A meta-analysis of the impact of monensin on growing and finishing beef cattle was conducted after a search of the literature. A total of 40 peer-reviewed articles and 24 additional trial reports with monensin feeding in beef cattle were selected, after meeting apriori quality criteria. Data for each trial were extracted and analyzed using meta-analysis software in STATA. Estimated effect size of monensin was calculated for feed efficiency (FE), ADG, and DMI. Monensin use in growing and finishing beef cattle reduced DMI (P < 0.001) and improved both ADG (P < 0.001) and FE (P < 0.001). The average concentration of monensin in feed across studies was 28.1 mg/kg feed (100% DM) and this resulted in approximately a 6.4% (but only 2.5 to 3.5% in the last 2 decades) increase in FE, 3% decrease in DMI, and 2.5% increase in ADG. All 3 outcomes displayed moderate and significant heterogeneity of monensin response (I(2), which is a measure of variation beyond chance, = 29% for FE, 42% for DMI, and 23% for ADG); therefore, random effects models were used for those outcomes. There were no single influential studies that overweighted the findings for any outcome. Meta-regression analysis of the effect sizes obtained from these data showed that dietary factors, dose, and study design were influential in modifying effect size of monensin treatment. Use of corn silage in the diet influenced the effect size of monensin for DMI and FE, with diets containing corn silage resulting in a greater improvement in FE and a larger effect on reducing DMI. Studies conducted to assess multiple doses of monensin showed similar effects to the use of corn silage in the diet. Studies conducted in the United States or with higher ADG in control animals (>1.17 kg/d) showed less effect of monensin on ADG. Pen-level studies showed a greater monensin increase on ADG than did those conducted on individual animals. Linear effect of monensin dose was observed for FE, DMI, and ADG outcomes, with greater effects on improving FE and reducing DMI with larger doses of monensin but lesser improvement in ADG with increasing dose. These findings confirm that monensin improves FE in growing and finishing beef cattle, and that this effect is linear with dose.

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Pathogen virulence factors and inflammation are responsible for tissue injury associated with respiratory failure in bacterial pneumonia, as seen in the bovine lung infected with Pasteurella haemolytica. Tilmicosin is a macrolide antibiotic used for the treatment of bovine bacterial pneumonia. Recent evidence suggests that tilmicosin-induced neutrophil apoptosis may have anti-inflammatory effects. Using bovine leukocytes, we sought to define whether live P. haemolytica affected tilmicosin-induced neutrophil apoptosis, assessed the proapoptotic effects of tilmicosin in comparison with other drugs, and characterized its impact on phagocytic uptake of neutrophils by macrophages. Induction of apoptosis in the presence or absence of P. haemolytica was assessed by using an enzyme-linked immunosorbent assay for apoptotic nucleosomes. In addition, fluorescent annexin-V staining identified externalized phosphatidylserine in neutrophils treated with tilmicosin, penicillin, ceftiofur, oxytetracycline, or dexamethasone. Neutrophil membrane integrity was assessed by using propidium iodide and trypan blue exclusion. As phagocytic clearance of apoptotic neutrophils by macrophages contributes to the resolution of inflammation, phagocytosis of tilmicosin-treated neutrophils by esterase-positive cultured bovine macrophages was assessed with light microscopy and transmission electron microscopy. Unlike bovine neutrophils treated with penicillin, ceftiofur, oxytetracycline, or dexamethasone, neutrophils exposed to tilmicosin became apoptotic, regardless of the presence or absence of P. haemolytica. Tilmicosin-treated apoptotic neutrophils were phagocytosed at a significantly greater rate by bovine macrophages than were control neutrophils. In conclusion, tilmicosin-induced neutrophil apoptosis occurs regardless of the presence or absence of live P. haemolytica, exhibits at least some degree of drug specificity, and promotes phagocytic clearance of the dying inflammatory cells.

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. 2009. The effect of ractopamine supplementation at 5 ppm of swine finishing diets on growth performance, carcass composition and ultimate pork quality. Can. J. Anim. Sci. 89: 53Á66. Five hundred thirty-six finishing pigs were placed on experiment for an average of 26 d prior to slaughter, to determine the effects of 5 mg ractopamine hydrochloride (RAC) per kg of diet on growth performance, carcass composition and the eating quality of pork. Treatments included a control diet similar to a western Canadian commercial finishing diet and a treatment diet containing 5 mg RAC kg(1 with elevated amino acids, vitamins and minerals. The experiment started when average animal weight was 86 kg; pigs were marketed at an average liveweight of 118 kg. Two pigs were selected from each of 32 pens in week 4 of the experiment, for detailed carcass and meat quality evaluation, providing 16 pigs per gender per treatment. RAC-fed pigs reached market weight 4 d sooner (PB0.05), grew 13% faster (PB0.05) and had 13% better feed efficiency (PB0.05) than the controls. RAC-fed pigs also had 1 mm less backfat and 2.5 mm thicker loins (PB0.05). Ultimate pH, purge loss and visual colour scores were unaffected by treatment but RAC-fed pigs had lower CIE a* and b* measurements (P B0.05). RAC had no effect on juiciness, flavour, saltiness or overall acceptability (P0.10), but increased WarnerÁBratzler shear force and reduced taste panel tenderness slightly (PB0.05). The inclusion of 5 mg RAC kg(1 in a commercial finishing diet will increase the rate and efficiency of gain and improve carcass composition. Minimal impact on pork quality can also be expected with the use of RAC fed at this level.Key words: Ractopamine, swine, carcass composition, pork quality, beta-adrenergic agonist Patience, J. F., Shand, P., Pietrasik, Z., Merrill, J., Vessie, G., Ross, K. A. et Beaulieu, A. D. 2009. Incidence d'un supple´ment de 5 ppm de ractopamine dans la ration de finition sur la croissance des porcs, la composition de la carcasse et la qualite´de la viande. Can. J. Anim. Sci. 89: 53Á66. Pendant une moyenne de 26 jours avant l'abattage, les auteurs ont donne5 mg de chlorhydrate de ractopamine (RAC) par kilo de ration a`536 porcs de finition afin de ve´rifier les effets de ce compose´sur la croissance des animaux, sur la composition de la carcasse et sur la qualite´gustative de la viande. Les traitements incluaient une ration te´moin semblable a`une ration de finition offerte dans le commerce, dans l'Ouest canadien, et une ration the´rapeutique enrichie d'acides amine´s, de vitamines et d'oligoe´le´ments renfermant 5 mg RAC par kilo. L'expe´rience a de´bute´quand les animaux avaient un poids moyen de 86 kg; les porcs ont e´te´mis en marche´a`un poids vif moyen de 118 kg. La quatrie`me semaine de l'expe´rience, les chercheurs ont se´lectionne´deux porcs dans chacun des 32 enclos pour proce´der a`une e´valuation minutieuse de leur carcasse et de la qualite´de leur viande, pour un total de 16 sujets par sexe et par traitement. Les animaux recevant du RAC ont ...