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Spoiled silages can harbor pathogenic and antimicrobial-resistant microbes. The potential of some antimicrobial additives to inhibit certain pathogenic and antimicrobial-resistant bacteria in air-exposed silage was measured using pure and mixed bacterial cultures. With pure cultures, laurate and monolaurin (5 mg·mL−1) caused decreases (P 7 log10 colony-forming units (CFU)·mL−1 in Listeria monocytogenes and Enterococcus faecalis compared to controls. Ten-fold higher amounts of these inhibitors were needed to equivalently decrease staphylococci. 2-Nitropropanol (1 mg·mL−1) decreased (P 10 CFU·mL−1 after 6 and 24 h incubations, respectively. In air-exposed whole-plant corn silage the inhibitors caused decreases, although not necessarily significant, of 0.7–2.2 log10 CFU·mL−1 in L. monocytogenes, staphylococci and culturable aerobes after 24 h incubation, with modest yet significant (P 10 CFU·mL−1) of yeasts and molds. Tests for carry-over effects against ruminal microbes revealed laurate, monolaurin, and 2-nitropropanol inhibited methanogenesis by >50% (P

Poultry litter is a valuable crude protein feedstuff for ruminants, but it must be treated to kill pathogens before feeding. Composting effectively kills pathogens, but it risks losing ammonia to volatilization or leaching during degradation of uric acid and urea. Hops bitter acids also exert antimicrobial activity against certain pathogenic and nitrogen-degrading microbes. Consequently, the present studies were conducted to test if adding bitter acid-rich hop preparations to simulated poultry litter composts may improve nitrogen retention while simultaneously improving pathogen killing. Results from an initial study, testing doses of Chinook or Galena hops preparations designed to each deliver 79 ppm hops β-acid, revealed that, after nine days simulated composting of wood chip litter, ammonia concentrations were 14% lower (p < 0.05) in Chinook-treated composts than untreated composts (13.4 ± 1.06 µmol/g). Conversely, urea concentrations were 55% lower (p < 0.05) in Galena-treated than untreated composts (6.2 ± 1.72 µmol/g). Uric acid accumulations were unaffected by hops treatments in this study but were higher (p < 0.05) after three days than after zero, six, or nine days of composting. In follow-up studies, Chinook or Galena hops treatments (delivering 2042 or 6126 ppm of β-acid, respectively) for simulated composts (14 days) of wood chip litter alone or mixed 3:1 with ground Bluestem hay (Andropogon gerardii) revealed that these higher dosages had little effect on ammonia, urea, or uric acid accumulations when compared to untreated composts. Volatile fatty acid accumulations measured in these later studies were affected by the hops treatments, with butyrate accumulations being lower after 14 days in hops-treated composts than in untreated compost. In all studies, beneficial effects of Galena or Chinook hops treatments were not observed on the antimicrobial activity of the simulated composts, with composting by itself decreasing (p < 0.05) counts of select microbial populations by more than 2.5 log10 colony forming units/g compost dry matter. Thus, while hops treatments had little effect on pathogen control or nitrogen retention within the composted litter, they did lessen accumulations of butyrate, which may prevent adverse effects of this fatty acid on palatability of litter fed to ruminants.

Our objective was to evaluate the interaction of supplemental essential oils (EO) and monensin (MON) on performance and digestion. Two levels of EO (0 vs 0.011% Xtract®) and two levels of MON (0 vs 33 mg/kg) were evaluated in a 2 × 2 factorial arrangement. Treatment effects on 216-d growth performance were evaluated in 96 Holstein steers. Supplemental MON enhanced (P ≤ 0.05) ADG, DMI and gain efficiency. Without EO, MON improved (P

We tested the effects of Galena or Chinook hops treatment (6% wt/wt) of simulated composts (13 d) of wood chip litter (WCL) alone or mixed 3:1 with ground Bluestem hay (BSH). Results revealed that net losses of urea and ammonia in the WCL litter composted without BSH (n = 3/treatment) were unaffected by hops treatment (P = 0.37 and 0.13, respectively), averaging 0.32 ± 0.7 and 0.03 ± 1.5 µmol/g, respectively). The loss of uric acid was 60% less (P = 0.04) in the Galena hops-treated WCL compost than in the negative control compost (13.9 ± 3.8 vs 24.4 ± 5.6 µmol/g, respectively) and intermediate in the Chinook-treated compost (16.0 ± 2.7 µmol/g). Nitrogen losses during compost of WCL: BSH (n = 2/treatment) were unaffected by hops treatment (P = 0.77, 0.73 and 0.14 for uric acid, urea and ammonia, respectively), averaging 12.21 ± 3.1, 0.64 ± 0.6 and 1.07 ± 0.1 µmol/g, respectively, respectively). Assessment of potential carry over effects of residual hops in the composts during in vitro rumen fermentation (0.2 g of treated and control compost, in triplicate, mixed with 10 mL freshly collected rumen fluid) for 24 h at 39oC under 100% CO2 revealed no effects of hops treatment on H2 accumulations in incubations with WCL or WCL: BSH composts (P = 0.22 and 0.17, respectively), averaging 0.23 ± 0.1 and 0.17 ± 0.1 µmol/mL fluid, respectively. Accumulations of CH4 in rumen incubations of WCL composts were unaffected by hops treatment (P = 0.24), averaging 15.07 ± 2.0 µmol/mL, but were increased (P = 0.0002) in incubations of WCL: BSH composts, averaging 14.1 ± 0.4 and 13. 8 ± 0.6 µmol/mL in Galena- and Chinook-treated compost compared with 11.2 ± 0.4 µmol/mL in control incubations. Results indicate hops treatment may lessen uric acid degradation composting poultry litter without inhibiting rumen fermentation.

Total antioxidant capacity (TAC) and physicochemical characteristics of meat were evaluated after supplementing different doses of propolis in broiler chickens’ diets at: 15, 30, 45 and 0 mg propolis/kg feed for Pr15, Pr30, Pr45 and Pr0, respectively. Two hundred one-day-old chickens were fed for 42 d and sacrificed. Breast meat samples were used for physicochemical determinations. Oxidative capacity was measured on days 0, 1, 3, 5, 7 and 9 of storage. There were no differences (P > 0.05) between the supplementation systems in either pH, luminosity index (L*), red (a*), yellow (b*), drip loss, cooking yield, protein, ash or moisture. Meat from chickens fed the highest propolis dose (Pr45) presented the lowest oxidative capacity (P

Physicochemical characteristics and lipid profile of beef from cattle feeding on grazing and feedlot were compared. Forty beef samples were collected from each feeding system. The samples were taken from the Longissimus dorsi muscle. There were no differences between the feeding systems (P > 0.05) with regard to pH, luminosity index (L*), red (a*), yellow (b*), drip loss, and cooking yield. Regarding the nutritional content, there were significant differences in moisture and fat contents (P 0.05). The main fatty acids found were oleic, palmitic, and stearic. There was a higher concentration of unsaturated fatty acids, especially conjugated linoleic acid, on that beef from grazing bovines (P

In experiment 1, 150 calf-fed Holstein steers (119 ± 6 kg) were used to evaluate the effects of level of supplemental condensed tannin (0, 14, and 28 g/kg diet DM) in a conventional steam-flaked corn-based growing-finishing diet on feedlot growth performance. There were no treatment effects on growth performance during the initial 56-d period. However, during the subsequent 56-d period, supplemental condensed tannin tended to increase average daily gain (ADG; linear effect, P = 0.09). The increase in ADG was consistent with the tendency for increased dry matter intake (DMI; linear effect, P = 0.08). Hence, differences in gain efficiency during the second 56-d period were not appreciably affected (P = 0.80). Supplemental condensed tannin did not affect overall (112-d) ADG, DMI, gain efficiency, or dietary NE. In a second experiment, six Holstein steers (179.4 ± 7.9 kg) with cannulas in the rumen and proximal duodenum were used in a replicated 3 × 3 Latin square design to evaluate treatment effects on characteristics of ruminal and total tract digestion. Treatments were the same as in Trial 1. Tannin supplementation decreased (linear effect, P = 0.03) ruminal OM digestion and tended to decrease (linear effect, P = 0.06) ruminal feed N degradation. Tannin supplementation decreased (linear effect, P = 0.03) ruminal pH, but did not affect (P > 0.20) ruminal molar proportions of volatile fatty acids and estimated methane production. In current study, supplemental tannin had marginal effects on overall growth performance of calf-fed Holstein steers, but reduced ruminal, postruminal, and total tract nitrogen digestion.

Staphylococci are important mastitic-pathogens of humans and livestock. Chlorate is reported to be a potent inhibitor against staphylococci but adaptation by the microbes can occur. Presently, we cultured multi-drug resistant Staphylococcus aureus strain ATCC 12600 anaerobically at 39oC in nitrate-supplemented (5 mM) Tryptic Soy broth. The broth was treated without (control) or alone with 5 mM sodium chlorate (ClO3) or 9 mM of either 2-nitro-1-propanol (NPOH), ethyl nitroacetate (ENA) or ethyl 2-nitropropionate (E2NPA) or with combinations of CLO3 and respective nitrocompound. Control and treated cultures were incubated in triplicate and growth was measured via absorbance (600 nm) at during 9 h. An analysis of variance revealed an inhibitory effect of treatments (P < 0.05; SEM = 0.078) on mean specific growth rates of S. aureus, with rates during logarithmic growth being most rapid in controls and cultures treated with ENA or EN2PA (1.45, 1.23 and 1.21 h-1, respectively) and more than 92% slower in NPOH and NPOH+CLO3-treated cultures (0.09 and 0.03 h-1, respectively). Growth rates of cultures treated solely with CLO3 (0.66 h-1) were more than 50% slower than controls and were decreased further in cultures treated with combinations of CLO3 plus E2NPA or ENA (0.39 and 0.45 h-1). After 9 h of growth, maximum optical densities (maxOD) were highest for controls and cultures treated with ENA or EN2PA (0.52, 0.52 and 0.50 maxOD, respectively), intermediate in cultures treated with CLO3 alone (0.21 maxOD) and lower yet in cultures treated with CLO3 plus ENA, E2NPA or NPOH (0.15, 0.11 and 0.02 maxOD, respectively). The maxOD for cultures treated with NPOH alone was 0.02 and did not differ from cultures treated with the combination of CLO3+NPOH. Results demonstrate marked synergistic and prolonging effects of combing ENA and E2NPA with CLO3 but no additional effect of the potent anti-staphylococcal activity of NPOH.

Plant extracts have been used over time in traditional medicine, mainly for their antimicrobial activity as well as for their medicinal effects. Plant-derived products contain secondary metabolites that prevent pathogenic microbial growth similar to conventional medicines. These secondary metabolites can enhance animal health and production in a more natural or organic manner and may contribute to the reduction in the use of pharmacological drugs in animal feed, which is of great concern for emerging microbial resistance. Plant secondary metabolites can be cost effective, while improving the production efficiency of ruminants, non-ruminants, and aquatic food animals. Among the plant-derived products is the Yucca schidigera extract (YSE), containing steroidal saponins as their main active component. YSE has multiple biological effects, including inhibition of some pathogenic bacteria, protozoa, and nematodes. YSE is used to control odor and ammonia and consistently enhance poultry production by enhancing intestinal health and function. In pigs, results are as yet inconclusive. In ruminants, YSE works against protozoa, has selective action against bacteria, and reduces the archaea populations; all these effects are reflected in the reduction in emissions of polluting gases, mainly methane, although the effects are not observed in all feeding conditions. These effects of YSE are discussed in this review. YSE has potential as a natural feed additive for sustainable animal production while contributing to the mitigation of contaminant gas emissions.

Objectives This study was conducted to examine the effect of urea fermentation potential (UFP) on digestive function, BUN, growth performance, and dietary energetics, in steers fed a finishing diet based on steam-flaked corn containing 15% dried distillers grains with solubles. Materials and Methods Four UFP levels were evaluated (−0.30, 0.10, 0.50, 0.90). The UFP levels were manipulated by dietary urea inclusion level of 1.20, 0.80, 0.40 and 0%, respectively (DM basis). Results and Discussion Dietary UFP did not affect (P > 0.10) ruminal digestion of feed N. Ruminal starch digestion decreased with increasing UFP (linear effect, P = 0.02). Ruminal digestion of starch and OM tended to be maximal (quadratic effect, P ≤ 0.07) at dietary UFP of 0.1%. Increasing UFP decreased flow to duodenum of nonammonia-N (linear effect, P = 0.04), and microbial N (linear effect, P = 0.05). Duodenal flow of feed N was not affected (P = 0.18) by dietary UFP. Increasing dietary UFP decreased total-tract digestion of OM (linear effect, P = 0.02), starch (linear effect, P = 0.03), and digestible energy (linear effect, P = 0.03). Increasing dietary UFP decreased ruminal pH (linear effect, P = 0.01) 1 h after feeding. Thereafter, the influence of dietary UFP on ruminal pH was not appreciable. Increasing dietary UFP decreased ruminal ammonia-N 1 h after feeding (linear effect, P Implications and Applications Even when finishing diet formulations otherwise exceed MP requirements, dietary UFP level remains a relevant factor to optimize dietary energy use. Dietary UFP levels greater than 0.50% could negatively affect digestion, gain efficiency, and dietary NE use.

Objectives The objective of this research was to evaluate the influence of rumen-protected methionine and lysine on growth performance of calf-fed Holstein steers during the initial 84-d feedlot phase and relate responses to measures of AA supply to the small intestine. Material and Methods Seventy-two Holstein steer calves (128 ± 9 kg) were blocked by weight and assigned to 12 pens (6 steers per pen). Steers were fed a diet based on steam-flaked corn formulated to provide 105% of theoretical MP requirements plus 0, 0.4, and 0.8% Smartamine ML (Adisseo, Alpharetta, GA; 55% l -lysine-HCl and 15% dl -methionine coated with a pH-sensitive polymer). Six Holstein steers (143 ± 13 kg) with cannulas in rumen and proximal duodenum were used in a crossover design to evaluate characteristics of digestion and AA supply to the intestine of the basal diet plus 0 versus 0.8% Smartamine ML. Results and Discussion Methionine and lysine supplementation did not affect DMI (P = 0.27) but enhanced ADG, gain efficiency (linear effect, P = 0.03), and estimated dietary NE (linear effect, P = 0.04). Amino acid supplementation increased (P Implications and Applications Supplementation with rumen-protected methionine and lysine may enhance gain efficiency and dietary energetics of growing Holstein calves during the early growing phase. The magnitude of the response is likely dependent on the otherwise general adequacy of nonspecific MP.

Medium chain fatty acid (MCFA) treatment of aerobically exposed silage during feed-out is a potential strategy to prevent growth of spoilage and pathogenic microbes. To evaluate the effects of feeding MCFA-treated silage on the rumen fermentability, we incubated 0.02 g of overnight air-exposed corn silage that had been treated individually without or with (0.75% wt/wt) C6, C8, C10 or C12 or with equal proportion mixtures of C6:C8:C10:C12 or C8:C10 with 10 mL freshly collected ruminal fluid. Additions were made while flushing with CO2 and tubes (3 tubes/treatment) were then capped and sealed. After 24 h incubation at 39oC, headspace gases and fluid volatile fatty acids were measure using gas chromatography techniques. Results from a completely randomized analysis of variance revealed higher hydrogen accumulations (P < 0.05) only in incubations containing silage treated with the C8:C10 MCFA mixture when compared to controls, with mean ± SD concentrations (µmol/mL incubation fluid) being 2.19 ± 1.6 versus 0.08 ± 0.04, respectively. Treatment effects were not observed (P > 0.05) on accumulations (µmol/mL) of methane (13.25 ± 2.5), acetate (19.66 ± 5.6), propionate (7.27 ± 2.0), butyrate (12.36 ± 2.7) or stochiometric estimates of amounts of hexose fermented (41.39 ± 9.7), although the acetate:propionate ratios of incubations of silage treated with C8 or the C8:C10 mixture were higher (P < 0.05) than those of untreated controls (3.46 ± 0.7, 3.46 ± 0.5 and 2.35 ± 0.1, respectively). Consequently, correspondingly estimates of fermentation efficiency, calculated based caloric energy values of amounts of acetate, propionate and butyrate relative to glucose, were slightly lower (P < 0.05) for the incubations of silage treated with C8 and the C8:C10 mix compared to controls (74.36 ± 1.1, 74.82 ± 0.2 and 76.55 ± 0.3 %, respectively). Results reveal little negative effect of MCFA treatment on ruminal fermentability of silage.

Introduction: Current diets of broiler chickens tend to increase protein levels to obtain high productive variables that are achieved in combination with genetic, management, and sanitary improvements, among others. An increase in dietary crude protein levels does not always accompany an increase in broiler productive efficiency due to multiple factors involved in the production system. The objective of this study was to evaluate the effect of increasing levels of dietary crude protein (CP) on productive performance, carcass characteristics, and chemical composition of breast and thigh meat in broiler chickens raised in the dry subtropics of northeastern Mexico.Method: The study used 200, 1-day-old male Ross broiler chicks. In a completely randomized design, birds were allocated to the four treatments with five replicates (floor pens) of ten birds each. The trial was divided in two phases (starter and finisher) of 21 days each (42 days total). Treatment diets (T) for starter and finisher phases had crude protein concentrations (CP; %) of 21 and 18.1 (T1), 21.4 and 18.5 (T2), 21.8 and 18.9 (T3), and 22.2 and 19.3 (T4), respectively. Within each feeding phase, the four treatment diets were formulated to similar levels of apparent metabolizable energy.Results: Protein concentrations had no effect (P > 0.05) on weight gain, while feed intake was greater in T1 (P < 0.05) than in T2 and T3. Feed conversion was better in T2 and T4 (P < 0.05) than in T1. There was no influence of treatment on carcass weight or carcass cuts (P > 0.05). Carcass yield was greater in T1 than in T3 (P < 0.05). Breast and thigh dry matter and ether extracts were similar (P > 0.05) between treatments. Breast crude protein was greater (P < 0.05) in T2 than in T3. The lowest (P < 0.05) CP concentration in thigh meat was in T3.Discussion or Conclusion: These results indicated that in the dry subtropics area of northeastern Mexico increases in CP above the level of T2 (21.4% and 18.5% CP in starter and finisher diets, respectively) did not improve broiler chicken productive performance, carcass characteristics or meat chemical composition.

Poultry litter is a potentially valuable crude protein feedstuff for ruminants but must be treated to kill pathogens before being fed. Composting kills pathogens but risks losses of nitrogen due to volatilization or leaching as ammonia. Treatment of poultry litter with ethyl nitroacetate, 3-nitro-1-propionate, ethyl 2-nitropropionate (at 27 µmol/g), decreased numbers of experimentally-inoculated Salmonella Typhimurium (>1.0 log10 compared to controls, 4.2 ± 0.2 log10 CFU/g) but not endogenous Escherichia coli early during simulated composting. By day 9 of simulated composting, Salmonella and E. coli were decreased to non-detectable levels regardless of treatment. Some nitro-treatments preserved uric acid and prevented ammonia accumulation, with 18% more uric acid remaining and 17–24% less ammonia accumulating in some nitro-treated litter than in untreated litter (18.1 ± 3.8 µmol/g and 3.4 ± 1.4 µmol/g, respectively). Results indicate that nitro-treatment may help preserve uric acid in composted litter while aiding Salmonella control.

The influence of sodium chlorate (SC), ferulic acid (FA), and essential oils (EO) was examined on the survivability of two porcine diarrhetic enterotoxigenic Escherichia coli (ETEC) strains (F18 and K88) and populations of porcine fecal bacteria. Fecal bacterial populations were examined by denaturing gradient gel electrophoresis (DGGE) and identification by 16S gene sequencing. The treatments were control (no additives), 10 mM SC, 2.5 mg FA /mL, a 1.5% vol/vol solution of an EO mixture as well as mixtures of EO + SC, EO + FA, and FA + SC at each of the aforementioned concentrations. EO were a commercial blend of oregano oil and cinnamon oil with water and citric acid. Freshly collected porcine feces in half-strength Mueller Hinton broth was inoculated with E. coli F18 (Trial 1) or E. coli K88 (Trial 2). The fecal-E. coli suspensions were transferred to crimp top tubes preloaded with the treatment compounds. Quantitative enumeration was at 0, 6, and 24 h. All treatments reduced (P < 0.05) the counts of E. coli F18 at 6 and 24 h. With the exception of similarity coefficient (%SC), all the other treatments reduced (P < 0.05) the K88 counts at 24 h. The most effective treatments to reduce the F18 and K88 CFU numbers were those containing EO. Results of DGGE revealed that Dice percentage similarity coefficients (%SC) of bacterial profiles among treatment groups varied from 81.3% to 100%SC. The results of gene sequencing showed that, except for SC at 24 h, all the other treatments reduced the counts of the family Enterobacteriaceae, while Lactobacillaceae and Ruminococcaceae increased and Clostridiaceae decreased in all treatments. In conclusion, all treatments were effective in reducing the ETEC, but EO mixture was the most effective. The porcine microbial communities may be influenced by the studied treatments.

To study the antimicrobial and uric acid-preserving activity of pine bark tannin on poultry litter composting, antibiotic-free wood chip-based poultry litter was distributed (11 g) to 50-mL conical centrifuge tubes and immediately amended with 1.3 mL0.4 M sodium phosphate buffer (control) or with 1.3 mL condensed tannins from pine bark (Pinus palustris; 9 % tannin wt/vol in water). All tubes (n = 3 tubes/treatment) were inoculated with a novobiocin and naladixic acid-resistant Salmo-nella typhimurium (STNN) to achieve 3.0 log10 CFU/g and incubated at 37oC for 3 days to simulate an initial compost period. Wildtype E. coli and the challenge STNN strain as well as concentrations of ammonia, uric acid and urea were measured on days 0 and 3. Pine bark tannin treatment decreased (p0.05). Ammonia accumulation decreased (p0.05). Results suggest that pine bark tannin treatment may preserve uric acid and reduce ammonia volatilization in composted litter while aiding Salmonella control.

This study was conducted to determine the effects of chlorate, a metabolic precursor of the bactericide chlorite, when administered without or with molybdate, an essential component of a co-enzyme contributing to nitrate reductase conversion of chlorate to chlorite, against methicillin-resistant staphylococci, important mastitic-pathogens of livestock. Two methicillin-resistant Staphylococcus aureus (strains CP and 49521) were individually cultured for 12 h at 39o C in nitrate-supplemented (5 mM) ½-strength Brain Heart Infusion broth (10 mL/tube) treated without (control) or with 5 mM chlorate (CL) or 5 mM chlorate plus 1 mM molybdate (CLMO). Control and treated cultures were incubated anaerobically in triplicate and growth was measured via absorbance at 600 nm. An analysis of variance revealed an inhibitory effect of treatments (P < 0.05) on maximum absorbances observed after the 12-h incubation, with maximum absorbances for CP (1.22, 0.10, and 0.46; SEM = 0.12) and 49521 (1.24, 0.22 and 0.06, SEM = 0.09) being higher in controls than in CL- and CLMO-treated cultures, respectively. Similarly, mean specific growth rates of S. aureus CP and 49521 were inhibited (P < 0.05) by both treatments during the first 6 h of growth, with rates being most rapid in control cultures, intermediate in CLMO-treated cultures and slowest in CL-treated cultures (0.68, 0.27 and 0.03 h-1, SEM= 0.15; and 0.92, 0.47 and 0.09 h-1, SEM = 0.08; for CP and 40521, respectively). Growth rates did not differ (P > 0.05) between controls or treatments during the last 6 h of incubation, averaging 0.74 and 0.75 h-1 for both CP and 49521 (SEM = 0.20 and 0.22, respectively). These results confirm that chlorate treatment inhibits methicillin-resistant Staphylococcus aureus strains CP and 49521 although moderate adaption by these strains began to occur after 6 h incubation which, contrary to expectation, was not overcome by co-treatment with molybdate.

In two trials was evaluated the influence of sodium chlorate (SC) and essential oils (EO) on the growth of Escherichia coli F18 and K88 (F18 and K88) incubated with porcine fecal bacteria. The treatments were 2 levels of SC (0 and 10 mM/mL) and 2 levels of Activo® (0 and 1.5%; vol/vol). Activo® (EW Nutrition, Des Moines, IA) is a blend of oregano oil and cinnamon oil (EO) with water and citric acid. In trial one, ½-strength Mueller Hinton broth mixed with porcine feces (0.5% w/vol) was inoculated with a novobiocin and naladixic acid resistant F18-strain. This fecal suspension was transferred to tubes (3/treatment) and anaerobically incubated at 39 oC for enumeration at 0, 6 and 24 h using MacConkey agar supplemented with novobiocin and naladixic acid with aerobic incubation at 37 oC. An interaction (EO x SC) at 6 and 24 was observed (P < 0.01). At 6 and 24 h, EO alone or combined with SC had the lowest counts of F18 (P < 0.05); SC alone had lower counts of F18 than control (P < 0.05). In trial 2 were used the same procedures of trial 1, except that K88 was inoculated in the porcine fecal suspension. There was an interaction at 6 h (P < 0.01) where EO had the lowest counts of K88. The control showed the highest counts of K88 (P < 0.05). There was no interaction at 24 h (P = 0.14). The counts of K88 were reduced by EO (P < 0.01), however the counts were not affected by SC (P = 0.14). It was concluded that SC reduced the counts of E. coli F18, but it had minimal effect on E. coli K88 in the challenged porcine feces; essential oils were effective to reduce the pathogenic bacteria in the porcine feces.

Nitrate supplementation into the ruminant diet can decrease ruminal methane emissions, but amounts needed to achieve appreciable decreases can risk ruminal accumulations of nitrite with potential for methemoglobinemia. A denitrifying rumen Paenibacillus fortis strain 79R4 (79R4) selected for enhanced nitrite-metabolizing ability has shown promise as a probiotic to decrease risks of nitrite toxicosis. Presently, a spray-dried prototype of this spore-forming, facultative anaerobe was tested during anaerobic culture (10 mL/tube) of rumen fluid freshly-collected from an alfalfa hay-fed cannulated Jersey cow. Cultures supplemented with 22 mM sodium nitrate and without or with inoculations of freshly-harvested (FH) cells or spray dried (SP) 79R4 spores (3 tubes/treatment; 108 cells/spores per tube) were cultured anaerobically (39oC for 24 h with 100% CO2). The FH- and SP- cells were grown aerobic, 72 h in tryptic soy broth, SP- cells were then processed and spray-dried. Nitrate-supplementation decreased (P = 0.0006; SEM = 0.31) methane production by the cultures, but this decrease was unaffected by 79R4 inoculation (2.57 µmol CH4/mL with no nitrate/no inoculum versus 0.15 µmol CH4/mL with nitrate/inoculum). Nitrate-metabolizing activity in nitrate-treated cultures were unaffected by 79R4 inoculations (P = 0.17; SEM = 0.15), rates being 0.95, 0.63 and 0.50 µmol nitrate/mL h-1 FH-, SP- and non-inoculated cultures, respectively. Nitrite accumulation rates (P = 0.10; SEM = 0.06) and peak nitrite concentrations (P = 0.06; SEM = 0.75) tended to be lower in SP- than in FH- and non-inoculated cultures (0.29, 0.47 and 0.47 µmol nitrite/mL h-1 and 3.33, 5.67 and 5.66 µmol/mL, respectively). Rates of ammonia accumulation were more rapid (P = 0.01; SEM = 0.01) in SP- and FH- than in non-inoculated cultures (0.16 and 0.15 versus 0.06 µmol/mL h-1, respectively). Results provide evidence that 79R4 prototype may aid rumen populations in detoxifying nitrite, therefore enhancing the abilities of high nitrate diets.

An in vitro incubation was carried out to evaluate the potential of hops (Humulus lupulus) as an alternative to antibiotics for upgrading animal production. Whole pellets of hops (Variety Galena) were ground and incubated in a batch culture of ruminal fluid (2000 mg of ground corn grain + 10 mL of fresh rumen liquor). Ruminal fluid was collected from two beef cows through an esophageal tube. The hops were incubated by 24 h at levels of 0, 800, 1600 and 2400 µg/mL. Data were analyzed statistically by analysis of variance using PROC GLM of SAS. Hops addition linearly decreased (P < 0.01) gas production (GP; 90.89, 61.73, 36.63 and 28.37 µmol/g respectively) and methane production (MP; 9.76, 1.70, 1.30 and 0.46 µmol/g respectively). The CO2 production linearly increased as levels of hops increased (P < 0.02; 87.5, 88.4, 98.1 and 99.3 µmol/g respectively). The ammonia-N production was reduced in treatment 2 with respect to other treatments (P < 0.03; 12.6, 9.2, 13.7 and 13.5 µmol/g). Effects on ruminal fermentation of corn grain were dose dependent of hops. Addition of hops in ruminant feeding may offer a means to decrease ruminal methane production. Further research is needed to test efficacy of hops on other in vivo rumen-fermentation parameters.

Eighteen beef cows with their calves were assigned to 3 groups considering body conditions scores at calving (BCSC): T1 (high BCSC, maintained throughout the study); T2 (low BCSC, increased...

The influence of supplement form (dry vs. liquid) on the feeding value of diets for feedlot cattle was evaluated. Treatments were: (1) dry supplement (DS); (2) liquid supplement (LS, all supplemental macro- and micro-minerals, salt, monensin and urea provided as a uniform blend with cane molasses; (3) LS minus monensin, that was provided in a 3% premix with dried distillers grains plus solubles before combination into a complete mixed diet (LS-MON) and (4) LS, except that condensed molasses solubles replaced 41% (DM basis) of the cane molasses solids (LSUF). In a 112-day trial involving 160 Holstein steers (473 ± 32 kg) cattle fed DS, LS, LS-MON and LSUF diets had similar (P > .10) ADG, DMI, feed efficiency and estimated dietary NE. The effects on characteristics of digestion were evaluate using four Holstein steers with cannulas in rumen and proximal duodenum. There were no treatment effects (P > .10) on ruminal digestion of OM, and feed N, microbial efficiency and ruminal N efficiency. It is concluded that the form of incorporation of minor dietary ingredients during batch mixing (dry premix or in combination with a liquid carrier) will not appreciably affect the feeding value of growing-finishing diets for feedlot cattle.

A feedlot growth-performance trial was conducted to evaluate the relative response to tempering when flake density (FD) of corn is increased from 0.31 kg/L (24 lb/bushel) to 0.39 kg/L (30 lb/bushel). Treatments were (1) non-tempered, FD = 0.31 kg/L; (2) non-tempered, FD = 0.39 kg/L; (3) tempered, FD = 0.31 kg/L and (4) tempered, FD = 0.39 kg/L. Tempering prior to flaking increased (21%, P

The objectives of this study were to evaluate the influence of level and source of supplemental Zn on growth performance and dietary energetics in calf-fed Holstein steers. A total of 168 steers (BW = 133 ± 7 kg) were used in a 336-d study. Treatments consisted of diets based on steam-flaked corn supplemented with (DM basis) (1) 20 mg of Zn/kg of DM as ZnSO4; (2) 10 mg of Zn/kg of DM as ZnSO4 plus 10 mg of Zn/kg of DM as Zn betaine; (3) 20 mg of Zn/kg of DM as Zn betaine; or (4) 40 mg of Zn/kg of DM as ZnSO4. Overall (d 1 to 336) there were no treatment effects (P > 0.10) on carcass-adjusted ADG, gain efficiency, and estimated dietary NE. At the 20 mg/kg level of Zn supplementation, the proportion of supplemental Zn provided as chelate did not influence overall ADG, gain efficiency, or dietary NE (P > 0.10). The proportion of Zn supplemented as chelate did not affect (P > 0.10) carcass weight, KPH, LM area, or marbling score. However, DP was greater (quadratic effect, P = 0.01) for steers receiving the 50:50 blend of ZnSO4 and Zn betaine. Carcass yield grade improved (linear component, P = 0.03) with proportion of supplemental Zn as chelate. We conclude that at a 20 mg/kg (DM basis) level of supplementation, Zn source does not affect growth performance of calf-fed Holstein steers. Increasing level of Zn supplementation (as ZnSO4) from 20 to 40 mg/kg will not further enhance overall performance responses.

Silages can harbor pathogenic and antimicrobial resistant microbes which risk infection of food-producing animals. Livestock producers need effective yet environmentally friendly interventions to preserve the feed value of these fermented materials. Medium chain fatty acids such as laurate and its glycerol monoester, monolaurin, are potent inhibitors of many Gram-positive bacteria and when tested at 5 mg/mL in anaerobic cultures (n = 3/treatment) inoculated with 105 colony forming units (CFU) of Listeria monocytogenes and grown at 37oC in ½ strength Brain Heart infusion broth achieved near complete elimination of viable cells after 6 h compared to a 2.2 ± 0.1 log10 CFU/mL increase observed in controls. Culture of a tetracycline-resistant Enterococcus faecalis with 5 mg laurate/mL likewise achieved near complete elimination of viable cells (5 log10 CFU/mL) by 6 h incubation. The bactericidal effect of 5 mg monolaurin was less against E. faecalis, achieving a decrease of 1.8 ± 0.2 log10 CFU/mL and not decreased further after 24 h. When tested against air-exposed silage, pH 7.53 (4 g), mixed with 4 mL water, 5 mg laurate or monolaurin decreased viability of experimentally-inoculated L. monocytogenes (105 CFU/g silage) more (P < 0.05) than untreated controls after 24 h aerobic incubation (22oC), with viable counts being decreased 6.3 ± 0.1, 5.9 ± 0.8 and 4.5 ± 0.1 log10 CFU/g, respectively. In contrast, viable recovery of the experimentally-inoculated (105 CFU/g) tetracycline-resistant E. faecalis was reduced more (P < 0.05) than controls (decreased 0.7 ± 0.1 log10 CFU/g) after 6 h incubation when similarly tested with laurate and monolaurin (1.7 ± 0.5 and 3.0 ± 0.9 log10 CFU/g, respectively) but counts after 24 h were similar, decreasing on average 2.0 ± 0.5 log10 CFU/g). Results indicate laurate and monolaurin may be useful in killing L. monocytogenes and tetracycline-resistant E. faecalis during silage feed-out.

Poultry litter, produced by intensive poultry production systems, is a potentially valuable crude protein feedstuff for ruminants if effectively treated to kill pathogens before feeding. Composting effectively kills pathogens but risks losses of ammonia during uric acid degradation. To test if hop extracts may help preserve uric acid concentrations during composting, 11-g portions of used wood chip litter (WCL, 88% dry matter) were treated with 6 mL water containing Galena or Chinook hop extracts to achieve 0.06 g of either extract/g WCL. Control WCL was treated with buffer alone. The WCL was distributed to 50-mL tubes (3 tubes/treatment), capped and incubated in Gas Pac jars for 8 days at 30oC, followed by 3 days at 37oC and an additional 2 days at 42oC to simulate a 13-day compost period. A repeated measures analysis of variance revealed a treatment by day interaction on uric acid (P < 0.05), with concentrations being highest upon initiation of composting (41.9 ± 3.6 µmol/g), lowest on day 13 for the untreated compost (17.5 ± 9.2 µmol/g) and intermediate for Galena and Chinook hop-treated compost (28.0 ± 4.7 and 25.8 ± 0.8 µmol/g, respectively). Effects of treatment, day of composting or their interaction, however, were not observed (P > 0.05) on concentrations of ammonia and urea, which averaged 1.2 ± 1.0 and 2.9 ± 0.6 µmol/g, respectively. As expected, an effect of day-of composting on survivability (P < 0.05) of select bacterial populations was confirmed, with counts being decreased more than 3.0 log10 units after 13 days composting than on day 0 for enterococci, staphylococci, lactic acid bacteria, coliforms and total aerobes (6.7 ± 0.09, 9.0 ± 0.01, 5.8 ± 0.16, 5.9 ± 0.09 and 9,9 ± 0.06 log10 CFU/g, respectively). These results indicate that hops-treatment may help preserve crude protein within WCL during composting.

Aerobic exposure of silage during the feed-out phase promotes growth of spoilage as well as pathogenic and multi-drug resistant (MDR) microbes which can risk infection of food-producing animals and the foods they produce. Livestock producers are interested in finding effective yet environmentally friendly interventions to preserve the nutritional value of these spoiled feedstuffs. We investigated the antimicrobial activity of 6 to 12 carbon-containing saturated fatty acids (C6, C8, C10 or C12) added (0.03 g) individually or as 1:1 mixtures of C6:C8:C10:C12 or C8:C10 to 4 g of overnight exposed silage suspended in 10 mL water. Net changes in colony counts, determined as the difference between counts measured after 0 and 24 h aerobic incubation (22oC) of untreated and treated silage suspensions (n = 3/treatment), were subjected to an analysis of variance. Populations of wild-type total aerobes and experimentally-inoculated MDR-Staphylococcus aureus were unaffected by treatment (P > 0.05), decreasing on average (± SD) 0.64 ± 0.40 and 1.09 ± 0.39 log10 CFU/g silage, respectively. Treatment effects (P < 0.05) were observed against experimentally-inoculated Listeria monocytogenes, with the C8:C10 mix decreasing this foodborne pathogen by 0.64 log10 CFU/g compared to a 0.95 log10/g increase in controls. Indigenous yeast and mold, considered responsible for spoilage, were decreased 2.12 and 3.07 log10 CFU/g by the C8 and C8:C10 treatments compared to 0.40 log10 CFU/g increase in controls. Indigenous lactic acid bacteria, considered beneficial, were decreased most potently by the C8 and C8:C10 treatments compared to controls (1.28, 0.66 and 0.37 log10 CFU/g, respectively). Indigenous enterococci decreased in all incubations, including controls (3.03 log10 CFU/g), compared to 4.69 to 5.03 log10 CFU/g decreases in C6, C8, C10, C12 and C8:C10 treatments. Results reveal that some fatty acid treatments inhibited pathogenic and spoilage microbes, yet treatment optimization is needed to avoid adverse effects against beneficial microbes.

The effect on growth performance of diets containing orange pulp fermented in solid substrate with the yeast Saccharomyces cerevisiae (S. cerevisiae) was evaluated in feedlot lambs. Fifteen non-castrated male lambs (Pelibuey x Dorper) with an initial weight of 22 ± 4 kg were distributed in individual pens in a completely randomized design. The feeding trial lasted 60 days. Treatments were: treatment 1 (T1), 50% commercial feed plus 50% wet basis (WB) of orange pulp fermented with yeast; treatment 2 (T2), 50% commercial feed plus 50% (WB) fresh orange pulp without yeast; and treatment 3 (T3) 100% commercial feed as a total mixed ration. The variables of the study were: average daily weight gain, feed consumption, feed conversion ratio, area of Longissimus dorsi and back fat thickness, the latter two measured at the end of the test using ultrasound. Daily weight gain was significantly lower (P0.05) weight gain; average daily gain (ADG) for T1, T2 and T3 was 0.270±0.027, 0.200±0.035 and 0.273±0.038 kg/d, respectively. Feed conversion ratio (feed consumed/weight gain) of lambs in T2 presented worth value (P 0.05). In conclusion, substituting orange pulp fermented in solid state with S. cerevisiae for 50% of a commercial diet resulted in similar productive behavior of confined sheep, whereas substitution with non-fermented orange pulp may reduce growth performance of lambs.

One hundred twenty-six Holstein steers (457.1 ± 27.5 kg BW) were used in a 127-d experiment to evaluate the influence of dietary cation–anion difference (DCAD) on growth performance and carcass characteristics. Treatments consisted of steam-flaked corn-based diets supplemented to provide DCAD of 34, 84 or 134 mEq/kg diet DM. There was no treatment effect (P > .20) on ADG, DMI, gain efficiency or dietary NE. Six Holstein steers (196 ± 3 kg) with cannulas in rumen and proximal duodenum were used in a replicated 3 × 3 Latin Square design to evaluated treatment effects on digestion characteristics. The DCAD did not affect (P > .20) ruminal or total digestion of OM, NDF, starch and N, or ruminal pH and VFA molar proportions. It is concluded that increasing DCAD of Holstein steers fed a conventional steam-flaked corn-based diet under conditions of high ambient temperature will not enhance growth performance.

The effect of different proportions of ground-to-whole sorghum grain on weight gain, Longissimus dorsi area (LDA) and subcutaneous fat (SF) was evaluated in 20 crossbred (75% Alpine and 25% Spanish...

The effect of initial implant type (short or long duration) and reimplant scheme on performance and carcass characteristics of calf-fed Holstein steers was evaluated. A total of 240 steers (113.5 ± 6.2 kg) were used in a 349-d trial. The 2 implant strategies were (1) implant on arrival with 43.9 mg of estradiol and reimplant on d 224 with 120 mg of trenbolone acetate and 24 mg of estradiol (Imp-2) and (2) implant on arrival with 100 mg of progesterone and 10 mg of estradiol benzoate and reimplant on d 112 and 224 with 120 mg of trenbolone acetate and 24 mg of estradiol (Imp-3). During the initial 112 d, performance was not affected by implant strategy. From d 112 to 212, Imp-3 had greater ADG (9.6%, P 0.75). Implant strategy had minor effects on carcass characteristics (P > 0.10). Although, LM area was greater (4%, P

Author(s): Torrentera, Noemi; Carrasco, Ramses; Salinas-Chavira, Jaime; Plascencia, Alejandro; Zinn, Richard A | Abstract: ObjectiveTwo trials were conducted in order to examine the effects of level of supplemental methionine on productive performance, dietary energetic, plasma amino acid concentration, and digestive function.MethodsDietary treatments consisted of a steam-flaked corn-based diet containing urea as the only source of supplemental nitrogen supplemented with no supplemental amino acid (control), or control plus 1.01% lysine and 0.032%, 0.064%, 0.096%, or 0.128% methionine. In Trial 1, 150 Holstein steer calves (127±4.9 kg) were utilized to evaluate the influence of treatments on growth-performance, dietary energetic, plasma amino acid concentration during the first 112 days of growing period. During the initial 56-d period calves received the 5 experimental diets. During the subsequent 56-d period all calves were fed the control diet.ResultsDuring the initial 56-d period, methionine supplementation increased (linear effect, pl0.01) plasma methionine. In the presence of supplemental lysine, increases on level of methionine in diet did not affect average daily gain. However, increased gain efficiency (quadratic effect, p = 0.03) and estimated dietary net energy (NE; linear effect, p = 0.05). Estimated metabolizable methionine supply was closely associated (R2 = 0.95) with efficiency NE utilization for maintenance and gain. During the subsequent 56-d period, when all calves received the control diet (no amino acid supplementation), plasma amino acid concentrations and growth performance was not different among groups. However, the effects of methionine supplementation during the initial 56-period carried over, so that following a 56-d withdrawal of supplementation, the overall 112-d effects on gain efficiency (quadratic effect, p = 0.05) dietary NE (linear effect, p≤0.05) remained appreciable. In Trial 2, 5 cannulated Holstein steers were used to evaluate treatment effects on characteristics of digestion and amino acid supply to the small intestine. There were no treatment effects on flow of dietary and microbial N to the small intestine. Postruminal N digestion increased (p = 0.04) with increasing level of supplemental methionine. Methionine supplementation linearly increased (pl0.01) duodenal flow of methionine. Likewise, lysine supplementation increased an average of 4.6% (p = 0.04) duodenal flow of lysine. In steers that received non-supplemented diet, observed intestinal amino acid supply were in good agreement with expected.ConclusionWe conclude that addition of rumen-protected methionine and lysine to diets may enhance gain efficiency and dietary energetics of growing Holstein calves. Observed amino acid supply to the small intestine were in good agreement with expected, supportive of NRC (2000, Level 1).

The influence of ferulic acid (FA) and sodium chlorate (SC) was evaluated in two trials on the growth of Escherichia coli F18 and K88 (F18 and K88) incubated with porcine fecal bacteria. Treatments were 2 levels of FA (0 and 5 mg/mL) and 2 levels of SC (0 and 10 mM/mL). In trial one, ½-strength Mueller Hinton broth mixed with porcine feces (0.5% w/v) was inoculated with a novobiocin and naladixic acid resistant F18-strain. This fecal suspension was transferred to tubes (3/treatment) and anaerobically incubated at 39 oC for enumeration at 0, 6 and 24 h using MacConkey agar supplemented with novobiocin and naladixic acid with aerobic incubation at 37 oC. An interaction (FA x SC) at 6 and 24 h was observed (P < 0.01). At 6 h of incubation, SC alone or combined with FA had the lowest counts (P < 0.05); FA alone was lower than control but higher than SC or SC+FA (P < 0.05). At 24 h, FA alone or combined with SC had the lowest counts (P < 0.05); SC was lower than control but higher than FA or SC+FA (P < 0.05). In trial 2 were used the same procedures of trial 1, except that K88 was used. There was an interaction at 6 h (P < 0.01) where the lowest counts were in FA+SC (P < 0.05). SC alone or FA alone were lower than control but higher than SC+FA (P < 0.05). There was no interaction at 24 h (P = 0.16), where FA reduced the K88 counts (P < 0.01), however it was not affected by SC (P = 0.12). In conclusion, SC reduced E. coli counts; however, at 24 h of incubation greater reductions were observed when FA alone or combined with SC was added into the incubation fluid with porcine feces.

Poultry litter is a potentially valuable crude protein feedstuff for ruminants but must be treated to kill pathogens before feeding. Composting effectively kills pathogens but risks losses of ammonia during uric acid degradation. Presently, 250-g portions of used wood chip litter (WCL, 73% dry matter) were treated with 125 mL 0.4 M phosphate buffer (pH 6.5) containing Chinook or Galena hop extracts to achieve 0.03 g beta-acid/g WCL. Control WCL was treated with buffer alone. The WCL was distributed (11 g) to 50-mL tubes (3 tubes/treatment per sampling day), inoculated with a marked challenge strain of Salmonella Typhimurium (ST) then capped and incubated at successive 3-day increments at 22(o)C, 37(o)C and 42(o)C. Repeated measures analysis of variance of ammonia, urea and uric acid measured in samples collected on days 0, 3, 6 and 9 revealed a main effect of day on uric acid (P < 0.05), which increased from day 0 to 3 (a high of 9.4 µmol/g) and declined thereafter to its low (4.1 µmol/g) on day 9. A day x treatment interaction was observed (P < 0.05) on ammonia accumulations which increased steadily, accumulating more on day 9 with Galena hops-treated WCL than with control- or Chinook hops-treated WCL (7.3, 6.6 and 5.6 µmol/g, respectively). A main effect of treatment but not day or their interaction was observed on urea accumulations, highest for control, lowest for Galena- and intermediate for Chinook hops-treated WCL (1.7, 0.5 and 1.0 µmol/g, respectively). Analysis of bacterial concentrations revealed little effect of treatment on bacterial counts; however, main effects of day on ST and E. coli were observed (P < 0.05) with both being decreased below detection limits (1 log(10) CFU/g) by day 9. These results indicate that composting combined with Chinook hops-treatment may help safely preserve crude protein of WCL.

Two essential oils (EO), thymol and carvacrol, were used in six ratio (100:00, 80:20, 60:40, 40:60, 20:80 and 00:100) combinations of both EO and in a dose of 0.2 g L−1 in bovine ruminal culture me...

The objective of this study was to determine the nutritional value of three leguminous trees heavily selected by goats in a xerophilous shrubland. Chemical composition and in vitro dry matter disappearance (IVDMD) of leaves and pods from leucaena (Leucaena leucocephala), mesquite (Prosopis laevigata), and huisache (Acacia farnesiana) is presented. Crude protein (CP) ranged from 17.3% for leaves of huisache to 21.9% for leucaena. The neutral detergent fiber (NDF) content ranged from 39.0 to 40.3 with no difference among fodder threes. Across tree species, mean IVDMD was 61.6% for pods and 52.2% for leaves. IVDMD for leaves was highest (p < 0.01) for leucaena (54.9%) and lowest for huisache (47.3%). Condensed tannins in an acetonic extract were highest for leaves of huisache (45.3 mg CE/g DM) and lowest for mesquite (25.9 mg CE/g DM). Pods and leaves of huisache presented the highest number of secondary metabolites, mainly related to hydroxybenzoic acid and flavonols; leucaena and mesquite presented mainly flavonols and anthocyanins. It was concluded that leaves and pods of leucaena, mesquite, and huisache constitute valuable forages for ruminant livestock due to their low fiber, high CP levels, moderate in vitro fermentation characteristics and high mineral content.

Two experiments were conducted to examine the influence of protein and virginiamycin (VM) supplementation on feedlot growth performance, digestion, and metabolizable AA (MAA) supply of calf-fed Holstein steers. Growth performance and dietary energetics were evaluated in 120 Holstein steers (127 ± 9 kg). During the initial 112-d feeding period, a steam-flaked corn-based diet was balanced to meet either 100% (MAB) or 87% (UREA) of MAA requirements. Diets were supplemented with or without 22.5 mg/kg VM in a 2 × 2 factorial arrangement. Subsequently (d 112 to 308), all steers received the UREA diet with or without VM. During the initial 112-d, MAB increased ADG, G:F, and dietary NE (0.01). Thereafter, when all steers received the UREA diet, ADG, G:F, and dietary NE were not different (0.10) across initial supplementation treatments. Overall (d 1 to 308), MAB did not affect ADG (0.10) but enhanced G:F efficiency ( = 0.03) and dietary NE ( = 0.05). During the initial 112-d period and through the remainder of the experiment, VM increased G:F (0.01) and dietary NE (0.01). Four Holstein steers (146 ± 4 kg) with cannulas in the rumen and proximal duodenum were used in a 4 × 4 Latin square design to evaluate initial 112-d treatment effects on digestive function. There were no treatment effects (0.10) on ruminal digestion of OM, NDF, starch, microbial efficiency, or total tract digestion of OM and NDF. The MAB increased indispensable AA flow to the small intestine (0.01) and total tract digestion of N (0.01) and starch ( = 0.04). Observed AA supply to small intestine was in agreement with expected supply ( = 0.96). Virginiamycin decreased ( = 0.04) nonammonia N flow to the small intestine and did not affect (0.10) total tract N digestion. Extrapolating from AA supplies in the metabolism study, MAB satisfied indispensable AA requirements during the initial 112-d period, whereas the UREA diet met 73.5% and 79.2% of methionine and lysine requirements, respectively. During the subsequent periods (d 112 to 308) indispensable AA supplies exceeded theoretical requirements. We conclude that enhancements in energy utilization when diets are balanced to meet MAA requirements of calf-fed Holstein steers during the initial 112-d feedlot period remain appreciable throughout time on feed. Virginiamycin enhanced efficiency of energy utilization throughout the feedlot growing-finishing period.