Effect of lasalocid, monensin or thiopeptin on lactic acidosis in cattle

The influence of virginiamycin on digestion and ruminal parameters under feedlot conditions

This experiment aimed to assess the impact of virginiamycin on in vitro gas production dynamics, rumen kinetics, and nutrient digestibility in beef steers fed a grain-based diet. Nine ruminally cannulated British-crossbred steers (596 ± 49 kg) were assigned to this experiment. Animals were housed in three pens (n = 3/pen) equipped with a Calan gate feed system and water troughs. Pens were enrolled in a 3 × 3 Latin square design containing three periods of 16 d, and a 5-d washout interval between periods. Dietary treatments consisted of virginiamycin (VM) administration at 0 (VM0), 180 (VM180), or 240 mg/d (VM240). During days 15 and 16 of each period, about 600 mL of rumen fluid and urine samples were collected before (0 h), and at 4, 8, 12, and 16 h after the morning feed (0730 hours), rumen inoculum was used to take pH and redox potential measurements immediately after collection using a portable pH and redox meter, and subsamples were taken for volatile fatty acids (VFA) and NH3-N analyses, and urine samples were composited daily and analyzed for creatinine and purine derivatives (PD) content to estimate microbial crude protein flow. During the 4-h post-morning feed rumen collection, rumen inoculum was utilized to perform in vitro gas production measurements. Fecal samples were collected on day 16 of each period to estimate nutrient digestibility using acid detergent insoluble ash as an internal marker. Animals were considered the experimental unit for the statistical analyses, and periods and squares were included as random variables. The total and rate of gas production were similar among treatments (P ≥ 0.17). The second-pool (i.e., fiber) gas production increased linearly as VM inclusion increased (P = 0.01), with VM240 being greater compared to VM180 and VM0 (7.84, 6.94, and 6.89 mL, respectively). Ruminal pH linearly increased as VM increased, with VM240 being greater than VM0 and VM180 intermediate (5.90, 5.82, and 5.86, respectively; P = 0.03). The VFA concentrations did not differ (P ≥ 0.13), but the acetate-to-propionate ratio was the highest in VM240 (P = 0.005). Branched-chain VFA increased (P ≤ 0.03) while lactate concentrations decreased (P = 0.005) linearly with VM. The ruminal NH3-N concentration was the lowest in the VM0 (P = 0.006). The estimated absorbed PD, purine derivative to creatinine index, and microbial N flow increased linearly with VM (P ≤ 0.07). The provision of VM influenced rumen dynamics in a dose-dependent manner.

Effect of biochanin A on the rumen microbial community of Holstein steers consuming a high fiber diet and subjected to a subacute acidosis challenge

Subacute rumen acidosis (SARA) occurs when highly fermentable carbohydrates are introduced into the diet, decreasing pH and disturbing the microbial ecology of the rumen. Rumen amylolytic bacteria rapidly catabolize starch, fermentation acids accumulate in the rumen and reduce environmental pH. Historically, antibiotics (e.g., monensin, MON) have been used in the prevention and treatment of SARA. Biochanin A (BCA), an isoflavone produced by red clover (Trifolium pratense), mitigates changes associated with starch fermentation ex vivo. The objective of the study was to determine the effect of BCA on amylolytic bacteria and rumen pH during a SARA challenge. Twelve rumen fistulated steers were assigned to 1 of 4 treatments: HF CON (high fiber control), SARA CON, MON (200 mg d^-1), or BCA (6 g d^-1). The basal diet consisted of corn silage and dried distiller’s grains ad libitum. The study consisted of a 2-wk adaptation, a 1-wk HF period, and an 8-d SARA challenge (d 1–4: 40% corn; d 5–8: 70% cracked corn). Samples for pH and enumeration were taken on the last day of each period (4 h). Amylolytic, cellulolytic, and amino acid/peptide-fermenting bacteria (APB) were enumerated. Enumeration data were normalized by log transformation and data were analyzed by repeated measures ANOVA using the MIXED procedure of SAS. The SARA challenge increased total amylolytics and APB, but decreased pH, cellulolytics, and in situ DMD of hay (P < 0.05). BCA treatment counteracted the pH, microbiological, and fermentative changes associated with SARA challenge (P < 0.05). Similar results were also observed with MON (P < 0.05). These results indicate that BCA may be an effective alternative to antibiotics for mitigating SARA in cattle production systems.

Characterization of Endolysin LyJH307 with Antimicrobial Activity Against Streptococcus Bovis

Simple Summary

Development of endolysin is a promising strategy because of having the ability to control problematic bacteria specifically. In this study, we developed and characterized the endolysin having lytic activity against Streptococcus bovis (S. bovis), which is one of the initiators of ruminal acidosis. Based on our findings, endolysin LyJH307 showed potent lytic activity in ruminal pH range and ruminal temperature. In addition, LyJH307 was effective against not only S. bovis isolated from rumen, but also several S. bovis groups. We suggest that LyJH307 may have a lytic effect in the ruminal condition and prevent acute ruminal acidosis by controlling S. bovis specifically.

Abstract

Streptococcus bovis (S. bovis) is one of the critical initiators of acute acidosis in ruminants. Therefore, we aimed to develop and characterize the endolysin LyJH307, which can lyse ruminal S. bovis. We tested the bactericidal activity of recombinant LyJH307 against S. bovis JB1 under a range of pH, temperature, NaCl, and metal ion concentrations. In silico analyses showed that LyJH307 has a modular design with a distinct, enzymatically active domain of the NLPC/P60 superfamily at the N-terminal and a cell wall binding domain of the Zoocin A target recognition domain (Zoocin A_TRD) superfamily at the C-terminal. The lytic activity of LyJH307 against S. bovis JB1 was the highest at pH 5.5, and relatively higher under acidic, than under alkaline conditions. LyJH307 activity was also the highest at 39 °C, but was maintained between 25°C and 55°C. LyJH307 bactericidal action was retained under 0-500 mM NaCl. While the activity of LyJH307 significantly decreased on treatment with ethylenediaminetetraacetic acid (EDTA), it was only restored with supplementation of 10 mM Ca²⁺. Analyses of antimicrobial spectra showed that LyJH307 lysed Lancefield groups D (S. bovis group and Enterococcus faecalis) and H (S. sanguinis) bacteria. Thus, LyJH307 might help to prevent acute ruminal acidosis.

Influence of dietary supplementation with Bacillus licheniformis and Saccharomyces cerevisiae as alternatives to monensin on growth performance, antioxidant, immunity, ruminal fermentation and microbial diversity of fattening lambs

Alternatives to antibiotics for improving productivity and maintaining the health of livestock health are urgently needed. The scope of this research was conducted to investigate the effects of two alternatives (Bacillus licheniformis and Saccharomyces cerevisiae) to monensin on growth performance, antioxidant capacity, immunity, ruminal fermentation and microbial diversity of fattening lambs. One hundred and sixty Dorper × Thin-tailed Han sheep (32 ± 3.45 kg BW) were randomly assigned into 5 treatments of n = 32 lambs/group. Lambs in the control group were fed a basal diet (NC) while the other four treatments were fed basal diets supplemented with monensin (PC), Bacillus licheniformis (BL), Saccharomyces cerevisiae (SC), and the combination of Bacillus licheniformis and Saccharomyces cerevisiae with protease (BS), respectively. The experiment lasted for 66 d. Feed intake was recorded every 2 d and lambs were weighed every 20 d. Ten lambs from each group were slaughtered at the end of the trial, and samples of serum and rumen fluid were collected. The results indicated that the dietary regimen did not affect the dry matter intake (DMI). The average daily gain (ADG) of BS treatment was significantly higher than NC group (P < 0.05). Compared with the NC treatment, the other four supplementation treatments increased the concentration of growth hormone (GH), insulin-like growth factor I (IGF-I) and insulin (INS) (P < 0.05). The malondialdehyde (MDA) and total antioxidant capacity (TAOC) showed no significant difference among the 5 treatments while the activity of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) of BS group was significantly increased (P < 0.05). The supplementation regimen decreased the concentration of ammonia Nitrogen (NH3-N) and increased the content of microbial crude proteins (MCP) (P < 0.05). The supplementation of antibiotics and probiotics reduced the concentrations of acetate and increased the concentrations of propionate (P < 0.05). The supplementation treatments increased the relative abundance of Lentisphaerae, Fibrobacteres and Tenericutes at the phylum level, whereas at the genus level, they increased the relative abundance of Fibrobacter (P < 0.05). Overall, this study confirmed the facilitating effect of B. licheniformis, S. cerevisiae and their compounds on growth performance, improve the antioxidant capacity and immune function, and beneficially manipulate ruminal fermentation and microbial diversity of fatting lambs.

Review: Enhancing gastrointestinal health in dairy cows

Due to their high energy requirements, high-yielding dairy cows receive high-grain diets. This commonly jeopardises their gastrointestinal health by causing subacute ruminal acidosis (SARA) and hindgut acidosis. These disorders can disrupt nutrient utilisations, impair the functionalities of gastrointestinal microbiota, and reduce the absorptive and barrier capacities of gastrointestinal epithelia. They can also trigger inflammatory responses. The symptoms of SARA are not only due to a depressed rumen pH. Hence, the diagnosis of this disorder based solely on reticulo-rumen pH values is inaccurate. An accurate diagnosis requires a combination of clinical examinations of cows, including blood, milk, urine and faeces parameters, as well as analyses of herd management and feed quality, including the dietary contents of NDF, starch and physical effective NDF. Grain-induced SARA increases acidity and shifts availabilities of substrates for microorganisms in the reticulo-rumen and hindgut and can result in a dysbiotic microbiota that are characterised by low richness, diversity and functionality. Also, amylolytic microorganisms become more dominant at the expense of proteolytic and fibrolytic ones. Opportunistic microorganisms can take advantage of newly available niches, which, combined with reduced functionalities of epithelia, can contribute to an overall reduction in nutrient utilisation and increasing endotoxins and pathogens in digesta and faeces. The reduced barrier function of epithelia increases translocation of these endotoxins and other immunogenic compounds out of the digestive tract, which may be the cause of inflammations. This needs to be confirmed by determining the toxicity of these compounds. Cows differ in their susceptibility to poor gastrointestinal health, due to variations in genetics, feeding history, diet adaptation, gastrointestinal microbiota, metabolic adaptation, stress and infections. These differences may also offer opportunities for the management of gastrointestinal health. Strategies to prevent SARA include balancing the diet for physical effective fibre, non-fibre carbohydrates and starch, managing the different fractions of non-fibre carbohydrates, and consideration of the type and processing of grain and forage digestibility. Gastrointestinal health disorders due to high grain feeding may be attenuated by a variety of feed supplements and additives, including buffers, antibiotics, probiotics/direct fed microbials and yeast products. However, the efficacy of strategies to prevent these disorders must be improved. This requires a better understanding of the mechanisms through which these strategies affect the functionality of gastrointestinal microbiota and epithelia, and the immunity, inflammation and 'gastrointestinal-health robustness' of cows. More representative models to induce SARA are also needed.

Comparative assessment of probiotics and monensin in the prophylaxis of acute ruminal lactic acidosis in sheep

Background

Acute ruminal lactic acidosis (ARLA) is a major nutritional and metabolic disorder usually characterized by excessive or non-adapted intake of diets rich in nonstructural carbohydrates. Feed additives that regulate the ruminal environment have been used to prevent ARLA, such as ionophores and, more recently, yeast culture. Thus, we aimed to compare the efficacy of a yeast-based culture (Saccharomyces cerevisiae) with that of monensin sodium in the prevention of ARLA in sheep. Eighteen male, crossbred, rumen-cannulated sheep were randomly distributed into three groups of six animals: control, yeast culture and monensin. Thirty days after the start of supplementation with yeast culture (4 × 10⁹ cfu/animal/day of S. cerevisiae) and monensin (33 mg/kg of total dry matter intake), 15 g/kg BW of sucrose was administered directly into the rumen of the animals to induce ARLA. Samples of blood and ruminal fluid were collected at the following time points: at baseline (T0 h) immediately before the induction of ARLA; 6 h (T6 h); 12 h (T12 h); 18 h (T18 h); 24 h (T24 h); 36 h (T36 h); and 48 h (T48 h) after ARLA induction.

Results

Ruminal pH was higher in monensin group at T12 h and in yeast culture group at T36 h when compared to control group. Lower values of L-Lactate were found at yeast culture group at T24 h and T36 h. Monensin showed prophylactic effect by decreasing the rate of ruminal pH decline and occasionally reducing ruminal acidosis, whereas probiotics resulted in less accumulation of lactic acid in the rumen and a lower degree of systemic acidosis.

Conclusion

The use of yeast culture can be beneficial in the prevention and treatment of ARLA in sheep, because it can effectively reduce the accumulation of lactic acid, and thereby increase ruminal pH and reduce ruminal osmolarity. On the other hand, monensin showed prophylactic effect by decreasing the rate of ruminal pH decline and occasionally reducing ruminal acidosis, however, it did not directly prevent these conditions.

The effects of monensin in diets fed to finishing beef steers and heifers on growth performance and fecal shedding of Escherichia coli O157:H7

Two experiments were conducted to study the effects of monensin dose on growth performance and O157:H7 shedding in finishing beef cattle. In Exp. 1, 198 heifers (298 ± 1.1 kg BW) were allocated to 1 of 2 treatments consisting of 1) 200 mg/heifer daily of monensin and 2) 400 mg/heifer daily of monensin and fed for 151 d. In Exp. 2, 199 steers (430 ± 1.9 kg BW) were stratified by BW and allocated to 1 of 2 treatments consisting of 1) 0 mg/steer daily of monensin and 2) 400 mg/steer daily of monensin and fed for 128 d. For both experiments, there were 4 pen replicates per treatment. For Exp. 1 and Exp. 2, the model included the fixed effect of treatment for growth performance measures and the fixed effects of treatment, time, and treatment × time interaction, respectively, for O157:H7 shedding. In Exp. 1, final BW was 1.9% greater for heifers fed 400 mg/d monensin than for heifers fed 200 mg/d monensin ( = 0.05). Furthermore, ADG was 4.9% greater ( = 0.05) and G:F was 3.1% greater ( = 0.04) when the heifers were fed 400 mg/d monensin vs. 200 mg/d monensin. Pen prevalence for O157:H7 ( = 0.96) and the percentage of animals in the pen shedding O157:H7 at enumerable levels ( = 0.82) did not differ between heifers fed 200 mg/d monensin and heifers fed 400 mg/d monensin over the 4 sampling periods. For Exp. 2, steers fed the supplement containing monensin had a 1.9% greater final BW ( = 0.04) and a 5.2% greater ADG ( = 0.02) than steers fed a control supplement without monensin. No differences in DMI or G:F were noted across the treatments ( ≥ 0.14). O157:H7 percentage of enumerable cattle within the pen was greater for the steers fed monensin than the control steers not fed monensin than the control steers not fed monensin ( = 0.02) over the 4 sampling periods. However, the percentage of animals in the pen shedding O157:H7 (prevalence positive) did not differ between treatments ( = 0.18), nor did the average fecal counts ( = 0.45). In conclusion, feeding a higher dose (400 mg/d) of monensin improved final BW and ADG compared with a low dose of monensin or a no-monensin control in steers and heifers across multiple years. The percentage of animals shedding O157:H7 at enumerable levels was greater for steers fed the monensin supplement than for steers fed the control supplement, yet the presence of monensin, irrespective of the dose, did not affect the percentage of animals in the pen shedding O157:H7.

Effects of Disodium Fumarate on In Vitro Rumen Fermentation, The Production of Lipopolysaccharide and Biogenic Amines, and The Rumen Bacterial Community

The effect of disodium fumarate (DF) on the ruminal fermentation profiles, the accumulation of lipopolysaccharide (LPS) and bioamines, and the composition of the ruminal bacterial community was investigated by in vitro rumen fermentation. The addition of DF increased the total gas production; the concentrations of propionate, valerate, total volatile fatty acids, and ammonia-nitrogen; and the rumen pH after a 24 h fermentation. By contrast, DF addition decreased the ratio of acetate to propionate and the concentrations of lactate, lipopolysaccharide, methylamine, tryptamine, putrescine, histamine, and tyramine (P < 0.05). Principal coordinates analysis and molecular variance analysis showed that DF altered the ruminal bacterial community (P < 0.05). At the phylum level, DF decreased the proportion of Proteobacteria, and increased the proportions of Spirochaetae and Elusimicrobia (P < 0.05). At the genus level, DF decreased the percentage of Ruminobacter, while increasing the percentage of Succinivibrio and Treponema (P < 0.05). Overall, the results indicate that DF modified rumen fermentation and mitigated the production of several toxic compounds. Thus, DF has great potential for preventing subacute rumen acidosis in dairy cows and for improving the health of ruminants.

Effect of biochanin A on corn grain (Zea mays) fermentation by bovine rumen amylolytic bacteria

AIMS

The objective was to determine the effect of biochanin A (BCA), an isoflavone produced by red clover (Trifolium pratense L.), on corn fermentation by rumen micro-organisms.

METHODS AND RESULTS

When bovine rumen bacterial cell suspensions (n = 3) were incubated (24 h, 39°C) with ground corn, amylolytic bacteria including group D Gram-positive cocci (GPC; Streptococcus bovis; enterococci) proliferated, cellulolytic bacteria were inhibited, lactate accumulated and pH declined. Addition of BCA (30 μg ml^-1 ) inhibited lactate production, and pH decline. BCA had no effect on total amylolytics, but increased lactobacilli and decreased GPC. The initial rate and total starch disappearance was decreased by BCA addition. BCA with added Strep. bovis HC5 supernatant (containing bacteriocins) inhibited the amylolytic bacteria tested (Strep. bovis JB1; Strep. bovis HC5; Lactobacillus reuteri, Selenemonas ruminatium) to a greater extent than either addition alone. BCA increased cellulolytics and dry matter digestibility of hay with corn starch.

CONCLUSIONS

These results indicate that BCA mitigates changes associated with corn fermentation by bovine rumen bacteria ex vivo.

SIGNIFICANCE AND IMPACT OF THE STUDY

BCA could serve as an effective mitigation strategy for rumen acidosis. Future research is needed to evaluate the effect of BCA on mitigating rumen acidosis in vivo.

Feeding subtherapeutic antimicrobials to low-risk cattle does not confer consistent performance benefits

Stanford, K., Gibb, D. J., Schwartzkopf-Genswein, K. S., Van Herk, F. and McAllister, T. A. 2015. Feeding subtherapeutic antimicrobials to low-risk cattle does not confer consistent performance benefits. Can. J. Anim. Sci. 95: 589–597. Two-hundred and forty steers were obtained from the same ranch in each of 2 yr. Growth performance, health status and carcass characteristics from steers fed subtherapeutic antimicrobials were compared with those of control steers without antimicrobial metaphylaxis. Experimental groups included Control, not fed antimicrobials; CTCS-700, fed 350 mg head−1 d−1 chlortetracycline (CTC) and 350 mg head−1 d−1 sulfamethazine; CTC-11, fed 11 mg kg−1 CTC; TYL, fed 11 mg kg−1 tylosin phosphate; and CTC-350, fed 350 mg head−1 d−1 CTC. Steers were housed in pens of 10 steers and fed antimicrobials during both backgrounding and finishing periods. The incidence of bovine respiratory disease, pinkeye and bloat did not differ among experimental groups, although the incidence of foot rot was lower in Control steers (P<0.05) than in steers receiving TYL. In both years of the study, overall performance (backgrounding+finishing) was not improved by subtherapeutic antimicrobials. Similarly, carcass characteristics and the incidence and severity of liver abscesses were not improved compared with Control steers by feeding subtherapeutic antimicrobials. The results of the present study demonstrate that low-risk steers may be managed in small pens with equivalent growth performance, carcass characteristics and health status to steers fed subtherapeutic antimicrobials.

CONSUMO E DIGESTIBILIDADE DE NUTRIENTES DA TORTA DE DENDÊ NA DIETA DE OVINOS

Objetivou-se encontrar o nível ótimo de inclusão da torta de dendê na dieta de ovinos. Foram utilizados 18 carneiros, castrados, sem raça definida alimentados com níveis de inclusão da torta de dendê de 0%, 7,5%, 15% e 22,5% na dieta total. Os animais foram mantidos em gaiolas metabólicas por 21 dias. Os dados foram submetidos a estudo de regressão com 5% de significância para as equações e coeficientes de regressão. A inclusão da torta de dendê provocou redução nos consumos de MS, hemicelulose, FDN, PB, NDT, CHOT e MM (P<0,01) e não houve diferenças significativas nos de celulose, FDA e CNF (P>0,05). Os consumos de EE e lignina foram crescentes (P<0,01). O teor de fibra das dietas aliado ao consumo de lignina pelos animais provocou redução nos coeficientes de digestibilidade da EB e de todos os nutrientes avaliados (MS, PB, celulose, hemicelulose, FDN; P<0,05). Houve redução na metabolizabilidade das dietas devido ao aumento da EB fecal (P<0,01). O balanço de nitrogênio foi positivo em todos os tratamentos. A inclusão da torta de dendê acima de 7,5% na dieta de ovinos provoca redução no CMS e na digestibilidade de nutrientes com possível comprometimento do desempenho, especialmente, em animais de alta produção.

Rumen fermentation and liveweight gain in beef cattle treated with monensin and grazing lush forage

OBJECTIVE

To determine the prevalence of subacute rumen acidosis (SARA) in beef cattle grazing lush pasture and the effect of monensin on reducing SARA and improving animal performance.

DESIGN

Commercial Angus and Murray Grey steers received a monensin slow-release capsule (n = 19) or remained untreated (n = 19). Cattle grazed an oats crop or tetraploid ryegrass pasture for a total of 91 days. Rumen fluid pH, volatile fatty acids (VFA) and lactic acid concentrations and body weight data were collected prior to treatment and again 28, 56 and 91 days after treatment. Changes in measures over time were analysed using mixed model repeated measures analysis. Differences in average daily gain between treatment groups were determined.

RESULTS

The prevalence of SARA was low during the study, with only one animal satisfying criteria for SARA at one time point. Cattle treated with monensin capsules were 11.9 kg heavier at the completion of the study compared with untreated controls (414.5 ± 3.88 kg vs 402.6 ± 4.03 kg, P = 0.04). Rumen VFA and L- and D-lactate levels did not differ between cattle treated with monensin and untreated cattle. However, the ratio of propionate to acetate plus two times butyrate was higher (P < 0.001) when cattle were treated with monensin.

CONCLUSIONS

Subacute rumen acidosis was not consistently detected under the conditions of the study. The higher body weight of cattle treated with monensin may have been due to improved energy utilisation of the pasture, indicated by increased propionate proportions in the rumen, rather than prevention of SARA.

Effect of plant extract supplementation on Escherichia coli O157:H7 and Salmonella carcass isolation in young Holstein bulls fed a high-concentrate diet

Ninety Holstein bulls were used in a complete randomized design to study the effect of a blend of plant extract (PE) supplementation on jejunum, cecum, and rectum microbiota (Escherichia coli and lactic acid bacteria [LAB]) and hide and carcass contamination (identification of E. coli O157:H7 and Salmonella). Three treatments--control (CTR), monensin (MON), and PE--were tested. Bulls were offered straw and concentrate ad libitum during 108 d. In the cecum, the percentage of LAB counts below 5 log CFU/ml was greater (P < 0.01) in MON (68.1%) than in CTR (34.6%) and PE (28.0%) treatments. On hide, Salmonella was detected (P < 0.05) in CTR (13.3%) and MON (10.0%) treatments, in contrast to PE (0%) treatment. In bulls fed high-concentrate diets supplemented with PE, no increase of carcass E. coli O157:H7 and Salmonella identification was observed.

Efeitos da adição de propilenoglicol ou monensina à silagem de milho sobre a cinética de degradação dos carboidratos e produção cumulativa de gases in vitro

Avaliaram-se os efeitos dos aditivos propilenoglicol e/ou monensina sobre a degradabilidade média e efetiva dos carboidratos totais, pH e produção cumulativa de gases da silagem de milho por meio da técnica in vitro semi-automática de produção de gases. Os tratamentos constituíram-se de silagem de milho (SM); SM associada ao propilenoglicol (SM+PG); SM associada à monensina (SM+MO); SM associada ao propilenoglicol e à monensina (SM+PG+MO) avaliados com duas, quatro, seis, 12, 24, 48 e 96 horas. A adição de monensina ou monensina associada ao propilenoglicol aumentou (P<0,05) a degradabilidade dos carboidratos totais às duas horas. SM+MO apresentou maior degradabilidade efetiva dos carboidratos totais em todas as taxas de passagem. A utilização de monensina reduziu a produção cumulativa de gases das 12 às 96 horas. Entre os tratamentos, SM+MO apresentou o menor potencial de produção de gases (221ml/g carboidratos totais) e o menor tempo de colonização (1,08 horas) em relação aos tratamentos SM e SM+PG (1,58 e 1,49 horas, respectivamente). A produção cumulativa de gases e degradabilidade dos carboidratos totais apresentaram elevada correlação, variando de 94 a 97% (P<0,01). O pH do meio foi inversamente correlacionado à degradabilidade dos carboidratos totais (r= -79%, P<0,01). O uso de monensina pode ser uma boa alternativa para se melhorarem os parâmetros da cinética de degradação da silagem de milho.

Efeitos da adição de monensina ou propilenoglicol à polpa cítrica sobre a cinética de degradação dos carboidratos totais e da produção cumulativa de gases in vitro

Avaliaram-se os efeitos da adição de propilenoglicol e/ou monensina sobre a degradabilidade média e efetiva dos carboidratos totais, pH e produção cumulativa de gases da polpa cítrica por meio da técnica in vitro semi-automática de produção de gases. Os tratamentos constituíram-se de polpa cítrica (PC); associada ao propilenoglicol (PC+PG); monensina (PC+MO); propilenoglicol e monensina (PC+PG+MO), avaliados com duas, quatro, seis, 12, 24, 48 e 96 horas. A degradabilidade efetiva dos carboidratos totais de PC+PG foi maior em todas as taxas de passagem estudadas. A produção cumulativa de gases e a degradação dos carboidratos totais apresentaram correlação elevada, variando de 92 a 97% (P<0,01). O pH do meio foi inversamente correlacionado ao aumento da degradabilidade dos carboidratos totais (r= -79%, P<0,01). O propilenoglicol promoveu a maior degradabilidade efetiva dos carboidratos totais e pode ser um bom aditivo a ser utilizado em associação com a polpa cítrica.

Ruminal acidosis in beef cattle: the current microbiological and nutritional outlook

Ruminal acidosis continues to be a common ruminal digestive disorder in beef cattle and can lead to marked reductions in cattle performance. Ruminal acidosis or increased accumulation of organic acids in the rumen reflects imbalance between microbial production, microbial utilization, and ruminal absorption of organic acids. The severity of acidosis, generally related to the amount, frequency, and duration of grain feeding, varies from acute acidosis due to lactic acid accumulation, to subacute acidosis due to accumulation of volatile fatty acids in the rumen. Ruminal microbial changes associated with acidosis are reflective of increased availability of fermentable substrates and subsequent accumulation of organic acids. Microbial changes in the rumen associated with acute acidosis have been well documented. Microbial changes in subacute acidosis resemble those observed during adaptation to grain feeding and have not been well documented. The decrease in ciliated protozoal population is a common feature of both forms of acidosis and may be a good microbial indicator of an acidotic rumen. Other microbial factors, such as endotoxin and histamine, are thought to contribute to the systemic effects of acidosis. Various models have been developed to assess the effects of variation in feed intake, dietary roughage amount and source, dietary grain amount and processing, step-up regimen, dietary addition of fibrous byproducts, and feed additives. Models have been developed to study effects of management considerations on acidosis in cattle previously adapted to grain-based diets. Although these models have provided useful information related to ruminal acidosis, many are inadequate for detecting responses to treatment due to inadequate replication, low feed intakes by the experimental cattle that can limit the expression of acidosis, and the feeding of cattle individually, which reduces experimental variation but limits the ability of researchers to extrapolate the data to cattle performing at industry standards. Optimal model systems for assessing effects of various management and nutritional strategies on ruminal acidosis will require technologies that allow feed intake patterns, ruminal conditions, and animal health and performance to be measured simultaneously in a large number of cattle managed under conditions similar to commercial feed yards. Such data could provide valuable insight into the true extent to which acidosis affects cattle performance.

Effects of prepartum administration of a monensin controlled release capsule on rumen pH, feed intake, and milk production of transition dairy cows

Effects of prepartum administration of a monensin controlled release capsule (CRC) on rumen pH, dry matter intake, and milk production during the transition period and early lactation were determined in 16 multiparous Holstein cows. Cows were divided into blocks of 2 depending on calving date. Cows were fed either a close-up dry cow or a lactating cow total mixed ration ad libitum. Rumen pH was monitored continuously using indwelling probes. Monensin did not affect average daily rumen pH, time below pH 6, time below pH 5.6, area below pH 6, and area below pH 5.6 throughout the experiment. Average daily pH, time below pH 6, and time below pH 5.6 before calving were 6.62, 65.6 min/d, and 17.6 min/d, respectively, and did not differ among the weeks before calving. Average daily pH, time below pH 6, and time below pH 5.6 were 6.19, 443.3 min/d, and 115.5 min/d, respectively, during the first week after calving, and were 6.36, 204.3 min/d, and 52.4 min/d, respectively, during the sixth week after calving. In the weeks after calving, average daily pH showed a quadratic increase, time below pH 6 showed a quadratic decrease, and time below pH 5.6 showed a linear decrease. Monensin did not affect dry matter intake and daily yields of milk, milk fat, and milk protein. Results suggest that prepartum administration of a monensin CRC did not increase rumen pH in multiparous cows fed the experimental diets during the transition period and early lactation.

Ionophore resistance of ruminal bacteria and its potential impact on human health

In recent years, there has been a debate concerning the causes of antibiotic resistance and the steps that should be taken. Beef cattle in feedlots are routinely fed a class of antibiotics known as ionophores, and these compounds increase feed efficiency by as much as 10%. Some groups have argued that ionophore resistance poses the same public health threat as conventional antibiotics, but humans are not given ionophores to combat bacterial infection. Many ruminal bacteria are ionophore-resistant, but until recently the mechanism of this resistance was not well defined. Ionophores are highly lipophilic polyethers that accumulate in cell membranes and catalyze rapid ion movement. When sensitive bacteria counteract futile ion flux with membrane ATPases and transporters, they are eventually de-energized. Aerobic bacteria and mammalian enzymes can degrade ionophores, but these pathways are oxygen-dependent and not functional in anaerobic environments like the rumen or lower GI tract. Gram-positive ruminal bacteria are in many cases more sensitive to ionophores than Gram-negative species, but this model of resistance is not always clear-cut. Some Gram-negative ruminal bacteria are initially ionophore-sensitive, and even Gram-positive bacteria can adapt. Ionophore resistance appears to be mediated by extracellular polysaccharides (glycocalyx) that exclude ionophores from the cell membrane. Because cattle not receiving ionophores have large populations of resistant bacteria, it appears that this trait is due to a physiological selection rather than a mutation per se. Genes responsible for ionophore resistance in ruminal bacteria have not been identified, but there is little evidence that ionophore resistance can be spread from one bacterium to another. Given these observations, use of ionophores in animal feed is not likely to have a significant impact on the transfer of antibiotic resistance from animals to man.

Nisin resistance of Streptococcus bovis

The growth of Streptococcus bovis JB1 was initially inhibited by nisin (1 microM), and nisin caused a more than 3-log decrease in viability. However, some of the cells survived, and these nisin-resistant cells grew as rapidly as untreated ones. To see if the nisin resistance was merely a selection, nisin-sensitive cells were obtained from agar plates lacking nisin. Results indicated that virtually any nisin-sensitive cell could become nisin-resistant if the ratio of nisin to cells was not too high and the incubation period was long enough. Isolates obtained from the rumen were initially nisin sensitive, but they also developed nisin resistance. Nisin-resistant cultures remained nisin resistant even if nisin was not present, but competition studies indicated that nisin-sensitive cells could eventually displace the resistant ones if nisin was not present. Nisin-sensitive, glucose-energized cells lost virtually all of their intracellular potassium if 1 microM nisin was added, but resistant cells retained potassium even after addition of 10 microM nisin. Nisin-resistant cells were less hydrophobic and more lysozyme-resistant than nisin-sensitive cells. Because the nisin-resistant cells bound less cytochrome c, it appeared that nisin was being excluded by a net positive (i.e., less negative) charge. Nisin-resistant cells had more lipoteichoic acid than nisin-sensitive cells, and deesterified lipoteichoic acids from nisin-resistant cells migrated more slowly through a polyacrylamide gel than those from nisin-sensitive cells. These results indicated that lipoteichoic acids could be modified to increase the resistance of S. bovis to nisin. S. bovis JB1 cultures were still sensitive to monensin, tetracycline, vancomycin, and bacitracin, but ampicillin resistance was 1,000-fold greater.

Ionophore use and toxicosis in cattle

Ionophores comprise a rapidly expanding class of antibiotics produced by filamentous branching bacteria of the order Actinomycetales. The use of ionophores as coccidiostats and growth promotants has resulted in the occurrence of toxicoses in target and nontarget species. Clinical and pathologic effects of ionophore poisoning are caused by bioactivity and damage to excitable tissues such as cardiac muscle, skeletal muscle, smooth muscle, and the nervous system. Ionophore toxicoses are often related to errors in feed mixing, so the practitioner should give primary importance to the removal of suspect feeds and testing to confirm excessive exposure.

Metabolic alterations associated with an attempt to induce laminitis in dairy calves

The objective of this study was to investigate metabolic alterations in young ruminating calves associated with the sudden introduction of readily fermentable diets in an attempt to induce laminitis. Sixteen dairy bull calves, at 17 wk of age were fed equal amounts of one of four diets that contained either 71 or 81% total digestible nutrients (TDN) and 15 or 20% crude protein in a 2 x 2 factorial with time as a factor. Jugular blood and ruminal fluid were sampled, and hoof temperature was measured postfeeding at frequent intervals over a subsequent 2-d period. Hooves were examined for abnormalities and the orientation of the pedal bone radiographed prior to the experiment, 48 to 72 h into the experiment and at 3 and 7 mo later. Calves responded acutely to the 81% TDN diets by inappetence, stiffness, and diarrhea. Ruminal pH was lower and both D- and L-lactate concentrations were greater in the rumens of calves fed the 81% TDN diets. Total ruminal volatile fatty acid concentration decreased as pH declined. Whole blood L-lactate did not differ across treatments, but blood D-lactate increased in calves fed the 81% TDN diets, peaking at 32 h (7.2 mM). Hoof temperature responses could not be explained by dietary treatments. Laminitis was not detected despite the reduction of ruminal pH and a manyfold increase in blood D-lactate.

Feedlot diseases

This article includes a brief discussion of common diseases, listed by body systems, affecting feedlot cattle. Each disease is approached from a practitioner's point of view. This includes interactions with other management factors, differential list, and practical diagnostic procedures. Also included are guidelines for initiating case management before a definitive diagnosis is made.

Effect of monensin on milk production by Holstein and Jersey cows

Effects of the administration of monensin via concentrates to dairy cows were studied in two trials. In one trial, 64 Holstein cows were assigned to four groups that received 0, 150, 300, or 450 mg/d of monensin from 5 to 24 wk postpartum. Milk production tended to increase (4.0, 3.3, and 5.4%, respectively) for the three groups of treated cows. Fat content was decreased by 0.09, 1.89, and 4.09 g/kg, respectively, for these same three groups. The effect on protein content was small and nonsignificant. Feed intake was reduced in treated cows, although not significantly, and feed efficiency was improved by monensin. In a confirmatory trial, 58 Holstein and 22 Jersey cows were allocated either to a control group or to a treatment group that received 300 mg/d of monensin from 5 to 36 wk postpartum during the first lactation and from 2 wk before calving to 36 wk postpartum during a subsequent lactation. During the first lactation, cows in the treatment group showed a 7% increase in milk production, a relative decrease (1.4 g/kg) in milk fat content, and equal protein content compared with cows in the control group. Body weight gain and body condition scores near the end of the treatment period were higher for cows in the treatment group. A decrease in blood ketone concentrations was found between 7 and 56 d of lactation. Treatment effects on milk production differed between breeds and within genetic lines. Jersey cows were less responsive than were Holstein cows, and Holstein cows with a high ratio of breeding values for protein and fat showed larger milk production responses. Results from the second lactation showed similar differences between the two groups as did those from the first lactation.

Use of potassium depletion to assess adaptation of ruminal bacteria to ionophores

When mixed ruminal bacteria from cattle fed timothy hay were suspended in a medium containing a low concentration of potassium, monensin and lasalocid catalyzed a rapid depletion of potassium from cells. The ionophore-mediated potassium depletion was concentration dependent, and it was possible to describe the relationship with saturation constants. Mixed ruminal bacteria never lost more than 50% of their potassium (Kmax = 46%), and the concentrations of monensin and lasalocid needed to cause half-maximal potassium depletion (Kd) were 178 and 141 nM, respectively. When cattle were fed 350 mg of monensin per day, the ratio of ruminal acetate to propionate decreased from 4.2 to 2.9, and the Kd of monensin was eightfold greater than the value for mixed ruminal bacteria from control animals. Monensin supplementation also caused a twofold increase in the Kd of lasalocid. Lasalocid supplementation (350 mg per day) had no effect on the ruminal acetate-to-propionate ratio, but it caused a twofold increase in the Kd values of monensin and lasalocid. Increases in Kd occurred almost immediately after ionophore was added to the ration, and the Kd values returned to their prefeeding values within 14 days of withdrawal. Ionophore supplementation had no effect on the Kmax values, and approximately 50% of the population was always highly ionophore resistant. Because the Kd values of even adapted ruminal bacteria were low (< 1.5 microM), it appears that a large proportion of the ruminal ionophore is bound nonselectively to feed particles or ionophore-resistant bacteria.

Dynamics of ruminal ciliated protozoa in feedlot cattle

Fluctuations in ciliated protozoan concentrations were monitored in 40 individually fed crossbred heifers that were stepped up to an 85% concentrate diet either slowly (12 days) or rapidly (3 days), with or without monensin (30 ppm). Ruminal fluid was withdrawn from all animals by stomach tube at the start of the study, after each group reached full feed, and at 14-day intervals thereafter throughout the finishing period until termination (day 119). Neither monensin nor speed of step-up affected (P greater than 0.10) total protozoan concentrations, ruminal pH, or lactic acid concentrations. Average protozoan concentrations peaked on day 5, progressively declined until day 56, and then increased (P less than 0.05), suggesting an adaptation to ruminal conditions. Concentrations of Isotricha spp. were higher (P less than 0.05) on the final two sampling dates than at any other time. After day 28, Entodinium, Isotricha, and Polyplastron were the only surviving genera. Protozoa were not detected in 11 heifers on day 42 and day 56, but only two animals were defaunated on day 119, indicating either exogenous or endogenous refaunation. Average protozoan concentrations were not different (P greater than 0.25) between ruminal samples collected by stomach tube the day before slaughter (2.8 x 10(5)/g) and digesta samples collected the next day (1.6 x 10(5)/g). In feedlot cattle, defaunation apparently is transitory and individual animals harbor a dynamic protozoan population that fluctuates in response to changing ruminal conditions.

Alteration of intracellular traffic by monensin; mechanism, specificity and relationship to toxicity

Monensin, a monovalent ion-selective ionophore, facilitates the transmembrane exchange of principally sodium ions for protons. The outer surface of the ionophore-ion complex is composed largely of nonpolar hydrocarbon, which imparts a high solubility to the complexes in nonpolar solvents. In biological systems, these complexes are freely soluble in the lipid components of membranes and, presumably, diffuse or shuttle through the membranes from one aqueous membrane interface to the other. The net effect for monensin is a trans-membrane exchange of sodium ions for protons. However, the interaction of an ionophore with biological membranes, and its ionophoric expression, is highly dependent on the biochemical configuration of the membrane itself. One apparent consequence of this exchange is the neutralization of acidic intracellular compartments such as the trans Golgi apparatus cisternae and associated elements, lysosomes, and certain endosomes. This is accompanied by a disruption of trans Golgi apparatus cisternae and of lysosome and acidic endosome function. At the same time, Golgi apparatus cisternae appear to swell, presumably due to osmotic uptake of water resulting from the inward movement of ions. Monensin effects on Golgi apparatus are observed in cells from a wide range of plant and animal species. The action of monensin is most often exerted on the trans half of the stacked cisternae, often near the point of exit of secretory vesicles at the trans face of the stacked cisternae, or, especially at low monensin concentrations or short exposure times, near the middle of the stacked cisternae. The effects of monensin are quite rapid in both animal and plant cells; i.e., changes in Golgi apparatus may be observed after only 2-5 min of exposure. It is implicit in these observations that the uptake of osmotically active cations is accompanied by a concomitant efflux of H+ and that a net influx of protons would be required to sustain the ionic exchange long enough to account for the swelling of cisternae observed in electron micrographs. In the Golgi apparatus, late processing events such as terminal glycosylation and proteolytic cleavages are most susceptible to inhibition by monensin. Yet, many incompletely processed molecules may still be secreted via yet poorly understood mechanisms that appear to bypass the Golgi apparatus. In endocytosis, monensin does not prevent internalization. However, intracellular degradation of internalized ligands may be prevented.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of the ionophores monensin and tetronasin on simulated development of ruminal lactic acidosis in vitro

A continuous coculture of four ruminal bacteria, Megasphaera elsdenii, Selenomonas ruminantium, Streptococcus bovis, and Lactobacillus sp. strain LB17, was used to study the effects of the ionophores monensin and tetronasin on the changes in ruminal microbial ecology that occur during the onset of lactic acidosis. In control incubations, the system simulated the development of lactic acidosis in vivo, with an initial overgrowth of S. bovis when an excess of glucose was added to the fermentor. Lactobacillus sp. strain LB17 subsequently became dominant as pH fell and lactate concentration rose. Both ionophores were able to prevent the accumulation of lactic acid and maintain a healthy non-lactate-producing bacterial population when added at the same time as an excess of glucose. Tetronasin was more potent in this respect than monensin. When tetronasin was added to the culture 24 h after glucose, the proliferation of lactobacilli was reversed and a non-lactate-producing bacterial population developed, with an associated drop in lactate concentration in the fermentor. Rises in culture pH and volatile fatty acid concentrations accompanied these changes. Monensin was unable to suppress the growth of lactobacilli; therefore, in contrast to tetronasin, monensin added 24 h after the addition of glucose failed to reverse the acidosis. Numbers of lactobacilli and lactate concentrations remained high, whereas pH and volatile fatty acid concentrations were low.

Susceptibility and resistance of ruminal bacteria to antimicrobial feed additives

Susceptibility and resistance of ruminal bacterial species to avoparcin, narasin, salinomycin, thiopeptin, tylosin, virginiamycin, and two new ionophore antibiotics, RO22-6924/004 and RO21-6447/009, were determined. Generally, antimicrobial compounds were inhibitory to gram-positive bacteria and those bacteria that have gram-positive-like cell wall structure. MICs ranged from 0.09 to 24.0 micrograms/ml. Gram-negative bacteria were resistant at the highest concentration tested (48.0 micrograms/ml). On the basis of their fermentation products, ruminal bacteria that produce lactic acid, butyric acid, formic acid, or hydrogen were susceptible and bacteria that produce succinic acid or ferment lactic acid were resistant to the antimicrobial compounds. Selenomonas ruminantium was the only major lactic acid-producing bacteria resistant to all the antimicrobial compounds tested. Avoparcin and tylosin appeared to be less inhibitory (MIC greater than 6.0 micrograms/ml) than the other compounds to the two major lactic acid-producing bacteria, Streptococcus bovis and Lactobacillus sp. Ionophore compounds seemed to be more inhibitory (MIC, 0.09 to 1.50 micrograms/ml) than nonionophore compounds (MIC, 0.75 to 12.0 micrograms/ml) to the major butyric acid-producing bacteria. Treponema bryantii, an anaerobic rumen spirochete, was less sensitive to virginiamycin than to the other antimicrobial compounds. Ionophore compounds were generally bacteriostatic, and nonionophore compounds were bactericidal. The specific growth rate of Bacteroides ruminicola was reduced by all the antimicrobial compounds except avoparcin. The antibacterial spectra of the feed additives were remarkably similar, and it appears that MICs may not be good indicators of the potency of the compounds in altering ruminal fermentation characteristics.

Rumen microbial changes in cattle fed diets with or without salinomycin

Four rumen-fistulated steers, randomly assigned to two groups (control and salinomycin fed) were used to monitor the changes in rumen microbial populations and volatile fatty acids (VFA) concentrations associated with feeding salinomycin (0.22 mg X kg-1 X day-1). Steers were adapted to an alfalfa hay and grain (80:20) diet before supplementing the diet with salinomycin, and then the diet was changed to 50:50 and 20:80 ratios of alfalfa hay to grain at 2-week intervals. Rumen samples for total and selective enumeration of anaerobic bacteria. VFA analysis, and enumeration of protozoa were collected during the 80:20 alfalfa hay-to-grain diet before salinomycin feeding, and during the 80:20, 50:50, and 20:80 hay-to-grain diets with salinomycin. At each sampling period, rumen samples were collected at 3 h after feeding on three consecutive days. Salinomycin feeding had no effect on rumen pH and total VFA concentration. The acetate-to-propionate ratio was significantly lower in salinomycin-fed steers than in the control. The molar proportion of butyrate increased in both control and salinomycin-fed steers. Total anaerobic bacterial counts were lower in salinomycin-fed steers than in the control steers after 8 weeks of salinomycin feeding. Salinomycin-resistant bacteria increased from 7.6 to 15.6% in salinomycin-fed steers but remained unchanged in control steers. Salinomycin had no effect on cellulolytic and lactate-utilizing bacteria, but the proportion of amylolytic bacteria was higher in salinomycin-fed steers than in control steers. The total number of protozoa decreased initially in salinomycin-fed steers. The initial reduction was due to reduced numbers of Entodinium species. Holotrichs were unaffected by salinomycin feeding.

Monensin-resistant bacteria in the rumens of calves on monensin-containing and unmedicated diets

Total and monensin-resistant anaerobic bacterial populations and volatile fatty acid concentrations were examined in the rumens of steers fed monensin-containing (33 mg/kg) and unmedicated diets. Total anaerobic counts on a habitat-simulating medium ranged from 7.1 X 10(8) to 7.1 X 10(9) CFU/g of rumen ingesta and were not significantly different in animals fed the two diets. The mean percentage of the anaerobic population resistant to monensin (10 micrograms/ml) was significantly greater in animals receiving the monensin-supplemented diet for 33 days than in those receiving the unmedicated diet (63.6 and 32.8%, respectively). Treatment group differences in monensin resistance tended to develop later than characteristic differences in acetate/propionate ratios. Relative proportions of resistant organisms in monensin-fed animals remained significantly greater for at least 18 days after monensin was deleted from the ration, whereas acetate/propionate ratios increased to values comparable to those in the control within 10 days. These data suggest that monensin-resistant bacteria may be present in greater numbers in the rumens of animals fed monensin-supplemented diets. However, greater proportions of monensin-resistant organisms were not necessarily associated with altered fermentation patterns.