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PubMed2002

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).

Animals↗
PubMed1993

Influence of sex and reproductive status on susceptibility of ruminants to nematode parasitism.

Bulls and rams are notorious among stockmen and stud breeders for their apparently greater susceptibility than cows, ewes, steers or wethers to diseases caused by excessive infection with parasitic nematodes. Extension advice given to farmers generally includes a recommendation to treat entire male animals as though they were weaners. In contrast, the scientific literature contains little documentation of this fact, although the phenomenon has been well-described in laboratory animals. Scientific interest in the susceptibility of lactating cows and especially ewes to nematode parasitism has been more extensive, but unproductive in terms of elucidating responsible mechanisms. Where ewes have acquired immunity to nematode infection, they tend to lose it around the time of parturition and during lactation, with important epidemiological and productivity consequences. In strains of sheep selected for resistance to nematode infection, principally through a more rapidly acquired immune response, resistant ewes still undergo a periparturient loss of immunity but retain their relative superiority over unselected or susceptible ewes. The mechanisms involve effects of hormones associated with lactation on the immune system, but an unequivocal role for prolactin or any other hormone has not yet been identified. Collaboration between immunologists, endocrinologists and parasitologists is required.

Animals↗
PubMed2000

A reversible protein phosphorylation system is present at the surface of infective larvae of the parasitic nematode Trichinella spiralis.

Trichinella spiralis infective larvae have externally oriented enzymes catalysing reversible protein phosphorylation on their surface. Incubation of larvae with exogenous ATP resulted in phosphorylation of surface bound and released proteins. Exposure of the parasites to bile, a treatment which renders them infective for intestinal epithelia, resulted in increased release of protein and an altered profile of phosphorylation. Both serine/threonine and tyrosine phosphorylation and dephosphorylation reactions took place at the parasite surface. Examination of the structural characteristics of the larvae following exposure to bile showed that the non-bilayer surface coat was not shed but was structurally reorganised.

Adenosine Triphosphate↗