Comparative cost-effectiveness of ivermectin versus topical organophosphate in feedlot yearlings. (1/46)

A replicated-pen field trial was performed under commercial feedlot conditions in western Canada to determine the cost-effectiveness of administering ivermectin to yearling beef cattle upon entry to the feedlot after the grazing season, and to establish the level of trichostrongylid gastrointestinal parasite infection in this population, as estimated by fecal egg counts. Six thousand eight hundred and eighty-three, mixed breed, yearling steers were randomly allocated upon arrival at the feedlot to one of 2 experimental groups as follows: Ivermectin, which received topical ivermectin (0.5%) at the rate of 1.0 mL/10 kg body weight; or Fenthion, which received topical fenthion (20%) at the rate of 12 mL/295 kg body weight. There were 15 pens in each experimental group. Final weight, weight gain, average daily gain, and dry matter intake to gain ratio were significantly (P < 0.05) improved in the Ivermectin group as compared with the Fenthion group. There were no significant (P > or = 0.05) differences in initial weight, days on feed, or daily dry matter intake between the experimental groups. The geometric mean fecal egg counts at the time of allocation were 14.7 eggs/5 g and 16.6 eggs/5 g for the Ivermectin and Fenthion groups, respectively (P > or = 0.05). There were no significant (P > or = 0.05) differences in morbidity or mortality between the experimental groups. In the economic analysis, the significant improvements in feedlot performance in the Ivermectin group resulted in a net economic advantage of $4.20 CDN per animal.  (+info)

Hypersensitivity reactions in small intestine. I Thymus dependence of experimental 'partial villous atrophy'. (2/46)

Rats infected with the intestinal nematode Nippostrongylus brasiliensis have crypt hyperplasia with villous atrophy in affected areas of the small intestine. In thymus-deprived (B) rats the course of infection is prolonged but, despite the presence of many worms in the intestinal lumen, villi and crypts appear largely normal. This suggests that the tissue damaged associated with N. brasilliensis infection is caused, not by the worms, but by a local thymus-dependent immune reaction. There is some evidence to implicate lymphocytes rather than antibodies in this reaction. It is already know that T-cell-associated damage to the small intestine, such as occurs in allograft rejection, produces subtotal villous atrophy. The present findings suggest that when T cell react locally with helminth antigens a similar type of damage occurs. The presence of a local cell-mediated immune reaction may be the common factor which causes villous atrophy and crypt hyperplasia in many small intestinal diseases, eg, viral enteritis, giardiasis, cow's milk allergy, and coeliac disease.  (+info)

The passive transfer of humoral immunity from sows infected with Hyostrongylus rubidus (Hassal and Stiles, 1892), the red stomach worm, to their offspring and its significance in the conferring of protective immunity. (3/46)

Sows repeatedly infected with large single doses of third stage infective Hyostrongylus rubidus larvae show an anamnestic circulating agglutinin response to the parasite as detected by the passive haemagglutination reaction. At farrowing the circulating antibody level dropped, whereas the colostral agglutinating antibody level increased for a period of a few hours. The predominant class of immunoglobulin which had agglutinating activity against H. rubidus was IgG. Offspring which had suckled the infected mothers had a demonstrable agglutinin titre 4 days after birth, whereas offspring which suckled non-infected mothers had no demonstable agglutinins. On infection of the offspring, those which suckled infected mothers showed a more rapid and pronounced increase and duration of circulating agglutinins than those which had suckled noninfected mothers. The parasitic burden, as determined by the duration of egg laying and total egg output, was considerably lower for the group reared on the infected mothers. These experiments show that passively transferred agglutinating antibodies, mainly of the IgG class, were associated with protection.  (+info)

A short-term divergent selection for resistance to Teladorsagia circumcincta in Romanov sheep using natural or artificial challenge. (4/46)

This experiment was conducted to assess the efficiency of selection on the basis of response to artificial challenges in order to breed sheep resistant to natural infection. A short-term divergent selection process was designed to estimate the genetic parameters of these two traits. Two flocks, including 100 Romanov ram lambs each, were challenged in 1990 when they were 6 months old. One flock received three artificial infections with 20 000 third-stage Teladorsagia circumcincta larvae, at intervals of 7 weeks. Faecal egg counts (FEC) were performed on Days 22, 25 and 28 post infection (p.i.) and the animals were drenched on Day 28 p.i. The other flock was grazed for 5 months on a pasture contaminated with the same species. Faecal samples were taken from the lambs at similar ages. About 5 rams with the lowest FEC and 5 with the highest FEC were selected in each flock and mated with unselected ewes. Their offspring (200 animals) were challenged in 1992, half in the same way as their sires, and the other half by the other method. Because of a drought in the summer of 1990, it was necessary to repeat part of the experiment, and in 1992 the 5 and 8 rams with the lowest and highest FEC, respectively, were selected from the offspring challenged on the pasture in 1992 and were mated with unselected ewes. Their progeny (about 80 animals) were challenged in 1994, half by natural infection, half by artificial infection. The mean FEC of the flock increased from the first to the third artificial infection. The natural infection was highly variable in different years, reflecting the difficulty of assessing resistance using this mode of challenge. Genetic parameters were estimated using animal models and REML solutions. The repeatabilities of the FEC following artificial and natural infection were 0.49 and 0.70 respectively within a period of one week, and 0.22 and 0.41 respectively for periods separated by intervals of 7 weeks; the heritabilities of the single egg count were 0.22 and 0.38 respectively. The genetic correlation was 0.87: the FEC recorded under natural or artificial infection appear to depend on the same genetic potential.  (+info)

Regulation of Teladorsagia circumcincta and Trichostrongylus colubriformis worm populations by grazing sheep with differing resistance status. (5/46)

In an experiment lasting 4 years, changes in the Teladorsagia circumcincta and Trichostrongylus colubriformis populations were compared in lambs and adult sheep with differing resistance statuses. Two flocks of 30 rams (resistant R and susceptible S) grazed separate pastures and 8 rams were slaughtered in the middle and at the end of each grazing season. Five groups of tracer lambs were added each year to estimate the pasture infectivity and were killed for worm counts. The availability of animals with differing resistance statuses (rams and tracer lambs) and differing levels of infection made it possible to investigate the number, size and fecundity of worms of these two species. The inflammatory response was measured in the rams by counting the globule leukocytes, mast cells and eosinophils in the fundic, pyloric and intestinal mucosa. In the tracer lambs, the daily egg production by the female worms of both species was negatively correlated with the worm burden. Worm length accounted for 60 and 70% of the variation in the number of eggs in utero for T. circumcincta and T. colubriformis respectively. Worm length was closely associated with the resistance status of the host; there were greater differences between lambs, and S and R rams for T. colubriformis. T. circumcincta worm lengths were not affected by the worm number. Globule leukocyte counts were related to the worm burdens, and mast cell counts to worm length in the R and S rams. The number, size and fecundity of the worms may well be regulated by similar mechanisms in both species, but T. colubriformis seemed to be more intensively regulated than T. circumcincta. This finding could be useful in devising more effective methods of parasite control.  (+info)

Proteomic approach to identify candidate effector molecules during the in vitro immune exclusion of infective Teladorsagia circumcincta in the abomasum of sheep. (6/46)

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Honest sexual signalling mediated by parasite and testosterone effects on oxidative balance. (7/46)

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Quantitative trait loci for resistance to trichostrongylid infection in Spanish Churra sheep. (8/46)

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