Copper oxide wire particles with special reference to parasitism in lambs

The interrelationship between copper oxide wire particles (COWP) treatment and parasitic infection was investigated. Particular emphasis was given to the effect of elevated abomasal pH due to parasitic infection on the solubility of COWP. In addition, the anthelmintic effect of COWP treatment on major gastro-intestinal nematodes was investigated. In vitro experiments examined the effect of abomasal pH on the solubility of COWP. The result clearly showed that solubility was highly pH dependent. The critical pH value for dissolution of copper from COWP was revealed to be 3.4, well within the physiological range encountered in the abomasum of sheep. Twenty five 6-8 week old lambs (Coopworth x Dorset Down) had cannulae surgically inserted into the proximal duodenum and were then allocated into five groups. Seventeen animals were infected with O. circumcincta infective larvae for 6 weeks (7,000 larvae d⁻¹ 5 d w⁻¹). When their proximal duodenal digesta pH showed a response to the parasitic challenge, samples of liver were obtained from all animals by biopsy. During the 6 weeks of the trial, pH of the proximal duodenal digesta, faecal copper excretion and blood parameters, viz. plasma copper and caeruloplasmin level, pepsinogen concentration and aspartate aminotransferase (AST) activity were measured. Post-mortem examinations were conducted 38 days after commencement of infection to recover parasites and COWP and allow liver copper level determination. Infection increased mean pH of abomasal digesta from 2.5 to 4.5 and had a significant effect on the efficacy of COWP. The mean liver copper concentration was significantly increased in all COWP treated animals, but the increment was significantly lower in infected animals compared with non-infected COWP treated animals. The effectiveness of COWP 22 days after treatment (proportion of administered copper apparently retained in the liver) was 0.7 % and 1.8 % for infected and control animals, respectively. However, significantly higher amounts of COWP were recovered from abomasa of infected animals than from non-infected control animals. The difference, possibly, reflected the poor dissolution of COWP in the elevated abomasal pH due to O. circumcincta infection. The mean increment of total liver copper content was negative in infected animals; -6.76 and -5.73 mg for anthelmintic treated and non-treated animals, whereas the value in non-infected control animals was +6.08 mg. Plasma pepsinogen levels were significantly lower in COWP treated animals than in nontreated animals. This indicated a possible anthelmintic effect of COWP. It was concluded that O. circumcincta infection caused a reduction in the effectiveness of COWP by elevating abomasal pH and also reducing the liver copper content by elevating abomasal pH and increasing endogenous loss of copper. To investigate the possible anthelmintic effect of COWP treatment, an in vitro trial using 3rd and 4th stage larvae and in vivo-grown adult worms of T. colubriformis was conducted prior to an in vivo trial. The effect of copper on mortality of 3rd stage larvae was examined after 24 h incubation in 0.15 M saline at pH 2, 3 and 5 and that of 4th stage and adult worms was carried out in defined medium M-199 supplemented with foetal calf serum for 72 hours. Copper derived from COWP was added to the medium to make final concentrations of 0, 1, 10, 100 and 1,000 µg ml⁻¹. The 3rd and 4th stage larvae were highly tolerant of copper. Mortality was influenced only at a concentration of 1,000 µg ml⁻¹, but most of the 4th stage larvae were stunted and 55 % were dead regardless of copper concentration 48 hours after incubation. Most of the adult worms recovered from infected animals were dead and remaining worms were sluggish and appeared to be slowly dying 24 hours after incubation regardless of copper concentration. A further animal experiment was conducted to investigate the effect of COWP treatment on gastro-intestinal nematode establishment using 84 (Coopworth x Dorset Down) lambs. They were allocated into eight groups on the basis of live weight and six groups were infected with 3rd stage larvae of one of the following parasites; 20,000 T. colubrijormis, 20,000 O. circumcincta and 3,000 H. contortus. There were two not infected control groups. Five days prior to infection one group from each of the parasite species and the control groups had been dosed with 5 g COWP. Live weight was measured each week and blood samples taken to determine plasma pepsinogen, copper and caeruloplasmin concentration, and AST activity. They were slaughtered 21 days after infection to recover parasites and COWP. Soluble copper concentrations in abomasal digesta of lambs treated with COWP were four times higher than those of their non-treated counterparts. The high soluble copper concentration coincided with significantly reduced abomasal worm burdens; parasite burdens were reduced by 96% in the case of H. contortus and by 56% in the case of O. circumcincta. However, no significant effect against T. colubrijormis was observed. The mean pH of abomasal digesta of lambs infected with O. circumcincta and not treated with COWP was significantly higher than those of similar animals treated with COWP. Overall, these studies demonstrated that there are complex interrelations between copper metabolism and abomasal infection which have implications both for the diagnosis of copper deficiency in the field and its alleviation by COWP treatment