Abstract: This study is an evaluation of resistance to natural infection by Cooperia spp. in Zebu x Holstein crossbreed calves in the tropics. Fourteen four-month-old calves were dewormed and moved to pastures naturally infested with gastrointestinal nematodes under sub-humid tropical conditions. Fecal samples were collected from each animal every seven days for three months to quantify the number of eggs per gram of feces (EPG), and nematode species identified with end-point PCR. Hair samples were collected for genotyping using the GeneSeek Genomic Profiler HD-V3 panel, which contains 139,376 SNP markers. Variation in EPG per individual ranged from a minimum of 7+7 to a maximum of 4,657+1,886 EPG. The PCR identified breed differences between the Zebu x Holstein crossbreeds. Genome-wide association studies detected five statistically significant haplotypes (P<0.001). The haplotype in chromosome 2 includes four markers, that in chromosome 10 includes three, that in chromosome 15 includes two, that in chromosome 23 includes four and chromosome X includes three. Of these regions only chromosome 23 was found to be associated with parasite resistance, measured as EPG phenotypes. The remaining chromosomes exhibited no association in the studied animals. These regions could be sequenced and tested for gene expression against Cooperia and other gastrointestinal nematodes.

Resumen: El objetivo del presente estudio fue evaluar la resistencia a la infección natural por Cooperia spp. en bovinos jóvenes cruzados Cebú x Holstein, en trópico. Catorce (14) becerros de cuatro meses de edad fueron tratados con desparasitante y trasladados a potreros naturalmente contaminados con nematodos gastrointestinales bajo condiciones de trópico sub-húmedo. Muestras de heces se colectaron cada siete días durante tres meses por individuo, para cuantificar el número de huevos por gramo de heces (HPG) e identificar el género por PCR de punto final. Se colectaron muestras de pelo para llevar a cabo estudios de asociación genómica utilizando la plataforma GeneSeek Genomic Profiler HD-V3 que contiene139,376 marcadores SNP. Los resultados obtenidos indican variación en el número de HPG por individuo (mínimo 7+7 y máximo 4657+1886 HPG). En los análisis de componentes principales se identificaron diferencias raciales entre los animales con genes de las razas Cebú y Holstein. Los estudios de asociación del genoma completo detectaron 5 haplotipos estadísticamente significativos (P<0.001). El haplotipo del cromosoma 2 incluye cuatro marcadores, el 10 incluye a tres, el 15 incluye a dos, el 23 cuatro y el del cromosoma X incluye tres. De estas regiones sólo el cromosoma 23 se encontró asociado a resistencia por parásitos, medidos como fenotipo de HPG; los cromosomas restantes identificados no mostraron asociación en ninguno de los individuos en estudio. Se considera que estas regiones podrían ser secuenciadas y probar la expresión de genes para la resistencia contra este nematodo y de otros nematodos del complejo gastrointestinal.

Resumo Fungos nematófagos das fezes de búfalo de água e do solo no sudeste do México foram isolados, e a atividade predatória in vitro contra larvas infectantes de Haemonchus contortus (L3) (HcL3) foi avaliada.Os fungos foram isolados por aspersão de solo e de fezes em placas de agar água. Foram preparadas seis séries de 10 placas de Petri contendo uma cultura de 7 dias de idade de cada fungo e uma série sem fungos como controle. Quinhentos HcL3 foram adicionadas a cada placa. As placas foram incubadas à temperatura ambiente. O número médio de HcL3 recuperadas foi considerado para estimar a taxa de redução larval. Quatro isolados de fungos nematófagos corresponderam a Arthrobotrys oligospora, var microspora (estirpes 4-276, 269 e 50-80) e um isolado identificado como A. oligospora, var. oligospora (isolados 48-80 de fezes de búfalo de água. Do solo, dos cinco isolados três corresponderam a A. musiformis (Bajío, Yumca e Macuspana isolados), e dois isolados foram identificados como A. oligospora (isolados de Comalcalco e Jalapa de Méndez). A atividade predatória de isolados de fezes de búfalo de água variou entre 85,9 e 100%. Enquanto isso, os fungos do solo variaram entre 55,5 e 100% (p≤0,05). Os fungos nematófagos obtidos podem ter importantes implicações nesse controle de parasitos de importância na indústria pecuária.

Abstract Nematophagous fungi from the feces of water buffalo and soil from southeastern Mexico were isolated, and their in vitro predatory activity against Haemonchus contortus infective larvae (L3) (HcL3) was assessed. The fungi were isolated by sprinkling soil or feces on water agar plates. Six series of 10 Petri dishes containing a 7-day-old culture of each fungus and a series without fungi as the control were prepared. Five hundred HcL3 were added to each plate. The plates were incubated at room temperature. The average of recovered HcL3 was considered to estimate the larval reduction rate. Four nematophagous fungi isolates corresponding to Arthrobotrys oligospora, var microspora (strains 4-276, 269 and 50-80) and one identified as A. oligospora,var. oligospora (isolates 48-80) were obtained from water buffalo feces. From the soil, five isolates were isolated; three corresponded to A. musiformis (Bajío, Yumca and Macuspana isolates), and two isolates were identified as A. oligospora (Comalcalco and Jalapa de Méndez isolates). The predatory activity of isolates from water buffalo feces ranged between 85.9 and 100%. Meanwhile, the fungi from the soil ranged between 55.5 and 100% (p≤0.05). The nematophagous fungi obtained could have important implications in the control of parasites of importance in the livestock industry.