Brachiaria species are the most important grasses for cattle production in Brazil. However, a limiting factor for the use of Brachiaria spp. is their toxicity. Most outbreaks of hepatogenous photosensitization are caused by B. decumbens; however B. brizantha, B. humidicola and B. ruziziensis can also cause poisoning. The poisoning affects cattle, sheep, goats and buffalo. Sheep are more susceptible than other animal species and the young are more susceptible than adults. There are differences in susceptibility among animals of the same species and it has been suggested that this resistance is genetic. Also has been suggested that buffalo and probably some sheep are resilient, i.e. when poisoned these animals have histologic lesions and high GGT serum concentrations, but do not show clinical signs. In general, saponin concentrations are higher in growing plants, but outbreaks occur all over the year, probably due to unexplained rise in saponin concentration in the plant. A clinical syndrome of progressive weight loss and death, without photosensitization, has been reported in cattle poisoned by B. decumbens. Main preventive measures are based on the selection of resistant or resilient animals and on the development of Brachiaria species or varieties with low saponin concentration.

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Intoxicação por Brachiaria spp. em ruminantes no Brasil

To establish the etiological relationship and the appearance of foamy macrophages in the liver of cattle from tropical regions of Brazil, liver samples from the files of the Pathology Section of Embrapa-Projeto Sanidade Animal, Rio de Janeiro, were reviewed. A total of 55 liver samples of cattle which died from different causes between 1970 and 1991 were reexamined. Only samples of animals which grazed known pastures were reviewed. Foamy macrophages were not seen in the samples from 1970 to 1975, although 40 samples (72%) were from this period. Foamy macrophages were observed from 1976 on, coinciding with the introduction of Brachiaria decumbens from Australian seeds into Brazil. Some samples were from cattle with histories of photosensitization, which were at that time attributed to Pithomyces chartarum. The results of this study indicate that the liver changes are related to prolonged ingestion of Brachiaria spp.

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Relação entre macrófagos espumosos ("foam cells") no fígado de bovinos e ingestão de Brachiaria spp no Brasil

The epidemiology, clinical signs and pathology of 29 outbreaks of spontaneous poisoning by Brachiaria spp. in beef cattle, which occurred from March 1996 to November 2009, in the state of Mato Grosso do Sul, were retrospectively studied. For this, the files of the Veterinary Pathology Laboratory at the Federal University of Mato Grosso do Sul were reviewed. Outbreaks occurred at different times of the year, including dry and rainy seasons. While photosensitization was the main clinical sign in cattle from 24 out of 29 outbreaks, in five of them the main clinical sign was progressive wasting, without photosensitization. Eleven outbreaks of photosensitization occurred in pastures of Brachiaria decumbens, two in mixed pastures of B. decumbens and B. brizantha, and one in B. brizantha. In 10 outbreaks the species of Brachiaria was not informed. Morbidity ranged from 0.2% to 50%, and fatality rates were between 44.4% and 100%. In cases of photosensitization brisket edema was the most frequent clinical sign observed. Dermatitis with thickened skin of the flank and perineal region, scar retraction of the ears, jaundice, ocular discharge, crusts in the eyes and ears, and ulceration of the ventral surface of the tongue were also observed. Nervous signs were observed in two cases and diarrhea in one. At necropsy the liver was enlarged, yellowish, with increased lobular pattern, and occasionally with depressed whitish areas. The kidneys were brownish and the urine dark. Upon histological examination of the liver the hepatocytes were swollen and vacuolized. Individual necrosis of hepatocytes, bile duct cell proliferation, biliary retention, and mild to moderate periportal fibrosis were also observed. In all cases foamy macrophages, most in groups, were observed mainly in the centrilobular region. In 21 cattle birefringent crystals were observed within the bile ducts. Five outbreaks of progressive wasting were observed in cattle grazing B. decumbens pastures. The main lesion was an enlarged yellowish liver. Histologic lesions were similar to those observed in cases of photosensitization. Birefringent crystals were observed in the liver of three cases, but foamy macrophages were found in all animals. It is concluded that B. decumbens is more toxic than B. brizantha and that the poisoning occurs at any time of the year. Nevertheless, research is still necessary to determine variations in the saponin content of Brachiaria species and the probable differences on susceptibility/resistance to the poisoning of cattle of different ages, breeds and from different regions.

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Intoxicação por Brachiaria spp. em bovinos no Mato Grosso do Sul

Infiltration by foamy macrophages and other lesions are reported in healthy cattle held in Brachiaria spp. pastures. With the objective to study histologic lesions in the liver and mesenteric lymph nodes in buffalo in the state of Para, samples of liver and lymph nodes of 142 buffalo Murah and 15 Nelore cattle were studied histologically. The samples were collected in an slaughterhouse and divided into groups of animals according to their origin and period of grazing Brachiaria spp. pastures. Group (G) 1 consisted of 79 buffalo from Marajo Island, raised in native pastures free of Brachiaria spp.; G2 was composed of 17 buffalo kept since birth in Brachiaria brizantha pastures; G3 was composed of 29 buffalo purchased in Marajo Island and introduced in B. decumbens pastures where they stayed for nearly 12 months; G4 consists of 17 buffalo purchased in Marajo Island and introduced in B. brizantha pastures where they stayed for nearly 18 months. G5 was composed of 15 Nelore cattle grazing B. brizantha during one year period. To assess the degree of liver injury, grades following a scale of 0 to 4 were established according to the quantity and size of groups of foamy macrophages. In G1, from the Marajo Island, there were no significant histological changes in liver and lymph nodes. Foamy macrophages and other lesions were observed in liver and lymph nodes of all samples from G1, G2, G3, and G4. The animals from G2 and G4, which remained a longer period in Brachiaria spp., showed more pronounced infiltration of foamy macrophages (P<0.05) than the animals of G3. Other lesions observed in the livers of these three groups were swollen, vacuolated or necrotic hepatocytes, mainly in the centrolobular region, and thickening of the Glisson's capsule with vacuolization and necrosis of subcapsular hepatocytes. These lesions were more pronounced in areas where exists higer infiltration of foamy macrophages. In cattle from G5 smaller groups of foamy macrophages were observed in the lymph nodes and were absent in the liver. These results suggest that the hepatic lesions observed in buffalo are caused by ingestion of Brachiaria spp. The presence of severe lesions in buffalo without clinical signs, much more severe than those observed and reported previously in cattle, as well as the low frequency of Brachiaria poisoning in buffalo grazing in Brachiaria spp. pastures, suggest that buffalo are resilient to Brachiaria spp. poisoning. In each group, there was no association between the weight at slaughter and the degree of lesion. It is also suggested that the observation of severe lesions of the liver, similar to those observed in this experiment, in animal that died from other diseases, can lead to a wrong diagnosis of Brachiaria poisoning.

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Alterações histológicas em fígados e linfonodos de búfalos (Bubalus bubalis) mantidos em pastagens de Brachiaria spp.

Poisonous plants affecting cattle in the Brazilian Central-Western region are reviewed. The most important poisonous plants in the region are Brachiaria spp., which cause hepatogenous photosensitization, and Palicourea marcgravii and Mascagnia pubiflora, which cause sudden death precipitated by exercise. Enterolobium contortisiliquum, Stryphnodendron obovatum, and Stryphnodendron fissuratum are trees whose pods cause digestive signs, photosensitization, and abortion. Vernonia mollissima and V. rubricaulis cause acute liver necrosis, but V. rubricaulis is much more important than V. mollisima as a cause of cattle losses. Other less important plants are Solanum glaucophyllum, which causes soft tissue calcification; Ipomoea carnea subsp. fistulosa, which causes nervous signs; Senna occidentalis and Senna obtusifolia, which cause segmental muscular necrosis; Tetrapterys multiglandulosa, which causes cardiac fibrosis, abortion, and neonatal mortality; Polygala klotzschii, which causes lymphatic tissue necrosis; and Pterodon emarginatus, a tree whose leaves cause liver necrosis. Rare outbreaks of poisoning by Lantana tiliaefolia, Cestrum laevigatum, Pteridium caudatum, and Crotalaria spp. also are observed.

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M Passipieri

Papers

Sintomas de fotossensibilidade em bezerros alimentados com leite materno