Variability in the Infection of F1 Katahdin x Pelibuey Crossbred Lambs to Gastrointestinal Parasitic Nematodes in a Warm Humid Climate
Background: In sheep production systems based on grazing, gastrointestinal nematodes (GIN) are one of the main problems faced by farmers. The occurrence of anthelmintic resistance in GIN has endangered the productive activity of sheep, so that one alternative has been through the selection of sheep....
| Autores: | , , |
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| Formato: | artículo |
| Estado: | Versión publicada |
| Fecha de publicación: | 2014 |
| País: | México |
| Recursos: | Universidad Autónoma Chapingo |
| Repositorio: | Redalyc-UACHP |
| OAI Identifier: | oai:redalyc.org:289029240084 |
| Acesso em linha: | https://www.redalyc.org/articulo.oa?id=289029240084 |
| Access Level: | acceso abierto |
| Palavra-chave: | Veterinaria sheep Cooperia curticei innate resistance acquired resistance parasitic nematodes |
| Resumo: | Background: In sheep production systems based on grazing, gastrointestinal nematodes (GIN) are one of the main problems faced by farmers. The occurrence of anthelmintic resistance in GIN has endangered the productive activity of sheep, so that one alternative has been through the selection of sheep. The selection programs are based on evaluation of parasitism by measuring the fecal egg counts (FEC) of GIN due to the high correlation between the FEC and worm burdens. The identification of resistant and susceptible lambs requires knowing the FEC after the infection. The aim of this research was to determine the intra-breed variability on FEC of GIN in Katahdin x Pelibuey grazing sheep. Materials, Methods & Results: The experiment was conducted in Tabasco, Mexico in a warm humid climate. The study was carried out in three stages: in stage I, the FEC was recorded in newly weaned lambs experimental infected with 1600 infective larvae (L3) of Haemonchus contortus and Cooperia curticei (85% and 15% respectively). Twenty lambs were drenched with albendazole and 20 more lambs were considered as control without any anthelmintic treatment. In stage II acquired resistance was determined in the same animal group after a break period following the same treatments. In stage III new lambs were introduced to paddocks and the FEC was recorded in their first infection. Every 15 days fecal sample, live weight and blood samples were taken to determine FEC, daily gain weight and packed cell volume. Data were analyzed with a model of repeated measures over time. In order to establish the level of anti-parasitic resistance in the lambs, a categorization of the lambs according to their FEC was performed based on the EPG mean and standard deviation. Subsequently another statistical analysis was performed by category to determine the EPG, PCV and DWG values per group. In primary infection, both lambs treated with albendazole and control group reached a maximum elimination at 32 days post-infection (4202 ± 558 EPG mean). In the second natural infection the same lambs had less FEC (989 ± 378 EPG), while in the newly weaned lambs of the third stage the FEC was rapidly increasing at 18 days (2950 ± 471). Derived from the categorization process of the lambs, it was observed that resistance animals had lower FEC (282 ± 197.5) and higher PCV (27.9 ± 2.5 %) than the susceptible animals (5424 ± 3790 FEC and 25.19 ± 1.95 %, respectively). However, weight gains were similar among the groups (0.04 ± 0.05 kg) and packed cell volume was similar between resistant and intermediate group. A negative correlation (r = -0.30) was obtained between PCV and FEC due to H. contortus population was abundant. Discussion: During the pre-patent period, no paddock contamination occurred; so, no lamb re-infections were expected. This fact can explain why the subsequent reduction in the larvae population occurred after 35 days infection. A similar behavior in the FEC was observed in single infections in |
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