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Se llevó a cabo una encuesta transversal en 54 unidades producti-vas familiares (UF) y 5 tambos caprinos comerciales (TC) en diferen-tes ecorregiones de Salta y Jujuy. El objetivo del trabajo fue estudiar la asociación entre la seroprevalencia de anticuerpos anti Toxoplasma gondii y aquellos factores relacionados con las unidades produc-tivas y sus caprinos. Se procesaron sueros mediante la técnica de Inmunofluorescencia Indirecta (n= 629) y por ELISA indirecto (n=619). Para el análisis estadístico de las variables se utilizó el chi-cuadrado, el Odds Ratio (OR) y la regresión logística. De las 59 majadas visitadas el 67,8% de ellas tuvo al menos un caprino seropositivo, mostrando disímil presencia entre las UF (66,7%) y los TC (80%). La prevalencia general fue del 18,2% (95% IC: 15,9-20,6%). Los factores de riesgo significativamente asociados a una seroprevalencia de T. gondii mayor a un 20% de los caprinos muestreados fueron un porcentaje de gatos mayor al 1,1% en relación con el total de cabras en servicio (OR 5,26; 95% IC: 1,62-17,1) y la práctica del ordeñe (OR 13,03; 95% IC: 2,19-80,3). Los presentes resultados muestran que las infestaciones por T. gondii en las majadas caprinas de Salta y Jujuy son importantes y ame-ritan profundizar los estudios

Las deficiencias minerales son un problema de gran impacto productivo a nivel mundial. En el Noroeste argentino (NOA) la cría extensiva es una de las actividades económicas más importantes y está en franco crecimiento. En el NOA, los estudios sobre enfermedades carenciales son escasos y parciales. El presente trabajo tiene por objeto describir variaciones estacionales de los niveles séricos de calcio, fósforo, magnesio, cobre y zinc en vacas de cría y terneras de recría. En un establecimiento ganadero se seleccionaron 20 vacas y 20 terneras que fueron mantenidos en condiciones de pastoreo y sin suplementación externa. Se efectuaron muestreos de sangre a intervalos de 3 meses durante un año. Se determinaron niveles séricos de calcio, magnesio, cobre y zinc por espectrofotometría de absorción atómica y de fósforo por espectrofotometría uv-visible. Los resultados indican la existencia de hipocupremia moderada a leve en las terneras (48,6±11μg/dL) durante todos los períodos muestreados. Las vacas presentaron valores promedio normales (66±3,5 μg/dL) pero cercanos al límite inferior durante algunos muestreos. Se observaron niveles subnormales de fósforo durante el verano (diciembre y marzo) en ambas categorías. Este trabajo sugiere que el cobre y el fósforo pueden comportarse como factores limitantes en las condiciones evaluadas. SUMMARY. Serum levels of minerals in beef heifers and cows in the cloudforest of Salta, Argentina. Mineral deficiencies are a problem of great productive impact worldwide. In the Argentine Northwest (NOA) extensive breeding is one of the most important economic activities and it is in frank growth. In the NOA, studies on deficiency diseases are scarce and partial. The present work aims to describe seasonal variations of serum levels of calcium, phosphorus, magnesium, copper and zinc in beef cows and rearing calves. In a farm, 20 cows and 20 weaned heifer calves were selected, which were maintained under grazing conditions and without external supplementation. Blood samples were taken at intervals of 3 months for one year. Serum levels of calcium, magnesium, copper and zinc were determined by atomic absorption spectrophotometry and phosphorus by UV-visible spectrophotometry. The results indicate the existence of moderated hypocupremia in the calves (48.6 ± 11μg / dl) during all sampled periods. Cows presented normal values (66 ± 3.5 μg / dl) but close to the lower limit during some sampling. Subnormal levels of phosphorus were observed during the summer (December and March) in both categories. This work confirms that copper and phosphorus can behave as limiting factors in the evaluated conditions.

La artritis y encefalitis Caprina (CAEV) puede presentar diferentes síntomas clínicos, siendo la artritis la más común. A fin de caracterizar la presencia de enfermedades en las majadas caprinas del noroeste argentino, se llevó a cabo una encuesta sanitaria a productores, con toma de muestras biológicas para el diagnóstico de enfermedades en la que fue incluida CAEV. Se efectuó un análisis serológico con un ELISA indirecto y se completó con un examen clínico general de los animales y toma de muestra de necropsia de algunos de los casos. En la Provincia de Salta, tres establecimientos fueron positivos, con un 6,25% de prevalencia. La seroprevalencia del hato con seguimiento de caso fue del 55% mientras que el 48% presentó signos clínicos donde la artritis de la articulación carpal fue la más frecuentemente afectada. El virus CAEV está distribuido en la provincia de Salta y la severidad de las lesiones observadas sugiere la presencia de nuevas cepas que deben ser investigadas conjuntamente al desarrollo de capacidades locales para el diagnóstico, clave de cualquier plan de erradicación. SUMMARY. Characterization of caprine arthritis-encephalitis disease in Salta and Jujuy provinces. Caprine arthritis and encephalitis virus (CAEV) may present different clinical symptoms, with arthritis being the most common. In order to characterize the presence of diseases in goats from the Argentinean northwest, a sanitary survey was carried out to producers, with biological sampling for the diagnosis of diseases in which CAEV was included. A serological analysis was performed with an indirect ELISA and was completed with a general clinical examination of the animals and a necropsy sample collection of some of the cases. In the Province of Salta, three establishments were positive, with a prevalence of 6.25%. The serum prevalence of the herd with case follow-up was 55%, while 48% presented clinical signs where arthritis of the carpal joint was most frequently affected. The CAEV virus is spread in the province of Salta and the severity of the observed lesions suggests the presence of new strains that should be investigated in combination with the development of local capacities for diagnosis, this is the key to any eradication plan.

El objetivo del presente trabajo fue estudiar la epidemiología de los nematodes gastrointestinales (NGI) en la recría bovina en la región del Chaco Serrano del Noroeste Argentino durante los períodos mayo-sept. 2014 y mayo-marzo 2015-16. En cada período se formaron tres grupos de 17 terneras de destete: GTS con tratamiento cada 45-50 días con moxidectina, GTL con 1 solo tratamiento: 6/2014 ivermectina y 7/2015 doramectina y GST sin tratamiento. Se realizaron conteos de huevos (hpg) y coprocultivos y se registró la ganancia de peso vivo (GPV). Al inicio en ambos períodos los hpg fueron moderados (=515±449, 2014; =484±464, 2015) elevándose hacia fines del otoño, para luego descender hacia la primavera. Los hpg del GTL mostraron postratamiento solo un descenso parcial y el GTS siempre tuvo valores de hpg muy bajos. Los géneros de nematodes predominantes fueron Cooperia (41,8%), y Haemonchus (53,7%). En ambos períodos el efecto de los tratamientos se evidenció desde el invierno, mostrando el GTS una mayor GPV (p

The objective of this work was to describe the dynamics of development and survival of the free-living stages of cattle gastrointestinal nematodes (GIN) in fecal matter (FM) and pasture during the dry season in the Lerma Valley, Salta province, northwestern Argentina (NWA) to contribute to GIN management. The climate in the region is characterized by a rainy summer followed by a dry season from middle autumn to early spring. Fecal matter from calves naturally infected with GIN was deposited on three experimental field plots in April, July and October 2019, corresponding to the beginning, middle and end of the dry season, respectively. Each experimental unit consisted of 7 stools of about 800 g and had four repetitions. To determine the development from egg to infective larvae (L3), the first sampling (5 g fecal matter) was performed from the 10th day post-contamination and continued every 3 days until L3 were found. Subsequently, a monthly sampling was made until two consecutive negative results were obtained. Sampling of pasture began three days after the L3 recovery from FM, and continued monthly until two negative results were obtained. The following parameters were evaluated: development time and development rate from egg to L3; permanence time of L3 in feces; time of appearance on pasture; migration rate; and permanence time of L3 on pasture. The main genera of parasites present were Cooperia and Haemonchus. Significant differences were observed in the development time among contamination months (p < 0.001); development time was highest in the July contamination (28 days), with October and April contamination averaging 9 and 10 days, respectively. Development time also showed significant differences (p < 0.01) among contamination months, being highest in October (31.48%). The highest permanence time in fecal matter values were recorded in the July contamination (183 days) and migration rate was highest in the October contamination (42.49%). The highest time of appearance on pasture value was recorded in the July contamination (117 days). Finally, the highest permanence time of L3 in feces values were detected in the October contamination (148 days). The results of this work show that fecal contamination in the NWA region in the dry season would play an epidemiological role in the GIN cycle as a source of infection for the next productive cycle in the rainy season., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The aims were to study the epidemiology and the effect of gastrointestinal nematodes (GINs) on yearling cattle in a semiarid region in Argentina and to evaluate the mineral serum levels. Ten- to twelve-month-old calves were monitored between November and April 2019. Animals were divided into three groups: untreated control (CONG; n = 20); group treated with moxidectin (MXD, 200 µg/kg) every 30-40 days (MXDG; n = 20); group equally MXD treated and mineral supplementation administered in November and January (MMG; n = 20). Individual GIN egg counts (epg) and fecal cultures were made every 30-40 days. Animal live weight gain was determined. On 7-11-18, 25-1-19, and 3-4-19, serum levels of Se, Cu, Zn, Mg, and Ca were determined by atom absorption spectrophotometry. At the start of the trial, epg values were low (x̄ = 5.5), which increased only in CONG towards the end of the assay (x̄ = 229). In both GMXD and MMG, epg remained very low (x̄ = 4.1). Cooperia spp. (81%) prevailed over Haemonchus spp. (9%) and Oesophagostomum spp. (9%). Deficiency of Se ranged between marginal and important, except for MMG, although mean values were always below normal. Cu was marginally deficient in CONG and MXDG on the first two sampling dates, whereas MMG had normal values after treatment. Mg had low values in the three groups (x̄ = 1.5 mg/dl), whereas Ca and Zn exhibited normal values. Live weight gain (LWG) was higher in MMG than in MXDG, with significant differences (p < 0.05) by mid-January and then, when epg increased, dewormed groups showed higher LWG (p < 0.034) than CONG. A negative effect of GINs on LWG was observed, as well as low to marginal levels of Se, Cu, and Mg., (© 2022. The Author(s), under exclusive licence to Springer Nature B.V.)

The objective of this work was to determine the seroprevalence of Neospora caninum in cattle in Valle de Lerma, province of Salta, Argentina, and the risk factors associated with the disease. Serum samples were taken from 40 cows in each dairy herd, which were analyzed by indirect ELISA to detect antibodies against N. caninum. Chronic and acute infections were discriminated by measuring the avidity of these antibodies. All the herds exhibited at least one seropositive animal, the mean being 35.3 ± 14.9% of positive animals. Specific antibodies were also detected in dogs present in 9of the herds, which showed a seropositivity value of 71.7% ± 19.9%. Among the seropositive animals, 56.3% showed acute infections. A negative association was found between seroprevalence and the avidity index of specific antibodies, indicating that the presence of animals with acute infections is associated with higher seroprevalence. Fields with grazing showed more recent infections. These results show for the first time the importance of this parasite in this particular region and the need to promote the development of control programs considering the different risk factors that affect the epidemiological situation of the disease., (Copyright © 2020 Asociación Argentina de Microbiología. Publicado por Elsevier España, S.L.U. All rights reserved.)

Selective breeding of genetically resistant animals is considered a promising strategy to face the problem of nematode resistance to anthelmintics and mitigate concerns about the presence of chemical residues in animal food products and the environment. Gastrointestinal nematode resistance is a complex, multifactorial trait related to host immunity. However, the mechanisms underlying host resistance and response to infection remain to be fully elucidated. In this context, the objective of this study was to provide insight into the chromosomal regions determining nematode resistance and resilience in Corriedale and resistance in Pampinta sheep breeds. A total of 170 single nucleotide polymorphisms (SNP) from 76 candidate genes for immune response were studied in 624 Corriedale and 304 Pampinta animals. Lambs underwent artificial or natural challenges with infective larvae mainly from Haemonchus contortus. Fecal egg counts, estimated breeding values for fecal egg counts, and rate of packed cell volume change and FAMACHA© score change over the challenge were used, when available, as indicators of host parasite resistance or resilience. Phenotype-genotype association studies were conducted and significance values obtained were adjusted for multiple testing errors. Eight SNPs, located on OARs 3, 6, 12, and 20, reached significance in Corriedale sheep under artificial challenge. Those SNP represent allelic variants from the MHC-Ovine Lymphocyte Antigen-DRA, two C-type lectin domain families, the Interleukin 2 receptor β, the Toll-like receptor 10, the Mannan binding lectin serine peptidase 2, and the NLR family, CARD domain containing 4 genes. On Pampinta lambs under natural challenge, we found three significant SNPs, located in the TIMP metallopeptidase inhibitor 3, the FBJ murine osteosarcoma viral oncogene homolog, and the Interleukin 20 receptor alpha genes, on OARs 3, 7, and 8, respectively. The results obtained herein confirm genomic regions previously reported as associated with nematode resistance in other sheep breeds, reinforcing their role in host response to parasites. These findings contribute to gain knowledge on parasite resistance and resilience in Corriedale sheep and report for the first time SNPs associated with resistance to gastrointestinal parasite infections in Pampinta breed., (Copyright © 2020 Elsevier B.V. All rights reserved.)

The aim of this work was to study the effect of gastrointestinal nematodes (GINs) on copper (Cu) and phosphorus (P) in blood of beef cattle in two ranches (R1 and R2) located in northwestern Argentina. In 2015-2016 (R1) and 2016-2017 (R2), in each ranch, 22 weaned female calves were divided into two groups: calves treated systematically with 200 mcg/kg moxidectin every 45-50 days (TG) and untreated calves (UTG). The following parameters were measured: number of fecal eggs (epg), fecal cultures, serum Cu and P levels, and live weight gain (LWG). Differences between groups were compared using analysis of variance and Tukey test. GIN infections in both ranches were subclinical and moderate, showing the highest epg (R1 = 907 ± 754; R2 = 1049 ± 1040) by mid-winter. Epg values of TG groups were always negligible (> 93% of moxidectin efficacy). The dominant nematode genera were Cooperia and Haemonchus. The average serum Cu values (μg/dl) indicated low (R1 = 49.7 ± 18) and severe (R2 = 27.2 ± 14) deficiency. The effect of treatments was evident in both ranches from late winter, with TG showing significantly (p < 0.01) higher serum levels in winter, spring, and early autumn (R1 = 65.1, 50.9, and 60.3; R2 = 48.0, 25.7, and 22.4) than UTG (R1 = 44.3, 33.9, and 32.9; R2 = 25.5, 18.2, and 16.4). There were no differences in serum P levels between groups. LWG of TG increased significantly (p < 0.008) (27.2% in R1 and 38.6% in R2), with respect to those of UTG. This study showed a negative effect of GIN on serum Cu values in moderately infected growing calves.

The aim of this work was to study the epidemiology and the harmful effect of gastrointestinal nematodes (GINs) on beef cattle in the piedmont forest and grassland region of northwestern Argentina, between March 2015 and March 2016. Sixty weaned female calves were divided into three groups: STG-calves treated systematically with 200 mcg/kg moxidectin every 40-50 days; LTG-calves treated as usually locally implemented, with 200 mcg/kg ivermectin on May 4 and August 5; and UTG-calves not receiving treatment. Moreover, a group of 20 untreated first-calving cows was monitored. Eggs per gram of faeces (epg) and faeces cultures were performed. Live weight gain (LWG) was recorded. Differences among groups were compared using analysis of variance and Tukey test. At the start of the experiment, mean epg was from moderate to high (595 ± 480); therefore, this group was treated in May. Mean UTG epg peaked (907 ± 754) in mid-winter, decreasing toward spring. LTG epg only decreased partially after treatment, showing 54.2% of ivermectin efficacy. Epg values of STG were always negligible values (95.8% of moxidectin efficacy). The dominant nematode genus was Cooperia (81.9%), followed by Haemonchus (15.5%). The effect of treatments was evident from middle autumn, with STG showing a significantly (p < 0.002) higher LWG than the other groups. Toward the end of the trial, LWG of STG and LTG increased by 27.2 and 8.2%, respectively, to those of UTG. This preliminary study showed a winter epg peak and a negative effect of GINs on LWG, even in moderately infected calves.

The aim of this work was to study the epidemiology and harmful effects of gastrointestinal nematodes (GINs) on dairy goats maintained in an intensive system. Two groups of goats were studied: untreated group (UG) (subdivided into UGjun goats that kidded in June, and UGjul goats that kidded in July) and treated group (TG) (with no subgroups, treated with monepantel: 3.75 mg/kg, orally, monthly). Eggs per gram (epg) in faeces were counted, faecal culture was performed to differentiate nematode genera and milk production was measured. Differences between groups were compared using least squares means analysis of variance (milk production and milking period length) and Kruskal-Wallis test (faecal egg counts). Nematode infection was moderate, with Haemonchus and Trichostrongylus being the dominant genera; the faecal egg counts reached the level of 2000 only once throughout the study. Goats that kidded in June had higher egg count after parturition (UGjun = 1564 epg), with significant differences (p &lt; 0.04) from those that still had not kidded (UGjul = 962 epg). Over the entire trial period, the mean total milk production of TG (399.5 L ± 34.0 L) was significantly higher (p &lt; 0.05) than that of UG (281.6 L ± 37.5 L), representing an increase of 41.8% in total milk yield. The results of this study show a post-partum peak in egg count and a negative effect of GINs on milk yield, even with moderate infections.

Risk factors for anthelmintic resistance (AR) on bovine ranches were studied. Data were derived from a survey made to 50 ranch owners, who had conducted a faecal egg-count-reduction test. The questionnaire contained descriptors of bovine ranch management and nematode control. A case-control design study was undertaken and AR cases were present in 26 herds. Associations between the binary outcome variable (AR versus not AR) and risk factors recorded in the questionnaire were evaluated. Variables associated with the presence of AR at P< 0.15 and/or odds ratio (OR) > 2 were subjected to a multivariable logistic regression model. The main effects contributing to general AR (avermectin AVM and/or benzimidazole) in the final model were total number of annual treatments (OR 7.68; 95% CI 2.4 to 28.3) and use of more than 75% of AVM in the past (OR= 18.6; 95% CI 1.3 to 97.3), whereas for AVM resistance alone were total number of AVM annual treatments (OR= 11.5; 95% CI 2.9 to 45.5) and number of AVM Nov-Jan treatments (OR= 5.8; 95% CI 1.71 to 47.9). The results showed that treatment frequency, date of treatment and frequency of treatment in the past with a single drug were the main risk factors involved in AR development.

The role of the drug efflux pump, known as P-glycoprotein, in the pharmacokinetic disposition (host) and resistance mechanisms (target parasites) of the macrocyclic lactone (ML) antiparasitic compounds has been demonstrated. To achieve a deeper comprehension on the relationship between their pharmacokinetic and pharmacodynamic behaviors, the aim of the current work was to assess the comparative effect of loperamide, a well-established P-glycoprotein modulator, on the ivermectin and moxidectin disposition kinetics and efficacy against resistant nematodes in cattle. Fifty (50) Aberdeen Angus male calves were divided into five (5) experimental groups. Group A remained as an untreated control. Animals in the other experimental Groups received ivermectin (Group B) and moxidectin (Group C) (200 microg/kg, subcutaneously) given alone or co-administered with loperamide (0.4 mg/kg, three times every 24 h) (Groups D and E). Blood samples were collected over 30 days post-treatment and drug plasma concentrations were measured by HPLC with fluorescence detection. Estimation of the anthelmintic efficacy for the different drug treatments was performed by the faecal egg count reduction test (FECRT). Nematode larvae were identified by pooled faecal cultures for each experimental group. Cooperia spp. and Ostertagia spp. were the largely predominant nematode larvae in pre-treatment cultures. A low nematodicidal efficacy (measured by the FECRT) was observed for both ivermectin (23%) and moxidectin (69%) in cattle, which agrees with a high degree of resistance to both molecules. Cooperia spp. was the most abundant nematode species recovered after the different drug treatments. The egg output reduction values increased from 23% to 50% (ivermectin) and from 69% to 87% (moxidectin) following their co-administration with loperamide. Enhanced systemic concentrations and an altered disposition of both ML in cattle, which correlates with a tendency to increased anthelmintic efficacy, were observed in the presence of loperamide. Overall, the in vivo modulation of P-glycoprotein activity modified the kinetic behavior and improved the efficacy of the ML against resistant nematodes in cattle. The work provides further evidence on the high degree of resistance to ML in cattle nematodes and, shows for the first time under field conditions, that modulation of P-glycoprotein may be a valid pharmacological approach to improve the activity and extend the lifespan of these antiparasitic molecules., (Copyright (c) 2010 Elsevier Inc. All rights reserved.)

66 Pampinta breed ewes were studied during milking to evaluate the infection and the effect of gastrointestinal nematode on milk production sheep system. Naturally infected ewes on pasture were randomly allocated to two groups: TG, suppressively treated group every four weeks with levamisole and UG, untreated group. Faecal nematode egg counts and larval differentiation were conducted monthly. Successive groups of worm free tracer lambs were grazed with ewes and then slaughtered for worm counts. Test-day milk yield of individual ewes was recorded and ewe machine-milking period length (MPL) were estimated. Faecal egg counts and tracer nematode numbers increased towards midsummer and declined sharply toward the end of the study. TG (188.0 +/- 60 liters) produced more (p < 0.066) milk liters than UG (171.9 +/- 52.2) and TG had significantly more extended (p < 0.041) MPL than those of UG. The present study showed that dairy sheep were negatively affected by worms, even when exposed to short periods of high acute nematode (mainly Haemonchus contortus) infection.

The quinazolines represent a useful natural product scaffold with demonstrated activities against disorders such as high blood pressure and benign prostatic hyperplasia. Here we report on the synthesis and biological activity of a series of quinazolines that were prepared by a one-pot synthesis of substituted cyclohexadiene enaminonitriles from methyl-ketones. The approach, which employs NaH, complements published procedures where LDA is utilized. While the NaH catalyzed reaction generates the cyclohexadiene enaminonitriles in high yields with heterocyclic substrates, the reaction fails to promote product formation of aliphatic alkyl substrates. On the contrary, the LDA mediated synthesis favors the long chain alkyl substituents while reactions involving the aromatic substrates result in low yields. The final conversion to the quinazolines is also a modification on literature protocols. In cellular assays, the quinazolines showed the most promising activity against Jurkat with CC(50) values in the low micromolar range. Weak activity was observed against microbial strains (Bacillus subtilis, Escherichia coli, and Saccharomyces cerevisiae). The substituted enaminonitrile intermediates also exhibited weak anti-microbial activity and cytotoxicity against human T-cell leukemia.

During the past three years there have been several reports of cattle anthelmintic resistance (AR) in Argentina. Twenty-five cattle herds in the west fattening area of the Pampeana Region were surveyed to assess the prevalence of AR and the species of nematode involved. The survey involved fattening and cow-calf systems with a mean of 6760 bovines. Resistance was determined in vivo by a faecal egg count reduction test (FECRT). Efficacies from the World Association for the Advancement of Veterinary Parasitology (WAAVP) formula were compared with those obtained from the Abbott formula. Sixty 6-12-month-old calves were selected from each property and divided into four groups, namely, IVM (ivermectin, 0.2mg/kg), BZD (fenbendazole, 5mg/kg or albendazole 7.5mg/kg), LVM (levamisole, 7.5mg/kg) and Control (untreated group). Nematode larvae were identified by four pooled faecal cultures for each group. Cooperia and Ostertagia were the predominant nematode larvae in pre-treatment cultures. The mean FECRT efficacies for IVM, BZD and LVM were 81.0+/-21%, 93.3+/-8% and 97.6+/-4%, respectively. AR was detected in 16 (64%) herds. IVM resistance was present in 15 herds and BZD resistance in eight herds (32%). Resistance to both ivermectin and fenbendazole was present in seven herds. LVM resistance was not detected. Cooperia was the predominant post-treatment nematode in all the herds with IVM resistance. In one herd with IVM resistance, Ostertagia counts were slightly increased over pretreatment counts. Ostertagia was the prevalent post-treatment genera in herds with BZD resistance. A high level of resistance to ivermectin was recorded in this fattening region of Argentina. Also several herds with resistance to benzimidazole were observed. These results show the importance of AR in Argentinian cattle production. High correlation between WAAVP and Abbott formulae was observed. However, under some uncertain diagnosis, both formulae could be applied as complementary to help result interpretations.

Seasonal population trends and effects of Oestrus ovis in naturally infected sheep were studied over 13 months, in the Western of the Pampeana region. At weaning, 140 growing lambs were randomly allocated to two groups: UG, untreated group and TG treated every 4 weeks with closantel (10 mg/kg). Successive Oestrus free tracer lambs (TL) by previous treatment (n = 65) were slaughtered after 20-30 exposition days for larval counts. Likewise, other group PL of 117 permanent untreated lambs was slaughtered from four to 17 months of age. Weighing and assessment of health signs of UG and TG and blood samples were monthly carried out. The prevalence of infection in permanent group varied from 33% to 100%. Mean number of larvae in PL was 6.1 with 3 L1, 1.4 L2 and 1.6 L3 during spring-summer and 17.9 with 16.9 L1, 0.5 L2 and 0.4 L3 during autumn-winter months. In PL the proportions of larvae in each of the different larval stages was similar during spring and summer, but a significant (P < 0.01) increase of L1 was detected during autumn and winter. The prevalence in tracer lambs was 100% during summer time and larvae were absent from 25-May to 25-October. Mean larval burdens of positive TL varied from 6.4 to one Oestrus and a significant peak (P < 0.05) of larvae was seen from December to March. Since March to November only L1 was recovered from TL. TG group showed a reduction in nasal discharge and in antibody ELISA levels, but no difference was observed in live weight gain between TG and UG. These results show a high prevalence during summer and that the perpetuation of Oestrus is ensured by an autumn period of arrested development and the over wintering larvae in the sheep heads.

The control of ruminant gastrointestinal nematodes and ectoparasites, one of the major production health problems, are heavily reliant on the systematic and sometimes abusive use of anthelmintic drugs. Endectocides are the most frequently used drugs, having high potency against arthropods and nematodes. Their dung pat residues enhance the risk of adverse effects on non-target invertebrates and on the general grazing cattle ecosystem. In this scenario, our objective is to review current knowledge of the agro-environmental and biodiversity impact and risks of endectocides in South America. The effects of faecal drug residues of ivermectin and doramectin on dung colonising invertebrates and dung degradation have been reported in studies carried out in the temperate centre of Argentina and in the subtropical region of Brazil. The results from Argentina showed a depression in invertebrate colonisation and degradation of dung recovered from endectocide treated cattle during the autumn. Comparisons have shown that ivermectin and doramectin have similar adverse effects. A decrease of Coleoptera larvae, Diptera larvae, Staphylinidae, Collembola, Acari and dung specific nematodes was noted in pats from both endectocides. The results from Brazil showed that dipterous larvae, Polyphaga coleopteran larvae and adults and mites were significantly reduced in the ivermectin treated group. The disturbances that macrocyclic lactones can produce on non-targeted invertebrates and on their associated participation in dung degradation and soil element recycling, are unpredictable and can negatively influence biodiversity and the agricultural ecosystem sustainability.

The relationship between somatic cell counts (SCC) and California mastitis test (CMT) results according to the infectious status of mammary halves and parity of Pampinta dairy ewes was evaluated. Tests were associated to bacteriological analysis and classified into three groups: uninfected (negative culture), infected by minor pathogens and infected by major pathogens. Coagulase-negative Staphylococcus (32.4%), Micrococcus spp. (32.4%), Corynebacterium spp. (5.4%), and Bacillus spp. (1.4%) were the minor pathogens isolated, while Staphylococcus aureus (27%) and Escherichia coli (1.4%) were the major pathogens isolated. A good correlation was found between the CMT and SCC, which included inflammatory and epithelial cells (r = 0.64; P < 0.0001). SCC averages for the CMT scores shown in parentheses were 223 576 (0); 245,248 (1); 397,778 (2); 1,159,109 (3) and 2,460,833 (4) cells/ml. The correlation between SCC and the infectious status of udder halves was 0.58 (P < 0.0001). The relationship between SCC and CMT profiles and infectious status studied by a discriminant analysis showed, with an accuracy of 65%, three infectious status groups. SCC arithmetic means were 244,470 cells/ml for negative culture, 1,044,100 cells/ml for minor pathogens and 2,045,652 cells/ ml for major pathogens. With the exception of 1-year-old ewes, no significant differences were observed in SCC as affected by age or parity.

The effect of previous suppressive anthelmintic treatments after weaning on parasitological parameters and weight gain of cattle was studied in the Pampeana region of Argentina. The study was carried out at two grazing fattening periods: April 1995/July 1996 and April 1997/July 1998. During both periods, 60 weaned calves that grazed contaminated pastures, were divided into three groups during the first part of the periods: GY1 group was treated every 2 weeks with doramectin while GY2 and GY3 groups remained untreated. During the second part of the periods, from October onwards GY1 and GY2 remained untreated and GY3 was treated every 2 weeks. In this second period two new groups of 20 weaning young calves were added: TG (treated every 2 weeks) and UG (untreated). Egg counts (EPG), larval cultures, pasture larval counts, serum pepsinogen (Pep) and live weight gain (LWG) were recorded monthly. Ostertagia, Cooperia, Trichostrongylus and Haemonchus were the predominant genera. Despite low levels of previous infection during the first part of the period, slight differences of EPG between GY1 (P<0.09) or UG (P<0.05) and GY2 were detected in the second part of the fattening period in 1995/1996. In 1997/1998 moderate infection levels during the first part of the period were observed. During the second part of this period, GY1 and UG showed higher (P<0.001) EPG than GY2, and only GY3 and TG had (P<0.05) lower Pep levels. Also, during the second part of 1997/1998, LWG responses of GY3 were higher (P<0.001) than those of GY1 and GY2. Live weight gain of GY2 exceeded GY1 by 10.7kg (P<0.006). Higher EPG and lower LWG of GY1 suggest that suppressive treatments negatively affected the level of resistance to infection of yearlings, but these effects were influenced by previous levels of nematode infection. The lack of differences between yearling (GY1) and calves (UG) groups suggest that, under the conditions of this study, there was no evidence that resistance to infection and the related parameters are influenced by the age.

Development, migration and survival of infective larvae (L3) were studied in the Western Pampeana Region. Faeces of naturally nematode infected cattle were deposited as artificial pats on plots during mid-spring-summer of 1994/1995 and 1995/1996. Since the start and during 1995, the study coincided with a severe drought, rainfalls being 29% below the 45-year means. The predominant genera recovered were Cooperia, Ostertagia and Haemonchus. Initial and peak recovery of L3 from pats occurred 8-15 and 15-21 days later respectively. A low percentage of L3 survived from November (0.3% L3) and January (0.06% L3) to the following autumn and winter. The mean persistence of larvae detected in pats or herbage was around 200 days from deposition. The migration of L3 from faecal pats to herbage started 15 to 30 days after deposition according to rainfall occurrence. Maximum herbage recoveries of L3 from pats deposited in late summer occur during autumn rainfalls. Only, few L3 were occasionally recovered from soil. Summer conditions were associated with rapid development and translation of L3 to herbage, but also with low L3 detection after initial recoveries. Faecal pats deposited from mid-summer were the main source of autumn herbage contamination.

The epidemiology of nematode infection was studied in fattening grazing cattle from weaning (April 1994) to market at the end of their second autumn (July 1995). Sixty Aberdeen Angus calves of seven months of age were randomly allocated by weight to two groups: GT, treated every three weeks with doramectin (200 mcg/kg); and GI, an infected group, only treated with fenbendazole (7.5 mg/kg) at weaning and on the 1st of October. The two groups were grazed together on contaminated lucerne pastures until July, on 'clean' oat pastures until October and again on contaminated lucerne until the end of the trial. Fecal egg counts (epg), herbage larvae (L3), serum pepsinogen (Pep) and blood eosinophils (Eo) were evaluated monthly. Eight steers were slaughtered for worm recovery, three in July 1994, three in December 1994 and two in July 1995. Grazing feed intake was estimated by fecal output (chromic oxide method)/l-diet digestibility and to measure non-specific response, Brucella antibodies were detected at 11 and 40 days post-vaccination in early winter. Fecal egg counts, Pep and Eo of GI increased (P<0.01) from April to July when there was a moderate-to-high level of infection. Ostertagia, Trichostrongylus and Cooperia were the predominant genera. By late winter, all parameters decreased on oat 'clean' pastures and increased again when cattle returned to moderately infected lucerne. During summer, the parameters measured reflected the negligible numbers of L3 on pastures until early autumn. At this time, increased numbers of L3 were followed by a moderate rise (P<0.01) of epg, Pep and Eo values. During winter, GT showed higher (P<0.04) Brucella antibody IgG titers while feed intake of GI was 24.9% depressed (P<0.02). There were total cumulative weight-gain (WG) differences (P<0.001) between groups (GT=263.1 kg; GI=214.3 kg). During the second autumn, the mean WG of GT steers was 16.6 kg greater (P<0.04) than that of GI. Vaccination titres against Brucella suggested non-specific depression of immunity, while higher Pep and Eo levels in second-year steers may have reflected hypersensitivity reactions.

Breeding cattle for resistance to nematode infection is mostly based on egg excretion. This, however, does not allow for generic identification of the nematodes involved. Unless we know whether the selected resistance is directed against one or several particular genera, a strong bias could be introduced in the selection programs. In order to estimate the likelihood of this potential bias we investigated nematode genera diversity in the progeny of four sires in 1992 and seven sires in 1994. Three of the four Aberdeen Angus sires used in 1992 were related while the seven sires in 1994 were unrelated. Diversity was assessed using at least ten individual faecal cultures for each progeny group during each of the two sampling periods (beginning and end of grazing period, April and September). It was estimated by the relative proportion of each genera (Ostertagia, Cooperia, Haemonchus, Trichostrongylus and Oesophagostomum) or by either the Shannon (genera diversity) or Pielou (genera evenness) index. The Shannon index was repeatable when measured at 2-week intervals within the same progeny group on ten random faecal samples. No significant difference was recorded between sire genera diversity over the two sampling periods. This indicated that hosts have a limited effect on the nematode genera diversity as assessed by faecal cultures, and that the selection of resistant hosts could probably be achieved using faecal egg counts.

Variations in the proportion of the less-frequent morph of Teladorsagia circumcincta, T. c. trifurcata, were studied under experimental conditions. Infections with older larvae (over 7 months of age at 4 degrees C) yield a lower proportion of T. c. trifurcata compared with those obtained from fresh larvae (15 days). This phenomenon could account for the reduction in the proportion of the morph trifurcata in two isolates that were acclimated to laboratory rearing for several generations. The infection mode (single or trickle infections did not significantly modify the proportions of both morphs. The morph trifurcata was found in higher proportions (> 5.5%) in more susceptible male and/or Romanov lambs, and in lower proportions (< 2.5%) in less susceptible female and/or Mérinos d'Arles lambs.

Breed differences in resistance or tolerance to naturally acquired gastrointestinal nematodes were compared between Aberdeen Angus (AA) and Santa Gertrudis (SG) weaned steer calves grazing in a temperate environment. Within breeds, one half of the calves was untreated: AAU (n = 17) and SGU (n = 18) while the other half was treated with moxidectin monthly: AAT (n = 14) and SGT (n = 14). All calves were grazed on the same contaminated pasture from autumn to winter, when each group was separated to uninfected paddocks for the remaining period of the study. Faecal egg counts, plasma pepsinogen levels (PPL), herbage larval counts and liveweight (LW) were recorded monthly. Egg counts and PPL of AAU and SGU increased from autumn to early winter when calves showed heavy parasitism (mainly Trichostrongylus axei) and severely sick calves needed emergency treatment. On the clean paddocks, parasitological parameters progressively decreased. Late winter egg counts were higher (P < 0.05) in SGU than in AAU. PPL of SGU were higher than AAU ones, but no significant differences were detected. Larval differential counts of SGU showed fewer Cooperia (P < 0.08) and higher T. axei (P < 0.002) proportions than those of AAU. Numbers of severely sick and dead SGU calves (61%) were greater (P < 0.01) than those numbers of AAU calves (17.5%). Cumulative LW gains differences within SG breed were higher (P < 0.0001) than those differences within AA breed (P < 0.003). LW gains of AAU during autumn-winter period were greater (P < 0.002) than those of SGU.(ABSTRACT TRUNCATED AT 250 WORDS)

Seasonal population trends of helminth parasites of growing lambs were investigated over 4 years. Successive worm-free lambs were grazed together with untreated lambs for 20-30 days and then slaughtered for helminth counts 2 weeks after their removal from pasture. Likewise untreated lambs from the same flock were slaughtered from 2 to 15 months of age for worm counts in the same way as tracer lambs. The predominant parasites were Haemonchus, Nematodirus and Trichostrongylus. Haemonchus contortus was found to be of major importance and the flock acquired massive worm burdens from summer to mid-autumn. Minimum burdens were seen from winter to early spring and maximum L4 stages were found from mid-autumn to early winter. Nematodirus burdens increased from December with a peak in late summer and then decreased to low values. Maximum larval availability was in autumn to early winter. Trichostrongylus (mainly T. colubriformis) populations increased in autumn and peaked in June-July, while the highest larval availability was in autumn. The minor genera recovered were Ostertagia, Cooperia, Trichuris, Oesophagostomum and Moniezia. Dictyocaulus, Chabertia and Teladorsagia were noted occasionally and liver flukes were not detected. No important and pathogenic numbers of L4 stages were seen and all predominant species were able to survive over summer or winter in pasture.

Hybrids of Ostertagia ostertagi and Ostertagia leptospicularis, derived from experimental infections in sheep, are described. Morphometrics of the hybrids were intermediate between those of parental lines for a large range of parameters (distance from apex to cervical papillae and length of esophagus for males and females, length of spicules for males, and length of vestibule, distance from vulva to the end of tail, width of tail at anus). The morphological relationship between hybrids and their parent species was assessed by discriminant analysis based on the relative values of these parameters (actual value/length of the worm). Each parental line, either bred in sheep or in the natural host, was morphologically similar and differed from hybrids.

The interbreeding of 6 species of ostertagiines was studied in a sheep model. Virgin young females of selected nonpolymorphic strains of Ostertagia ostertagi, Ostertagia leptospicularis, and Teladorsagia circumcincta were mated with various male ostertagiines. Interbreeding was successful between O. ostertagi and Ostertagia lyrata, O. leptospicularis and Ostertagia kolchida, and T. circumcincta and Teladorsagia trifurcata, respectively. Their offspring were fertile and resembled one parent or the other without intermediate forms: each pair is a polymorphic species. Infertile hybrids, intermediate in form, were obtained from interbreeding between O. ostertagi and O. leptospicularis and they remain valid species.

The epidemiology and the effects of nematode infections on cow-calf systems were followed from 3 weeks before calving to 7 months afterwards. Two groups, each of 15 cow-calf pairs grazed on separate lucerne pastures. Group I (GI) were treated monthly with oxfendazole (4.5 mg kg-1), cows being dosed from calving and calves starting 45 days later. Animals in Group II (GII) were not treated. The egg output of the cows was very low. An increase was recorded 2 months after parturition, consisting mainly of Ostertagia spp. The egg output and worm burdens of calves remained low until late summer and reached a peak in autumn. Ostertagia, Cooperia and Haemonchus were the main genera recovered from slaughtered calves. The pasture contamination and tracer calf worm counts remained consistently low until autumn when they began to increase. Inhibited early fourth stage larvae of Ostertagia were recovered during spring. After calving, the live-weight gains (LWG) of treated GI cows were significantly higher (P less than 0.004) than those of GII cows, whereas the LWG of GI calves were significantly higher during December (P less than 0.037) and March (P less than 0.029) than those of GII calves. There were significant (P less than 0.04) cumulative LWG responses between GI and GII calves with no differences in cow cumulative LWG at the end of the trial. For spring-born calves, these results suggest that strategic deworming programs in cow-calf systems may produce benefits.

Interbreeding in two nematode species, Teladorsagia circumcincta and Ostertagia leptospicularis, was studied in lambs using small populations. Offspring from a single mated female were investigated for T. circumcincta. The following protocol was found to be satisfactory for small populations: virgin females and adult males were obtained from donor lambs infected artificially and transferred into the abomasa of fistulated sheep or lambs being treated with a long-acting corticosteroid. Infective larvae obtained from cultures of faeces of fistulated sheep were given to a recipient lamb and when this animal was slaughtered it was possible to examine the adult nematodes resulting from the interbreeding. Interbreeding between one male and one female was not successful while there was limited recovery of infective larvae from the implantation of a single mated female.

The nematode species Spiculopteragia spiculoptera, Spiculopteragia asymmetrica and Ostertagia leptospicularis were recovered from the abomasum of wild red deer, Cervus elaphus, in the forest area of the semi-arid Pampeana Region of La Pampa (Argentina) for the first time. Oesophagostomum venulosum and Dictyocaulus spp. were also found.

The effect of previous pasture management and ivermectin treatment on gastrointestinal parasitism, weight gain and carcase composition of steers was studied in the semiarid Pampeana region of Argentina from April 1986 to April 1987. Three groups, each of 15 weaned calves, were grazed on separate lucerne pastures. Group 1 control calves, which grazed paddocks previously grazed by nematode-infected weaners and yearlings with a high nematode egg output, were only medicated when heavy parasitism was recorded. Group 2 calves, which grazed paddocks previously infected by steers at least two and a half years old with low nematode egg output, were treated strategically with ivermectin. Group 3 calves, which grazed on 'clean' paddocks, were treated monthly with ivermectin. Group 1 calves showed heavy parasitism and parasitological parameters were higher than in groups 2 and 3. The liveweight gain responses of groups 2 and 3 were significantly greater than those of group 1 (P less than 0.001) during autumn, winter and early spring. At the end of the study when cattle reached market condition, the liveweight gains of groups 2 and 3 were 74.1 and 81.9 kg, respectively, greater than group 1. Carcase analyses showed significantly greater weight and killing-out percentages in groups 2 and 3 than in group 1. Reduced total bone, muscle and fat weights were observed in group 1.

The seasonal population trends of cattle nematodes in tracer calves are described from 1981 to 1987. Successive worm-free calves were grazed with growing beef cattle for 20-30 days at 6 week intervals and then slaughtered for nematode counts 2 weeks after their removal from pasture. Ostertagia, Cooperia, Trichostrongylus and Haemonchus were the main genera recovered. O. ostertagi was the most often found and acquisition of inhibition-prone larvae began in late winter and reached a peak in spring, while maximum larval availability was in autumn. The seasonal inhibition and larval availability pattern for T. axei was similar to that of Ostertagia. Cooperia showed greatest inhibition during winter with maximum larval availability in autumn and spring. Haemonchus was more prevalent during summer to early autumn and no inhibition was observed. It was concluded that infective larval availability for tracer calves was highest during autumn, and most reduced in summer. All predominant species were able to survive over summer on pasture.

Gastrointestinal parasitism of Zebu crossbred (Z), Hereford (H), and Hereford X Brahman (HB) weaned steer calves was observed from March 1985 to May 1986. Three groups of 60 calves were randomised and in each group the three breeds were equally present. Calves in GI were untreated, in GII were treated strategically and in GIII treated monthly with anthelmintic. The effects of anthelmintic treatments on the growth of cattle were assessed by comparing mean live-weight gain (MLG) responses of treated and untreated calves grazing the same permanent pasture. Worm recovery and egg counts increased from autumn to winter. After abundant July rainfalls, herbage infective larvae (L3) and worm burdens (mainly Ostertagia) reached the highest levels and Z calves presented symptoms of clinical parasitism. After high availability of L3 in spring, L3 and egg counts decreased to the end of the study. From the end of winter until summer a high percent of inhibited Ostertagia EL4 was seen. Blood samples showed reduced serum copper lower levels for GI. MLG responses of Z treated calves were significantly higher during the autumn-spring and summer-autumn periods. MLG responses of treated H calves were significant only during the winter-spring period. For HB calves there were no significant MLG responses during any period. The highest monthly treatment response was observed during winter and early spring. All strategic treatments gave significant MLG responses in spring and late summer. Initial effects of parasitism, from autumn until early spring had the greatest consequences in current and later productivity. For Z calves herbage L3, worm burdens, egg counts and MLG responses were higher than for H and HB calves. The Z breed were significantly heavier (+22.7%) at the end of the experiment in GIII than in GI. Similar trends were recorded, significantly, for H breed (+17.7%) and not statistically significant for HB (+12.7%). Under our temperate conditions it seems that H and HB calves showed greater capacity to resist nematode infection than Z calves.