Context The use of two feed additives, to maximise rumen fermentation, in finishing diets offered to feedlot cattle may positively impact performance. Aims This study, conducted at the São Paulo State University feedlot, Botucatu campus, Brazil, was designed to evaluate the effects of the combined use of monensin (MON; 30 mg/kg of dry matter; (DM)) and virginiamycin (VM; 25 mg/kg of DM) in high-concentrate diets during the adaptation and finishing periods on feedlot performance, carcass traits, feeding behaviour, blood gas profile, rumen morphometrics and apparent total tract digestibility of nutrients of Nellore cattle. Methods The experiment was designed as a completely randomised block, replicated six times (3 bulls/pen), in which 72 20 months of age yearling Nellore bulls (388.0 ± 31.1 kg) were fed in 24 pens for 90 days according to the treatments: (1) MON during the entire feeding period (T1), (2) MON + VM during adaptation and only VM during the finishing period (T2), (3) MON + VM during the entire feeding period (T3), and (4) VM during the adaptation and MON + VM during the finishing period (T4). The adaptation program consisted of ad libitum feeding of three diets over the adaptation period of 19 days with concentrate level increasing from 69% to 84% of diet DM. Key results Overall, bulls fed on T2 had a greater DM intake (P < 0.01), final bodyweight (P = 0.04), average daily gain (P = 0.03), hot carcass weight (P < 0.01), final Longissimus muscle area (P = 0.05), Longissimus muscle area daily gain (P = 0.01), improved carcass G:F (P < 0.01) and increased dressing percentage (P < 0.01). Similarly, bulls fed on T2 were faster to consume 1 kg of either DM (P < 0.01) or neutral detergent fibre (P < 0.01) after 60 days on feed. Furthermore, bulls fed on T2 presented a greater (P = 0.05) cell proliferation index in the rumen papillae. Conclusions According to the results, Nellore yearling bulls should be fed high-concentrate diets containing MON and VM during adaptation, and only VM during the finishing period to improve overall feedlot performance. Implications The use of both MON and VM proved to be helpful only during the adaptation period.

Mycoplasma (M.) hyopneumoniae is the main pathogen of porcine enzootic pneumonia (PEP). Its controlling is challenging, and requires alternative strategies. This study aimed to develop an oral vaccine against M. hyopneumoniae using a nanostructured mesoporous silica (SBA-15) as an adjuvant, and compare its effect with an intramuscular (IM) commercial vaccine (CV). Fifty 24 day-old M. hyopneumoniae-free piglets composed five equal groups for different immunization protocols, consisting of a CV and/or oral immunization (OI). Control piglets did not receive any form of immunization. All piglets were challenged with M. hyopneumoniae strain 232 on D49 by tracheal route. IgA antibody response in the respiratory tract, bacterial shedding and serum IgG were evaluated. The piglets were euthanized on 28 (D77) and 56 (D105) days post-infection. Lung lesions were macroscopically evaluated; lung fragments and bronchoalveolar fluid (BALF) were collected for estimation of bacterial loads by qPCR and/or histopathology examination. All immunization protocols induced reduction on Mycoplasma-like macroscopic lung lesions. IgA Ab responses anti-M. hyopneumoniae, the expression of IL-4 cytokine and a lower expression of IL-8 were induced by CV and OI vaccines, while IgG was induced only by CV. Oral immunization using silica as a carrier-adjuvant can be viable in controlling M. hyopneumoniae infection.

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O objetivo deste trabalho foi descrever um surto de intoxicação por ionóforo em um rebanho de ovinos, onde vinte animais morreram após o uso de monensina sódica na dieta. Os sinais clínicos apresentados pelos animais incluíram hipertermia, anorexia, diarréia, taquicardia, resistência a exercícios e marcha irregular. Na necropsia de um animal, foram constatadas áreas pálidas na musculatura esquelética e no miocárdio, hemorragias no epicárdio e edema pulmonar. O exame histopatológico revelou degeneração e necrose hialina segmentar multifocal das miofibras, que perderam o padrão normal de estriação e se apresentaram intensamente eosinofílicas.

Direct detection of Mycoplasma hyopneumoniae through molecular tools is a growing trend for early diagnosis, highlighting the importance of knowing M. hyopneumoniae dynamics in the respiratory tract upon infection. This study focused on monitoring the infection level and its effects in different anatomic sites of the respiratory tract of experimentally infected swine in four time-points post-infection. To this end, 24 pigs were allocated to either non-inoculated group (n = 8) or inoculated group (n = 16). On day 0 post-infection (dpi), animals of the inoculated group were intratracheally inoculated with M. hyopneumoniae. Nasal swabs were collected weekly for qPCR detection of bacterial shedding. At 14, 28, 42, and 56 dpi, four animals from the inoculated group and two from the control group were necropsied. Bronchoalveolar lavage fluid (BALF) and samples from three different anatomical tracheal sections (cranial - CT, medium - MT, lower - LT) were collected for qPCR and histopathology. Bacterial loads (qPCR) in tracheal samples were: 4.47 × 102 copies∕μL (CT), 1.5 × 104- copies∕ μL (MT) and 1.4 × 104 copies∕μL (LT samples). M. hyopneumoniae quantification in BALF showed the highest load at 28 dpi (2.0 × 106 copies∕ μL). Microscopic lesions in LT samples presented the highest scores at 56 dpi and were significantly correlated with the pathogen load on 14 dpi (0.93) and 28 dpi (0.75). The greatest bacterial load of M. hyopneumoniae in CT samples and BALF was registered at 28 dpi, and it remained high in BALF and LT throughout the 56 dpi. The pathogen was able to persist during the whole experimental period, however higher estimated quantification values were registered in the lower parts of the respiratory tract, especially at 56 dpi. These findings are important for improving diagnostics, treatment, and control measures of M. hyopneumoniae infection in swine herds.

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