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Biomedical subjects

I A Barger

Publications and source records attributed to I A Barger.

At least 37 records · Page 2Linked to original sources
PubMed1988

Transport of serum IgA into bile of sheep infected with Fasciola hepatica.

Sheep infected with Fasciola hepatica were studied for their ability to transport intravenously injected radiolabelled IgA from serum to bile. The results show that there was an apparent reduction in the selectivity of transport of IgA into bile in infected animals compared with uninfected controls. However, in infected animals the biliary flow rate was approximately twice that of uninfected animals, and the total amount of radiolabelled IgA transported was similar irrespective of infection status. The possible relevance of the elevated biliary flow rate is discussed with respect to the pharmacokinetics of drugs used for the chemotherapy of helminth infections in sheep.

Animals↗
PubMed1986

Haemonchus contortus and other trichostrongylid infections in parturient, lactating and dry ewes.

From autumn (April) to spring (November), groups of pregnant and dry Merino ewes grazed pasture contaminated with infective larvae of Haemonchus contortus, Ostertagia circumcincta and Trichostrongylus colubriformis. A periparturient rise in faecal egg counts occurred in the pregnant ewes, following the maturation in early spring of arrested fourth-stage larvae of H. contortus and failure of pregnant ewes to expel the resulting adult worms. Peak egg counts were seen in September, just before lambing. In dry ewes, egg counts were slightly elevated at the time of the rise in the pregnant ewes, but fell to very low levels as adult worms developing from previously arrested larvae were expelled. Lactating ewes acquired greater burdens of O. circumcincta and T. colubriformis than did dry ewes, but were equally refractory to new infections with H. contortus. It is therefore suggested that the impairment of immunity to helminth infection seen in reproductive ewes may be more specific than was previously envisaged.

Animals↗
PubMed1984

Wool production of sheep chronically infected with Haemonchus contortus.

A chronic infection was established in a group of twenty 18-month-old non-reproductive Merino ewes by oral administration of 3000 infective H. contortus larvae twice weekly for 12 weeks. Their live-weights and wool production were compared with those of 20 uninfected ewes grazing the same pasture. In the infected sheep, faecal egg counts increased over a period of 9 weeks to reach a mean of 5000 eggs per gram, accompanied by small, but significant effects on packed-cell volume and live-weight. The effects of infection on wool growth were also small, and not statistically significant, although there was evidence of a faster seasonal decline in wool growth in infected sheep. It was concluded that mortality induced by acute infection is the most important economic effect of this parasite.

Animals↗
PubMed1984

Survival of infective larvae of nematode parasites of cattle during drought.

In a study originally designed to determine the seasonal origin of the high levels of availability of nematode larvae to cattle in winter and spring, plots were serially contaminated with eggs of Ostertagia ostertagi and Cooperia oncophora by naturally-infected calves at monthly intervals from February 1980 to September 1980. The availability of infective larvae was monitored by monthly pasture sampling and larval recovery. Because of the intervention of a 15 month drought, recoveries of larvae from the pastures were very low until March 1981 (autumn in Australia) when large numbers of larvae appeared on pastures contaminated in the preceding spring. Examination of dry dung pats at that time showed that significant numbers of larvae were present in pats deposited up to a year previously, and particularly in pats deposited in May, August and September. Following the resumption of normal rainfall in May 1981, larval numbers in pats rapidly declined and concentrations of larvae on the pastures increased to extremely high levels. It is suggested that survival of infective larvae in dry dung pats was enhanced by the drought, with implications for control of nematode infections of cattle, particularly in winter rainfall environments.

Animals↗
PubMed1979

The role of inhibited larvae in the epidemiology of ovine haemonchosis.

Three paddocks were contaminated with Haemonchus contortus eggs from early spring to mid summer by yearling sheep. In Paddock 1, all contamination was derived from worms that had been previously inhibited in their development. The contamination in Paddock 2 was produced only by infections recently acquired from pasture, and in Paddock 3 contamination was attributable to both sources. When the yearling sheep were replaced in mid-summer by newly weaned lambs, severe outbreaks of haemonchosis occurred on all paddocks. It was concluded that inhibited H. contortus larvae are capable of producing sufficient eggs, when they resume development, to initiate an outbreak of haemonchosis in susceptible sheep.

Animals↗