Impact of a mixed culture of Lactobacillus casei and L. lactis on in vitro ruminal fermentation and the growth of feedlot steers fed barley-based diets

2009 ◽  
Vol 89 (2) ◽  
pp. 263-271 ◽  
Author(s):  
J. Baah ◽  
Y. Wang ◽  
T A McAllister
Keyword(s):  
Growth Performance ◽  
Mixed Culture ◽  
Lactobacillus Casei ◽  
Carcass Characteristics ◽  
Barley Grain ◽  
Feedlot Cattle ◽  
Ruminal Fermentation ◽  
Feedlot Steers ◽  
Barley Silage

The effect of a direct-fed microbial (DFM) poduct containing a mixed culture of Lactobacillus casei and L. lactis on in vitro ruminal fermentation of barley-grain/barley-silage-based backgrounding and finishing diets and on growth performance and carcass characteristics of feedlot cattle was evaluated during backgrounding (84 d) and finishing (140 d) of 100 Hereford × Angus steers (initial body weight = 280 ± 15.5 kg). The inclusion rates of DFM in the in vitro study were 4, 8, 12 and 16 million colony forming units (CFU) of lactic acid bacteria (LAB) kg-1 DM of substrate. Total in vitro volatile fatty acids (VFA) production increased at 6 and 12 h of incubation (P < 0.01; linear response) when the backgrounding diet was supplemented with DFM. Dry matter digestibility and VFA production also increased (P < 0.05) during a 12-h fermentation of the finishing diet. Steers were randomly allocated to one of four dietary treatments that comprised feeding DFM tp provide 0 (control), 4 × 107, 8 × 107, or 12 × 107 CFU kg-1 diet DM. Average daily gain (ADG, kg) and feed efficiency (G:F; kg gain kg-1 DM consumed) of steers improved (P = 0.002 and 0.001, respectively) as a result of feeding DFM during the backgrounding period, but not during the finishing period. Saleable meat and rib eye area decreased (P = 0.038, linear; and P = 0.041, quadratic) with DFM supplementation. The results indicated that supplementing barley-grain/barley-silage-based feedlot cattle diets with 12 × 107 CFU of the mixed culture of lactobacilli used in these studies could improve ruminal fermentation, ADG and G:F in backgrounding feedlot steers. However, supplementation during the finishing period may not be warranted in terms of growth performance and carcass characteristics. Differences in the microbial ecology of the intestinal tract as a result of differences in diet composition may account for the varied response between the backgrounding and finishing periods.Key words: Beef cattle, direct-fed microbial, growth performance, Lactobacillus casei, Lactobacillus lactis, ruminal fermentation

scholarly journals Optimum roughage proportion in barley-based feedlot cattle diets: growth performance, feeding behavior, and carcass traits

2020 ◽  
Vol 98 (10) ◽  
Author(s):  
Karen M Koenig ◽  
Gwinyai E Chibisa ◽  
Gregory B Penner ◽  
Karen A Beauchemin
Keyword(s):  
Feeding Behavior ◽  
Growth Performance ◽  
Dry Matter ◽  
Carcass Traits ◽  
Barley Grain ◽  
Feedlot Cattle ◽  
Experimental Unit ◽  
Finishing Diets ◽  
Ruminal Acidosis ◽  
Barley Silage

Abstract High grain diets are fed to finishing beef cattle to maximize animal performance in a cost-effective manner. However, a small amount of roughage is incorporated in finishing diets to help prevent ruminal acidosis, although few studies have examined optimum roughage inclusion level in barley-based diets. The objective of the study was to evaluate the effects of roughage proportion in barley-based finishing diets on growth performance, feeding behavior, and carcass traits of feedlot cattle. Crossbred beef steers (n = 160; mean body weight ± SD, 349.7 ± 21.4 kg) were allocated to 20 pens that were assigned randomly to four dietary treatments (five pens of eight steers per treatment). The treatment diets contained barley silage at 0%, 4%, 8%, and 12% of dietary dry matter (DM). The remainder of the diets (DM basis) consisted of 80%, 76%, 72%, and 68% barley grain, respectively, 15% corn dried distiller’s grains, 5% mineral and vitamin supplement, and 32 mg monensin/kg diet DM. The diets were fed as total mixed rations for ad libitum intake (minimum of 5% refusal) once per day. Cattle were weighed on 2 consecutive days at the start and end of the experiment and on 1 d every 3 wk throughout the experiment (124 d). Two pens for each treatment group were equipped with an electronic feeding system (GrowSafe Systems Ltd., Calgary, Alberta) to monitor feed intake and feeding behavior of individual cattle. The data for dry matter intake (DMI), average daily gain (ADG), gain:feed (G:F) ratio, and carcass traits were analyzed as a completely randomized design with fixed effect of barley silage proportion and pen replicate as experimental unit. Feeding behavior data were analyzed similarly, but with animal as experimental unit. Averaged over the study, DMI increased linearly (11.1, 11.3, 11.7, 11.8 kg/d; P = 0.001) as barley silage proportion increased from 0%, 4%, 8%, and 12% of DM, but ADG was not affected (carcass-adjusted,1.90, 1.85, 1.87, 1.89 kg/d; P ≥ 0.30). Consequently, G:F ratio decreased linearly (carcass-adjusted, 168.9, 163.8, 158.5, 160.6 g/kg DMI; P = 0.023). When averaged over the study, proportion of barley silage in the diet had no linear or quadratic effects (P &gt; 0.10) on meal frequency, duration of meals, intermeal duration, or meal size, but eating rate decreased linearly with increasing silage proportion (P = 0.008). There was no diet effect on liver abscesses (P ≥ 0.92), and effects on carcass characteristics were minor or nonexistent. We conclude that increasing the proportion of barley silage in a feedlot finishing diet at the expense of barley grain to minimize the incidence of ruminal acidosis may decrease feed conversion efficiency.

scholarly journals Effects of increasing dietary level of a commercial liquid supplement on growth performance and carcass characteristics in feedlot steers

2018 ◽  
Vol 2 (2) ◽  
pp. 216-222
Author(s):  
Tara L Felix ◽  
Chloe J Long ◽  
Madeline R Stierwalt ◽  
Pedro H V Carvalho ◽  
Howard M Blalock
Keyword(s):  
Growth Performance ◽  
Block Design ◽  
Carcass Characteristics ◽  
Feedlot Cattle ◽  
Corn Silage ◽  
Distillers Grains ◽  
Dietary Level ◽  
Distillers Grains With Solubles ◽  
Feedlot Steers ◽  
Randomized Complete Block Design

Abstract Feeding cattle liquid supplements has become increasingly popular in the feedlot industry; however, optimal inclusion of liquid supplements in feedlot cattle diets is not known. The objectives of this study were to determine the optimal inclusion of liquid supplementation to maximize growth performance and improve carcass characteristics, as well as estimate the energy value of liquid supplementation when used as a direct corn replacement, for feedlot steers fed a concentrate-based diet. Two hundred and eighty steer calves were stratified by BW into light (BW = 208 ± 9 kg; n = 24) and heavy (BW = 275 ± 8 kg; n = 16) pens. Pens within BW block were randomly assigned to 1 of 4 supplements: 1) dry at 4.5% inclusion (0LIQ), 2) liquid (a proprietary blend from Quality Liquid Feeds; Dodgeville, WI) at 4.5% inclusion (4.5LIQ), 3) liquid at 9% inclusion (9LIQ), or 4) liquid at 13.5% inclusion (13.5LIQ). The remainder of the diet was 47.5% to 55.5% dry rolled corn, 20% corn silage, and 20% modified wet distillers grains with solubles (DM basis). Data were analyzed as a randomized complete block design and linear and quadratic were examined to determine effects of increasing dietary concentrations of liquid. Steers fed 4.5LIQ and 9LIQ had greater (quadratic; P ≤ 0.05) final BW, HCW, and NEm and NEg, and less DMI as a percent of BW compared to steers fed 13.5LIQ. Steers fed 0LIQ were intermediate and not different from other treatments. However, ADG and total BW gain did not differ (P ≥ 0.15) among treatments. Despite the lack of treatment effect on live measures of gain, feeding steers 4.5LIQ and 9LIQ resulted in greater carcass ADG (quadratic; P = 0.03), total carcass gain (quadratic; P = 0.04), and more efficient carcass gain (quadratic; P ≤ 0.01) compared to carcasses from steers fed 13.5LIQ. Feeding steers a liquid supplement at 9% of the diet, DM allowed for the greatest final BW and ADG in this study; however, there was no benefit of increasing liquid to 13.5%.

Canola screenings as a fiber source in barley-based feedlot diets: effects on rumen fermentation and performance of steers

2000 ◽  
Vol 80 (1) ◽  
pp. 161-168 ◽  
Author(s):  
S. J. Pylot ◽  
J. J. McKinnon ◽  
T. A. McAllister ◽  
A. F. Mustafa ◽  
J. Popp ◽  
...  
Keyword(s):  
Control Diet ◽  
Latin Square ◽  
Dietary Treatment ◽  
Barley Grain ◽  
Feedlot Cattle ◽  
Beef Steers ◽  
Ruminal Fermentation ◽  
Finishing Diets ◽  
And Performance ◽  
Barley Silage

Two experiments were conducted to determine the feeding value of canola screenings in combination with barley grain for beef steers. Four dietary treatments were used. These included canola screenings:barley grain ratios of 100:0; 75:25, 50:50, and 25:75 (as-fed basis). In a metabolic trial, the effects of dietary treatment on ruminal fermentation parameters were determined in a 4 × 4 Latin square design experiment using four ruminally fistulated steers. In a production trial, 66 individually fed steers were used in an 83-d finishing trial to determine the performance and carcass characteristics of feedlot cattle fed different levels of canola screenings. A barley grain/barley silage-based control diet was also fed for comparison purposes. Ruminal pH decreased (P < 0.05) while total volatile fatty acid concentrations increased (P < 0.05) as the level of barley grain in the diet increased. Ruminal NH3–N followed a pattern (P < 0.05) similar to that of pH. Inclusion level of canola screenings had no effect on DM intake. However, ADG and feed efficiency increased (P < 0.05) as the level of barley grain in the diet increased. Increasing the level of barley grain in the finishing diet decreased (P < 0.05) lean meat yield and increased (P < 0.05) carcass fat. It was concluded that canola screenings can be included as a source of fiber in barley-based diets. However, levels in excess of 500 g kg−1 reduced the performance of feedlot steers. Performance and cost of gain with 250 and 500 g kg−1 canola screenings in barley-based finishing diets were comparable with those fed an 800 g kg−1 barley grain and 200 g kg−1 barley silage diet. Key words: Canola screenings, ruminal fermentation, feedlot steer performance

scholarly journals Effect of exogenous glucoamylase inclusion on in vitro fermentation and growth performance of feedlot steers fed a dry-rolled corn-based diet

2021 ◽  
Author(s):  
A M Pittaluga ◽  
S Yu ◽  
W Li ◽  
J C McCann
Keyword(s):  
Growth Performance ◽  
Batch Culture ◽  
Dry Matter ◽  
Carcass Characteristics ◽  
Feed Conversion ◽  
Muscle Area ◽  
In Vitro Fermentation ◽  
Molar Proportion ◽  
Feedlot Steers

Abstract The objective was to evaluate the effect of adding an exogenous glucoamylase (GA) enzyme from the fungus Trichoderma reesei on in vitro fermentation, growth performance, and carcass characteristics of feedlot steers fed a dry-rolled corn-based diet. Experiment 1 evaluated 3 levels of added enzyme (0, 0.24, and 0.72 GA enzyme units) and 2 corn particle sizes (CPS; 2 and 4 mm) in a factorial arrangement using a 7 h in vitro batch culture fermentation. Addition of GA increased (P &lt; 0.01) in vitro dry matter disappearance by 13% and decreased final pH (P &lt; 0.01). Molar proportion of propionate increased with GA inclusion (P &lt; 0.01). A smaller CPS increased (P &lt; 0.01) in vitro dry matter disappearance and total volatile fatty acid and decreased final pH (P &lt; 0.01). A smaller CPS also decreased (P &lt; 0.01) the molar proportion of acetate and increased (P &lt; 0.01) the molar proportion of butyrate. In Experiment 2, Angus × Simmental steers (n = 105; initial BW = 329 ± 38 kg) were used to evaluate the inclusion of an exogenous GA on growth performance and carcass characteristics. Steers were fed a basal diet consisting of 60% dry-rolled corn, 17.5% modified distillers grains with solubles, 12.5% corn silage and 10% dry supplement on a dry matter basis for 136 d. Steers were blocked by weight and allotted to pens. Pens were randomly assigned to one of 3 treatments (5 pens/treatment): diet with no GA (CON), low inclusion of GA (122 enzyme units/kg DM; LGA), or high inclusion of GA (183 enzyme units/kg DM; HGA). Inclusion of GA did not affect (P ≥ 0.23) final BW, DMI, or ADG for the 136-d feeding period. Feed conversion was affected (P = 0.02) by treatment with steers fed HGA having ~8% greater G:F compared with LGA and CON. Treatment did not affect (P = 0.32) fecal starch. Inclusion of GA did not affect (P ≥ 0.19) carcass traits including HCW, 12 th rib fat thickness, yield grade, longissimus muscle area, or marbling score. Overall, results suggest inclusion of exogenous GA enzyme increased in vitro dry matter disappearance in batch culture and improved feed conversion in steers fed 183 enzyme units/kg DM during the finishing phase.

Effects of corn-, wheat- or triticale dry distillers’ grains with solubles on in vitro fermentation, growth performance and carcass traits of lambs

2010 ◽  
Vol 90 (1) ◽  
pp. 99-108 ◽  
Author(s):  
L E McKeown ◽  
A V Chaves ◽  
M Oba ◽  
M E.R. Dugan ◽  
E Okine ◽  
...  
Keyword(s):  
Growth Performance ◽  
Dry Matter ◽  
Carcass Characteristics ◽  
Barley Grain ◽  
Distillers Grains ◽  
Canola Meal ◽  
Feed Conversion ◽  
Distillers Grains With Solubles ◽  
Dietary Treatments

The objective of this study was to determine the effect of replacing a mixture of canola meal and barley grain with corn-, wheat- or triticale dry distillers’ grains with solubles (DDGS) at 20% of dietary dry matter (DM) on in vitro ruminal fermentation in bovine ruminal fluid and on growth performance and carcass characteristics of lambs. Sixty ram lambs (22.6 ± 3.0 kg) were randomly assigned to one of four dietary treatments and given individual ad libitum access to feed until they attained slaughter weight. The control diet consisted (DM basis) of 54% barley grain, 16% sunflower hulls, 11.5% beet pulp, 10% canola meal, 2.5% canola oil and 6.0% molasses, vitamins and minerals mixture. For the three DDGS dietary treatments, 10% barley grain and 10% canola meal were replaced with 20% corn-, wheat-or triticale-DDGS. The source of DDGS did not influence (P > 0.51) dry matter intake (DMI) or average daily gain (ADG). Feed conversion (feed:gain) of lambs fed wheat DDGS was approx. 12% poorer (P < 0.05) than that of lambs fed control or corn DDGS diets. In vitro data suggest that the inefficient gain may have been attributable to greater (P < 0.05) ammonia concentration at 24 h and lower digestibility of wheat DDGS. Carcass traits, including hot carcass weight, body wall thickness and saleable meat yield, were not affected (P > 0.60) by dietary treatment. Total saturated, monounsaturated and polyunsaturated fatty acids in subcutaneous fat were also not affected by DGGS source (P ≥ 0.13). There was no treatment effect (P = 0.33) on concentrations of t11-18:1, but feeding triticale DDGS increased the concentration (P = 0.04) of c9, t11-conjugated linoleic acid (CLA). In conclusion, DDGS from corn, wheat or triticale can replace a mixture of barley grain and canola meal at 20% of dietary DM without adversely affecting DMI, ADG or carcass characteristics of growing lambs, although wheat DDGS may reduce feed conversion ratio (feed:gain). Including triticale DDGS may also improve the fatty acid profile of subcutaneous fat.Key words: Lamb, corn, wheat, triticale, distillers’ grains, performance, carcass characteristics

Effect of low and high oil corn distillers' grain on rumen fermentation, growth performance and carcass characteristics of lambs

2011 ◽  
Vol 51 (8) ◽  
pp. 708 ◽  
Author(s):  
A. S. O'Hara ◽  
A. Tanner ◽  
T. A. McAllister ◽  
D. J. Gibb ◽  
F. van Herk ◽  
...  
Keyword(s):  
Growth Performance ◽  
Block Design ◽  
Carcass Characteristics ◽  
Rumen Fermentation ◽  
Barley Grain ◽  
Canola Meal ◽  
High Oil Corn ◽  
Corn Ddgs

The objective of this study was to determine the effect of replacing a mixture of canola meal and barley grain in the diet with (low and high oil) corn dried distillers’ grains with solubles (DDGS) or wheat DDGS on rumen fermentation, feed intake, growth performance and carcass traits in lambs. Seventy Canadian Arcott lambs (24.7 ± 3.21 kg) were used in a completely randomised block design over a 14-week trial. Experimental diets were provided ad libitum as pelleted total mixed rations. In the treatment diets, canola meal and barley grain were replaced with 200 g/kg of dietary DM of either high oil corn DDGS, low oil corn DDGS or wheat DDGS. A positive control diet was added to match the lipid content of 39 g/kg DM of the high oil corn DDGS diet. An in vitro rumen digestibility trial was conducted using ruminal fluid obtained from three non-lactating Holstein dairy cows. Rumen contents were also collected from each lamb at the time of slaughter for testing in vivo rumen fermentation. Data from both the in vivo and in vitro results were analysed using the MIXED procedure of SAS. The in vitro incubations revealed both corn DDGS diets produced less microbial N and microbial DM than control and wheat DDGS diets; however, this difference was too minimal to affect growth performance. Similarly, there was no dietary effect on (P > 0.05) on in vivo ruminal fermentation or carcass characteristics (P ≥ 0.19) of the lambs. Lambs fed low oil corn DDGS had lower average daily gains (P < 0.03) than those fed either high oil corn DDGS or wheat DDGS however they did not differ from those fed the control. This research demonstrated that replacing canola meal and portions of barley grain with 200 g/kg DM of either high oil corn DDGS, low oil corn DDGS or wheat DDGS in finishing lamb ratios could effectively maintain healthy rumen function, growth performance and carcass characteristics.

Effects of distillers’ dried grains with solubles from corn, wheat or a 50:50 corn:wheat blend on performance, carcass characteristics and serum sulphate levels of feedlot steers

2012 ◽  
Vol 92 (3) ◽  
pp. 343-351 ◽  
Author(s):  
S. Amat ◽  
S. Hendrick ◽  
T. A. McAllister ◽  
H. C. Block ◽  
J. J. McKinnon
Keyword(s):  
Dry Matter ◽  
Control Diet ◽  
Average Daily Gain ◽  
Carcass Characteristics ◽  
Barley Grain ◽  
Barley Straw ◽  
Partial Replacement ◽  
Distillers Dried Grains ◽  
Feedlot Steers ◽  
Barley Silage

Amat, S., Hendrick, S., McAllister, T. A., Block, H. C. and McKinnon, J. J. 2012. Effects of distillers’ dried grains with solubles from corn, wheat or a 50:50 corn:wheat blend on performance, carcass characteristics and serum sulphate levels of feedlot steers. Can. J. Anim. Sci. 92: 343–351. Two trials were conducted to evaluate the effects of corn (CDDGS), wheat (WDDGS) or a 50:50 corn:wheat blend (BDDGS) dried distillers’ grains with solubles (DDGS) on performance (Trials 1 and 2), carcass traits (Trial 2) and serum sulphate level (Trial 2) of steers. In Trial 1, 396 steers (281.1±19.6 kg) were fed one of three backgrounding diets. The control diet was 34.3% barley grain, 26.0% grass hay, 10.3% barley straw, 22.8% barley silage and 6.7% supplement [dry matter (DM) basis]. For the two treatments, 17% of the barley was replaced with CDDGS or WDDGS. In Trial 2, 288 steers (273.9±18.5 kg) were backgrounded and finished. Backgrounding diets were identical to Trial 1, with a third treatment where 17% of the barley grain was replaced with BDDGS. The control finishing diet was 86.8% barley grain, 7.4% barley silage and 5.8% supplement (DM basis). Treatments included replacement of 40% of the barley grain (DM basis) with CDDGS, BDDGS or WDDGS. In Trial 1, there was no effect of DDGS on dry matter intake (DMI) (P=0.49), average daily gain (ADG) (P=0.64), feed efficiency (P=0.06), ultrasound fat (USFAT) (P=0.90) or longissimus dorsi (USLD) (P=0.071) area. In Trial 2, overall, DMI of cattle fed WDDGS was higher (P=0.03) than control or CDDGS cattle, with BDDGS intermediate. In contrast, ADG was higher (P<0.01) for the CDDGS and BDDGS than either the control or WDDGS fed cattle. The CDDGS and BDDGS cattle were more efficient (P<0.01) than those fed WDDGS with the controls intermediate. Cattle fed CDDGS or WDDGS exhibited higher (P<0.01) serum sulphate levels compared with BDDGS or control cattle, reflecting differences in sulphur intake. The results indicate that CDDGS is a superior energy source to WDDGS and that both sources of DDGS can be used as a partial replacement for barley in backgrounding and finishing diets for cattle.

Quality and precision processing of barley grain affected intake and digestibility of dry matter in feedlot steers

2013 ◽  
Vol 93 (2) ◽  
pp. 251-260 ◽  
Author(s):  
W. Z. Yang ◽  
M. Oba ◽  
T. A. McAllister
Keyword(s):  
Digestive Tract ◽  
Dry Matter ◽  
Latin Square ◽  
Barley Grain ◽  
Feedlot Cattle ◽  
Ruminal Ph ◽  
Feedlot Steers ◽  
Acid Detergent Fibre ◽  
Barley Silage ◽  
The Impact

Yang, W. Z., Oba, M. and McAllister, T. A. 2013. Quality and precision processing of barley grain affected intake and digestibility of dry matter in feedlot steers. Can. J. Anim. Sci. 93: 251–260. A study was conducted to determine the impact of barley quality and precision processing to account for the impact of variable kernel uniformity on ruminal pH and fermentation, and digestibility in the digestive tract of steers. Eight ruminally cannulated steers were used in a replicated 4×4 Latin square experiment. The four diets consisted of light-weight barley (LB) precision-processed with roller setting based on kernel size; heavy-weight barley (HB) precision-processed; LB and HB grain mixed equal parts then processed at a single roller setting (CON); or LB and HB precision-processed and mixed equal parts (PP). The diets consisted of 10% barley silage and 90% concentrate [dry matter (DM) basis]. Dry matter intake by steers fed LB was greater (P=0.04) than by steers fed HB. Intakes of DM and other nutrients were greater (P=0.04) for steers fed PP than for steers fed CON. There were no differences (P>0.14) in ruminal pH and fermentation among treatments. Digestibility of DM in the total digestive tract tended (P=0.06) to be less with LB than with HB. Precision processing increased digestibility of crude proteion (P=0.04) and acid detergent fibre (P=0.06) resulting in a trend (P=0.10) towards increasing organic matter digestibility as compared with CON. The results suggest that screening of blended barley into more uniform fractions and precision processing of each fraction could increase intake of digestible nutrients for feedlot cattle.

scholarly journals Effect of Subtherapeutic Administration of Antibiotics on the Prevalence of Antibiotic-Resistant Escherichia coli Bacteria in Feedlot Cattle

2008 ◽  
Vol 74 (14) ◽  
pp. 4405-4416 ◽  
Author(s):  
T. W. Alexander ◽  
L. J. Yanke ◽  
E. Topp ◽  
M. E. Olson ◽  
R. R. Read ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Environmental Factors ◽  
Barley Grain ◽  
Feedlot Cattle ◽  
Antibiotic Resistant ◽  
Fecal Samples ◽  
E Coli ◽  
Feedlot Steers ◽  
Escherichia Coli Bacteria ◽  
Barley Silage

ABSTRACT Antibiotic-resistant Escherichia coli in 300 feedlot steers receiving subtherapeutic levels of antibiotics was investigated through the collection of 3,300 fecal samples over a 314-day period. Antibiotics were selected based on the commonality of use in the industry and included chlortetracycline plus sulfamethazine (TET-SUL), chlortetracycline (TET), virginiamycin, monensin, tylosin, or no antibiotic supplementation (control). Steers were initially fed a barley silage-based diet, followed by transition to a barley grain-based diet. Despite not being administered antibiotics prior to arrival at the feedlot, the prevalences of steers shedding TET- and ampicillin (AMP)-resistant E. coli were >40 and <30%, respectively. Inclusion of TET-SUL in the diet increased the prevalence of steers shedding TET- and AMP-resistant E. coli and the percentage of TET- and AMP-resistant E. coli in the total generic E. coli population. Irrespective of treatment, the prevalence of steers shedding TET-resistant E. coli was higher in animals fed grain-based compared to silage-based diets. All steers shed TET-resistant E. coli at least once during the experiment. A total of 7,184 isolates were analyzed for MIC of antibiotics. Across antibiotic treatments, 1,009 (13.9%), 7 (0.1%), and 3,413 (47.1%) E. coli isolates were resistant to AMP, gentamicin, or TET, respectively. In addition, 131 (1.8%) and 143 (2.0%) isolates exhibited potential resistance to extended-spectrum β-lactamases, as indicated by either ceftazidime or cefpodoxime resistance. No isolates were resistant to ciprofloxacin. The findings of the present study indicated that subtherapeutic administration of tetracycline in combination with sulfamethazine increased the prevalence of tetracycline- and AMP-resistant E. coli in cattle. However, resistance to antibiotics may be related to additional environmental factors such as diet.

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