The efficacy of Michel's dose and move system on gastrointestinal nematode infections in diary calves.

The efficacy of a move to aftermath in July combined with moxidectin or fenbendazole treatment for the control of parasitic gastroenteritis (PGE) in calves was evaluated in three field experiments in the Netherlands. In all five treated groups high gastrointestinal nematode infections and PGE were prevented by a dose and move in July. Cooperia infections increased to moderate levels in two groups treated with moxidectin and one group treated with fenbendazole. In both other groups and also for Ostertagia in these three groups, low to extremely low infections were acquired. In the first experiment high primary infections, resulting in high faecal egg counts and a moderate increase of blood pepsinogen values occurred before the dose and move. Nevertheless, these primary infections were not high enough to result in PGE. In both other experiments primary infection levels were low and faecal egg counts increased to 100-650 eggs/g faeces at the end of the grazing season. The blood pepsinogen values of non-treated control groups demonstrated that it took more than a month after their move to aftermath before substantial reinfection occurred on the new pasture. In the first and the last experiment only, high Ostertagia and Cooperia infections developed in the control group at the end of the grazing season, though it did not result in clinical PGE. The experiments demonstrate all theoretical risks of the dose and move system: (1) PGE early in the grazing season as a result of high overwintered pasture infectivity. (2) PGE just before the move as a result of an early midsummer increase in pasture infectivity. (3) PGE around housing as a result of insufficient suppression of pasture infectivity late in the grazing season. (4) Underexposure to nematode infections due to a high suppression of nematode infections. Nevertheless, it can be concluded that under normal conditions the dose and move system remains to be a valuable and easily applicable system for the control of PGE.

Use of cloned excretory/secretory low-molecular-weight proteins of Cooperia oncophora in a serological assay.

The potential of Cooperia oncophora excretory/secretory (ES) proteins as antigens in a serological assay which aims to establish exposure levels in cattle was assessed. ES proteins were analyzed by one- and two-dimensional polyacrylamide gel electrophoresis and immunoblotting. The N-terminal domains of two ES proteins were sequenced, and the corresponding cDNAs were cloned. Two cDNAs, designated CoES14.0 and CoES14.2, were expressed in Escherichia coli. The recombinant proteins were tested in an indirect enzyme-linked immunosorbent assay (ELISA) in which crude worm antigen (CWA) was used as a reference standard. In total, 67 reference serum samples were used: 27 negative serum samples, 29 C. oncophora-specific serum samples, 7 Dictyocaulus viviparus-specific serum samples, and 4 Ostertagia ostertagi-specific serum samples. This showed respective sensitivities and specificities of 17 and 84%, 0 and 100%, and 100 and 100% by the ELISAs with the three different types of proteins (CWA, CoES14.0, and CoES14.2, respectively). Since the CoES14.2 ELISA had the best sensitivity and specificity with reference sera, its specificity was further validated in an antigen inhibition ELISA. In this assay CoES14.2 and CWA preparations of C. oncophora, Cooperia curticei, O. ostertagi, Nematodirus helvetianus, Fasciola hepatica, D. viviparus, Haemonchus placei, and Trichostrongylus colubriformus were used as competitor antigens. This experiment showed that only the homologous antigens C. oncophora CWA and CoEs14.2 resulted in 100% inhibition. The CWA preparations of all other nematodes did not affect the ELISA, even if concentrations of 250 times the 50% inhibitory concentration of C. oncophora CWA were used. These results indicate that CoES14.2 does not share cross-reactive epitopes with heterologous CWAs. Finally, we tested the CoES14.2 ELISA with sequential serum samples from naturally infected groups of animals. The optical density values that were obtained correlated well with exposure levels based on cumulative egg excretion. Thus, the CoES14.2 ELISA seems to be a very sensitive tool for estimating exposure levels in cattle.