An attempt was made to clarify the association between zinc (Zn) and antioxidants due to Zn supplementation on lipid peroxidation occurring during Brachiaria decumbens intoxication. The concentration of Zn, copper, malondialdehyde (MDA), superoxide dismutase (SOD), and gluthathione peroxidase (GSH-Px) were determined in tissues. There was a gradual increment in the concentration of Zn and MDA in serum and hepatocytic SOD in groups given Zn + B decumbens. A decline in erythrocytic GSH-Px and SOD, and lower concentration of reduced glutathione in hepatocyte cytosols were also detected in these sheep. It is highly suggestive that Zn supplementation may depress antioxidant status and enhance lipid peroxidation during B decumbens intoxication.
Samples of Brachiaria decumbens collected from 5 farms representing the Peninsular Malaysia were subjected to selected trace mineral and phytate analyses to explain the pathogenesis of B decumbens intoxication. Concentrations of Cu, Zn, Fe and Mo were comparable to other grasses while that of phytate was low. The molar ratios of Cu:Zn, Cu:Mo, and Cu:Fe warrant that Cu deficiency is involved in the toxicity of B decumbens. This might aggravate the development of photosensitization of unpigmented or lightly pigmented areas of affected animals. The Zn:phytate ratio could predispose to Zn deficiency during intoxication.
The influence of copper (Cu) overload on hepatic lipid peroxidation and antioxidation defense capacity was studied by overloading rats with copper sulphate orally (500 mg Cu/kg bw) 5 d/w for 8 w. Malondialdehyde (MDA), Cu-Zn superoxide dismutase (SOD), and Se-glutathione peroxidase (GSH-Px) were measured in serum and liver homogenate at 2, 4 and 8 w of dosing. Liver Cu concentration and alanine aminotransferase (ALT) activity were also determined. As Cu loading progressed, there were multiparameter changes with significant ALT elevation, increased MDA concentrations in serum and liver homogenate, and dramatic declines of SOD and GSH-Px activities in erythrocytes and whole blood respectively, along with marked elevation of hepatic Cu in the Cu-dosed group. Excessive Cu accumulation in the liver depressed SOD and GSH-Px activities and resulted in high MDA in serum and liver homogenate due to the lipid peroxidation induced by the Cu overload.
The influence of dietary protein supplementation upon resistance to haemonchosis was examined in Dorsimal (Polled Dorset x Malin) lambs offered two levels of protein. Lambs were offered either a complete basal ruminant diet (15% crude protein (CP)) or the same diet supplemented with fish meal as a source of rumen bypass protein (19% CP). Lambs from each dietary treatment group were given either a 7-week trickle infection with Haemonchus contortus infective larvae (L3) or remained uninfected. All lambs were drenched with anthelmintic at week 8 post-infection (PI), challenged with a single dose of 5000 H. contortus L3 one week later, and killed 14 days post-challenge (PC). Lambs on the supplemented diet that were trickle infected showed a significant reduction in egg output. Supplementation and previous infection did not affect either growth rate, worm burden, worm development or haematological parameters. There was a trend for enhanced growth among supplemented non-infected lambs in comparison to lambs which received the basal ration.
Severe neurological dysfunction was observed in sheep 4 weeks after grazing on Signal grass (Brachiaria decumbens). These neurological disorders included the stamping of forelegs, star-gazing, incoordination, head-pressing against the fence and circling movements. Histologically, numerous vacuolations of various sizes were observed in the white matter of the brain giving rise to a spongy appearance.
Although Brachiaria decumbens was not toxic when fed to cattle, the infusion of rumen liquor from B. decumbens intoxicated sheep into the rumen of cattle produced evidence suggesting hepatic and renal dysfunction. Several biochemical changes were observed including increases in serum aspartate amino transferase, serum creatinine and blood urea nitrogen and a marked reduction in the plasma bromosulphthalein clearance.