RESUMO
Se utilizaron 24 corderos Katahdin x Pelibuey, distribuidos al azar en cuatro grupos desafiados con los siguientes tratamientos: a) 25 larvas infectantes (L3) de nematodos gastrointestinales (NGI) por kg de peso vivo (PV); b) 50 L3 PV, c) 100 L3 PV y el grupo testigo (0 larvas). El experimento se dividió en tres etapas: 1) infección experimental y estabulación de corderos, 2) reinfección en pastoreo y 3) estabulación. En cada etapa se determinó el número de huevos de nematodos por gramo de heces (HPG), el peso vivo (PV) y el volumen celular aglomerado (VCA). El análisis se realizó con medidas repetidas en el tiempo. Los corderos infectados con 100 L3 tuvieron mayor HPG (1.642 ± 1.183) que los infectados con 50 L3 (1.140 ± 1.313 HPG) y los de 25 L3 (458 ± 371 HPG). Con 50 L3 los corderos tuvieron el menor VCA (23,7 ± 4,8%). Con 100 L3 se observó menor VCA que el grupo testigo y el de 25 L3 (26,2 ± 3,9; 28,0 ± 4,1 y 27,3 ± 4,2 %, respectivamente). Las ganancias de peso se redujeron respecto al testigo en un 22% en los de 25 larvas, 60% en los de 50 larvas y 61% en los de 100 larvas. El grupo infectado con 100 larvas obtuvo, durante la segunda etapa, el menor HPG (2.033 ± 2.553 HPG), un incremento del VCA (27,8%) y mayor ganancia de peso (3,7 kg) que los otros grupos, por lo que se concluye que con la dosis de 100 L3 se obtienen menores conteos fecales de huevos de NGI, mayor VCA y mejor ganancia de peso bajo condiciones de reinfección en pastoreo.
24 Katahdin x Pelibuey male lambs were used. The lambs were random in four groups with the following treatments: a) 25 infective larvae (L3) of gastrointestinal nematodes (GIN) per kg of body weight (BW), b) 50 L3 BW, c) 100 L3 BW and the control group (0 L3). The experiment was divided into three stages: 1) Experimental infection in stabling, 2) grazing infection and 3) housed lambs. At each stage were determined the number of nematode eggs per gram of feces (EPG), body weight and packed cell volume (PCV). The data analysis was performed using a repeated measures model in time. The lambs infected with 100 L3 had higher EPG (1642 ± 1183) in comparison with the treatment of 50 L3 (1140 ± 1313 EPG) and 25 L3 (458 ± 371 EPG). With 50 L3 the lambs had the lowest PCV (23.7 ± 4.8%). With the application of 100 L3 also had lower PCV than control group and 25 L3 (26.2 ± 3.9, 28.0 ± 4.1 and 27.3 ± 4.2%, respectively). It was observed a decrease in weight gain of all infected groups compared to the control group, by 22% in lambs with 25 larvae, 60% in the 50 larvae and 61% in animals of 100 larvae. During the second stage, the group infected with 100 larvae there was a reduction of EPG (2033 ± 2553 EPG), an increase in PCV (27.8%) and increased kg (3.7 kg) with respect to other infected for this reason was concluding that lambs receiving 100 L3 had lowest nematode faecal egg count, highest PCV and gain daily weight during the grazing reinfection.
RESUMO
This study aimed to evaluate the variability in the fecal egg count (FEC) and the parasitic burden of naive hair sheep after grazing in nematode infected paddocks. The research was carried out in Tabasco, Mexico, during two periods (August and December). In each period 32 lambs were grazed for one month on African star grass (Cynodon plectostachyus) contaminated with gastrointestinal parasitic nematodes. FEC, packed cell volume (PCV) and body weight (BW) were recorded. Gastrointestinal worms were recovered at necropsy. Data were analyzed with the MIXED procedure of SAS using a model of repeated measurements over time. A higher number of Haemonchus contortus worms was found in December (2814±838) than in August (1166±305). The opposite occurred with Cooperia curticei (2167±393 and 3638±441, respectively). The FEC and correlation coefficient in respect to the worm burden were higher in December (6516 ± 1599, r=0.83, respectively) than in August (4364±771, r=0.44, respectively). A high variability in resistance-susceptibility to gastrointestinal nematodes (GIN) occurred in Katahdin × Pelibuey lambs after grazing.