Effects of feeding 10-G direct-fed microbial on feedlot performance, carcass characteristics, and prevalence of Salmonella in subiliac lymph nodes of feedlot steers

Abstract

Yearling crossbred beef steers [n = 6,400; initial body weight (BW) 358 kg] were used to investigate the efficacy of a direct-fed microbial upon animal growTh performance, carcass characteristics, and prevalence of Salmonella in subiliac lymph nodes after a feeding duration of 182 d. Steers were allocated to 1 of 32 pens [n = 200/pen] within 16 total blocks, and assigned to 1 of 2 dietary treatments; no probiotic (CON) or 2 g*steer^-1*d^-1 of Lactobacillus acidophilus, Enterococcus faecium, Pediococcus pentosaceus, Lactobacillus brevis and Lactobacillus plantarum providing a total of 1 billion CFU (10-G). At harvest, subiliac lymph nodes were randomly obtained from 40 animals from each pen for blocks 1 through 10. Data were analyzed as a randomized complete block design, and pen served as the experimental unit. No differences (P ≥ 0.26) were observed between treatments for DMI, final BW, average daily gain, or feed efficiency. When evaluating carcass characteristics, there were no differences (P ≥ 0.15) for hot carcass weight or liver abscess prevalence. However, dressed carcass yield differed (P = 0.02) between treatments (CON = 64.74%, 10-G = 64.52%). No differences (P ≥ 0.12) were observed for marbling score, longissimus muscle area, 12^th rib s.c. fat depth, or USDA quality grade outcomes. Lower frequency (P < 0.01; CON = 36.95%, 10-G = 23.60%) of Salmonella positive subiliac lymph nodes was observed for cattle supplemented dietary 10-G, whereas concentration of Salmonella quantifiable samples did not differ (P = 0.23) between treatments (CON = 0.84 Log₁₀CFU/g, 10-G = 0.63 Log₁₀CFU/g). In conclusion, the supplementation of 10-G direct fed microbial did not influence live or carcass performance within this trial; however, prevalence of Salmonella positive subiliac lymph nodes was reduced.

Direct-fed microbial, 10-G, reduces the prevalence of Salmonella in beef carcass subillac lymph nodes.

INTRODUCTION

Non-typhoidal Salmonella is the leading cause of bacterial foodborne illness in the United States, with an estimated 1.35 million cases annually (CDC, 2019). Salmonella has been identified within beef products in multiple countries including the U.S. (Rose et al., 2002; Bosilevac et al., 2009), Mexico (Zaidi et al., 2008), and Egypt (Sallam et al., 2014). During the years 2014–2023, Salmonella contaminated beef was reported to be responsible for 22 outbreaks; primary serotypes associated with those illnesses were Brandenburg, Newport, and Typhimurium (CDC, 2024). Although this pathogen is reported to be carried on the hide of feedlot cattle (Arthur et al., 2008a), lymph nodes are of primary concern in ground beef products because of their frequent incorporation into ground beef trimmings (Arthur et al., 2008b; Koohmaraie et al., 2012) and their ability to harbor Salmonella (Samuel et al., 1980; Arthur et al., 2008b; Brown et al., 2020).

Pre-harvest interventions to reduce Salmonella risk may include cross-protective vaccines (Mahan et al., 2012; Heithoff et al., 2015), direct-fed microbials (DFMs; Stephens et al., 2007; Flach et al., 2022; Mayer et al., 2022; Word et al., 2022), and bacteriophages (Xie et al., 2016). Post-harvest interventions, such as carcass washes, have been reported to be mostly ineffective at reducing Salmonella contamination from lymph nodes encased in fat (Hanson et al., 2016).

Direct-fed microbials including Lactobacillus acidophilus and Propionibacterium freudenreichii are often used in the cattle feeding industry to improve feeding performance (Krehbiel et al., 2003). Lactobacillus acidophilus and Propionibacterium freudenreichii (Stephens et al., 2007; Flach et al., 2022), Lactobacillus acidophilus, Enterococcus faecium, Pediococcus pentosaceus, Lactobacillus brevis and Lactobacillus plantarum (Mayer et al., 2022), and Bacillus subtilis (Word et al., 2022) have been reported to reduce the pathogenic load of Salmonella in fecal contents and lymph nodes of cattle. Previous literature has reported that DFMs reduce pathogenic microorganisms through alleviation of intestinal inflammation (Salminen et al., 1996), competitive attachment to the intestinal mucosa (Muralidhara et al., 1977), and modulating immune function (Erickson and Hubbard, 2000; Isolauri et al., 2001).

Specifically regarding the DFM marketed as 10-G (containing Lactobacillus acidophilus, Enterococcus faecium, Pediococcus pentosaceus, Lactobacillus brevis and Lactobacillus plantarum), previous research has conflicting results. Mayer et al. (2022) reported a decrease in subiliac lymph node Salmonella prevelance, a tendency to increase Choice and decrease Select quality grades, and decreased proportion of animals with major liver abscesses for cattle supplemented 10-G. In contrast, Tilton et al. (2024) reported no differences for any live performance, carcass characteristics, liver, or Salmonella outcomes between cattle supplemented 10-G and negative controls. Similarly, Neuhold et al. (2012) only observed a difference in visually-estimated percentage of kidney, pelvic, and heart fat, with the 10-G treatment having greater internal fat than the control treatment. These three studies yielded vastly different results, thus, the objective of this trial was to evaluate the effects of feeding 10-G direct-fed-microbial on feedlot performance, carcass characteristics, and prevalence of Salmonella in subiliac lymph nodes of feedlot steers.

MATERIALS AND METHODS

All live animal experimental procedures followed the guidelines described in the Guide for the Care and Use of Agricultural Animal in Agricultural Research and Teaching (FASS, Savoy, IL).

Cattle Processing and Experimental Design

A priori power calculations suggested approximately 15 replicates per treatment were necessary to detect a 1% difference in daily gain, feed efficiency, and carcass weight between treatments (1 – β = 0.80).

Crossbred yearling steers were received from Texas, New Mexico, Georgia, and Oklahoma between 17 March 2022 and 04 May 2022, at a commercial feedlot in the Texas panhandle. Steers were blocked by day of arrival (15 independent days) into 16 blocks (32 pens total); each pen was consistently stocked at a density of 200 animals per pen. Pen served as the experimental unit in this randomized complete block design. At initial processing, every two steers within each arrival source were allocated randomly as they exited the processing barn into 1 of 2 treatments: 0 g*animal^-1*d^-1 (CON) or 2 g*animal^-1*d^-1 (10-G; providing 500 million CFU per g of Lactobacillus acidophilus, Enterococcus faecium, Pediococcus pentosaceus, Lactobacillus brevis, and Lactobacillus plantarum). Standard feedlot treatment and disease controls were implemented and consistent for all cattle across experimental treatments. Each block was managed similarly in respects to final weight, shipment, and harvest, with each pen within a block being marketed to an equal days on feed (DOF).

At the time of initial processing, individual body weight (BW) was collected, and a unique lot identification ear tag was applied to each steer. To be eligible for inclusion in this study, steers were required to have an individual body weight (BW) between 317.5 and 385.6 kg. Steers were implanted with Revalor-XS (Merck Animal Health, Madison, NJ), administered Bovi-Shield GOLD (Zoetis, Parsippany, NJ) for viral respiratory pathogens and UltraChoice 7 (Zoetis) for clostridial species. Internal and external parasites were controlled via administration of Noromectin (Norbrook Inc, Lenexa, KS) and Synanthic (Boehringer Ingelheim Vetmedica, St Joseph, MO).

Steers were fed twice daily, a common diet only differing by inclusion or exclusion of the 10-G probiotic (Table 1). Steers received a complete starter feed (RAMP; Cargill Corn Milling, Dalhart, TX) as the starter diet, in which 10-G was not included. All other basal diets were formulated to meet or exceed the National Research Council (2000)  feeding requirements. Following the completion of the starter diet regimen, granular 10-G was supplemented via the micro-machine (Comco, Ida Grove, IA) at a target dosage of 2.0 g*animal^-1*d^-1. Diets were made daily, and samples were taken weekly for chemical composition assays determined by Servi-tech Laboratories (Amarillo, TX).

Table 1.

Ingredient formulation and analyzed composition of intermediate and finishing diets, and diets during the beta-agonist feeding period^1,2

	Intermediate diet		Finishing diet		Beta-agonist diet
Ingredient	CON	10-G	CON	10-G	CON	10-G
Steam-flaked corn, %	43.0	43.0	65.8	65.8	69.0	69.0
Wheat silage, %	18.6	18.6	2.5	2.5	6.1	6.1
Corn silage, %	3.6	3.6	7.8	7.8
Sweet Bran Plus, %3,4	29.6	29.6	17.3	17.3	16.1	16.6
Whey/Urea Blend, %	2.6	2.6	4.2	4.2	4.1	4.1
Tallow, %	2.7	2.7	2.4	2.4	1.7	1.7
Chemical Composition5
Crude Protein, %	14.6	14.4	13.9	14.0	13.2	13.4
NDF, %	26.8	27.5	16.8	16.3	15.7	16.1
ADF, %	14.9	15.7	8.0	7.8	7.0	7.1

¹Treatments included no DFM (direct-fed microbial) contained in the diet (CON) and a diet containing L. acidophilus, E. faecium, P. pentosaceus, L. brevis, and L. plantarum fed at 2 g/steer/d providing 1 × 10⁹ CFU (10-G) (Life Products, Inc., Norfolk, NE).

²All values on a DM basis.

³Wet corn gluten feed (Sweet Bran), alfalfa hay, and cottonseed hulls, Cargill, Dalhart, TX.

⁴Supplments included Monensin sodium 90.7 g/lb (Huvepharma, Peachtree City, GA.), Tylosin phosphate 100 g/lb (Huvepharma, Peachtree City, GA.), and Ractopamine hydrochloride 45.4 g/lb (Zoetis, Parsippany, NJ.).

⁵As determined by Servi-tech Laboratories (Amarillo, TX).

Study cattle were observed daily by pen riders, between 0600 and 1000 hours, with a single pen rider examining both pens within a statistical block when possible. Cattle were treated between 0900 and 1400 hours, and all pulls within a block were treated at the same hospital facility. Cattle pulled for the treatment of bovine respiratory disease (BRD) and that

had a temperature greater than 104^oF or that had moderate to severe signs of depression or weakness were administered tildipirosin (Zuprevo18; Merck Animal Health) at a dose of 4 mg/kg BW according to Beef Quality Assurance guidelines. Standard feedlot protocols were implemented for the treatment of diseases unrelated to BRD and were consistent for cattle between experimental treatments. Cattle were railed if pulled for a disease for which no practical treatment plan was available at the feedlot and/or if the animal had been treated more than twice. Mortalities were subject to postmortem examination by a licensed veterinarian or trained feedlot employee.

Sample and Data Collection

Steers were fed an average of 182 d (range of 177 to 195 d) prior to being transported 56 km to a commercial beef processor (USDA Establishment #3D; JBS; Cactus, TX) for harvest. Carcass data were collected by trained personnel from the West Texas A&M University—Beef Carcass Research Center (Canyon, TX). Visual lot tags were recorded, and each carcass was assigned an individual identification tag for carcass evaluation. A modified Elanco Liver Check System (Brown and Lawrence, 2010) was utilized for evaluation of liver outcomes (edible = no abscesses, A- = 1 or 2 small abscesses, A = 2 to 4 small active abscesses, A+ = 1 or more large active abscesses, A + Adhesion = liver adhered to the diaphragm and/or gastrointestinal tract, A + Open = open liver abscess, A + Adhesion/Open = liver adhered to the diaphragm and/or gastrointestinal tract and open liver abscess). Additionally, other liver abnormalities were recorded, including telangiectasias, cirrhosis, flukes, and contamination. During the harvest process, 40 animals (representing ≥ 20% of pen individuals) from each pen were randomly chosen for subiliac lymph node (SLN) collection. Each SLN was excised intact and placed in an individual bag with a label corresponding to the feedlot pen. Samples of SLN were chilled on wet ice and shipped overnight to Food Safety Net Services (San Antonio, TX) for third-party Salmonella determinations. Carcass characteristics (marbling, quality grade, 12^th-rib back fat, longissimus muscle area, and yield grade) were obtained from vision grading (VBG 2000, Marel E + V, Oranienburg, Germany) camera data.

Salmonella Analysis

Upon arrival at Food Safety Net Services, SLN were trimmed of excess fat and fascia, submerged in boiling water for 3 to 5 s, weighed, placed in a stomacher bag (Seward Model 400 or equivalent, Bohemia, NY) and pulverized. If total SLN weight was greater than 10 g, 80 mL of BAX MP (Hygiena, Camarillo, CA) media was used, if SLN weight was less than 10 g, 40 mL of media was used. To achieve a homogenized sample, BAX MP media was added to the stomacher bag and hand massaged. Once homogenized, 3 mL of the solution was removed and incubated for 6 h at 42^◦C (AOAC# 081201). Following incubation, samples were examined for Salmonella with the BAX Q7 machine, utilizing the real time (RT) assay (Hygiena, Camarillo, CA). If the sample was negative, incubation was initiated for another 12 to 18 h and reexamined. Results were then analyzed and quantified via the Hygiena Quant Calculator to determine Log₁₀CFU/g.

Statistical Analysis

The experimental design of this study was a randomized complete block design with a one-way treatment structure (negative control or 10-G). Pen was the experimental unit. Continuous variables were analyzed using the GLIMMIX procedure of SAS (version 9.4, SAS Inst. Inc., Cary, NC). The default Gaussian distribution and Identity link were used. Dietary treatment was the fixed effect and block was a random effect; the LSMEANS option was used to generate pen-level treatment means. Additionally, because a difference was observed (P = 0.0483) in the initial BW between treatments, initial BW was tested in the statistical model as a covariate for growth and weight variables (average daily gain, gain:feed, BW, hot carcass weight, dressed carcass yield). Inclusion of initial BW as a covariate did not improve the statistical model for growth and weight and was removed in the final model. Frequency of liver scores as well as frequency of quality grade and yield grade outcomes were analyzed as a series of binomial proportions using the GLIMMIX procedure and the SOLUTION option. Pen-level treatment frequencies were generated using the ILINK option. The Binomial distribution and Logit link were used. Authors recognize that multiple binomial comparisons increase risk of type-I errors. Salmonella prevalence was analyzed as a binomial proportion using the GLIMMIX procedure and the SOLUTION option. The Binomial distribution and Logit link were used. Differences were considered significant at P ≤ 0.05 and trends are noted at 0.05 < P ≤ 0.10.

Blinding

Personnel directly and indirectly involved with this study including pen riders, cattle doctors, feed managers, feed truck drivers, transporters, the beef processor, carcass data and subiliac lymph node collectors, the microbiology laboratory, and the study sponsor were blinded to treatment until after statistical analysis had concluded and results were determined. Only the principal live phase investigator, feedlot managers, and feed manufacturing manager were aware of treatment codes.

RESULTS AND DISCUSSION

Animal Accountability

The trial began with n = 3,200 steers in the CON treatment and n = 3,200 steers in the 10-G treatment; n = 6,288 animals were harvested at the commercial abattoir (n = 3,140 for CON treatment; n = 3,148 for 10-G treatment). Some animals did not complete the study due to death (n = 30 for CON treatment; n = 24 for 10-G treatment) or removal as a railer (n = 28 for CON treatment; n = 21 for 10-G treatment).

Live Performance

Animal growth performance data are presented in Table 2. Initial BW differed (P = 0.05) between treatments (10-G = 359.3 and CON = 358.1 kg). There were no differences in DMI, average daily gain (ADG), gain:feed (G:F), or final BW (P ≥ 0.26) between steers fed CON and 10-G diets, respectively. Previous studies utilizing 10-G have reported that supplementation with Lactobacillus acidophilus, Enterococcus faecium, Pediococcus pentosaceus, Lactobacillus brevis and Lactobacillus plantarum did not alter ADG, DMI, or G:F (Neuhold et al., 2012; Luebbe et al., 2013; Kenney et al., 2015; Mayer et al., 2022; Tilton et al., 2024). Similarly, Elam et al. (2003), Luebbe et al. (2013), Cull et al. (2015), and Wilson et al. (2016) reported that dietary supplementation with Lactobacillus acidophilus and Propionibacterium freudenreichii did not alter ADG or DMI; however, Cull et al. (2015) reported improved G:F for DFM supplemented cattle whereas Elam et al. (2003), Luebbe et al. (2013) and Wilson et al. (2016) reported no difference in G:F. Krehbiel et al. (2003) reported that steers receiving diets inclusive of Lactobacillus acidophilus and Propionibacterium freudenreichii had a greater ADG, heavier final BW, a tendency for greater DMI, and no difference in G:F. Word et al. (2022) indicated that supplementation with Bacillus subtilis tended to improve ADG and G:F with no difference in DMI.

Table 2.

Live growth performance and health outcomes of steers fed 10-G compared with non-supplemented control steers

	TRT1
Item	CON	10-G	SEM	P-value
n pens	16	16	-	-
n steers	3200	3200	-	-
Initial BW2, kg	358.1	359.3	1.42	0.05
Final BW, kg	641.0	640.2	3.56	0.63
DMI2, kg	9.63	9.67	0.08	0.26
ADG2, kg	1.52	1.52	0.02	0.78
G:F2	0.157	0.156	0.06	0.45
Railers, %	0.85	0.64	-	0.33
Mortality, %	0.94	0.75	-	0.43
Morbidity, %	18.41	17.44	-	0.33

¹Treatments included no DFM (direct-fed microbial) contained in the diet (CON) and a diet containing L. acidophilus, E. faecium, P. pentosaceus, L. brevis, and L. plantarum fed at 2 g/steer/d providing 1 × 10⁹ CFU (10-G) (Life Products, Inc., Norfolk, NE).

²ADG = Average daily gain; BW = Body weight; DMI = Dry matter intake; G:F = gain to feed.

The current study did not observe differences (P ≥ 0.33) in morbidity, mortality, or railers between CON and 10-G treatments. Few studies report morbidity or mortality associated with DFM supplementation. Mayer et al. (2022) and Tilton et al. (2024) both reported equivalent frequency of morbitities and mortalities between cattle supplemented Lactobacillus acidophilus, Enterococcus faecium, Pediococcus pentosaceus, Lactobacillus brevis and Lactobacillus plantarum and those offered the control ration. In contrast, Word et al. (2022) reported decreased morbidity concomitant with no change in mortality when cattle were supplemented Bacillus subtilis.

Liver Outcomes

Liver outcome frequencies did not differ (P ≥ 0.12) between the 10-G and CON treatments for any liver outcome (Table 3). Proportion of edible livers was observed to be 74.48 and 73.11% for the CON and 10-G treatments, respectively. In contrast, the proportion of abscessed livers was 20.42% and 20.99% for the CON and 10-G treatments, respectively. These edible and abscess rates are similar to that reported by Brown and Lawrence (2010) and Herrick et al. (2022). These data are contradictory to those reported by Mayer et al. (2022), in which 10-G reduced the proportion of livers exhibiting a major abscess (A+, A + Open, A + Adhesion, and A + Adhesion/Open) and tended to decrease the total percentage of abscessed livers. Similar to the current study, Neuhold et al. (2012), Luebbe et al. (2013), and Tilton et al. (2024) reported the addition of 10-G within the diet did not alter liver abscess prevalence or severity between treatments. Luebbe et al. (2013) and Wilson et al. (2016) also indicated that supplementation with Lactobacillus acidophilus and Propionibacterium freudenreichii did not alter liver abscess scores. Moreover, Word et al. (2022) reported no change in liver score outcomes when cattle were supplemented Bacillus subtilis.

Table 3.

Liver scores of steers fed 10-G compared with non-supplemented control steers

	TRT1
Item	CON	10-G	SEM	P-value
Liver score2, %
Edible	74.48	73.11	-	0.27
Abscessed	20.42	20.99	-	0.61
A-	10.50	10.76	-	0.76
A	1.17	1.40	-	0.43
A+	0.96	0.60	-	0.12
A + Open	0.66	0.84	-	0.41
A + Adhesion	5.73	5.90	-	0.79
A + Adhesion/Open	0.52	0.48	-	0.84
Other
Flukes	1.88	1.49	-	0.25
Telangiectasias	0.31	0.34	-	0.85
Cirrhosis	0.30	0.22	-	0.56
Contamination	2.22	3.63	-	0.14

¹Treatments included no DFM (direct-fed microbial) contained in the diet (CON) and a diet containing L. acidophilus, E. faecium, P. pentosaceus, L. brevis, and L. plantarum fed at 2 g/steer/d providing 1 × 10⁹ CFU (10-G) (Life Products, Inc., Norfolk, NE).

²Modified Elanco Liver Check System (Brown and Lawrence, 2010). Edible = no abscesses, A- = 1 or 2 small abscesses, A = 2 to 4 small active abscesses, A+ = 1 or more large active abscesses, A + Adhesion = liver adhered to the diaphragm or gastrointestinal tract, and A + Open = open liver abscesses, A + Adhesion/Open = liver adhered to the diaphragm or gastrointestinal tract and open abscess.

Carcass Performance

Hot carcass weight did not differ (P = 0.16; CON = 414.7 kg, 10-G = 413.2 kg) between treatments (Table 4), however, dressed yield tended (P = 0.07) to be greater for the CON treatment (CON = 64.74 %, 10-G = 64.52%). Several studies have reported no difference in HCW for cattle fed 10-G (Luebbe et al., 2013; Kenney et al., 2015;  Neuhold et al., 2012; Mayer et al., 2022; Tilton et al., 2024). Luebbe et al. (2013) and Wilson et al. (2016) also reported no difference in HCW resulting from supplementation of Lactobacillus acidophilus and Propionibacterium freudenreichii whereas Krehbiel et al. (2003) and Cull et al. (2015) were able to detect subtle increases in HCW (0.95% and 0.37%, respectively). The dressed yield findings are unexpected given that many previous reports (Elam et al., 2003; Krehbiel et al., 2003; Neuhold et al., 2012; Kenney et al., 2015; Wilson et al., 2016; Mayer et al., 2022; Word et al., 2022; Tilton et al., 2024) suggest no change in dressed carcass yield should be expected when cattle are supplemented a DFM, regardless of the specific bacteria used. Longissimus muscle area (P = 0.28), 12^th rib fat depth (P = 0.96), mean marbling score (P = 0.62), calculated empty body fat (P = 0.92), quality grade distribution (P ≥ 0.10), and yield grade distribution (P ≥ 0.44) did not differ between dietary treatments. Lack of carcass differences is not surprising; equivocal carcass performance outcomes are common in the literature in response to supplementation with Lactobacillus acidophilus, Enterococcus faecium, Pediococcus pentosaceus, Lactobacillus brevis and Lactobacillus plantarum (Luebbe et al., 2013; Kenney et al., 2015; Neuhold et al., 2015; Mayer et al., 2022; Tilton et al., 2024), or Lactobacillus acidophilus and Propionibacterium freudenreichii (Elam et al., 2003; Krehbiel et al., 2003; Cull et al., 2015; Wilson et al., 2016), or Bacillus subtilis (Word et al., 2022). In contrast, Mayer et al. (2022) reported a tendency for the proportion of USDA Choice carcasses to be greater for cattle fed 10-G concomitant with a downward shift in the proportion of USDA Select carcasses in favor of the 10-G treatment.

Table 4.

Carcass quality and yield characteristic of steers fed 10-G compared with non-supplemented control steers

	TRT1
Item	CON	10-G	SEM	P-value
Hot carcass weight, kg	414.7	413.2	1.94	0.16
Dressed yield, %	64.71	64.54	0.13	0.07
Longisimus muscle area, cm2	100.19	99.75	0.60	0.28
12th-rib fat depth, cm	1.30	1.29	0.03	0.96
Marbling Score2	429	427	3.98	0.62
EBF3, %	28.63	28.61	0.18	0.92
Quality grade, %
Prime	0.77	1.21	-	0.10
Choice	54.53	53.09	-	0.28
Select	43.94	44.88	-	0.48
Other	0.69	0.72	-	0.89
Yield grade, %
YG 1	18.96	18.16	-	0.44
YG 2	41.32	41.23	-	0.95
YG 3	31.09	31.58	-	0.68
YG 4	6.53	7.00	-	0.47
YG 5	0.62	0.52	-	0.61

¹Treatments included no DFM (direct-fed microbial) contained in the diet (CON) and a diet containing L. acidophilus, E. faecium, P. pentosaceus, L. brevis, and L. plantarum fed at 2 g/steer/d providing 1 × 10⁹ CFU (10-G) (Life Products, Inc., Norfolk, NE).

²300 = Slight, 400 = Small, 500 = Modest, and 600 = Moderate.

³Empty body fat calculated using EBF, % = 17.76107 + (4.68142 × FT) + (0.01945 × HCW) + (0.81855 × QG) − (0.06754 × LMA), where FT = 12th-rib fat thickness in cm, HCW = hot carcass weight in kg, QG = quality grade (4 = Select, 5 = Choice−, 6 = Choice, 7 = Choice+, and 8 = Prime), and LMA = longissimus muscle area in cm2 (Guiroy et al., 2001).

Salmonella Outcomes

Steers fed 10-G had fewer (P < 0.01; 23.60%) Salmonella positive subiliac lymph nodes when compared to CON fed steers (36.95%; Table 5). Log concentration of quantifiable Salmonella subiliac lymph nodes did not differ (P = 0.23) between treatments (CON = 0.84 log CFU/g; 10-G = 0.63 log CFU/g). Liu et al. (2018) reported that Lactobacillus plantarum inhibited Salmonella growth, enhancing immune reponses by preventing adhesion to the epithelial cells.

Table 5.

Subiliac lymph node Salmonella prevalence and concentration of steers fed 10-G compared with non-supplemented control steers

	TRT1
Item	CON	10-G	SEM	P-value
Salmonella prevalence, %	36.95	23.60	-	<0.01
Salmonella log CFU/g (mean of quantifiable samples)	0.84	0.63	0.12	0.23

¹Treatments included no DFM (direct-fed microbial) contained in the diet (CON) and a diet containing L. acidophilus, E. faecium, P. pentosaceus, L. brevis, and L. plantarum fed at 2 g/steer/d providing 1 × 10⁹ CFU (10-G) (Life Products, Inc., Norfolk, NE).

Mixed results exist in the literature regarding effect of DFMs upon Salmonella prevalence and concentration. Mayer et al. (2022) reported similar findings to the current study, in which the 10-G dietary treatment resulted in a lower frequency of Salmonella positive SLN; however, concentration of Salmonella within SLN did not differ. Flack et al. (2022) reported decreased Salmonella prevalence within SLN for cattle fed Lactobacillus animalis and Propionobacterium freudenreichii; however, no difference in SLN Salmonella prevalence for cattle fed Lactobacillus salivarious. Additionally, Vipham et al. (2015) reported a reduction of Salmonella within SLN of commercial feedlot cattle fed Lactobacillus animalis and Propionibacterium freudenreichii. Brown et al. (2020) reported reduced Salmonella positive inguinal lymph nodes in left carcass sides when cattle were fed Lactobacillus acidophilus and Propionibacterium acidilactici or Lactobacillus reuteri and other Lactobacillus strains; however, no difference was detected for inguinal lymph nodes in right carcass sides or in the three other lymph nodes tested in both sides of carcasses. In contrast, Word et al. (2022) reported no difference in Salmonella prevalence within SLN for cattle fed Bacillus subtilis and Tilton et al. (2024) reported no difference in SLN Salmonella prevalence for cattle fed 10-G.

CONCLUSION

These data indicate that dietary supplementation with 10-G did not influence feedlot performance or carcass traits. Conversely, the addition of 10-G significantly reduced Salmonella prevalence within the subiliac lymph node, which may result in reducing the number of foodborne illnesses caused by Salmonella and inherently improve public health outcomes.

Conflict of interest statement

K. Martens is an employee of Life Products Inc.; remaining authors declare no conflict of interest.

Author Contributions

Aubrey Thompson (Data curation, Formal analysis, Writing - original draft), Tony Bryant (Data curation, Investigation, Project administration, Writing - review & editing), Jenny Jennings (Data curation, Project administration), Kevin Martens (Conceptualization, Funding acquisition, Methodology), Loni Lucherk (Data curation, Supervision), Travis Tennant (Data curation, Investigation, Methodology, Project administration, Supervision), and Ty Lawrence (Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Supervision, Writing - review & editing)