± 45 g). Samples of feed left in the bunk were dried in a forced-air oven at 100° C for approximately 24 h to determine DM contents. The DM delivered to each pen was calculated by subtracting dry feed refusals from total DM delivered to each pen. The number of animals housed in each pen was multiplied by the number of days in the weigh period to determine animal days, which were then divided into the corrected total DM delivered to each pen to obtain the average DMI per steer for the period.

Weekly feed samples were taken from the mixer/delivery unit to determine the DM content of the diets. These samples were then composited for 28-d periods and ground to pass a Wiley mill (2-mm screen). In Exp. 1, ground samples were analyzed (AOAC, 1990Go) for DM (method 930.15), CP (method 954.01), ADF (method 973.18), Ca (method 968.08), and P (method 965.17) in laboratory facilities at Texas Tech University. In Exp. 2, samples were analyzed for DM, CP, ADF, Ca, and P by a commercial laboratory (SDK Laboratories, Hutchinson, KS). Results for chemical analyses are shown, along with the ingredient composition, in Table 1Go.

Carcass Evaluation

Based on BW and visual appraisal, blocks of cattle were sent to a commercial slaughter facility in Plainview, Texas, when approximately 60% of the group of cattle was expected to grade USDA Choice. Carcass data were obtained by personnel of West Texas A&M University Cattlemen’s Carcass Data Service in Exp. 1 and by Texas Tech University Meat Laboratory personnel in Exp. 2. Carcass measurements included HCW, LM area, marbling scores, KPH, 12th-rib fat thickness, calculated USDA yield grade (USDA, 1997Go), and USDA quality grade (based on marbling and maturity scores determined for each carcass).

Statistical Analyses

Before pooling the results of the 2 experiments, experiment x treatment interactions were tested using the GLM procedure (SAS Inst. Inc., Cary NC). Interactions were observed for ADG (P = 0.04) and G:F (P = 0.06) from d 0 to 28, G:F from d 0 to 84 (P = 0.02), and carcass yield grade (P = 0.05); however, the treatment effect was not significant (P > 0.30) for these variables, and the decision was made to consider experiment and experiment x treatment as random effects in a mixed model. Thus, data from the 2 experiments were subsequently pooled and analyzed as a randomized complete block design using the MIXED procedure of SAS. Pen was the experimental unit for all analyses. Variables included were BW, DMI, ADG, G:F, HCW, carcass-adjusted variables (determined using carcass-adjusted final BW, which was calculated as HCW divided by the average dressing percentage for all 4 treatments within an experiment), and other nondiscrete carcass characteristics. The model statement included the fixed effect of treatment, with random effects of experiment, block within experiment, and the experiment x treatment interaction. The Glimmix procedure of SAS was used to analyze the proportion of cattle in each pen grading USDA Choice or greater. The model was the same as for the performance data. For all analyses, specific orthogonal contrasts were used to test the following: (1) control vs. NP 51 and (2) linear and quadratic effects of strain NP 51 dose.


   RESULTS AND DISCUSSION
Top
 Abstract
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
LITERATURE CITED
 
Performance data are presented in Table 2Go. No differences for final BW, carcass-adjusted final BW, period DMI, or total DMI (P > 0.10) were detected among treatments. Similar findings were reported recently by Peterson et al. (2007)Go, who fed the same NP 51 strain as we did (equivalent to our H treatment) but did not include P. freudenreichii (strain NP 24). Previous research has often shown no difference in DMI between control and DFM-treated steers (Gill et al., 1987Go; Ware et al., 1988Go). Rust et al. (2000)Go also reported no differences for overall average DMI between control and DFM-treated cattle. Those authors fed a control diet and treatment diets supplying 106 cfu/(steer · d) of L. acidophilus strain NP 45, 106 cfu/(steer · d) of 2 strains of L. acidophilus (strains NP 45 and NP 51), or 108 cfu/ (steer · d) of strains NP 45 and NP 51; all DFM diets also supplied 109 cfu/(steer · d) of P. freudenreichii strain NP 24. In contrast to the present results, DFM steers had a heavier final BW than control steers (Rust et al., 2000Go). Galyean et al. (2000)Go evaluated performance differences between control and different doses (per steer daily) and combinations of L. acidophilus (control; 1 x 106 cfu of L. acidophilus strain NP 45; 1 x 104 cfu of L. acidophilus strain NP 45 + 1 x 104 cfu of L. acidophilus strain NP 51; and 1 x 106 cfu of L. acidophilus strain NP 45 +1 x 106 cfu of L. acidophilus strain NP 51). As in the Rust et al. (2000)Go study, all DFM treatments supplied 1 x 109 cfu/(steer · d) of P. freudenreichii strain NP 24. No difference for total DMI was noted among treatments, but final BW and carcass-adjusted final BW were greater for the average of all DFM treatments vs. the control diet. Kiesling et al. (1982)Go supplemented steers with either a viable Lactobacillus culture or no DFM and reported no differences in final BW after a 28-d receiving study and a subsequent 209-d finishing trial. The DMI during the finishing phase, however, was greater by calves treated with a DFM during the 28-d receiving study.


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  		Table 2. Pooled results for effects of graded doses of live cultures of Lactobacillus acidophilus and Propionibacterium freudenreichii on performance by feedlot cattle in Exp. 1 and 2
 
No differences (P > 0.10) among treatments were observed for ADG (Table 2Go), except the tendency for a quadratic effect of NP 51 dose from d 0 to 56 (P = 0.08) and from d 0 to the end (P = 0.10). Carcass-adjusted ADG did not differ (P > 0.10) among treatments. Swinney-Floyd et al. (1999)Go reported increased ADG by calves that received DFM treatments (either Propionibacterium strain P-63 alone or combined with L. acidophilus strain LA53545) at the beginning of the finishing phase; however, the response diminished over the entire 120-d feeding period. As noted previously, Kiesling et al. (1982)Go conducted a 28-d receiving and a subsequent 209-d finishing trial. No differences in ADG between calves treated with a DFM and control calves were noted during the 28-d receiving phase; however, calves treated with the DFM during receiving had greater ADG during the finishing period than control calves. Gill et al. (1987)Go reported that supplementing newly received calves with 0.7 x 109 cfu/animal daily of live bacteria (Fastrak; Conklin Company Inc., Shakopee, MN) increased ADG by 9.3% compared with control calves. Ware et al. (1988)Go combined data from 8 feedlot trials at 6 different locations and reported that steers receiving L. acidophilus [1 x 108 cfu/(steer · d) of strain BT1386] had increased ADG (approximately 4%) and better G:F (approximately 3%) than control steers. Likewise, Galyean et al. (2000)Go found that ADG by finishing beef steers from d 0 to 56, d 0 to end, and on a carcass-adjusted basis was greater (P ≤ 0.08) for the average of all DFM treatments (described previously) vs. the control treatment.

Gain efficiency based on live weight was greater (P = 0.02) for the average of the 3 NP 51 doses than for the control, but within the DFM treatments, G:F responded quadratically to NP 51 dose from d 0 to 56 (P = 0.04) and from d 0 to end (P = 0.05). In contrast to G:F based on live weight, carcass-adjusted G:F tended (P = 0.14) to decrease linearly as NP 51 dose increased, reflecting differences in dressing percent. In a 28-d receiving or subsequent 209-d finishing trial, Kiesling et al. (1982)Go reported no differences in G:F for control vs. DFM-treated calves. As a result of an increased ADG and no changes in DMI, Gill et al. (1987)Go reported that G:F for DFM-treated calves was improved 9.5% over that of control calves. Swinney-Floyd et al. (1999)Go did not provide DMI results for a 120-d finishing trial; however, using either Propionibacterium strain P-63 alone or combined with L. acidophilus strain LA53545 improved G:F by treated steers, without increasing ADG for the feeding period. Galyean et al. (2000)Go noted that G:F was improved for the average of all DFM treatments vs. the control treatment for d 0 to 56 (P = 0.01) and d 0 to 112 (P = 0.10) but was not different for the overall feeding period. As a result of increased ADG and no change in DMI, Rust et al. (2000)Go reported that G:F for the entire feeding period was improved for 2 treatments (109 cfu) of P. freudenreichii (strain NP 24) + 106 cfu/ (steer · d) of L. acidophilus (strain NP 45) and 109 cfu of P. freudenreichii (strain NP 24) + 106 cfu/(steer · d) from each of 2 strains of L. acidophilus strains (strains NP 45 and NP 51) over that of control steers. Recently, Brown et al. (2006)Go fed a control diet or a diet top-dressed with L. acidophilus (supplied 5 x 108 cfu/animal daily) for 28 d followed by P. freudenreichii (supplied 1 x 109 cfu/animal daily) from d 29 to slaughter. For the overall feeding period, DMI, carcass-adjusted ADG, and carcass-adjusted G:F were not altered by treatment.

The mechanism by which DFM sometimes improve animal performance is not clearly understood. In most cases, research has shown that feeding lactate-utilizing bacteria, lactate-producing bacteria, or both to feedlot cattle results in a 2.5 to 5% increase in ADG and an approximately 2% improvement in G:F, whereas DMI results are inconsistent (Krehbiel et al., 2003Go). Krehbiel et al. (2003)Go suggested that DFM might enhance energy production and efficiency of energy utilization by increasing ruminal propionate concentration. Furthermore, DFM could decrease the risk for subacute acidosis by decreasing the time ruminal pH remains below 5.6 (Krehbiel et al., 2003Go), but data to support these mechanisms are lacking.

Effects of treatments on carcass characteristics are presented in Table 3Go. Hot carcass weight did not differ (P > 0.10) among treatments. Dressing percent tended (P = 0.12) to be less for NP 51-fed steers, with a tendency of a linear decrease (P = 0.13) as the NP 51 dose increased. Reasons for this change in dressing percent are not readily evident, and this change is not necessarily consistent with other results in the literature. No differences were observed in other carcass characteristics (P > 0.10), except a tendency for a quadratic response in marbling score (P = 0.11) and percentage of USDA Choice cattle (P = 0.10), which were greatest with the M treatment. Ware et al. (1988)Go reported that L. acidophilus BT1386-treated steers had no differences in USDA yield and quality grades or dressing percentage compared with controls. Carcass characteristics also were not changed by DFM treatments in the studies conducted by Swinney-Floyd et al. (1999)Go and Rust et al. (2000)Go. Galyean et al. (2000)Go noted increased HCW (P ≤ 0.05) for the average of DFM treatments vs. control, but other carcass characteristics did not differ among treatments. Huck et al. (2000)Go fed heifers a control diet or 1 of 4 treatments (10 pens/treatment): (1) L. acidophilus BG2FO4 for the entire period, (2) P. freudenreichii P-63 for the entire period; (3) L. acidophilus BG2FO4 for 28 d, followed by P. freudenreichii P-63 for the remainder of the period; and (4) P. freudenreichii P-63 for 28 d, followed by L. acidophilus BG2FO4 for the remainder of the period. These authors reported a trend for the percentage of Choice or Prime carcasses to be greater when P. freudenreichii P-63 was fed for the entire feeding period than for other treatments. Brown et al. (2006)Go observed increased 12th-rib fat for cattle fed the control diet compared with cattle fed a finishing diet containing L. acidophilus for 28 d followed by P. freudenreichii from d 29 to slaughter.


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  		Table 3. Pooled results for effects of graded doses of live cultures of Lactobacillus acidophilus and Propionibacterium freudenreichii on carcass characteristics of finishing beef steers in Exp. 1 and 2
 
With respect to shedding of E. coli O157, results for fecal samples taken during the course of Exp. 1 and 2, as well as hide samples at the time of shipment to slaughter, have been summarized elsewhere. For Exp. 1, Younts-Dahl et al. (2005)Go reported that the L, M, and H treatments resulted in a lower prevalence (P < 0.01) of E. coli O157 throughout the feeding period than the C treatment, with a linear decrease (P < 0.01) in prevalence as the dose of L. acidophilus strain NP 51 increased. Similarly, the DFM treatments decreased prevalence on hides at slaughter by an average of approximately 46%. For Exp. 2, Stephens et al. (2007)Go reported that cattle fed the L and H doses of NP 51 were 69 and 74% less likely (P < 0.01), respectively, to have detectable E. coli O157 in their feces than C cattle, but the M dose did not affect fecal presence of E. coli O157. Only the L dose decreased (P = 0.05) E. coli O157 isolated from hides.

In the current study, ADG and DMI were not affected by DFM treatments. The G:F expressed on a live-weight basis was improved for the overall feeding period by approximately 2 to 3% with L (1 x 107 cfu) and H (1 x 109 cfu) doses of L. acidophilus strain NP 51, but the M dose (1 x 108 cfu) had little effect on G:F compared with the control treatment. Reasons for the quadratic effect of NP 51 dose are not clear and deserve further study. In addition, carcass characteristics were not markedly affected by the DFM treatments in the current study, but dressing percent tended to be decreased with the DFM treatments. Unfortunately, many previous studies with DFM have not specified the dose or the particular strain(s) of microorganisms used. Our results suggest that microbial strain and dose effects are important factors to consider when determining the optimal use strategy for a DFM based on L. acidophilus plus a fixed dose of P. freudenreichii. Similarly, based on results from samples collected from cattle in our 2 experiments and reported elsewhere, strain and dose factors also seem to be important for effects of L. acidophilus on fecal and hide prevalence of E. coli O157.


   Footnotes
 
1 Supported, in part, by funds from Nutrition Physiology Corp. (Guymon, OK). The Jessie W. Thornton Chair in Animal Science Endowment at Texas Tech University also provided funding to support this research. We thank K. Robinson and R. Rocha at Texas Tech University for technical support. Back

2 Corresponding author: judson.vasconcelos{at}ttu.edu

Received for publication August 16, 2007. Accepted for publication November 21, 2007.


   LITERATURE CITED
Top
 Abstract
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 LITERATURE CITED
 


AOAC. 1990. Official Methods of Analysis. 14th ed. Assoc. Off. Anal. Chem., Arlington, VA.

Brashears, M. M., M. L. Galyean, G. H. Loneragan, J. E. Mann, and K. Killinger-Mann. 2003. Prevalence of Escherichia coli O157:H7 and performance by beef feedlot cattle given Lactobacillus direct-fed microbials. J. Food Prot. 66:748–754.[Medline]

Brown, M. S., C. Smith, and D. Mitchell. 2006. Effects of Micro-Cell on feedlot performance by yearling beef steers. Pages 67–70 in Beef Cattle Research in Texas 2006. http://animalscience.tamu.edu/main/academics/beef/bcrt/BCR2006Final.pdf Accessed May 15, 2007.

Galyean, M. L., G. A. Nunnery, P. J. Defoor, G. B. Salyer, and C. H. Parsons. 2000. Effects of live cultures of Lactobacillus acidophilus (Strains 45 and 51) and Propionibacterium freudenreichii PF-24 on performance and carcass characteristics of finishing beef steers. Burnett Center Progress Report No. 8. http://www.afs.ttu.edu/burnett_center/progress_reports/bc8.pdf Accessed Sep. 15, 2003.

Gill, D. R., R. A. Smith, and R. L. Ball. 1987. The effect of probiotic feeding on health and performance of newly-arrived stocker calves. Okla. Agric. Exp. Stn. MP-119:202–204.

Huck, G. L., K. K. Kreikemeier, and G. A. Ducharme. 2000. Effects of feeding two microbial additives in sequence on growth performance and carcass characteristics of finishing beef steers. http://www.oznet.ksu.edu/library/lvstk2/srp850.pdf Accessed Sep. 15, 2003.

Kiesling, H. E., G. P. Lofgreen H, and J. D. Thomas. 1982. A viable Lactobacillus culture for feedlot cattle. Proc. West. Sec. Am. Soc. Anim. Sci. 33:53–56.

Krehbiel, C. R., S. R. Rust, G. Zhang, and S. E. Gilliland. 2003. Bacterial direct-fed microbials in ruminant diets: Performance response and mode of action. J. Anim. Sci. 81:E120–E132.[Abstract/Free Full Text]

Peterson, R. E., T. J. Klopfenstein, G. E. Erickson, J. Folmer, S. Hinkley, R. A. Moxley, and D. R. Smith. 2007. Effect of Lactobacillus acidophilus strain NP51 on Escherichia coli O157:H7 fecal shedding and finishing performance in beef feedlot cattle. J. Food Prot. 70:287–291.[Medline]

Rust, S. R., K. Metz, and D. R. Ware. 2000. Effects of BovamineTM rumen culture on the performance and carcass characteristics of feedlot steers. http://beef.ans.msu.edu/Extension/Publications/Beef__Sheep_and_Forage_Researc/MSU_Beef_Sheep_and_Forage_Report_2000.pdf Accessed Sep.15, 2003.

Stephens, T. P., G. H. Loneragan, and M. M. Brashears. 2007. Reduction of Escherichia coli O157 and Salmonella in feces and on hides of feedlot cattle using various doses of a direct-fed microbial. J. Food Prot. 70:2386–2391.[Medline]

Swinney-Floyd, D., B. A. Gardner, F. N. Owens, T. Rehberger, and T. Parrot. 1999. Effect of inoculation with either Propionibacterium strain P-63 alone or combined with Lactobacillus acidophilus strain LA53545 on performance of feedlot cattle. J. Anim. Sci. 77(Suppl. 1):77. (Abstr.)

USDA. 1997. Standards for grades of carcass beef. Agric. Mark. Serv., USDA, Washington, DC.

Ware, D. R., P. L. Read, and E. T. Manfredi. 1988. Pooled summary of eight feedlot trials evaluating performance and carcass characteristics of steers fed Lactobacillus acidophilus strain BT1386. J. Anim. Sci. 66(Suppl. 1):436. (Abstr.)

Younts-Dahl, S. M., G. D. Osborn, M. L. Galyean, J. D. Rivera, G. H. Loneragan, and M. M. Brashears. 2005. Reduction of Escherichia coli O157 in finishing beef cattle by various doses of Lactobacillus acidophilus in direct-fed microbials. J. Food Prot. 68:6–10.[Medline]



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