Repeatability of measurements of packed cell volume and egg count as indicators of endoparasite load and their relationship with sheep productivity

Field study on nematode resistance in Nelore-breed cattle

The present study evaluated Nelore cattle with different degrees of resistance to natural infections by gastrointestinal nematodes. One hundred weaned male cattle, 11-12 months of age, were kept on the same pasture and evaluated from October 2003 to February 2004. Faecal and blood samples were collected for parasitological, haematological and immunological tests. In February 2004, the 10 most resistant and the 10 most susceptible animals were selected based on individual means of nematode faecal egg counts (FEC). Such animals were slaughtered for worm burden determination and nematode species identification. The repeatability estimates for FEC (+/-S.D.), log-transformed FEC and packed-cell volume (PCV) in all animals were 0.3 (+/-0.05), 0.26 (+/-0.04) and 0.42 (+/-0.05), respectively. The resistant group showed lower FEC and worm burdens than the susceptible group (P<0.05). There were no significant differences between groups regarding mean body weight, weight gain, PCV and total serum protein values (P>0.05). The resistant group showed higher total serum IgE levels (P<0.05) and higher mean eosinophil blood counts. However, the latter was statistically significant only 42 days after the beginning of the study. Nematodes Cooperia punctata and Haemonchus placei were predominant and the correlation between Cooperia and Haemonchus burdens was 0.64 (P<0.05), which indicated that animals presenting increased numbers of one of those genera probably had increased numbers of the other. The current study provides further evidence of IgE active role in nematode immunity and suggests that total serum IgE level might serve as an additional marker to select Nelore cattle that are responsive to H. placei and C. punctata infections.

Relação entre desempenho e infecções por nematódeos gastrintestinais em bovinos Nelore em crescimento

Este estudo teve por objetivo verificar a associação entre o desempenho e a carga parasitária de 28 machos inteiros da raça Nelore (a partir de um ano de idade), naturalmente infectados por nematódeos gastrintestinais. De novembro de 1999 a junho de 2000, os animais foram pesados quinzenalmente, período no qual foram colhidas amostras de fezes e de sangue para a realização, respectivamente, de exames coprológicos e sangüíneos. Os dados da contagem de ovos por grama de fezes (OPG) ajustaram-se ao modelo de distribuição binomial negativa, indicando que a distribuição de nematódeos no rebanho é agregada. Não ficou evidenciada associação entre ganho de peso e contagem de OPG, e entre contagem de OPG e volume globular (VG). De 10 coeficientes de correlação entre ganho de peso e VG, oito foram negativos, mas apenas dois significativos (P<0,05). As estimativas de repetibilidade da contagem de OPG, LOG (OPG+1) e VG foram de 0,26, 0,25 e 0,33, respectivamente. Cooperia punctata foi a espécie mais freqüentemente encontrada parasitando os animais. Além dessa espécie, foram detectados os seguintes nematódeos: Haemonchus placei, Haemonchus similis, Trichostrongylus axei, Bunostomum phlebotomum e Oesophagostomum radiatum. O parasitismo por nematódeos gastrintestinais aparentemente não prejudicou o desenvolvimento dos animais estudados.

Seasonal patterns of strongyle infections in grazing sheep under the traditional production system in the region of Trikala, Greece

Ten 4-month-old female sheep of the Karagouniko dairy breed were used to monitor the seasonal fluctuations of strongyle infections in sheep during the first year of grazing under the traditional production system in the region of Trikala, Greece, where control of nematodes is currently based exclusively on the frequent use of anthelmintics which might contribute to the appearance of anthelmintic resistance. The sheep grazed communal pasture plots and did not receive any anthelmintic treatment during the entire study period. Faecal egg counts (epg), plasma pepsinogen levels, blood values, and genera of parasitic strongyles recovered from coprocultures were recorded monthly. Mean epg for strongyle-type eggs were significantly higher during summer. Mean plasma pepsinogen levels were significantly higher during spring and summer. The genera of parasitic strongyles recovered from the faecal cultures were Haemonchus, Ostertagia, Trichostrongylus, Cooperia, Nematodirus, Oesophagostomum, and Chabertia. The percentages of larvae for Haemonchus, Ostertagia, Cooperia, and Oesophagostomum were significantly higher during winter. The percentages of larvae for Trichostrongylus were significantly higher during summer. During summer, levels of RBC, HGB, and HCT were depressed and levels of MCV, MCH, and MCHC were elevated. Mean epg for strongyle-type eggs had a significant inverse correlation with RBC, HGB, HCT, and positive correlation with MCH, MCHC, and percentages of eosinophils in differential leucocyte counts. The seasonal pattern of infection observed in the present study indicates that it is possible to decrease the number of treatments to one per year, thus, reducing the possibility for the appearance of anthelmintic resistance.