Experimental oral administration of pollen beetle (Astylus atromaculatus) to cattle results in an acute lethal gastrointestinal disease.

In the summer of 2023, ingestion of Astylus atromaculatus (pollen beetle) was linked to spontaneous fatal disease in grazing cattle and sheep in Argentina and Uruguay. While the disease was experimentally reproduced in sheep and guinea pigs in the 1970's, no experimental reproductions have been attempted in cattle, and controversy exists as to whether this insect is indeed noxious to cattle and at which dose. Here, we demonstrate that A. atromaculatus causes acute fatal disease in Hereford calves at single oral dosages of 2.5, 4.5, 10.0, and 15.0 g of insect/kg body weight. Death or severe disease necessitating euthanasia occurred at 38 to 48 hours postinoculation regardless of the dose, suggesting that the single fatal dosage is likely <2.5 g/kg body weight (this dose representing approximately 850 mL of intact beetles in a 100 kg calf). Clinically, the disease was characterized by acute anorexia, prolonged recumbency, reluctance to move, listlessness/apathy, depression, ruminal hypomotility and tympany, hypothermia, bruxism with frothing at the mouth, and mucoid diarrhea progressing to death. Hematologic and biochemical alterations included hemoconcentration, stress/acute inflammatory leukogram, negative energy balance, and ketosis. The pathological hallmark of this experimental disease is acute necrotizing omaso-reticulo-rumenitis, fibrinohemorrhagic enteritis, and exfoliative colitis with intralesional chitinous insect fragments. While A. atromaculatus might contain a gastrointestinal toxin or pathogen, extensive toxicological testing failed to identify a causative toxin. Other pathomechanisms such as direct physical damage caused by insect fragments on the alimentary tract seem plausible, although further studies are needed to elucidate the pathogenesis of A. atromaculatus-associated disease.

Fasciola hepatica infection modifies IgG1 specific immune response to foot-and-mouth disease virus induced by vaccination.

Fasciola hepatica, a worldwide distributed helminth, has a robust immunoregulatory effect in the host, increasing the susceptibility to secondary infections. Foot and mouth disease (FMD) is a highly contagious acute vesicular viral disease effectively controlled by vaccination in endemic regions. Despite the evidence of immunoregulatory effects, the impact of fasciolosis on the immune response induced by FMD vaccination in cattle has never been assessed. Our objective was to evaluate whether the infection by F. hepatica in cattle influences the long-term immunity elicited by the currently used commercial FMD-inactivated vaccines. Aberdeen Angus steers negative for F. hepatica were vaccinated twice against FMD virus (FMDV) during the first 6 months of age using a commercial oil vaccine formulated with A24/Cruzeiro and O1/Campos strains. When maternal antibodies against F. hepatica were weaned (18--20 months of age) animals were divided into groups of 12 and infected or mock-infected with 500 metacercariae/animal. Individual serum samples were collected at 0-, 28-, 59-, 87- and 157-days post-infection (dpi). Indirect ELISAs were used to detect A24/Cruzeiro specific bovine IgG and IgG subtypes. The total IgG antibody levels and avidity against FMDV did not show significant differences between all the groups. The commercial vaccine induced higher IgG2 than IgG1 titers in vaccinated animals. Anti-FMDV IgG1 levels significantly decreased in the infected group at 28 dpi. In addition, the avidity of IgG1 FMDV-specific antibodies at day 28 in the infected group was reduced compared to the control. These results show that F. hepatica infection modified anamnestic responses against FMDV, reducing serum IgG1 titers and avidity. To our knowledge, this is the first report of immune-regulation of F. hepatica altering the immune response of FMD vaccines, one of the most globally used animal vaccines.

Molecular of Anaplasma marginale Theiler (Rickettsiales: Anaplasmataceae) in horseflies (Diptera: Tabanidae) in Uruguay.

Anaplasma marginale is transmitted biologically by infected ticks or mechanically by biting flies and contaminated fomites. In tick-free areas, such as southern Uruguay, horseflies could be the principal vectors of this pathogen for bovines, causing anaplasmosis. The objective of this work was to detect the presence of A. marginale by MSP-5 PCR and Sanger sequencing in the most prevalent species of horseflies obtained using different collection methods in Colonia, Tacuarembó and Paysandú, Uruguay. Eight horsefly species were tested (Dasybasis missionum, Poeciloderas lindneri, Tabanus campestris, T. claripennis, T. fuscofasciatus, T. platensis, T. tacuaremboensis and T. triangulum); four species were found to be positive for A. marginale, with D. missionum and P. lindneri having the most frequent infections, while only one individual each of T. fuscofasciatus and T. tacuaremboensis was positive. Both D. missionum and P. lindneri were positive for A. marginale in tick-free areas, and the implications are discussed in this report.

Liver function markers and haematological dynamics during acute and chronic phases of experimental Fasciola hepatica infection in cattle treated with triclabendazole.

Fasciola hepatica, a worldwide-distributed liver fluke, is one of the causative agents of fasciolosis, a zoonotic disease that affects livestock and humans. In livestock, fasciolosis causes huge economic losses worldwide, reducing animal fertility, milk production, weight gain and condemnation of livers. In spite of the availability of drugs, such as triclabendazole (TCZ), for the treatment of fasciolosis, they do not necessarily prevent liver damage or parasite reinfection and can eventually increase parasite resistance. The aim of this research was to relate the hepatic function, haematological parameters, leukocyte counts in circulation and parasite egg shedding during F. hepatica acute and chronic phases of infection in cattle as well as to determine how these parameters change with TCZ-treatment of chronically infected cattle. Our results show that increased levels of serum aspartate aminotransferase (AST) and gamma glutamyltransferase (GGT) were detected in early stages of the experimental infection. Moreover, high circulating eosinophil count and plateletcrit levels were correlated with fluke number in livers from infected cattle. On the other hand, although TCZ-treatment in the chronic phase of infection reduced parasite burden and damage in the liver, it was not able to completely avoid them. In conclusion, our work sheds light into the physiopathological mechanisms induced during fluke infection in cattle, revealing the complexity of the host response to the infection, together with the effects of TCZ-treatment in chronically infected animals.

Nierembergia rivularis poisoning in cattle.

Nierembergia rivularis causes enzootic calcinosis (EC) in sheep. In this work, we describe EC caused by N. rivularis in cattle. For 3 years cattle grazing in 7 paddocks were evaluated. Cows with clinical signs compatible with EC were detected in only one paddock with a morbidity of 9.4%, 24.5%, and 34.5% during the summer of 2019, 2020, and 2021, respectively. Affected cows weighed 55 kg less (p < 0.01) than cows without signs of the same paddock, and 19.6% of these cows had hypercalcemia and/or hyperphosphatemia. Typical soft tissue calcification was observed in 3 autopsied cows. Additionally to the arterial calcification, 2 cows had multiple mineralized foci in several veins. In the Paddock A where EC occurred, the pasture contained 7-12% N. rivularis. In the other 6 paddocks (Paddocks B-G) where EC had not occurred, the pasture had 0.2-3.5% N. rivularis. Cows grazing in Paddock A had ∼30% lower pregnancy rates than cows from Paddocks B-G. At the slaughterhouse, the carcasses of 45 cows from Paddock A weighed 17.6% (p < 0.01) less than 93 carcasses of cows from Paddocks B-G. Furthermore, the carcasses of cows from Paddock A were classified as low quality. Eight cows with EC signs from Paddock A and 10 cows without EC signs from Paddocks B-G were removed to a Lolium multiflorum pasture. After 120 days of grazing, the cows from Paddock A gained 45.2% less (p < 0.01) live weight than cows from Paddocks B-G. Poisoning with N. rivularis may cause significant economic losses in Uruguay due to low fertility rates and weight gain of affected cattle.

Endemic Xanthium strumarium poisoning in cattle in flooded areas of the Araguari River, Minas Gerais, Brazil.

In this paper, we describe poisoning outbreaks of Xanthium strumarium in cattle on the borders of the Araguari River, Southeastern Brazil. In this region, several hydroelectric plants promote transient flooding, which creates a favorable environment for the invasion of X. strumarium in extensive areas, often as the predominant species in those areas. The outbreaks occurred between July and September (dry season). Bovines of all ages were affected, including suckling animals. Mortality varied from 2% to 5.5%. The animals exhibited ataxia, weakness, loss of balance, recumbency, and the majority were found dead. Laboratory results showed a marked increase in the serum activities of alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, and gamma-glutamyltransferase. Histological and ultrastructural changes in the liver consisted of centrilobular necrosis and hemorrhage. On toxicological evaluation, the dicotyledons contained 0.30 µg/mg of atractyloside and 0.37 µg/mg of carboxyatractyloside. Considerable economic loss has occurred in this region due to the lack of knowledge regarding X. strumarium as a toxic plant and its adaptation to the environmental and climatic conditions of the region, which have made the condition endemic.

Osteomalacia as a result of phosphorus deficiency in beef cattle grazing subtropical native pastures in Uruguay.

We investigated 2 outbreaks of osteomalacia as a result of phosphorus (P) deficiency in herds of lactating beef cows grazing subtropical native pastures in Uruguay. Cows exhibited pica, difficulty to stand and walk, rib fractures, and body weight loss even with adequate forage availability. Osteopenia and severe osteomalacia were observed on gross and histologic examination. The concentrations of bicarbonate-extractable P in soil (4.0, 4.1 mg P/kg), total P in pasture (0.9, 1.1 g P/kg), inorganic P in serum (1.0, 0.71 mmol P/L), and P in bone (73 mg P/mL) were all low. Although injectable and mineral salt supplements provided additional P in both outbreaks, these supplementary amounts were insufficient to prevent P deficiency. The P ingested by the cows from the pasture and supplements would have provided 20-55% of their daily P requirements of ~21 g P/d. Osteomalacia occurred in cattle at the 2 ranches as a result of severe P deficiency in the soil and forage, and inadequate P supplementation. Following diagnosis, control of P deficiency in beef cattle requires estimation of the amount of pasture P ingested and provision of sufficient additional supplementary P to meet the animals' requirements.

Effect of pre-slaughter fasting duration on physiology, carcass and meat quality in beef cattle finished on pastures or feedlot.

Pre-slaughter fasting duration affect blood parameters related to stress and metabolism, decrease live and carcass weights and impact beef quality of cattle. In three experiments, 1100 steers and heifers, finished on feedlot or on pasture, were evaluated to assess the influence of the site and duration of fasting before slaughter on physiological, carcass and meat quality traits. Cattle were allocated to one of two fasting duration - long (23-29 h) or short (2-6 h) - and to one of two sites of fasting- farm or abattoir. All animals had access to water ad libitum until slaughter, except during transportation. Cattle were assigned to two (long fasting on abattoir/normal lairage time, short fasting on farm/minimal lairage time) or three (long fasting on abattoir/normal lairage time, short fasting on farm/minimal lairage time, long fasting on farm/minimal lairage time) treatments. Seventeen slaughters were considered in a randomized complete block design. There was no effect of the site of fasting on any variable. Cattle with short fasting duration had higher carcass weights and water consumption than those under long fasting duration. Haematocrit, globulin, total protein, and lactate dehydrogenase at the time of slaughter increased with fasting duration. There was no effect of the duration of fasting on blood ions, meat quality traits, urine pH, liver weight and volume, and skin dry matter. A reduction in the fasting duration returned to farmers and abattoirs 1.2% additional kilograms of carcass, suggesting an improvement in animal welfare according to a better hydration level of cattle at the time of slaughter.

Diversity and seasonality of horse flies (Diptera: Tabanidae) in Uruguay.

Horse flies (Diptera: Tabanidae) cause direct and indirect losses in livestock production and are important vectors of pathogens. The aim of this study was to determine the diversity and seasonality of horse fly species at an experimental farm in Tacuarembó and the diversity of species in different departments of Uruguay. For 20 months, systematic collections were performed in two different environments at the experimental farm using Nzi and Malaise traps. In addition, nonsystematic collections were performed at farms located in the departments of Paysandú, Tacuarembó and Colonia. A total of 3,666 horse flies were collected, and 16 species were identified. These species included three species that had not been previously recorded in Uruguay, namely, Dasybasis ornatissima (Brèthes), Dasybasis missionum (Macquart), and Tabanus aff. platensis Brèthes, and a species that had not been previously taxonomically described (Tabanus sp.1). Among the systematically captured samples, the most abundant species were Tabanus campestris Brèthes, T. aff. platensis and D. missionum, representing 77.6% of the collected specimens. The horse fly season in Tacuarembó started in September and ended in May. No horse flies were caught during winter. Variations in the prevalences of species in the different departments were observed, which indicates the need for new sampling efforts.

Resistance to Haemonchus contortus in Corriedale sheep is associated to high parasite-specific IgA titer and a systemic Th2 immune response.

Gastrointestinal nematode infections, including Haemonchus contortus, are one of the main causes of economic losses to ovine farmers worldwide. In order to contribute to the control of nematode infections and avoid parasite spreading we generated divergent resistant and susceptible sheep breeds and evaluated the adaptive immunity of these animals developed upon experimental infection against H. contortus. The selection of resistant or susceptible animals from the Corriedale Breed has been based on Expected Progeny Differences for faecal egg counts per gram. Furthermore, animals from the resistant Corriedale line were inseminated with imported semen from Australian Rylington Merino rams. Thus, the objective of this work was to analyze the adaptive immune response in both susceptible and resistant obtained lambs. Our results indicate that there is a potent parasite-specific local and systemic immune response in resistant animals and that although susceptible lambs can produce high levels of IgA antibodies during the infection, their antibody response is delayed which, together with an impaired specific-Th2 response, does not contribute to initial parasite elimination. Our results shed light into the immune mechanisms that mediate resistance to H. contortus and could constitute important assets to sheep farmers, not only as a means to detect resistance, but also to enhance the efficiency of selection in stud flocks.

Efficiency of a walk-through fly trap for Haematobia irritans control in milking cows in Uruguay.

Haematobia irritans (horn fly) is a bloodsucking insect that affects grazing cattle. Since this fly's introduction into Uruguay in 1992, pest management practices used to control the insect have been exclusively based on the use of insecticides, which has caused synthetic pyrethroid resistance. The use of insecticides is a major constraint to livestock production due to food safety and environmental concerns. This study evaluated the effectiveness of a walk-through fly trap for horn fly control. The field trail was conducted in 18 trail evaluations dates from 2015 to 2016 in Holstein-Frisian lactating cows on two dairy farms in southern Uruguay. The traps were placed at the exit of the milking parlor. Two digital cameras were used to record video at the entrances and exits of the traps. On each of the 18 trail evaluation, between 30 and 158 cows were randomly selected for fly counting according to video records. On Farm 1, a total of 718 cows were assessed. The median number of flies per cow at the entrance of the traps was 22 (ranging from 1 to 199), while the median number at the exit was three flies per cow (ranging from 0 to 22). The median efficiency of the trap was 88%. Farm 2 had 345 observations, and the median fly count at the entrance of the traps was of 22 flies per cow (ranging from 1 to 129) and four flies at the exit (ranging from 0 to 35) with a median efficiency of 82%. It was observed that the effectiveness of the fly traps varied depending on the number of flies at entry, the season of the year and the farm site. In conclusion, fly traps could be used for the control of H. irritans in milking cows without the use of insecticides.