T. A. McAllister

Effect of steroidal saponin from Yucca schidigera extract on ruminal microbes

The effects of steroidal saponins (SAP) isolated from Yucca schidigera extract on ruminal bacteria and fungi were investigated in pure culture studies. Prevotella bryantii, Ruminobacter amylophilus, Selenomonas ruminantium and Streptococcus bovis were cultured through ten 24‐h transfers in ruminal fluid medium containing 0 or 25 µg SAP ml−1 (measured as smilagenin equivalents). The four strains, each non‐exposed or pre‐exposed to SAP, were then inoculated into medium containing 0 or 250 µg smilagenin equivalents ml−1 and 24‐h growth curves were determined. The cellulolytic ruminal bacteria Ruminococcus flavefaciens, Fibrobacter succinogenes and Rc. albus were cultured for 72 h on Whatman no. 1 filter paper in medium containing 0, 9, 90 or 180 µg SAP ml−1 for the determination of filter paper digestion and endoglucanase activity. The ruminal bacteria differed in their responses to SAP. Steroidal saponins in the medium reduced the growth of Strep. bovis (P < 0·01 at 2, 3, 4, 5, 6 and 8 h), P. bryantii (P < 0·05 at 4, 5, 6, 8, 10 and 24 h) and Rb. amylophilus (P < 0·05 at 14 and 24 h), but the growth of S. ruminantium was enhanced (P < 0·05) at 10, 14 and 24 h. The growth curves of all four non‐cellulolytic species were similar (P > 0·05) between pre‐exposed and non‐exposed cultures and the concentrations of total SAP and soluble (deglycosylated) SAP in the liquid fraction were unchanged (P > 0·05) over time. Steroidal saponins inhibited the digestion of filter paper by all three cellulolytic bacteria, but F. succinogenes was less (P < 0·05) sensitive to SAP and more (P < 0·05) effective at deglycosylating SAP than were Rc. flavefaciens or Rc. albus. Transmission electron microscopy revealed that SAP altered the cell walls of the SAP‐inhibited non‐cellulolytic bacteria. The ruminal fungi, Neocallimastix frontalis and Piromyces rhizinflata, were cultured on filter paper in medium containing 0, 0·45, 2·25 or 4·5 µg SAP ml−1. Filter paper digestion by both fungi was completely inhibited by 2·25 µg SAP ml−1. Steroidal saponins from Y. schidigera inhibit cellulolytic ruminal bacteria and fungi, but their effects on amylolytic bacteria are species dependent and similar to the effects of ionophores. As such, SAP may be useful in nutritional applications targeting starch‐digesting ruminal micro‐organisms.

Transmission and control of Escherichia coli O157:H7 — A review

Escherichia coli 157:H7 has evolved as an important foodborne pathogen since its initial description in 1982. Outbreaks of illness associated with E. coli O157:H7 have been reported throughout the northern hemisphere, most frequently in Canada, the United States, Japan, and the United Kingdom. In Canada, infections due to E. coli O157: H7 appear to be more common in the western provinces than in the east, in rural vs. urban environments, and during summer as opposed to winter months. Undercooked ground beef has been implicated as the primary vehicle in E. coli O157:H7 infection, but contaminated fruits, vegetables and water have also been linked to E. coli O157:H7 outbreaks. Epidemiological investigations demonstrate that dairy and beef cattle are primary reservoirs of this organism, carrying it asymptomatically and shedding it intermittently and seasonally in their feces. Surveys in Canada and the United States indicate widespread distribution of E. coli O157:H7 in cattle operations. The prevalence of E....

Feeding saponin-containing Yucca schidigera and Quillaja saponaria to decrease enteric methane production in dairy cows.

An experiment was conducted in vitro to determine whether the addition of saponin-containing Yucca schidigera or Quillaja saponaria reduces methane production without impairing ruminal fermentation or fiber digestion. A slightly lower dose of saponin was then fed to lactating dairy cows to evaluate effects on ruminal fermentation, methane production, total-tract nutrient digestibility, and milk production and composition. A 24-h batch culture in vitro incubation was conducted in a completely randomized design with a control (no additive, CON) and 3 doses of either saponin source [15, 30, and 45 g/kg of substrate dry matter (DM)] using buffered ruminal fluid from 3 dairy cows. The in vivo study was conducted as a crossover design with 2 groups of cows, 3 treatments, and three 28-d periods. Six ruminally cannulated cows were used in group 1 and 6 intact cows in group 2 (627 +/- 55 kg of body weight and 155 +/- 28 d in milk). The treatments were 1) early lactation total mixed ration, no additive (control; CON); 2) CON diet supplemented with whole-plant Y. schidigera powder at 10 g/kg of DM (YS); and 3) CON diet supplemented with whole-plant Q. saponaria powder at 10 g/kg of DM (QS). Methane production was measured in environmental chambers and with the sulfur hexafluoride (SF(6)) tracer technique. In vitro, increasing levels of both saponin sources decreased methane concentration in the headspace and increased the proportion of propionate in the buffered rumen fluid. Concentration of ammonia-N, acetate proportion, and the acetate:propionate ratio in the buffered rumen fluid as well as 24-h digestible neutral detergent fiber were reduced compared with the CON treatment. Medium and high saponin levels decreased DM digestibility compared with the CON treatment. A lower feeding rate of both saponin sources (10 g/kg of DM) was used in vivo in an attempt to avoid potentially negative effects of higher saponin levels on feed digestibility. Feeding saponin did not affect milk production, total-tract nutrient digestibility, rumen fermentation, or methane production. However, DM intake was greater for cows fed YS and QS than for CON cows, with a tendency for greater DM intake for cows fed YS compared with those fed QS. Consequently, efficiency of milk production (kg of milk/kg of DM intake) was lower for cows fed saponin compared with controls. The results show that although saponin from Y. schidigera and Q. saponaria lowered methane production in vitro, the reduction was largely due to reduced ruminal fermentation and feed digestion. Feeding a lower dose of saponin to lactating dairy cows avoided potentially negative effects on ruminal fermentation and feed digestion, but methane production was not reduced. Lower efficiency of milk production of cows fed saponin, and potential reductions in feed digestion at high supplementation rates may make saponin supplements an unattractive option for lowering methane production in vivo.

Digestion, ruminal fermentation, ciliate protozoal populations, and milk production from dairy cows fed cinnamaldehyde, quebracho condensed tannin, or Yucca schidigera saponin extracts.

Four ruminally cannulated lactating cows were used in a 4 x 4 Latin square design (28-d periods) to determine the effects of cinnamaldehyde (CIN; 1 g/cow per day), condensed tannins from quebracho trees (QCT, containing 70% tannins, 150 g/cow per day), and saponins from Yucca schidigera extract (YSE, containing 10% saponins; 60 g/cow per day) on digestion, ruminal fermentation characteristics, protozoal populations, and milk production. Intake of dry matter was not affected by the addition of CIN or QCT, but cows fed YSE had lesser intake than cows fed the control diet (21.8 vs. 23.2 kg/d). Apparent total-tract digestibilities of dry matter, organic matter, crude protein, neutral detergent fiber, and acid detergent fiber were unaffected by dietary treatments. Supplementation with CIN, QTE, or YSE did not affect in situ ruminal degradation of soybean meal, grass silage, or corn grain. Ruminal pH (6.67), total volatile fatty acid concentration (135 mM), and molar proportions (mol/100 mol of total volatile fatty acid) of acetate (65.0), propionate (19.6), and butyrate (11.2) were similar among treatments. Ruminal NH(3)-N concentration was not changed by the addition of CIN and YSE, but tended to decrease in cows fed QCT compared with cows fed the control diet (132 vs. 160 mg/L). Total numbers of ruminal protozoa were not changed by adding CIN, QCT, or YSE in the diet (5.85 log(10)/mL). However, the number of Isotricha was greater in ruminal fluid of cows fed CIN than in ruminal fluid of cows fed the control diet (4.46 vs. 4.23 log(10)/mL). Milk production (33.1 kg/d), milk fat (4.3%), and milk protein (3.5%) remained unchanged between dietary treatments. Results of this study show that under our experimental conditions, supplementing dairy cow diets with CIN, QCT, or YSE had limited effects on digestion, ruminal fermentation characteristics, and protozoal populations. The lack of effects observed in this study suggests that these antimicrobials require administration at greater doses to favorably alter rumen microbial fermentation.

Effects of an exogenous enzyme preparation on microbial protein synthesis, enzyme activity and attachment to feed in the Rumen Simulation Technique (Rusitec).

The effects of an exogenous enzyme preparation, the application method and feed type on ruminal fermentation and microbial protein synthesis were investigated using the rumen simulation technique (Rusitec). Steam-rolled barley grain and chopped alfalfa hay were sprayed with water (control, C), an enzyme preparation with a predominant xylanase activity (EF), or autoclaved enzyme (AEF) 24 h prior to feeding, or the enzyme was supplied in the buffer infused into the Rusitec (EI). Microbial N incorporation was measured using (15NH4)2SO4 in the buffer. Spent feed bags were pummelled mechanically in buffer to segregate the feed particle-associated (FPA) and feed particle-bound (FPB) bacterial fractions. Enzymes applied to feed reduced neutral-detergent fibre content, and increased the concentration of reducing sugars in barley grain, but not alfalfa hay. Ruminal cellulolytic bacteria were more numerous with EF than with C. Disappearance of DM from barley grain was higher with EF than with C, but alfalfa was unaffected by EF. Treatment EF increased incorporation of 15N into FPA and FPB fractions at 24 and 48 h. In contrast, AEF reduced the 24 h values, relative to C; AEF and C were similar at 48 h. Infused enzyme (EI) did not affect 15N incorporation. Xylanase activity in effluent was increased by EF and EI, compared to C, but not by AEF. Xylanase activity in FPA was higher at 48 h than at 24 h with all treatments; it was higher with EF than C at 24 and 48 h, but was not altered by AEF or EI. Applying enzymes onto feeds before feeding was more effective than dosing directly into the artificial rumen for increasing ruminal fibrolytic activity.

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

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.

Effect of exogenous enzymes on digestibility of barley silage and growth performance of feedlot cattle

Barley silage was sprayed with water or with a 2:1 combination of commercial cellulase and xylanase preparations, or the enzymes were introduced directly into the rumen, in a digestibility study (replicated incomplete 3 × 3 Latin square) using 10 sheep. Apparent digestibilities of dry matter (DM) and neutral detergent fibre (NDF) were lower (P   0.05) intake of DM, organic matter or digestible organic matter, or digestibilities of DM or NDF, ruminal pH, xylanase activity, endoglucanase activity or ruminal cellulolytic bacterial populations. Treating the silage portion of an 82.5% barley silage backgrounding diet with the enzyme mix at 0, 1.25, 3.5 or 5.0 L t−1 DM tended to linearly increase (P = 0.08) final weights of steers (n = 24). Average daily gain tended to be (P = 0.06) and feed intake and feed efficiency were (P = 0.04 and P = 0.03, respectively) quadratically related to these ...

CONJUGATED LINOLEIC ACID-ENRICHED BEEF PRODUCTION

Canadian beef consumption is approximately 31 kg per annum, or a third of all meats consumed. Beef is a nutrient-rich food, providing good quality protein, vitamins B-6 and B-12, niacin, iron, and zinc. However, animal fats have gained the reputation of being less healthy. The identification of the anticarcinogenic effects of beef extracts due to the presence of conjugated linoleic acid (CLA) has heightened interest in increasing the amount of CLA deposited in beef. Beef cattle produce CLA and deposit these compounds in the meat; thus, beef consumers can receive bioformed CLA. Beef contains both of the bioactive CLA isomers, namely, cis-9, trans-11 and trans-10, cis-12. The relative content of these CLA isomers in beef depends on the feeds consumed by the animals during production. Feeding cattle linoleic acid-rich oils for extended periods of time increases the CLA content of beef. Depending on the type and relative maturity of the pasture, beef from pasture-fed cattle may have a higher CLA content than beef from grain- or silage-fed cattle. In feedlot animals fed high-grain diets, inclusion of dietary oil along with hay during both the growth and finishing phases led to an increase in CLA content from 2.8 to 14 mg/g beef fat, which would provide 77 mg CLA in an 85-g serving of beef. The CLAs appear to be concentrated in intramuscular and subcutaneous fat of beef cattle, with the CLA trans-10, cis-12 isomer being greater in the subcutaneous fat.

Effect of dried distillers’ grains from wheat on diet digestibility and performance of feedlot cattle

In a 55-d backgrounding period, 120 (n = 22) British cross heifers (312 ± 20 kg) received diets containing 55% barley silage, 5% supplement and 0 (n = 24), 20 (n = 24), or 40% (n = 22) wheat distillers’ dried grains with solubles (DDGS). The remainder of the diet was steam-rolled barley. Replacing half (20%) or all (40%) of the barley with DDGS did not affect dry matter intake (DMI) (P = 0.61), average daily gain (ADG) (P = 0.86), or gain:feed (P = 0.94), indicating the energy content of DDGS is similar to that of barley when included in backgrounding diets. During a 133-d finishing period, DDGS were included at 0, 20, 40, or 60% of diet dry matter (DM) or at 60% plus additional calcium, provided as 1% limestone (n = 24). Additional calcium did not (P > 0.1) affect DMI, ADG, or gain:feed. Increasing levels of DDGS linearly increased (P = 0.001) DMI and reduced (P = 0.04) gain:feed and diet NEg content (P = 0.001), but had no effect on ADG (P = 0.20). Feeding 60% DDGS reduced (P < 0.01) DM digestibility as...

Effect of sainfoin on in vitro digestion of fresh alfalfa and bloat in steers

The effects of sainfoin (Onobrychis viciifolia) on digestion of alfalfa (Medicago sativa) were investigated in vitro and in vivo. Fresh alfalfa and sainfoin were incubated in an artificial rumen (Rusitec) in ratios of 100:0, 75:25, 50:50, 25:75 and 0:100 (as-fed). Disappearances of dry matter and N from sainfoin were 77 and 65% of those from alfalfa, respectively. Protease and endoglucanase activities, NH3-N and methane production declined (P   0.05), but cells incorporated more 15NH3N as sainfoin in the diet increased. Chopped leaves (100:0, 95:5 and 90:10 alfalfa:sainfoin) were incubated for 48 h with diluted ruminal fluid containing 0 or 50 mg polyethylene glycol, which binds tannins. Gas and volatile fatty acid productions were similar (P > 0.05) across treatments, but including 10% sainfoin (without polyethylene glycol) reduced (P < 0.05) NH3 concentrations between 8 and 24 h. Sainfoin tannins reduced degradation...