Effects of Menthol Supplementation in Feedlot Cattle Diets on the Fecal Prevalence of Antimicrobial-Resistant Escherichia coli.

The pool of antimicrobial resistance determinants in the environment and in the gut flora of cattle is a serious public health concern. In addition to being a source of human exposure, these bacteria can transfer antibiotic resistance determinants to pathogenic bacteria and endanger the future of antimicrobial therapy. The occurrence of antimicrobial resistance genes on mobile genetic elements, such as plasmids, facilitates spread of resistance. Recent work has shown in vitro anti-plasmid activity of menthol, a plant-based compound with the potential to be used as a feed additive to beneficially alter ruminal fermentation. The present study aimed to determine if menthol supplementation in diets of feedlot cattle decreases the prevalence of multidrug-resistant bacteria in feces. Menthol was included in diets of steers at 0.3% of diet dry matter. Fecal samples were collected weekly for 4 weeks and analyzed for total coliforms counts, antimicrobial susceptibilities, and the prevalence of tet genes in E. coli isolates. Results revealed no effect of menthol supplementation on total coliforms counts or prevalence of E. coli resistant to amoxicillin, ampicillin, azithromycin, cefoxitin, ceftiofur, ceftriaxone, chloramphenicol, ciprofloxacin, gentamicin, kanamycin, nalidixic acid, streptomycin, sulfisoxazole, and sulfamethoxazole; however, 30 days of menthol addition to steer diets increased the prevalence of tetracycline-resistant E. coli (P < 0.02). Although the mechanism by which menthol exerts its effects remains unclear, results of our study suggest that menthol may have an impact on antimicrobial resistance in gut bacteria.

Effects of crystalline menthol on blood metabolites in Holstein steers and in vitro volatile fatty acid and gas production.

Fifty-two Holstein steers (573 ± 9.92 kg BW) were used to determine if oral administration of crystalline menthol would induce changes in endogenous secretions of IGF-1 and circulating concentrations of glucose, lactate, and plasma urea nitrogen (PUN). Steers were blocked by BW and assigned within block to treatment. Treatments consisted of 0, 0.003, 0.03, or 0.3% crystalline menthol (DM basis) added to the diet. Animals were housed in individual, partially covered pens equipped with feed bunks and automatic water fountains. On d 1 of the experiment, blood samples were obtained via jugular venipuncture at 0, 6, 12, 18, and 24 h after feeding. Treatment administration commenced on d 2, and blood samples were again drawn at 0, 6, 12, 18, and 24 h after feeding. This blood-sampling schedule was repeated on d 9, 16, 23, and 30. Plasma was analyzed for PUN, glucose, and lactate concentrations. Serum was used to analyze IGF-1 concentration. Body weights were measured on d 1, 9, 16, 23, and 30. To accompany the live animal phase, in vitro fermentations were performed using ruminal fluid cultures. Measurements included VFA concentrations and fermentative gas production for cultures containing crystalline menthol at 0, 0.003, 0.03, or 0.3% of substrate DM. Addition of menthol to the diet of steers resulted in a treatment × day interaction ( < 0.01) for concentrations of IGF-1, PUN, and plasma glucose. Cattle fed 0 and 0.003% menthol had greater serum IGF-1 concentrations on d 2 compared with steers fed 0.03% menthol. Steers fed 0% menthol had greater serum IGF-1 concentrations on d 9 compared with steers fed 0.03 and 0.3% menthol, whereas no differences were observed on d 23 or 30. Plasma glucose was similar among treatments until d 23, when steers supplemented with 0.03% menthol had lower glucose concentrations. Plasma urea nitrogen concentrations were not different among treatments; however, PUN concentrations varied by day. A linear response was detected for BW ( = 0.03), with steers consuming 0% menthol having the greatest BW and steers that consumed 0.3% menthol having the lightest BW until d 30. A menthol × day interaction was observed for daily feed deliveries ( < 0.01): cattle fed 0.3% menthol consumed less feed from d 5 through 12. Furthermore, in vitro gas production and VFA concentrations were unaffected by addition of menthol ( > 0.21). In conclusion, menthol supplementation minimally affected blood parameters associated with growth or ruminal fermentative activity.

Effects of flaxseed encapsulation on biohydrogenation of polyunsaturated fatty acids by ruminal microorganisms: feedlot performance, carcass quality, and tissue fatty acid composition.

The objective of this study was to evaluate the efficacy of protecting PUFA within ground flaxseed against ruminal biohydrogenation by encapsulating them in a matrix consisting of a 1:1 blend of ground flaxseed and dolomitic lime hydrate (L-Flaxseed). Crossbreed heifers ( = 462, 346 ± 19 kg) were blocked by weight and randomly assigned to pens. Pens were assigned to 1 of 6 dietary treatments in a randomized complete block design. Treatment 1 consisted of a combination of 54.6% steam-flaked corn (SFC), 30.0% wet corn gluten feed, 8.0% roughage, and supplement (0% flaxseed). In treatments 2 and 3, a proportion of SFC was replaced with 3 and 6% flaxseed, respectively; in treatments 4, 5, and 6, SFC was replaced with 2, 4, or 6% L-Flaxseed, respectively. Cattle were fed for 140 or 168 d and then harvested in a commercial abattoir where carcass data were collected. Approximately 24 h after harvest, carcasses were evaluated for 12th-rib fat thickness, KPH, LM area, marbling score, and USDA yield and quality grades. Samples of LM were also obtained for determination of long-chain fatty acid profiles. Cattle that were fed diets with 4 and 6% L-Flaxseed consumed less feed than other treatments ( < 0.05), which adversely affected ADG. Compared with cattle fed 0% flaxseed, cattle in these treatments had lower final BW (18 and 45 kg less for the 4 and 6% L-Flaxseed treatments, respectively), less ADG (0.16 and 0.48 kg/day less for the 4 and 6% L-Flaxseed treatments, respectively), and lower carcass weights, dressing percentages, LM areas, backfat thicknesses, and marbling scores ( < 0.05). The addition of flaxseed or 2% L-Flaxseed did not affect performance or carcass traits ( > 0.05). Supplementation with flaxseed increased ( < 0.05) the concentration of α-linolenic acid (ALA) in meat (0.173, 0.482, 0.743 mg/g for 0, 3, and 6% flaxseed, respectively). Furthermore, proportionate increases in the ALA content of muscle tissue were 47% greater when flaxseed was encapsulated within the dolomitic lime hydrate matrix (0.288, 0.433, 0.592 mg/g for 2, 4, and 6% L-Flaxseed, respectively). Both products showed a linear response in ALA concentration ( > 99%; increases for Flaxseed and L-Flaxseed of 0.095 and 0.140 mg of ALA/g of tissue for each percentage of flaxseed added). This study indicates that a matrix consisting of dolomitic lime hydrate is an effective barrier to ruminal biohydrogenation of PUFA; however, adverse effects on DMI limit the amounts that can be fed.

Effects of in-feed copper and tylosin supplementations on copper and antimicrobial resistance in faecal enterococci of feedlot cattle.

AIMS: The objective was to investigate whether in-feed supplementation of copper, at elevated level, co-selects for macrolide resistance in faecal enterococci. METHODS AND RESULTS: The study was conducted in cattle (n = 80) with a 2 × 2 factorial design of copper (10 or 100 mg kg(-1) of feed) and tylosin (0 or 10 mg kg(-1) of feed). Thirty-seven isolates (4·6%; 37/800) of faecal enterococci were positive for the tcrB and all were Enterococcus faecium. The prevalence was higher among cattle fed diets with copper and tylosin (8·5%) compared to control (2·0%), copper (4·5%) and tylosin (3·5%) alone. All tcrB-positive isolates were positive for erm(B) and tet(M) genes. Median copper minimum inhibitory concentrations (MICs) for tcrB-positive and tcrB-negative enterococci were 20 and 4 mmol l(-1) , respectively. CONCLUSIONS: Feeding of elevated dietary copper and tylosin alone or in combination resulted in an increased prevalence of tcrB and erm(B)-mediated copper and tylosin-resistant faecal enterococci in feedlot cattle. SIGNIFICANCE AND IMPACT OF THE STUDY: In-feed supplementation of elevated dietary copper has the potential to co-select for macrolide resistance. Further studies are warranted to investigate the factors involved in maintenance and dissemination of the resistance determinants and their co-selection mechanism in relation to feed-grade antimicrobials' usage in feedlot cattle.

Effects of feeding diets rich in α-linolenic acid and copper on performance, carcass characteristics, and fatty acid profiles of feedlot heifers.

Our objective was to evaluate whether feeding elevated Cu concentrations in conjunction with Linpro, a co-extruded blend of field peas and flaxseed, affected in vitro fermentation, performance, and plasma lipid profiles of fattening beef heifers. In study 1, 2 in vitro trials were conducted as randomized complete experiments with a 2×2 factorial treatment arrangement (10 or 100 mg/kg added Cu and 0 or 10% Linpro, DM basis) to determine VFA/gas production and IVDMD. Linpro contains 12% α-linolenic acid and added vitamins and minerals. In study 2, a randomized complete block experiment with a 2×2 factorial treatment arrangement was conducted with the same previously described treatment. Crossbred yearling heifers (n=261; 351±23 kg initial BW) were blocked by weight into heavy and light groups and randomly assigned to experimental pens containing 10 or 11 heifers each. In study 1, no interactions between levels of Cu and Linpro were observed. Copper concentration did not affect IVDMD (P>0.2) but increased (P<0.05) by 1.2% when Linpro was included. Final pH was not effected by added Cu (P>0.05), but pH increased when Linpro was added (P<0.05). Total VFA were greater in high-Cu treatments (P=0.038) and molar proportions were not affected (P>0.34). Linpro had no effect on total VFA (P=0.46) and molar proportions of propionate and isobutyrate increased whereas acetate and the acetate:propionate ratio decreased (P<0.01). Linpro increased the production of H2S (30% higher; P=0.05), and Cu inclusion slightly increased CO2 proportion (64.06 vs. 67.58% for Linpro vs. Cu treatments, respectively). In study 2, there were no interactions between levels of Linpro and supplemental Cu except for plasma n-6:n-3 ratio (P<0.01). Final BW were similar for cattle fed 0 and 10% Linpro (581 vs. 588 kg; P>0.20), but cattle fed diets with Linpro consumed less feed (14.08 vs. 13.59 kg/d; P<0.05) and were therefore more efficient (0.129 vs. 0.137 for 0 vs. 10% Linpro, respectively; P<0.01). Carcass traits were not affected by treatment. Feeding elevated levels of Cu did not appreciably alter PUFA proportions in plasma and LM. Plasma and LM concentrations of omega-3 fatty acids, including C18:3, C20:5, and C22:5, were greater for heifers fed Linpro (P<0.05). Increasing dietary Cu was not effective as a strategy for decreasing ruminal biohydrogenation and subsequent tissue deposition of PUFA.