Isolation and characterization of a gene encoding carbonic anhydrase from Ostertagia ostertagi and quantitative measurement of expression during in vivo exsheathment.

The first event in the establishment of Ostertagia ostertagi infection in cattle is exsheathment. Exsheathment is the process whereby the L(2) cuticle retained from the previous molt is cast from the L3. For those trichostrongyle nematode species with a predilection site in the abomasum, such as O. ostertagi, exsheathment is initiated as the larvae pass through the rumen. Although the stimulus for exsheathment is not known, previously reported biochemical studies suggest a major role for the enzyme carbonic anhydrase (CA). Partial support for this hypothesis comes from the reported failure of the Haemonchus contortus L3 to exsheath following pretreatment with ethoxzolamide, a known inhibitor of CAs. Although convincing, a CA has not been previously reported from a trichostrongylid nematode. Therefore, our objective was to isolate a CA gene from O. ostertagi L3 and begin initial characterization studies. This work resulted in the successful isolation, cloning and sequencing of the first CA isolated from a gastrointestinal nematode. The gene, designated OoCA, shows 90.5% sequence identity with the CA eukaryotic consensus sequence, 78% similarity to the Caenorhabiditis elegans cah-6 and 55% similarity to the human CAIII. Sequence analysis of the genomic DNA encoding OoCA shows 8 exons and 7 introns covering 4.5kb. The first 1758 bases of the promoter region suggest OoCA may be regulated in part by transcription factors associated with hypoxic signaling and development. The mRNA profile of OoCA in exsheathing O. ostertagi L3 suggests this particular CA may play a role in immediate early developmental events following exsheathment initiation.

Exsheathment of Ostertagia ostertagi infective larvae following exposure to bovine rumen contents derived from low and high roughage diets.

The objective of this study was to characterize the exsheathment kinetics of Ostertagia ostertagi infective larvae (L3) following in vivo exposure to bovine rumen contents derived from low and high roughage diets. O. ostertagi L3 were placed in disposable dialysis bags and incubated for various time points between 0 and 360 min in the rumen of a fistulated steer maintained on a 71% grain diet or a 100% grass diet. The maximum percentage of exsheathed L3 was observed 120 min post-exposure to grass-derived rumen contents, while maximum exsheathment for L3 exposed to grain-derived rumen contents did not occur until 360 min. This work provides the first report of the in vivo exsheathment kinetics for O. ostertagi in its bovine host. Results of this study also support earlier reports that rumen pH may affect the exsheathment efficiency of abomasal trichostrongylids.

Effect of horn fly and internal parasite control on growth of beef heifers.

The effects of horn fly and gastrointestinal nematode control on body weight gain of yearling Angus-Brangus cross heifers were evaluated in three separate studies during the years 1999, 2000 and 2002. In each year, the studies started in late May and lasted for 150, 148 and 123 days, respectively. In all three studies, the tag treatment (10% lambdacyhalothrin+13% piperonyl butoxide impregnated ear tags) provided excellent horn fly control. In the three studies, the average weekly horn fly counts for tagged heifers were 1, 3, and 0 flies per side while the average on untreated heifers was 52, 163 and 90 flies per side. In studies 1 and 2, there was no difference (P>0.1) in weight gain between tagged and untreated heifers, but in study 3, tagged heifers gained 50% more weight (P<0.001) than the untreated heifers. For gastrointestinal nematode control, ivermectin (IVM) was administered on Day 0 in studies 1 and 3 using a sustained release bolus and on Day 0 and subsequent 56-day intervals in study 2 using either the injectable or pour-on formulation. Heifers treated with IVM in studies 1 and 3 had significantly lower (P<0.05) GI nematode fecal egg counts compared to control heifers. In study 2, IVM treated heifers also had significantly lower GI nematode fecal egg counts compared to control heifers, except for Day 90 when no differences in fecal egg counts were observed between IVM pour-on treated and control heifers. Weight gain of heifers that received IVM was significantly greater (P<0.005) than untreated heifers in each of the three studies. IVM treated heifers gained 45, 61 and 184% more weight than the untreated heifers during the three studies. There was no interaction (P>0.1) between the main treatment effects of fly control and gastrointestinal nematode control.

Effect of gastrointestinal nematode and liver fluke infections on weight gain and reproductive performance of beef heifers.

Spring born, crossbred beef heifers (n=372) were utilized over four years to measure reductions in body weights, reproductive performance and calf weights caused by gastrointestinal nematodes (primarily Ostertagia ostertagi) and the bovine liver fluke (Fasciola hepatica) and to differentiate losses attributable to each type of parasitism. Each year, weaned heifers were allotted to one of the four treatment regimens: Group 1, untreated controls; Group 2, treated for nematodes; Group 3, treated for liver fluke; and Group 4, treated for both nematodes and liver fluke. Nematodes were controlled with subcutaneous injections of either ivermectin (Ivomec, Merial) or doramectin (Dectomax, Pfizer), both at the recommended dose of 200 ug/kg bodyweight. Clorsulon (Curatrem, Merial) drench was given at the recommended rate of 7 mg/kg bodyweight to control flukes. Treatments and fecal collections were initiated at allotment each year and were repeated at 28-84-day intervals until palpation for pregnancy diagnosis. Open heifers were removed from the study at this time. Treatment dates were based on expected length of treatment efficacy, the stage of growth of the heifers and the seasonal risk of infection by the parasites. Pregnant females were pooled and received their assigned treatments prior to their calving and breeding seasons and remained together until their calves were weaned. Heifers treated for nematode infections were heavier and had higher condition scores (P<0.01) than untreated control heifers at initiation of breeding, and maintained that difference through pregnancy diagnosis. Liver fluke infection did not affect heifer gains or condition scores prior to palpation (P<0.01). At palpation, heifers treated for both forms of parasitism had the highest condition scores and weight gains (P<0.01), and also higher pregnancy rates than control heifers and heifers treated for nematodes only (P<0.01). Pregnancy rates for heifers treated for flukes only were not significantly different from those treated for both nematodes and flukes. Heifers treated for nematodes weaned heavier calves than those not treated for nematodes (P<0.05).

Effects of parenteral administration of doramectin or a combination of ivermectin and clorsulon on control of gastrointestinal nematode and liver fluke infections and on growth performance in cattle.

OBJECTIVE: To compare effects of an injectable doramectin preparation with those of an injectable ivermectin-clorsulon preparation on control of gastrointestinal nematodes and liver flukes and on growth performance in cattle. DESIGN: Randomized complete block design. ANIMALS: 60 crossbred calves. PROCEDURES: Calves (20/treatment group) were treated with doramectin or ivermectin-clorsulon or were not treated. Fecal samples were collected for nematode and Fasciola hepatica egg counts on day 0 and for up to 140 days after treatment. Cattle were weighed before treatment and at 28-day intervals until day 140. RESULTS: From day 7 through day 49, nematode egg counts for calves treated with doramectin or with ivermectin-clorsulon were significantly lower than those for untreated control calves. As the study progressed beyond day 56, the percentages of cattle with fluke eggs in their feces increased, but differences in regard to these percentages were not detected among the 3 groups. Average daily gain for the doramectin-treated cattle (0.79 kg/d [1.74 lb/d]) was significantly greater than that for the cattle treated with ivermectin-clorsuIon (0.71 kg/d [1.56 lb/d]); values for both groups were significantly greater than that for the control cattle (0.62 kg/d [1.37 lb/d]). CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that doramectin had a greater impact on subclinical gastrointestinal tract parasitism in calves, as demonstrated by growth performance, than did ivermectin-clorsulon. In the Gulf Coast region of the United States, spring-born nursing beef calves may have minimal grazing exposure to F hepatica during the peak fluke transmission period; therefore, mature fluke burdens may be negligible at the beginning of the fall season.